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INTRODUCTION
In recent years, legislative and market requirements have driven the need to reduce fuel consumption while meeting increasingly stringent exhaust emissions. This trend has dictated increasing complexity in automotive engines and new approaches to engine design. A key research objective for the automotive engineering community has been the potential combination of gasoline-engine specific power with diesel-like engine efficiency in a cost-competitive, production-feasible power train. One promising engine development route for achieving these goals is the potential application of lean burn direct injection (DI) for gasoline engines. In carburetors the fuel is sucked due to the pressure difference caused by the incoming air. This will affect the functioning of the carburetor when density changes in air are appreciable. There was a brief period of electronically controlled carburetor, but it was abandoned due to its complex nature. On the other hand in fuel injection the fuel is injected into the air.
TRANSITION OF FUEL SUPPLY SYSTEM
The transition of the fuel supply system used in automobiles is graphically shown below. In carburetor the fuel from the fuel chamber is sucked in by the pressure variation caused due to the incoming air. The fuel then mixes with the air and reaches the cylinder through the inlet manifold. Where as in a port injection system the fuel to the cylinder is supplied by a separate fuel injector placed near the inlet valve of the cylinder. And in a direct injection system the fuel to the cylinder is supplied by a fuel injector placed inside the cylinder.
OPERATING DIFFICULTIES FOR A CARBURETOR.
Some problems associated with comfortable running of the carburetor are discussed here.
1. Ice formation: The vaporisation of the fuel injected in the current of the air requires latent heat and the taken mainly from the incoming air. As a result of this, the temperature of the air drops below the dew point of the water vapour in the air and it condenses and many times freeze into ice if the temperature falls below dew point temperature.
2. Vapour Lock: The improved volatility of modern fuels and the necessity of providing heat to prevent the ice formation, has created carburetion difficulties due to vaporisation of fuel in pipes and float chamber. The heating may also occur due to petrol pipes being near the engine. If the fuel supply is large and supply is small, a high velocity will result causing high vacuum. This causes considerable drop which may also cause the formation of vapour bubbles. If these bubbles formed accumulate at the tube bend, then they may interrupt the fuel flow from the tank or the fuel pump and engine will stop because of lack of fuel. Vapour lock is formed because of rapid bubbling of fuel and usually happens in hot summer.
3. Back Firing: During the starting of an engine under cold working conditions, the usual manipulation of the choke varies the mixture from too lean to too rich. A very lean mixture will burn very slowly and the flame may still exist in cylinder when the exhaust valve is about to open. The fresh charge in the intake manifold is about to open. The fresh charge in the intake manifold is not so diluted as when inducted into the cylinder and mixed with the clearance gases and consequently burn more rapidly than the charge in the cylinder. If lean charge comes in contact with flames existing in the cylinder, there will be flash of flame back through the intake manifold, burning the charge therein and causing the customary back firing in the carburetor.
ADVANTAGES OF FUEL INJECTION OVER CARBURETOR
The fuel injection eliminates several intake manifold distribution problems. One of the most difficult problems in a carbureted system is to get the same amount and richness of air-fuel mixture to each cylinder. The problem is that the intake manifold acts as a storing device, sending a richer air fuel mixture to the end cylinders. The air flows readily around the corners and through various shaped passages. However the fuel, because it is heavier is unable to travel as easily around the bends in the intake manifold. As a result, some of fuel particles continue to move to the end of the intake manifold, accumulating there. This enriches the mixture going the end cylinder. The center cylinder closest to the carburetor gets the leanest mixture¬¬¬¬¬. The port injection solves this problem because the same amount of fuel is injected at each intake valve port. Each cylinder gets the same amount of air-fuel mixture of the same mixture richness.
Another advantage of the fuel injection system is that the intake manifold can be designed for the most efficient flow of air only. It does not have to handle fuel. Also, because only a throttle body is used, instead of a complete carburetor, the hood height of the car can be lowered.
With fuel injection, fuel mixture requires no extra heating during warm up. No manifold heat control valve or heated air system is required. Throttle response is faster because the fuel is under pressure at the injection valves at all times. An electric fuel pump supplies the pressure. The carburetor will depend on differences in air pressure as the force that causes the fuel to feed into the air passing through.
Fuel injection has no choke, but sprays atomized fuel directly into the engine. This eliminates most of the cold start problems associated with carburetors.
Electronic fuel injection also integrates more easily with computerized engine control systems because the injectors are more easily controlled than a mechanical carburetor with electronic add-ons.
Multi port fuel injection (where each cylinder has its own injector) delivers a more evenly distributed mixture of air and fuel to each of the engine's cylinders, which improves power and performance.
Sequential fuel injection (where the firing of each individual injector is controlled separately by the computer and timed to the engine's firing sequence) improves power and reduces emissions.
ELECTRONIC FUEL INJECTION
The main components of electronic fuel injection are described below.
1. Engine Control Unit (ECU)
2. Sensors
3. Fuel Injectors
Engine Control Unit (ECU): This unit is the heart of electronic injection system which is responsible for metering the quantity of fuel supplied to each cylinder. The unit contains a number of printed circuits boards on which, a series of transistors, diodes and other electronic components are mounted. This makes the vital data analysing circuits responding to various input signals. After processing the input data, the power output circuits in the control unit generates current pulses which are transmitted to the solenoid injectors to operate the injector for the required period.
For example, when the pedal of the vehicle is stepped on, the throttle valve (this is the valve that regulates how much air enters the engine) opens up more, letting in more air. The engine control unit (ECU) "sees" the throttle valve open with the help of sensors and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens; otherwise, when the gas pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it. Sensors monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right.
The ECU generally works in two operating modes, namely open loop and closed loop. In closed loop Oxygen sensor is used to sense the quantity of excess Oxygen in the smoke and this information is used for the next cycle of injection. This is also called feedback mode. On the other hand in open loop system the Oxygen sensor is not used.
Engine Sensors: In order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to monitor a huge number of input sensors. Here are just a few:
¢ Mass airflow sensor - Tells the ECU the mass of air entering the engine
¢ Oxygen sensor - The device measures the amount of oxygen in the exhaust gas and sends this information to the electronic control unit. If there is too much oxygen, the mixture is too lean. If there is too little, the mixture is too rich. In either case, the electronic control unit adjusts the air fuel ratio by changing the fuel injected. It is usually used with closed loop mode of the ECU.
¢ Throttle position sensor - Monitors the throttle valve position (which determines how much air goes into the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary
¢ Coolant temperature sensor - Allows the ECU to determine when the engine has reached its proper operating temperature
¢ Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping (which would indicate a high electrical load)
¢ Manifold absolute pressure sensor - Monitors the pressure of the air in the intake manifold. The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced.
¢ Engine speed sensor - Monitors engine speed, which is one of the factors used to calculate the pulse width.
¢ Crank Angle sensor - Monitors the position of the piston and gives the information to the ECU. Accordingly the ECU adjusts the valve timing.
Fuel Injectors:
The solenoid-operated fuel injector is shown in the figure above. It consists of a valve body and needle valve to which the solenoid plunger is rigidly attached. The fuel is supplied to the injector under pressure from the electric fuel pump passing through the filter. The needle valve is pressed against a seat in the valve body by a helical spring to keep it closed until the solenoid winding is energized. When the current pulse is received from the electronic control unit, a magnetic field builds up in the solenoid which attracts a plunger and lifts the needle valve from its seat. This opens the path to pressurised fuel to emerge as a finely atomised spray.
The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU. The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors.
ELECTRONIC FUEL INJECTION
There are two types of electronic fuel injection. They are,
1. Multipoint Fuel Injection (MPFI)
2. Gasoline Direct Injection (GDI)
MULTI POINT FUEL INJECTION (MPFI)
Engines with multi port injection have a separate fuel injector for each cylinder, mounted in the intake manifold or head just above the intake port.
Thus, a four-cylinder engine would have four injectors, a V6 would have six injectors and a V8 would have eight injectors. Multi port injection systems are more expensive because of the added number of injectors. But having a separate injector for each cylinder makes a big difference in performance. The same engine with multi port injection will typically produce 10 to 40 more horsepower than one with carburetor because of better cylinder-to-cylinder fuel distribution.
Injecting fuel directly into the intake ports also eliminates the need to preheat the intake manifold since only air flows through the manifold. This, in turn, provides more freedom for tuning the intake plumbing to produce maximum torque.
GASOLINE DIRECT INJECTION (GDI)
Fig7: A GDI System
In conventional engines, fuel and air are mixed outside the cylinder. This ensures waste between the mixing point and the cylinder, as well as imperfect injection timing. But in the GDI engine, petrol is injected directly into the cylinder with precise timing, eliminating waste and inefficiency. By operating in two modes, Ultra-Lean Combustion Mode and Superior Output Mode, the GDI engine delivers both unsurpassed fuel efficiency and superior power and torque. The GDI engine switches automatically between modes with no noticeable shift in performance. All the driver notices is a powerful driving experience, and much lower fuel bills. It's the best engine on the market. A Gasoline direct injection system consist various components as shown in the figure below.
MAJOR OBJECTIVES OF THE GDI ENGINE
Ultra-low fuel consumption, which betters that of diesel engines.
Superior power to conventional MPI engines
THE DIFFERENCE BETWEEN NEW GDI AND CURRENT MPI
For fuel supply, conventional engines use a fuel injection system, which replaced the carburetion system. MPI or Multi-Point Injection, where the fuel is injected to each intake port, is currently the one of the most widely used systems. However, even in MPI engines there are limits to fuel supply response and the combustion control because the fuel mixes with air before entering the cylinder. Mitsubishi set out to push those limits by developing an engine where gasoline is directly injected into the cylinder as in a diesel engine, and moreover, where injection timings are precisely controlled to match load conditions. The GDI engine achieved the following outstanding characteristics.
¢ Extremely precise control of fuel supply to achieve fuel efficiency that exceeds that of diesel engines by enabling combustion of an ultra-lean mixture supply.
¢ Very efficient intake and relatively high compression ratio unique to the GDI engine deliver both high performance and response that surpasses those of conventional MPI engines.
OUTLINE: Major Specifications (Comparison with MPFI)
Item GDI Conventional MPFI
Bore x Stroke (mm) 81.0 x 89.0
Displacement 1834
Number of Cylinders IL-4
Number of Valves Intake: 2, Exaust: 2
Compression Ratio 12.0 10.5
Combustion Chamber Curved Top Piston Flat top Piston
Intake Port Upright Straight Standard
Fuel System In-Cylinder Direct Injection Port Injection
Fuel Pressure (MPa) 50 3.3
TECHNICAL FEATURES
The GDI engines foundation technologies
TECHNICAL FEATURES
The GDI engines foundation technologies
There are four technical features that make up the foundation technologies are described below.
The Upright Straight Intake Port supplies optimal airflow into the cylinder.
The Curved-top Piston controls combustion by helping shape the air-fuel mixture.
The High Pressure Fuel Pump supplies the high pressure needed for direct in-cylinder injection.
The High Pressure Swirl Injector controls the vaporization and dispersion of the fuel spray.
MAJOR CHARACTERISTICS OF THE GDI ENGINE
Lower fuel consumption and higher output: Using methods and technologies, the GDI engine provides both lower fuel consumption and higher output. This seemingly contradictory and difficult feat is achieved with the use of two combustion modes. Put another way, injection timings change to match engine load.
For load conditions required of average urban driving, fuel is injected late in the compression stroke as in a diesel engine. By doing so, an ultra-lean combustion is achieved due to an ideal formation of a stratified air-fuel mixture. During high performance driving conditions, fuel is injected during the intake stroke. This enables a homogeneous air-fuel mixture like that of in conventional MPI engines to deliver higher output.
Two Combustion Modes: In response to driving conditions, the GDI engine changes the timing of the fuel spray injection, alternating between two distinctive combustion modes- stratified charge (Ultra-Lean combustion), and homogenous charge (Superior Output combustion).
Under normal driving conditions, when speed is stable and there is no need for sudden acceleration, the GDI engine operates in Ultra-Lean Mode. A spray of fuel is injected over the piston crown during the latter stages of the compression stroke, resulting in an optimally stratified air-fuel mixture immediately beneath the spark plug. This mode thus facilitates lean combustion and a level of fuel efficiency comparable to that of a diesel engine.
The GDI engine switches automatically to Superior Output Mode when the driver accelerates, indicating a need for greater power. Fuel is injected into the cylinder during the piston's intake stroke, where it mixes with air to form a homogenous mixture. The homogenous mixture is similar to that of a conventional MPI engine, but by utilising the unique features of the GDI, an even higher level of power than conventional petrol engines can be achieved.
In-cylinder Airflow: The GDI engine has upright straight intake ports rather than horizontal intake ports used in conventional engines. The upright straight intake ports efficiently direct the airflow down at the curved-top piston, which redirects the airflow into a strong reverse tumble for optimal fuel injection.
Precise Control over the Air/Fuel Mixture: The GDI engine's ability to precisely control the mixing of the air and fuel is due to a new concept called wide spacing," whereby injection of the fuel spray occurs further away from the spark plug than in a conventional petrol engine, creating a wide space that enables optimum mixing of gaseous fuel and air.
In stratified combustion (Ultra-Lean Mode), fuel is injected towards the curved top of the piston crown rather than towards the spark plug, during the latter stage of the compression stroke. The movement of the fuel spray, the piston head's deflection of the spray and the flow of air within the cylinder cause the spray to vapourise and disperse. The resulting mixture of gaseous fuel and air is then carried up to the spark plug for ignition. The biggest advantage of this system is that it enables precise control over the air-to-fuel ratio at the spark plug at the point of ignition.
The GDI engine's intake ports have been made straight and upright to create a strong flow that facilitates mixing of the air and fuel. Air is drawn smoothly and directly down through the intake ports toward the cylinder, where the piston head redirects it, forcing it into a reverse vertical tumble flow, the most effective flow pattern for mixing the air and fuel and carrying the mixture up to the spark plug. The GDI engine's pistons boast unique curved tops-forming a rounded combustion chamber-the most effective shape for carrying the gaseous fuel up to the spark plug.
In addition to its ability to mix thoroughly with the surrounding air, the fuel spray does not easily wet the cylinder wall or the piston head. In homogeneous combustion (Superior Output Mode), fuel is injected during the intake stroke, when the piston is descending towards the bottom of the cylinder, vapourising into the air flow and following the piston down. Again, it's all in the timing. By selecting the optimum timing for the injection, the fuel spray follows the movement of the piston, but cannot catch up. In this case, as the piston moves downward and the inside of the cylinder become larger in volume, the fuel spray disperses widely, ensuring a homogenous mixture.
Fuel Spray: Newly developed high-pressure swirl injectors provide the ideal spray pattern to match each engine operational modes. And at the same time by applying highly swirling motion to the entire fuel spray, they enable sufficient fuel atomization that is mandatory for the GDI even with a relatively low fuel pressure of 50kg/cm2.
Optimized Configuration of the Combustion Chamber: The curved-top piston controls the shape of the air-fuel mixture as well as the airflow inside the combustion chamber, and has an important role in maintaining a compact air fuel mixture. The mixture, which is injected late in the compression stroke, is carried toward the spark plug before it can disperse.
Realization of lower fuel consumption
In conventional gasoline engines, dispersion of an air-fuel mixture with the ideal density around the spark plug was very difficult. However, this is possible in the GDI engine. Furthermore, extremely low fuel consumption is achieved because ideal stratification enables fuel injected late in the compression stroke to maintain an ultra-lean air-fuel mixture.
An engine for analysis purpose has proved that the air-fuel mixture with the optimum density gathers around the spark plug in a stratified charge. This is also borne out by analyzing the behavior of the fuel spray immediately before ignition and the air-fuel mixture itself.
As a result, extremely stable combustion of ultra-lean mixture with an air-fuel ratio of 40 is achieved as shown below.
Combustion of Ultra-lean Mixture
In conventional MPI engines, there were limits to the mixtures leanness due to large changes in combustion characteristics. However, the stratified mixture of the GDI enabled greatly decreasing the air-fuel ratio without leading to poorer combustion. For example, during idling when combustion is most inactive and unstable, the GDI engine maintains a stable and fast combustion even with an extremely lean mixture of 40 to 1 air-fuel ratio.
VEHICLE FUEL CONSUMPTION
Fuel Consumption during Idling: The GDI engine maintains stable combustion even at low idle speeds. Moreover, it offers greater flexibility in setting the idle speed.
Compared to conventional engines, its fuel consumption during idling is 40% less.
Fuel Consumption during Cruising Drive: At 40km/h, for example, the GDI engine uses 35% less fuel than a comparably sized conventional engine.
Better Fuel Efficiency: The concept of wide spacing makes it possible to achieve a stratified mixture, enabling the GDI engine to offer stable, ultra-lean combustion, allowing a significant improvement in fuel efficiency. In addition to ultra-lean combustion, the GDI engine achieves a higher compression ratio because of its anti-knocking characteristic and precise control of injection timing. These features contribute to drastically lower fuel consumption. The GDI engine improves fuel economy by 33% in the Japanese 10-15 mode driving cycle which represents typical urban driving conditions.
Emission Control: Previous efforts to burn a lean air-fuel mixture have resulted in difficulty to control NOx emission. However, in the case of GDI engine, 97% NOx reduction is achieved by utilizing high-rate EGR (Exhaust Gas Ratio) such as 30% that is allowed by the stable combustion unique to the GDI as well as a use of a newly developed lean-NOx catalyst.
REALIZATION OF SUPERIOR OUTPUT
To achieve power superior to conventional MPI engines, the GDI engine has a high compression ratio and a highly efficient air intake system, which result in improved volumetric efficiency. In high-load operation, a homogeneous mixture is formed. (When extra power is needed, the GDI engine switches automatically to Superior Output Mode.) Because it burns a homogenous mixture in this mode, the GDI engine functions like any other MPI engine. However, by maximising its technical features, the GDI engine achieves substantially higher power than a conventional engine.
One of the principal reasons for this is that a fine spray of fuel is injected in a wide shower directly into the cylinder, where it vapourises instantly into the air flow. This causes the air to cool and contract, allowing additional air to be drawn in and improving volumetric efficiency. The cooling of the intake air prevents knocking, and results in higher power output.
Another reason for the GDI engine's ability to offer such superb power is that it prevents knocks. With conventional MPI engines, strong knocking occurs during acceleration. This is caused by petrol adhering to the intake ports. The low-octane elements of the fuel are forced into the cylinder immediately after accelerating, where they mix with air and ignite, causing knocking. With the GDI engine, fuel is injected directly into the cylinder and burned completely, meaning that transient knocking is suppressed. This in turn, allows higher output in the early stages of acceleration, when power is most needed. The most significant feature of petrol direct-injection is the fact that engine technology has finally achieved precise control over formation of the air/fuel mixture. We have capitalised on this achievement to develop an innovative anti-knock technology called Two-Stage Mixing. In high load, when it is necessary to supply large amounts of fuel, a homogenous air/fuel mix is used to prevent partially dense mixtures that cause soot to form. In contrast, the new Two-Stage Mixing technology prevents soot even during stratified mix, when a dense mixture forms. This is how knocking can be prevented.
In Two-Stage Mixing, about 1/4 of the total volume of fuel is injected during the intake stroke. This forms an ultra-lean fuel mixture which is too lean to burn under normal conditions. The remaining fuel is injected during the latter stages of the compression stroke. The key is that the air/fuel mixture is divided into a very lean air/fuel mixture and a rich air/fuel mixture. Knocking occurs most frequently in a stochiometric mixture, but is less likely to occur when the mixture becomes leaner or richer. Because the rich mixture is formed immediately before ignition, there is no time for the chemical reaction that causes knocking to take place. This is another of the factors that prevent knocking.
More important to note, is that the emission of soot is prevented, even when a dense air/fuel mixture is formed, and excess air is not sufficient. If air were the only gas present in the combustion chamber-as is the case with an ordinary diesel engine-the enriched charge would cool, causing soot to form. With Two-Stage Mixing, the enriched charge, created in the part of the chamber where the dense air/fuel mixture exists, shifts toward the other side of the chamber, where the mixture is leaner, as it burns. At this point, the enriched charge causes the ultra-lean mixture, which is too lean to burn under ordinary circumstances, to ignite. The combustion of the ultra-lean mixture, in turn, causes the enriched charge to re-ignite. It is this process that suppresses the formation of soot. This is the first time in the long history of petrol engines that direct control of combustion has been used to suppress knocking, and it further underscores the importance of achieving precise control over the air/fuel mixture.
Improved Volumetric Efficiency: Compared to conventional engines, the Mitsubishi GDI engine provides better volumetric efficiency. The upright straight intake ports enable smoother air intake. And the vaporization of fuel, which occurs in the cylinder at a late stage of the compression stroke, cools the air for better volumetric efficiency.
Increased Compression Ratio: The cooling of air inside the cylinder by the vaporization of fuel has another benefit, to minimize engine knocking. This allows a high compression ratio of 12, and thus improved combustion efficiency.
ACHIEVEMENTS
Engine performance: Compared to conventional MPI engines of a comparable size, the GDI engine provides approximately 10% greater outputs and torque at all speeds.
Vehicle Acceleration: In high-output mode, the GDI engine provides outstanding acceleration. The following chart compares the performance of the GDI engine with a conventional MPI engine.
CONCLUSION
Advantages
Frequent operation in stratified mode.
Reduction of CO2 production by nearly 20 percent.
Provides improved torque.
Fulfills future emissions requirements.
97% NOx reduction is achieved.
Improve the brake specific fuel consumption.
Smooth transition between operation modes.
Consumer Benefit
Reduced fuel consumption 15-20%
Higher torque 5-10%
Up to 5% more power
Spontaneous response behavior
REFERENCES
1) ENERGY & ENVIRONMENTAL ANALYSIS, INC. Cost & Benefits of the Gasoline Direct Injection Engine, Arlington, VA 22209.
2) YONG-JIN KIM, Effect of Motion on Fuel Spray Characteristics in A GDI Engine, Institute for Advanced Engineering, 1999-01-0177.
3) DOMKUNDWAR, A course in IC engines.
4) CROUSE/ANGLIN, Automotive mechanics.
5) mitsubishi-motors.co.jp
6) auto.howstuffswork.com
7) boschusa.com
8) delphi.com

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INTRODUCTION
For many years, innovative engine technology has been a development priority of Mitsubishi Motors. In particular, Mitsubishi has sought to improve engine efficiency in an endeavor to meet growing environmental demands, such as those for energy conservation and the reduction of CO2 emission to limit the negative impact of the green-house effect.
In Mitsubishis endeavor to design and build ever more efficient engines, it has devoted significant resources to developing a gasoline direct injection engine. For years, automotive engineers have believed this type of engine has the greatest potential to optimize fuel supply and combustion, which in turn can deliver better performance and lower fuel consumption. Until now, however, no one has successfully designed an in-cylinder direct injection engine for use on production vehicles. A result of Mitsubishis engine development capabilities, Mitsubishis advanced Gasoline Direct Injection GDI engine is the realization of engineering dream.
MITSUBISHI GASOLINE DIRECT INJECTION GDI ENGINE
MAJOR OBJECTIVES OF THE GDI ENGINE
¢ Ultra-low fuel consumption that betters that of even diesel engines
¢ Superior power to conventional MPI engines
1. THE DIFFERENCE BETWEEN NEW GDI AND CURRENT MPI
For fuel supply, conventional engines use a fuel injection system, which replaced the carburetion system. MPI or Multi-Point Injection, where the fuel is injected to each intake port, is currently the one of the most widely used systems. However, even in MPI engines there are limits to fuel supply response and the combustion control because the fuel mixes with air before entering the cylinder. Mitsubishi set out to push those limits by developing an engine where gasoline is directly injected into the cylinder as in a diesel engine, and moreover, where injection timings are precisely controlled to match load conditions. The GDI engine achieved the following outstanding characteristics.
¢ Extremely precise control of fuel supply to achieve fuel efficiency that exceeds that of diesel engines by enabling combustion of an ultra-lean mixture supply.
¢ Very efficient intake and relatively high compression ratio unique to the GDI engine deliver both high performance and response that surpasses those of conventional MPI engines.
For Mitsubishi, the technology realized for this GDI engine will form the cornerstone of the next generation of high efficiency engines and, in its view, the technology will continue to develop in this direction.
TRANSITION OF FUEL SUPPLY SYSTEM
2. OUTLINE
(1) MAJOR SPECIFICATIONS
(2) ENGINE DIAGRAM
TECHNICAL FEATURES
¢ Upright straight intake ports for optimal airflow control in the cylinder
¢ Curved-top pistons for better combustion
¢ High pressure fuel pump to feed pressurized fuel into the injectors
¢ High-pressure swirl injectors for optimum air-fuel mixture
1. LOWER FUEL CONSUMPTION AND HIGHER OUTPUT
(1) OPTIMAL FUEL SPRAY FOR TWO COMBUSTION MODE
Using methods and technologies unique to Mitsubishi, the GDI engine provides both lower fuel consumption and higher output. This seemingly contradictory and difficult feat is achieved with the use of two combustion modes. Put another way, injection timings change to match engine load
For load conditions required of average urban driving, fuel is injected late in the compression stroke as in a diesel engine. By doing so, an ultra-lean combustion is achieved due to an ideal formation of a stratified air-fuel mixture. During high performance driving conditions, fuel is injected during the intake stroke. This enables a homogeneous air-fuel mixture like that of in conventional MPI engines to deliver higher output.
ULTRA-LEAN COMBUSTION MODE
Under most normal driving conditions, up to speeds of 120km/h, the Mitsubishi GDI engine operates in ultra-lean combustion mode for less fuel consumption. In this mode, fuel injection occurs at the latter stage of the compression stroke and ignition occurs at an ultra-lean air-fuel ratio of 30 to 40 (35 to 55, included EGR).
SUPERIOR OUTPUT MODE
When the GDI engine is operating with higher loads or at higher speeds, fuel injection takes place during the intake stroke. This optimizes combustion by ensuring a homogeneous, cooler air-fuel mixture that minimized the possibility of engine knocking.
(2) THE GDI ENGINES FOUNDATION TECHNOLOGIES
There are four technical features that make up the foundation technology. The Upright Straight Intake Port supplies optimal airflow into the cylinder. The Curved-top Piston controls combustion by helping shape the air-fuel mixture. The High Pressure Fuel Pump supplies the high pressure needed for direct in-cylinder injection. And the High Pressure Swirl Injector controls the vaporization and dispersion of the fuel spray.
These fundamental technologies, combined with other unique fuel control technologies, enabled Mitsubishi to achieve both of the development objectives, which were fuel consumption lower than those of diesel engines and output higher than those of conventional MPI engines. The methods are shown below.
IN-CYLINDER AIRFLOW
The GDI engine has upright straight intake ports rather than horizontal intake ports used in conventional engines. The upright straight intake ports efficiently direct the airflow down at the curved-top piston, which redirects the airflow into a strong reverse tumble for optimal fuel injection.
FUEL SPRAY
Newly developed high-pressure swirl injectors provide the ideal spray pattern to match each engine operational modes. And at the same time by applying highly swirling motion to the entire fuel spray, they enable sufficient fuel atomization that is mandatory for the GDI even with a relatively low fuel pressure of 50kg/cm2.
OPTIMIZED CONFIGURATION OF THE COMBUSTION CHAMBER
The curved-top piston controls the shape of the air-fuel mixture as well as the airflow inside the combustion chamber, and has an important role in maintaining a compact air fuel mixture. The mixture, which is injected late in the compression stroke, is carried toward the spark plug before it can disperse.
Mitsubishis advanced in-cylinder observation techniques including laser-methods are utilized to determine the optimum piston shape.
2. REALIZATION OF LOWER FUEL CONSUMPTION
(1) BASIC CONCEPT
In conventional gasoline engines, dispersion of an air-fuel mixture with the ideal density around the spark plug was very difficult. However, this is possible in the GDI engine. Furthermore, extremely low fuel consumption is achieved because ideal stratification enables fuel injected late in the compression stroke to maintain an ultra-lean air-fuel mixture.
An engine for analysis purpose has proved that the air-fuel mixture with the optimum density gathers around the spark plug in a stratified charge. This is also borne out by analyzing the behavior of the fuel spray immediately before ignition and the air-fuel mixture itself.
As a result, extremely stable combustion of ultra-lean mixture with an air-fuel ratio of 40 (55 , EGR included) is achieved as shown below.
(2) COMBUSTION OF ULTRA-LEAN MIXTURE
In conventional MPI engines, there were limits to the mixtures leanness due to large changes in combustion characteristics. However, the stratified mixture of the GDI enabled greatly decreasing the air-fuel ratio without leading to poorer combustion. For example, during idling when combustion is most inactive and unstable, the GDI engine maintains a stable and fast combustion even with an extremely lean mixture of 40 to 1 air-fuel ratio (55 to 1, EGR included)
3) VEHICLE FUEL CONSUMPTION
FUEL CONSUMPTION DURING IDLING
The GDI engine maintains stable combustion even at low idle speeds. Moreover, it offers greater flexibility in setting the idle speed.
Compared to conventional engines, its fuel consumption during idling is 40% less.
Fuel Consumption During Cruising Drive
At 40km/h, for example, the GDI engine uses 35% less fuel than a comparably sized conventional engine.
Fuel Consumption In City Driving
In Japanese 10E15 mode tests ( representative of typical Japanese urban driving ), the GDI engine used 35% less fuel than comparably sized conventional gasoline engines. Moreover, these results indicate that the GDI engine uses less fuel than even diesel engines.
EMISSION CONTROL
Previous efforts to burn a lean air-fuel mixture have resulted in difficulty to control NOx emission. However, in the case of GDI engine, 97% NOx reduction is achieved byutilizing high-rate EGR (Exhaust Gas Ratio) such as 30% that is allowed by the stable combustion unique to the GDI as of a newly developed lean-NOx catalyst.
Newly Developed Lean NOx Catalyst (HC Selective Deoxidization Type)
VEHICLE ACCELERATION
In high-output mode, the GDI engine provides outstanding acceleration.
The following chart compares the performance of the GDI engine with a conventional MPI engine.
3. REALIZATION OF SUPERIOR OUTPUT
(1) BASIC CONCEPT
To achieve power superior to conventional MPI engines, the GDI engine has a high compression ratio and a highly efficient air intake system, which result in improved volumetric efficiency.
IMPROVED VOLUMETRIC EFFICIENCY
Compared to conventional engines, the Mitsubishi GDI engine provides better volumetric efficiency. The upright straight intake ports enable smoother air intake. And the vaporization of fuel, which occurs in the cylinder at a late stage of the compression stroke, cools the air for better volumetric efficiency.
INCREASED COMPRESSION RATIO
The cooling of air inside the cylinder by the vaporization of fuel has another benefit, to minimize engine knocking. This allows a high compression ratio of 12, and thus improved combustion efficiency.
(2) ACHIEVEMENT
ENGINE PERFORMANCE
Compared to conventional MPI engines of a comparable size, the GDI engine provides approximately 10% greater outputs and torque at all speeds.
CONCLUSION
The gasoline direct injection engines can be widely used in modified cars which prefer the power of the car and also to ordinary cars which prefer better fuel efficiency .In the era of high petrol consumption and heavy air pollution the adaptation of gasoline direct injection can play a vital role which gives a total answer to the scenario. The initial cost of the engine can be affordable to the common man when the engine is used or produced in greater number .Another is the compression ratio and also the fuel efficiency which is more than that of ordinary diesel engines. Also is the less amount of pollution which is due to the fewer amounts of unburned fuels due to the injection inside the manifold.
REFERENCES
¢ howstuffworks.com
¢ mitsubhishimotors.com
¢ delphi.com
¢ audiworld.com

Direct Fuel Injection

Direct fuel injection defined
Direct fuel injection is a fuel-delivery technology that allows gasoline engines to burn fuel more efficiently, resulting in more power, cleaner emissions, and increased fuel economy.
How direct fuel injection works
Gasoline engines work by sucking a mixture of gasoline and air into a cylinder, compressing it with a piston, and igniting it with a spark; the resulting explosion drives the piston downwards, producing power. Traditional (indirect) fuel injection systems pre-mix the gasoline and air in a chamber just outside the cylinder called the intake manifold. In a direct-injection system, the air and gasoline are not pre-mixed; air comes in via the intake manifold, while the gasoline is injected directly into the cylinder.
Advantages of direct fuel injection
Combined with ultra-precise computer management, direct injection allows more accurate control over fuel metering (the amount of fuel injected) and injection timing (exactly when the fuel is introduced into the cylinder). The location of the injector also allows for a more optimal spray pattern that breaks the gasoline up into smaller droplets. The result is more complete combustion -- in other words, more of the gasoline is burned, which translates to more power and less pollution from each drop of gasoline.
Disadvantages of direct fuel injection
The primary disadvantages of direct injection engines are complexity and cost. Direct injection systems are more expensive to build because their components must be more rugged -- they handle fuel at significantly higher pressures than indirect injection systems and the injectors themselves must be able to withstand the heat and pressure of combustion inside the cylinder.
How much more powerful and efficient is direct injection?
Cadillac sells the CTS with both indirect and direct injection versions of its 3.6 liter V6 engine. The indirect engine produces 263 horsepower and 253 lb-ft of torque, while the direct version develops 304 hp and 274 lb-ft. Despite the additional power, EPA fuel economy estimates for the direct injection engine are 1 MPG higher in the city (18 MPG vs 17 MPG) and equal on the highway. Another advantage: Cadillac's direct injection engine runs on regular (87 octane) gasoline. Competing cars from Infiniti and Lexus, which use 300 hp V6 engines with indirect injection, require premium fuel.
Renewed interest in direct fuel injection
Direct injection technology has been around since the mid-20th century; however, few automakers adopted it for mass-market cars. Electronically-controlled indirect fuel injection did the job nearly as well at a significantly lower cost, and offered huge advantages over the mechanical carburetor, which was the dominant fuel delivery system until the 1980s. However, recent developments such as skyrocketing fuel prices and stricter fuel economy and emissions legislation have led many automakers to begin developing direct fuel injection systems. You can expect to see more and more cars make use of direct injection in the near future.
Diesels and direct fuel injection
Virtually all diesel engines use direct fuel injection. However, because diesels use a different process to combust their fuel (gasoline engines compress a mixture of gasoline and air and ignite it with a spark; diesels compress air only, then spray in fuel which is ignited by the heat and pressure), their injection systems differ in design and operation from gasoline direct fuel injection systems.

[attachment=3517]

Gasoline Direct Injection

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Prepared By:
PAPPU SINGH 1JS06ME027

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Introduction
Advantages of Fuel Injection over Carburetor
Electronic Fuel Injection
Multi Point Fuel Injection
Gasoline Direct Injection
The Difference Between New GDI And Current MPI
Technical features
Major characteristics of the GDI engine
Realization of lower fuel consumption
Vehicle Fuel Consumption
Realization of Superior Output
Achievements
Conclusion


ADVANTAGES OF FUEL INJECTION OVER CARBURETOR
¤ Fuel injection has no choke, but sprays atomized fuel directly into the engine.
¤ Electronic fuel injection also integrates more easily with computerized engine control systems.

¤ Multi port fuel injection delivers a more evenly distributed mixture of air and fuel to each of the engine's cylinders.
¤ Sequential fuel injection improves power and reduces emissions.


Fuel Injectors
A fuel injector is nothing but an electronically controlled valve.
When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle.
It is controlled by the ECU.
A pipe called the fuel rail supplies pressurized fuel to all of the injectors.



MULTI POINT FUEL INJECTION SYSTEM
Have a separate fuel injector for each cylinder .
Have better cylinder to cylinder distribution.
Eliminate the need to preheat the intake manifold


BASIC TECHNICAL FEATURES OF GDI ENGINE
The Upright Straight Intake Port.
The Curved-top Piston.
The High Pressure Fuel Pump.
The High Pressure Swirl Injector.


CONCLUSION

Frequent operation in stratified mode.
Reduction of CO2 production by nearly 20 percent.
Provides improved torque 5-10%
Fulfills future emissions requirements.
97% NOx reduction is achieved.
Improve the brake specific fuel consumption.
Smooth transition between operation modes.
Reduced fuel consumption 15-20%
Up to 5% more power
Spontaneous response behavior

[attachment=3524]

GASOLINE DIRECT INJECTION

1.0 INTRODUCTION

Gasoline direct injection (GDI) engine technology has received considerable attention over the last few years as a way to significantly improve fuel efficiency without making a major shift away from conventional internal combustion technology. In many respects, GDI technology represents a further step in the natural evolution of gasoline engine fueling systems. Each step of this evolution, from mechanically based carburetion, to throttle body fuel injection, through multi-point and finally sequential multi-point fuel injection, has taken advantage of improvements in fuel injector and electronic control technology to achieve incremental gains in the control of internal combustion engines. Further advancements in these technologies, as well as continuing evolutionary advancements in combustion chamber and intake valve design and combustion chamber flow dynamics, have permitted the production of GDI engines for automotive applications. Mitsubishi, Toyota and Nissan all market four- stroke GDI engines in Japan.

Major Objectives of the GDI engine
¢ Ultra-low fuel consumption that betters that of even diesel engines
¢ Superior power to conventional MPI engines
Sophisticated high-pressure injectors capable of producing very fine, well-defined fuel sprays, coupled with advanced charge air control techniques, now make stable GDI combustion feasible. There are impediments to widespread GDI introduction, however, especially in compliance with stringent emission standards. This report addresses both the efficiencies inherent in GDI technology and the emissions constraints that must be addressed before GDI can displace current spark-ignition engine technology.
In this seminar I am intending to familiarize the working of this technology, which has the capability to become the turning point in the development of diesel engine technology.

WHY NOT CARBURETTOR

All Internal combustion engines burn fuel in air and every fuel has ideal air ratio at which it will ignite or burn as completely as possible. The challenge that faces engineers is to introduce the perfect or precise proportions of fuel and air required for complete combustion. This is commonly referred to as the stoichiometric ratio. Petrol has a stoichiometric ratio of 14.7:1(14.7 parts of air with 1 part of fuel by weight). This ratio has to be maintained under the varying engine loads and conditions. The carb earlier did this metering with its ancillaries. But the carb has its limits and though performance and economy with modern carbs were acceptable, a seamless power delivery and emissions often suffered.

Carburetor has following disadvantages

¢ Vapour lock
¢ Perfect air/fuel mixture cannot be obtained
¢ Lack of throttle response
¢ Low volumetric efficiency
¢ Icing “ problem in aircraft engines
¢ Mechanical device
¢ Compromises on emission

2.0 Transition of fuel supply


3.0 Major characteristics of the GDI engine
3.1. Lower fuel consumption and higher output
(1) Optimal fuel spray for two-combustion mode
Using methods and technologies unique to Mitsubishi, the GDI engine provides both lower fuel consumption and higher output. This seemingly contradictory and difficult feat is achieved with the use of two combustion modes. Put another way, injection timings change to match engine load.
For load conditions required of average urban driving, fuel is injected late in the compression stroke as in a diesel engine. By doing so, an ultra-lean combustion is achieved due to an ideal formation of a stratified air-fuel mixture. During high performance driving conditions, fuel is injected during the intake stroke. This enables a homogeneous air-fuel mixture like that of in conventional MPI engines to deliver higher output.
Ultra-lean Combustion Mode
Under most normal driving conditions, up to speeds of 120km/h, the Mitsubishi GDI engine operates in ultra-lean combustion mode for less fuel consumption. In this mode, fuel injection occurs at the latter stage of the compression stroke and ignition occurs at an ultra-lean air-fuel ratio of 30 to 40 (35 to 55, included EGR).

Superior Output Mode
When the GDI engine is operating with higher loads or at higher speeds, fuel injection takes place during the intake stroke. This optimizes combustion by ensuring a homogeneous, cooler air-fuel mixture that minimized the possibility of engine knocking.


(2) The GDI engines foundation technologies
There are four technical features that make up the foundation technology. The Upright Straight Intake Port supplies optimal airflow into the cylinder. The Curved-top Piston controls combustion by helping shape the air-fuel mixture. The High Pressure Fuel Pump supplies the high pressure needed for direct in-cylinder injection. And the High Pressure Swirl Injector controls the vaporization and dispersion of the fuel spray.

These fundamental technologies, combined with other unique fuel control technologies, enabled Mitsubishi to achieve both of the development objectives, which were fuel consumption lower than those of diesel engines and output higher than those of conventional MPI engines. The methods are shown below.

In-cylinder Airflow
The GDI engine has upright straight intake ports rather than horizontal intake ports used in conventional engines. The upright straight intake ports efficiently direct the airflow down at the curved-top piston, which redirects the airflow into a strong reverse tumble for optimal fuel injection



Fuel Spray
Newly developed high-pressure swirl injectors provide the ideal spray pattern to match each engine operational modes. And at the same time by applying highly swirling motion to the entire fuel spray, they enable sufficient fuel atomization that is mandatory for the GDI even with a relatively low fuel pressure of 50kg/cm2



Optimized Configuration of the Combustion Chamber
The curved-top piston controls the shape of the air-fuel mixture as well as the airflow inside the combustion chamber, and has an important role in maintaining a compact air fuel mixture. The mixture, which is injected late in the compression stroke, is carried toward the spark plug before it can disperse.
Mitsubishis advanced in-cylinder observation techniques including laser-methods are utilized to determine the optimum piston shape.

3.2. Realization of lower fuel consumption

3.2.1 Basic Concept

In conventional gasoline engines, dispersion of an air-fuel mixture with the ideal density around the spark plug was very difficult. However, this is possible in the GDI engine. Furthermore, extremely low fuel consumption is achieved because ideal stratification enables fuel injected late in the compression stroke to maintain an ultra-lean air-fuel mixture.
An engine for analysis purpose has proved that the air-fuel mixture with the optimum density gathers around the spark plug in a stratified charge. This is also borne out by analyzing the behavior of the fuel spray immediately before ignition and the air-fuel mixture itself.
As a result, extremely stable combustion of ultra-lean mixture with an air-fuel ratio of 40 (55, EGR included) is achieved as shown below.





3.2.2 Combustion of Ultra-lean Mixture

In conventional MPI engines, there were limits to the mixtures leanness due to large changes in combustion characteristics. However, the stratified mixture of the GDI enabled greatly decreasing the air-fuel ratio without leading to poorer combustion. For example, during idling when combustion is most inactive and unstable, the GDI engine maintains a stable and fast combustion even with an extremely lean mixture of 40 to 1 air-fuel ratio (55 to 1, EGR included)


3.2.3 Vehicle Fuel Consumption
Fuel Consumption during Idling
The GDI engine maintains stable combustion even at low idle speeds. Moreover, it offers greater flexibility in setting the idle speed.
Compared to conventional engines, its fuel consumption during idling is 40% less.


Fuel Consumption during Cruising Drive
At 40km/h, for example, the GDI engine uses 35% less fuel than a comparably sized conventional engine


Fuel Consumption in City Driving
In Japanese 10E15 mode tests (representative of typical Japanese urban driving ), the GDI engine used 35% less fuel than comparably sized conventional gasoline engines. Moreover, these results indicate that the GDI engine uses less fuel than even diesel engines.


Emission Control
Previous efforts to burn a lean air-fuel mixture have resulted in difficulty to control NOx emission. However, in the case of GDI engine, 97% NOx reduction is achieved by utilizing high-rate EGR (Exhaust Gas Ratio) such as 30% that is allowed by the stable combustion unique to the GDI as well as a use of a newly developed lean-NOx catalyst.

Newly Developed Lean NOx Catalyst (HC selective deoxidization type)


3.3. Realization of Superior Output

3.3.1 Basic concept
To achieve power superior to conventional MPI engines, the GDI engine has a high compression ratio and a highly efficient air intake system, which result in improved volumetric efficiency.

Improved Volumetric Efficiency
Compared to conventional engines, the Mitsubishi GDI engine provides better volumetric efficiency. The upright straight intake ports enable smoother air intake. And the vaporization of fuel, which occurs in the cylinder at a late stage of the compression stroke, cools the air for better volumetric efficiency.


Increased Compression Ratio
The cooling of air inside the cylinder by the vaporization of fuel has another benefit, to minimize engine knocking. This allows a high compression ratio of 12, and thus improved combustion efficiency

3.3.2 Achievement
Engine performance
Compared to conventional MPI engines of a comparable size, the GDI engine provides approximately 10% greater output and torque at all speeds.

Vehicle Acceleration
In high-output mode, the GDI engine provides outstanding acceleration.
The following chart compares the performance of the GDI engine with a conventional MPI engine.


4. The difference between new GDI and current MPI

For fuel supply, conventional engines use a fuel injection system, which replaced the carburetion system. MPI or Multi-Point Injection, where the fuel is injected to each intake port, is currently the one of the most widely used systems. However, even in MPI engines there are limits to fuel supply response and the combustion control because the fuel mixes with air before entering the cylinder. Mitsubishi set out to push those limits by developing an engine where gasoline is directly injected into the cylinder as in a diesel engine, and moreover, where injection timings are precisely controlled to match load conditions. The GDI engine achieved the following outstanding characteristics.
¢ Extremely precise control of fuel supply to achieve fuel efficiency that exceeds that of diesel engines by enabling combustion of an ultra-lean mixture supply.
¢ Very efficient intake and relatively high compression ratio unique to the GDI engine deliver both high performance and response that surpasses those of conventional MPI engines.

Improved fuel conversion economy (up to 25% potential improvement, resulting from :
Less pumping loss (unthrottled, stratified mode);
Higher compression ratio (charge cooling with injection during induction
Lower octane requirement (charge cooling with injection during induction);
Increased volumetric efficiency (charge cooling with injection during induction);
Improved transient response.
Less acceleration-enrichment required (no manifold film)
More precise air-fuel ratio control
More rapid starting;
Less cold-start over-fueling required.
Extended EGR tolerance limit (to minimize the use of throttling)
Selective emissions advantages
Reduced CO2 emissions
5.0 OUTLINE

5.1 Major Specifications


5.2 Engine Diagram


5.3 Technical features
¢ Upright straight intake ports for optimal airflow control in the cylinder
¢ Curved-top pistons for better combustion
¢ High pressure fuel pump to feed pressurized fuel into the injectors
¢ High-pressure swirl injectors for optimum air-fuel mixture
OPERATION
Fuel is delivered to the fuel rail (pressure accumulator) by the high-pressure pump. Hydraulic connections join the fuel rail to the solenoid-operated high-pressure fuel injectors. A closed control loop comprising the fuel pressure sensor, pressure control valve and electronic control unit controls the pressure of the hydraulic system individually for all operating points. The injection pressure, start of injection and injection lime can be freely selected (within predefined limits) for each operating point of the engine. The shape of the injection jet is adapted to the requirements of the engine.
The tried and tested MOTRONIC, which has been extended to include special functions for gasoline direct injection, is responsible for engine management. The MED 7 coordinates the different torque parameters according to the position of the accelerator pedal and undertakes the necessary control actions in the engine.
A hot-film air-mass sensor measures the air mass drawn in by the engine. The MED 7 has an ETC system, i.e. the degree of acceleration required by the driver is detected buy a pedal travel sensor and the sensor signal is passed on to the control unit. The control unit regulates the electronically controlled throttle valve under consideration of other vehicle and engine data

The direct-injection spark-ignition engine has different operating modes. The advantage of GDI with its internal mixture formation is increased compression with improved efficiency.
Lower part-load range with a very lean mixture ( > 1) and targeted stratified charging during operation without throttle: The fuel is injected directly into the cylinders in the compression stroke shortly before ignition. The useful speed range is limited in the case of stratified charging. The advantage of this stratified operating mode is the reduction in charge cycle losses caused by operation without throttle. Here, fuel is the only factor controlling performance. With the homogeneous ( = 1) operating mode, the fuel is injected during the induction stroke. This mode can be used across the entire speed / load range. Here, as with intake manifold injection, performance is controlled by charging and ignition. With the homogeneous lean ( > 1) operating mode (as with the "homogenous" mode); injection takes place during the induction stroke. The quantity of fuel is, however, less (excess air). As with stratified mode, fuel is also the factor controlling performance in this operating mode.
The engine management system maintains the torque at a constant level during load changes between these two operating modes (homogeneous and stratified mode) by adapting the quantity of fuel, air charge, and ignition angle according to the driver's requirements.

The high rate of exhaust gas recalculations in spark-ignition engines with direct injection reduces the volume of untreated NOx emissions (upstream of the catalytic converter). Newly developed catalytic converter systems also reduce the remaining nitrogen oxides to below the levels required by law, even during operation with a lean mixture.
Todays direct injection systems can reduce fuel consumption by up to 15% and therefore, effectively lower the amount of traffic-related C02 emissions. The system satisfies the EU IV exhaust-emission standard and has an EOBD self-diagnosis which complies with the European standard.

6.0 CONCLUSION
The world need to protect the environment , and the more stringent emission regulations that evolved year after year have challenged vehicle manufacturers among other things to produce vehicles that not only conform to regulations but also consistently exceed them. The GDI engine does this and has technology (adaptive learning) to ensure that as the engine ages it will continue to conform by adjusting itself as the engine components and emission devises wear . It is expected that by the year 2005 when more stringent emissions regulations will be enforced in the market , technologies like that offered with the GDI engine will be in a position to ensure that air quality standards and emissions levels can be meet.
Gasoline direct injection (GDI) engine technology has received considerable attention over the last few years as a way to significantly improve fuel efficiency without making a major shift away from conventional internal combustion technology. In many respects, GDI technology represents a further step in the natural evolution of gasoline engine fueling systems.

References
1. Internal Combustion Engines By: Anand V Domkundwar.
2. Internal Combustion Engines By: Mathur & Sharma.
3. howstuffworks.com
4. mitsubishi-np.in
5. autoworld.com
6. visionengineer.com
7. http://seminarsprojects.in

[attachment=4524]

GASOLINE DIRECT INJECTION (GDI)
abstract

In recent years, legislative and market requirements have driven the need to reduce fuel consumption while meeting increasingly stringent exhaust emissions. This trend has dictated increasing complexity in automotive engines and new approaches to engine design. A key research objective for the automotive engineering community has been the potential combination of gasoline-engine specific power with diesel-like engine efficiency in a cost-competitive, production-feasible power train. One promising engine development route for achieving these goals is the potential application of lean burn direct injection (DI) for gasoline engines. In carburetors the fuel is sucked due to the pressure difference caused by the incoming air. This will affect the functioning of the carburetor when density changes in air are appreciable. There was a brief period of electronically controlled carburetor, but it was abandoned due to its complex nature. On the other hand in fuel injection the fuel is injected into the air.
TRANSITION OF FUEL SUPPLY SYSTEM
The transition of the fuel supply system used in automobiles is graphically shown below. In carburetor the fuel from the fuel chamber is sucked in by the pressure variation caused due to the incoming air. The fuel then mixes with the air and reaches the cylinder through the inlet manifold. Where as in a port injection system the fuel to the cylinder is supplied by a separate fuel injector placed near the inlet valve of the cylinder. And in a direct injection system the fuel to the cylinder is supplied by a fuel injector placed inside the cylinder.

[attachment=4954]

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Gasoline direct injection

INTRODUCTION

In recent years, legislative and market requirements have driven the need to reduce fuel consumption while meeting increasingly stringent exhaust emissions. This trend has dictated increasing complexity in automotive engines and new approaches to engine design. A key research objective for the automotive engineering community has been the potential combination of gasoline-engine specific power with diesel-like engine efficiency in a cost-competitive, production-feasible power train. One promising engine development route for achieving these goals is the potential application of lean burn direct injection (DI) for gasoline engines. In carburetors the fuel is sucked due to the pressure difference caused by the incoming air. This will affect the functioning of the carburetor when density changes in air are appreciable. There was a brief period of electronically controlled carburetor, but it was abandoned due to its complex nature. On the other hand in fuel injection the fuel is injected into the air. The objective can be attained by using gasoline direct injection technology in the automobiles.
In internal combustion engines, gasoline direct injection is a variant of fuel injection employed in modern four- stroke petrol engines. The petrol/gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder. This helps in preventing leakage loss, that occurs in the conventional carburetor when the fuel is being transferred from fuel tank to the engine cylinder.

GASOLINE DIRECT INJECTION (GDI)
In conventional engines, fuel and air are mixed outside the cylinder. This ensures waste between the mixing point and the cylinder, as well as imperfect injection timing. Gasoline direct injection engine generates the air fuel mixture in the combustion chamber. During the induction stroke only the combustion air flows through the open intake valve. The fuel is then directly injected into the combustion chamber by the fuel injector. But in the GDI engine, petrol is injected directly into the cylinder with precise timing, eliminating waste and inefficiency.

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[attachment=4964]

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This article is presented by:
VISHU KUMAR
Dept Of Mechanical Engg
MITK.

GASOLINE DIRECT INJECTION

Gasoline direct injection:
GDI is a variant of fuel injection employed in modern four stroke petrol engines. The gasoline or petrol is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder.
SYSTEM
Fuel pump: fuel injected engines often use electric fuel pumps that are mounted inside the fuel tank. And some fuel injected engines have two fuel pumps: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine.

High Pressure lines:
This tube or pipe connects pump to the common rail. The pipe assembly transports fuel at high pressure between pump, rail and injectors, remains completely sealed and resistant to pressure changes.

Thats great work
thanks for u all

[attachment=11102]
GASOLINE DIRECT INJECTION
1.0 INTRODUCTION
Gasoline direct injection (GDI) engine technology has received considerable attention over the last few years as a way to significantly improve fuel efficiency without making a major shift away from conventional internal combustion technology. In many respects, GDI technology represents a further step in the natural evolution of gasoline engine fueling systems. Each step of this evolution, from mechanically based carburetion, to throttle body fuel injection, through multi-point and finally sequential multi-point fuel injection, has taken advantage of improvements in fuel injector and electronic control technology to achieve incremental gains in the control of internal combustion engines. Further advancements in these technologies, as well as continuing evolutionary advancements in combustion chamber and intake valve design and combustion chamber flow dynamics, have permitted the production of GDI engines for automotive applications. Mitsubishi, Toyota and Nissan all market four- stroke GDI engines in Japan.
Major Objectives of the GDI engine
• Ultra-low fuel consumption that betters that of even diesel engines
• Superior power to conventional MPI engines
Sophisticated high-pressure injectors capable of producing very fine, well-defined fuel sprays, coupled with advanced charge air control techniques, now make stable GDI combustion feasible. There are impediments to widespread GDI introduction, however, especially in compliance with stringent emission standards. This report addresses both the efficiencies inherent in GDI technology and the emissions constraints that must be addressed before GDI can displace current spark-ignition engine technology.
In this seminar I am intending to familiarize the working of this technology, which has the capability to become the turning point in the development of diesel engine technology.
WHY NOT CARBURETTOR?
All Internal combustion engines burn fuel in air and every fuel has ideal air ratio at which it will ignite or burn as completely as possible. The challenge that faces engineers is to introduce the perfect or precise proportions of fuel and air required for complete combustion. This is commonly referred to as the stoichiometric ratio. Petrol has a stoichiometric ratio of 14.7:1(14.7 parts of air with 1 part of fuel by weight). This ratio has to be maintained under the varying engine loads and conditions. The carb earlier did this metering with its ancillaries. But the carb has its limits and though performance and economy with modern carbs were acceptable, a seamless power delivery and emissions often suffered.
Carburetor has following disadvantages
• Vapour lock
• Perfect air/fuel mixture cannot be obtained
• Lack of throttle response
• Low volumetric efficiency
• Icing – problem in aircraft engines
• Mechanical device
• Compromises on emission
2.0 Transition of fuel supply
3.0 Major characteristics of the GDI engine
3.1. Lower fuel consumption and higher output
(1) Optimal fuel spray for two-combustion mode
Using methods and technologies unique to Mitsubishi, the GDI engine provides both lower fuel consumption and higher output. This seemingly contradictory and difficult feat is achieved with the use of two combustion modes. Put another way, injection timings change to match engine load.
For load conditions required of average urban driving, fuel is injected late in the compression stroke as in a diesel engine. By doing so, an ultra-lean combustion is achieved due to an ideal formation of a stratified air-fuel mixture. During high performance driving conditions, fuel is injected during the intake stroke. This enables a homogeneous air-fuel mixture like that of in conventional MPI engines to deliver higher output.
Ultra-lean Combustion Mode
Under most normal driving conditions, up to speeds of 120km/h, the Mitsubishi GDI engine operates in ultra-lean combustion mode for less fuel consumption. In this mode, fuel injection occurs at the latter stage of the compression stroke and ignition occurs at an ultra-lean air-fuel ratio of 30 to 40 (35 to 55, included EGR).
Superior Output Mode
When the GDI engine is operating with higher loads or at higher speeds, fuel injection takes place during the intake stroke. This optimizes combustion by ensuring a homogeneous, cooler air-fuel mixture that minimized the possibility of engine knocking.
(2) The GDI engines foundation technologies
There are four technical features that make up the foundation technology. The Upright Straight Intake Port supplies optimal airflow into the cylinder. The Curved-top Piston controls combustion by helping shape the air-fuel mixture. The High Pressure Fuel Pump supplies the high pressure needed for direct in-cylinder injection. And the High Pressure Swirl Injector controls the vaporization and dispersion of the fuel spray.
These fundamental technologies, combined with other unique fuel control technologies, enabled Mitsubishi to achieve both of the development objectives, which were fuel consumption lower than those of diesel engines and output higher than those of conventional MPI engines. The methods are shown below.
In-cylinder Airflow
The GDI engine has upright straight intake ports rather than horizontal intake ports used in conventional engines. The upright straight intake ports efficiently direct the airflow down at the curved-top piston, which redirects the airflow into a strong reverse tumble for optimal fuel injection
Fuel Spray
Newly developed high-pressure swirl injectors provide the ideal spray pattern to match each engine operational modes. And at the same time by applying highly swirling motion to the entire fuel spray, they enable sufficient fuel atomization that is mandatory for the GDI even with a relatively low fuel pressure of 50kg/cm2
Optimized Configuration of the Combustion Chamber
The curved-top piston controls the shape of the air-fuel mixture as well as the airflow inside the combustion chamber, and has an important role in maintaining a compact air fuel mixture. The mixture, which is injected late in the compression stroke, is carried toward the spark plug before it can disperse.
Mitsubishis advanced in-cylinder observation techniques including laser-methods are utilized to determine the optimum piston shape.
3.2. Realization of lower fuel consumption
3.2.1 Basic Concept
In conventional gasoline engines, dispersion of an air-fuel mixture with the ideal density around the spark plug was very difficult. However, this is possible in the GDI engine. Furthermore, extremely low fuel consumption is achieved because ideal stratification enables fuel injected late in the compression stroke to maintain an ultra-lean air-fuel mixture.
An engine for analysis purpose has proved that the air-fuel mixture with the optimum density gathers around the spark plug in a stratified charge. This is also borne out by analyzing the behavior of the fuel spray immediately before ignition and the air-fuel mixture itself.
As a result, extremely stable combustion of ultra-lean mixture with an air-fuel ratio of 40 (55, EGR included) is achieved as shown below.

[attachment=12863]
[attachment=12864]


Gasoline Direct Injection (GDI)
M. Tech Seminar

Submitted by:
Arjun Lal
Roll no. - 06020605
IDD, Part-V (10th Sem.)
Specialization- Thermal & Fluid
Department of Mechanical Engineering
Institute of Technology
Banaras Hindu University

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Abstract:
In recent years, legislative and market requirements have driven the need to reduce fuel consumption while meeting increasingly stringent exhaust emissions. This trend has dictated increasing complexity in automotive engines and new approaches to engine design. Conventional gasoline engines are designed to use an electronic fuel injection system, replacing the traditional mechanical carburetion system. Multi-point injection (MPI), where the fuel is injected through each intake port, is currently one of the most widely used systems. Although MPI provides a drastic improvement in response and combustion quality, it is still limited due to fuel and air mixing prior to entering the cylinder.
To further increase response time and combustion efficiency, while lowering fuel consumption and increasing output, systems may use direct injection. Gasoline direct injection (GDI) engines are engineered to inject the gasoline directly into the cylinder in a manner similar to diesel direct injection engines. Direct injection is designed to allow greater control and precision, resulting in better fuel economy. In response to driving conditions, the GDI engine changes the timing of the fuel spray injection, alternating between two distinctive combustion modes- stratified charge (Ultra-Lean combustion), and homogenous charge (Superior Output combustion).
Direct injection is also designed to allow higher compression ratios, delivering higher performance with lower fuel consumption. Its main benefit is it saves fuel and emission is very less. Frequent operation in stratified mode leads to reduction of CO2 production by nearly 20 percent. It also provides improved torque & smooth transition between operation modes.


INTRODUCTION
In recent years, legislative and market requirements have driven the need to reduce fuel consumption while meeting increasingly stringent exhaust emissions. This trend has dictated increasing complexity in automotive engines and new approaches to engine design. A key research objective for the automotive engineering community has been the potential combination of gasoline-engine specific power with diesel-like engine efficiency in a cost-competitive, production-feasible power train. One promising engine development route for achieving these goals is the potential application of lean burn direct injection (DI) for gasoline engines. In carburetors the fuel is sucked due to the pressure difference caused by the incoming air. This will affect the functioning of the carburetor when density changes in air are appreciable. There was a brief period of electronically controlled carburetor, but it was abandoned due to its complex nature. On the other hand in fuel injection the fuel is injected into the air.
TRANSITION OF FUEL SUPPLY SYSTEM
The transition of the fuel supply system used in automobiles is graphically shown below. In carburetor the fuel from the fuel chamber is sucked in by the pressure variation caused due to the incoming air. The fuel then mixes with the air and reaches the cylinder through the inlet manifold. Where as in a port injection system the fuel to the cylinder is supplied by a separate fuel injector placed near the inlet valve of the cylinder. And in a direct injection system the fuel to the cylinder is supplied by a fuel injector placed inside the cylinder.



OPERATING DIFFICULTIES FOR A CARBURETOR
Some problems associated with comfortable running of the carburetor are discussed here.
1. Ice formation: The vaporisation of the fuel injected in the current of the air requires latent heat and the taken mainly from the incoming air. As a result of this, the temperature of the air drops below the dew point of the water vapour in the air and it condenses and many times freeze into ice if the temperature falls below dew point temperature.
2. Vapour Lock: The improved volatility of modern fuels and the necessity of providing heat to prevent the ice formation, has created carburetion difficulties due to vaporisation of fuel in pipes and float chamber. The heating may also occur due to petrol pipes being near the engine. If the fuel supply is large and supply is small, a high velocity will result causing high vacuum. This causes considerable drop which may also cause the formation of vapour bubbles. If these bubbles formed accumulate at the tube bend, then they may interrupt the fuel flow from the tank or the fuel pump and engine will stop because of lack of fuel. Vapour lock is formed because of rapid bubbling of fuel and usually happens in hot summer.
3. Back Firing: During the starting of an engine under cold working conditions, the usual manipulation of the choke varies the mixture from too lean to too rich. A very lean mixture will burn very slowly and the flame may still exist in cylinder when the exhaust valve is about to open. The fresh charge in the intake manifold is about to open. The fresh charge in the intake manifold is not so diluted as when inducted into the cylinder and mixed with the clearance gases and consequently burn more rapidly than the charge in the cylinder. If lean charge comes in contact with flames existing in the cylinder, there will be flash of flame back through the intake manifold, burning the charge therein and causing the customary back firing in the carburetor.
ADVANTAGES OF FUEL INJECTION OVER CARBURETOR
 The fuel injection eliminates several intake manifold distribution problems. One of the most difficult problems in a carbureted system is to get the same amount and richness of air-fuel mixture to each cylinder. The problem is that the intake manifold acts as a storing device, sending a richer air fuel mixture to the end cylinders. The air flows readily around the corners and through various shaped passages. However the fuel, because it is heavier is unable to travel as easily around the bends in the intake manifold. As a result, some of fuel particles continue to move to the end of the intake manifold, accumulating there. This enriches the mixture going the end cylinder. The center cylinder closest to the carburetor gets the leanest mixture¬¬¬¬¬. The port injection solves this problem because the same amount of fuel is injected at each intake valve port. Each cylinder gets the same amount of air-fuel mixture of the same mixture richness.
 Another advantage of the fuel injection system is that the intake manifold can be designed for the most efficient flow of air only. It does not have to handle fuel. Also, because only a throttle body is used, instead of a complete carburetor, the hood height of the car can be lowered.
 With fuel injection, fuel mixture requires no extra heating during warm up. No manifold heat control valve or heated air system is required. Throttle response is faster because the fuel is under pressure at the injection valves at all times. An electric fuel pump supplies the pressure. The carburetor will depend on differences in air pressure as the force that causes the fuel to feed into the air passing through.
 Fuel injection has no choke, but sprays atomized fuel directly into the engine. This eliminates most of the cold start problems associated with carburetors.
 Electronic fuel injection also integrates more easily with computerized engine control systems because the injectors are more easily controlled than a mechanical carburetor with electronic add-ons.
 Multi port fuel injection (where each cylinder has its own injector) delivers a more evenly distributed mixture of air and fuel to each of the engine's cylinders, which improves power and performance.
 Sequential fuel injection (where the firing of each individual injector is controlled separately by the computer and timed to the engine's firing sequence) improves power and reduces emissions.


ELECTRONIC FUEL INJECTION
The main components of electronic fuel injection are described below.
1. Engine Control Unit (ECU)
2. Sensors
3. Fuel Injectors
Engine Control Unit (ECU): This unit is the heart of electronic injection system which is responsible for metering the quantity of fuel supplied to each cylinder. The unit contains a number of printed circuits boards on which, a series of transistors, diodes and other electronic components are mounted. This makes the vital data analysing circuits responding to various input signals. After processing the input data, the power output circuits in the control unit generates current pulses which are transmitted to the solenoid injectors to operate the injector for the required period.
For example, when the pedal of the vehicle is stepped on, the throttle valve (this is the valve that regulates how much air enters the engine) opens up more, letting in more air. The engine control unit (ECU) "sees" the throttle valve open with the help of sensors and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens; otherwise, when the gas pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it. Sensors monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right.
The ECU generally works in two operating modes, namely open loop and closed loop. In closed loop Oxygen sensor is used to sense the quantity of excess Oxygen in the smoke and this information is used for the next cycle of injection. This is also called feedback mode. On the other hand in open loop system the Oxygen sensor is not used.



Engine Sensors: In order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to monitor a huge number of input sensors. Here are just a few:



• Mass airflow sensor - Tells the ECU the mass of air entering the engine
• Oxygen sensor - The device measures the amount of oxygen in the exhaust gas and sends this information to the electronic control unit. If there is too much oxygen, the mixture is too lean. If there is too little, the mixture is too rich. In either case, the electronic control unit adjusts the air fuel ratio by changing the fuel injected. It is usually used with closed loop mode of the ECU.
• Throttle position sensor - Monitors the throttle valve position (which determines how much air goes into the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary
• Coolant temperature sensor - Allows the ECU to determine when the engine has reached its proper operating temperature
• Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping (which would indicate a high electrical load)
• Manifold absolute pressure sensor - Monitors the pressure of the air in the intake manifold. The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced.
• Engine speed sensor - Monitors engine speed, which is one of the factors used to calculate the pulse width.
• Crank Angle sensor - Monitors the position of the piston and gives the information to the ECU. Accordingly the ECU adjusts the valve timing.

Fuel Injectors:
The solenoid-operated fuel injector is shown in the figure above. It consists of a valve body and needle valve to which the solenoid plunger is rigidly attached. The fuel is supplied to the injector under pressure from the electric fuel pump passing through the filter. The needle valve is pressed against a seat in the valve body by a helical spring to keep it closed until the solenoid winding is energized. When the current pulse is received from the electronic control unit, a magnetic field builds up in the solenoid which attracts a plunger and lifts the needle valve from its seat. This opens the path to pressurised fuel to emerge as a finely atomised spray.
The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU. The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors.

[attachment=12933]
CHAPTER 1
INTRODUCTION
In recent years, legislative and market requirements have driven the need to reduce fuel consumption while meeting increasingly stringent exhaust emissions. This trend has dictated increasing complexity in automotive engines and new approaches to engine design. A key research objective for the automotive engineering community has been the potential combination of gasoline-engine specific power with diesel-like engine efficiency in a cost-competitive, production-feasible power train. One promising engine development route for achieving these goals is the potential application of lean burn direct injection (DI) for gasoline engines. In carburetors the fuel is sucked due to the pressure difference caused by the incoming air. This will affect the functioning of the carburetor when density changes in air are appreciable. There was a brief period of electronically controlled carburetor, but it was abandoned due to its complex nature. On the other hand in fuel injection the fuel is injected into the air. The objective can be attained by using gasoline direct injection technology in the automobiles.
In internal combustion engines, gasoline direct injection is a variant of fuel injection employed in modern four- stroke petrol engines. The petrol/gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder. This helps in preventing leakage loss, that occurs in the conventional carburetor when the fuel is being transferred from fuel tank to the engine cylinder.
CHAPTER 2
GASOLINE DIRECT INJECTION (GDI)
In conventional engines, fuel and air are mixed outside the cylinder. This ensures waste between the mixing point and the cylinder, as well as imperfect injection timing. Gasoline direct injection engine generates the air fuel mixture in the combustion chamber. During the induction stroke only the combustion air flows through the open intake valve. The fuel is then directly injected into the combustion chamber by the fuel injector. But in the GDI engine, petrol is injected directly into the cylinder with precise timing, eliminating waste and inefficiency.
2.1 COMPONENTS OF THE GDI:
1 HIGH PRESSURE PUMP
2 HIGH PRESSURE PIPE LINES
3 FILTER
4 COMMON RAIL
5 INJECTORS
6 SENSORS
7 ENGINE CONTROL UNIT (ECU)
2.1.1 HIGH PRESSURE PUMPS:
A fuel pump is a frequently (but not always) essential component on a car or other internal combustion engine device. Many engines do not require any fuel pump at all, requiring only gravity to feed fuel from the fuel tank through a line or hose to the engine but in non-gravity feed designs, fuel has to be pumped from the fuel tank to the engine and delivered under low pressure to the carburetor or under high pressure to the fuel injection system. Often, carbureted engines use low pressure mechanical pumps that are mounted outside the fuel tank, whereas fuel injected engines often use electric fuel pumps that are mounted inside the fuel tank (and some fuel injected engines have two fuel pumps: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine).
Fig1 cross section of electrical pump
(Courtesy: Bosch fuel pump Toyota Motor Sale, U.S.A., Inc. from #850 EFI Course Book)
In many modern cars the fuel pump is usually electric and located inside of the fuel tank. The pump creates positive pressure in the fuel lines, pushing the gasoline to the engine. Placing the pump in the tank puts the component least likely to handle gasoline vapor well (the pump itself) farthest from the engine, submersed in cool liquid. Another benefit to placing the pump inside the tank is that it is less likely to start a fire. Though electrical components (such as a fuel pump) can spark and ignite fuel vapors, liquid fuel will not explode. And therefore submerging the pump in the tank is one of the safest places to put it. In most cars, the fuel pump delivers a constant flow of gasoline to the engine, fuel not used is returned to the tank.
2.1.2 HIGH PRESSURE LINES:
Fig 2 high pressure lines
(Courtesy: " OMC Ficht fuel injection engines hit the market", PR Newswire, July 31, 1996)
The Common Rail High Pressure (HP) pipe is made up of a formed pipe with sealing interfaces at both ends with fastening screws or nuts. The pipe assembly transports fuel at high pressure between pump, rail and injectors, remaining completely sealed and resistant to pressure changes. The assembly provides a minimum pressure loss against all internal and external influences, such as temperature, corrosion, and engine fluids.
2.1.3 FILTERS:
Due to the high injection pressures involved in a Common Rail system, the cleanliness of fuel is critical. One of the most important system components is the fuel filter which acts as the engine’s first line of defence. Effective filtration and petrol fuel conditioning are essential to protect the Common Rail fuel injection equipment from water and particle contamination. As little as 2 microns of dirt can completely damage the filter components and cylinder lining.
Fig 3 exploded view of the filter.
(Courtesy: automotive engineering by Kirpal Singh vol 2#281)
Fuel filter is located along the fuel lines, either in the engine compartment or underneath the car by the fuel tank. It is the responsibility of the fuel filter to trap large particles in the fuel in order to prevent them from getting into the engine. Because of the tremendous force behind the up-and-down motion of the engine's pistons, which compress the air-fuel mixture so that it will burn more efficiently, any large particles in the fuel could potentially cause serious damage to the engine. Large particles in the fuel also have the ability to clog fuel injectors, depriving a cylinder of precious fuel and requiring that the injector be cleaned or replaced. Therefore, maintaining a clean fuel filter is imperative to the performance of a car's engine.
2.1.4 COMMON RAILS:
Fig 4 common rail
(courtesy: direct injection gasoline by F. Zhao and D.T Harrington)
Common rail [1p425] direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines. It features a high-pressure (over 1,000 psi) fuel rail feeding individual valves. Modern common rail systems, whilst working on the same principle, are governed by an engine control unit (ECU) which opens each injector electronically rather than mechanically. In common rail systems a high pressure pump stores a reservoir of fuel at high pressure — up to and above 2,000 bars. The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel. This simplifies the purpose of the high pressure pump in that it only has to maintain a commanded pressure at a target (either mechanically or electronically controlled). The fuel injectors are typically ECU-controlled. When the fuel injectors are electrically activated a hydraulic valve (consisting of a nozzle and plunger) is mechanically or hydraulically opened and fuel is sprayed into the cylinders at the desired pressure. Since the fuel pressure energy is stored remotely and the injectors are electrically actuated the injection pressure at the start and end of injection is very near the pressure in the accumulator (rail), thus producing a square injection rate. If the accumulator, pump, and plumbing are sized properly, the injection pressure and rate will be the same for each of the multiple injection events. Common rail engines require no heating up time and produce lower engine noise and emissions than older systems.

[attachment=13292]
1. Introduction
The basic goals of the automotive industry; a high power, low specific fuel consumption,
low emissions, low noise and better drive comfort. With increasing the vehicle number, the
role of the vehicles in air pollution has been increasing significantly day by day. The
environment protection agencies have drawn down the emission limits annually.
Furthermore, continuously increasing price of the fuel necessitates improving the engine
efficiency. Since the engines with carburetor do not hold the air fuel ratio close to the
stoichiometric at different working conditions, catalytic converter cannot be used in these
engines. Therefore these engines have high emission values and low efficiency. Electronic
controlled Port Fuel Injection (PFI) systems instead of fuel system with carburetor have been
used since 1980’s. In fuel injection systems, induced air can be metered precisely and the
fuel is injected in the manifold to air amount. By using the lambda sensor in exhaust system,
air/fuel ratio is held of stable value. Fuel systems without electronic controlled it is
impossible to comply with the increasingly emissions legislation.
If port fuel injection system is compared with carburetor system, it is seen that has some
advantages. These are;
1. Lower exhaust emissions.
2. Increased volumetric efficiency and therefore increased output power and torque.
The carburetor venturi prevents air and, in turn, volumetric efficiency decrease.
3. Low specific fuel consumption. In the engine with carburetor, fuel cannot be
delivered the same amount and the same air/fuel ratio per cycle, for each cylinder.
4. The more rapid engine response to changes in throttle position. This increases the
drive comfort.
5. For less rotation components in fuel injection system, the noise decreases
(Heywood, 2000; Ferguson, 1986).
Though the port fuel injection system has some advantages, it cannot be meet continuously
increased the demands about performance, emission legislation and fuel economy, at the
present day (Stone, 1999). The electronic controlled gasoline direct injection systems were
started to be used instead of port fuel injection system since 1990’s.
2 Fuel Injection
The Gasoline Direct Injection (GDI) engines give a number of features, which could not be
realized with port injected engines: avoiding fuel wall film in the manifold, improved
accuracy of air/fuel ratio during dynamics, reducing throttling losses of the gas exchange by
stratified and homogeneous lean operation, higher thermal efficiency by stratified operation
and increased compression ratio, decreasing the fuel consumption and CO2 emissions, lower
heat losses, fast heating of the catalyst by injection during the gas expansion phase,
increased performance and volumetric efficiency due to cooling of air charge, better coldstart
performance and better the drive comfort (Zhao et al., 1999; Karamangil, 2004; Smith et
al., 2006).
2. The Performance and Exhaust Emissions of The Gasoline Direct Injection
(GDI) Engine
2.1 Performance of the GDI Engine
The parameters that have the greatest influence on engine efficiency are compression ratio
and air/fuel ratio. The effect of raising compression ratio is to increase the power output
and to reduce the fuel consumption. The maximum efficiency (or minimum specific fuel
consumption) occurs with a mixture that is weaker than stoichiometric (Çelik, 2007).
Because the port fuel injection engines work at stoichiometric air/fuel ratio, it is impossible
to see more improvement in the fuel economy. In these engines, the compression ratio is
about 9/1-10/1. To prevent the knock, the compression ratio cannot be increased more. For
the same engine volume, the increasing volumetric efficiency also raises the engine power
output.
GDI engine operate with lean mixture and unthrottled at part loads, this operation provide
significantly improvements in fuel economy. At full load, as the GDI engine operates with
homogeneous charge and stoichiometric or slightly rich mixture, this engine gives a better
power output (Spicher et al., 2000). In GDI engine, fuel is injected into cylinder before spark
plug ignites at low and medium loads. At this condition, Air/Fuel (A/F) ratio in cylinder
vary, that is, mixture in front of spark plug is rich, in other places is lean. In all cylinder A/F
ratio is lean and A/F ratio can access until 40/1. In homogeneous operation, fuel starts
injecting into cylinder at intake stroke at full loads (Alger et al., 2000; Çnar, 2001). The fuel,
which is injected in the intake stoke, evaporates in the cylinder. The evaporation of the fuel
cools the intake charge. The cooling effect permits higher compression ratios and increasing
of the volumetric efficiency and thus higher torque is obtained (Muñoz et al., 2005). In the
GDI engines, compression ratio can gain until 12/1 (Kume, 1996). The knock does not occur
because only air is compressed at low and medium loads. At full load, since fuel is injected
into cylinder, the charge air cool and this, in turn, decreases knock tendency.
Since the vehicles are used usually in urban traffic, studies on improving the urban driving
fuel economy have increased. Engines have run usually at part loads (low and medium
loads) in urban driving. Volumetric efficiency is lower at part loads, so engine effective
compression ratio decreases (e.g. from 8/1 to 3/1-4/1), engine efficiency decreases and fuel
consumption increases. The urban driving fuel economy of the vehicles is very high (Çelik,
1999). Distinction between the highway fuel economies of vehicles is very little. As majority
Gasoline direct injection 3
of the life time of the vehicles pass in the urban driving, the owners of the vehicles prefer the
vehicles of which the urban driving fuel economy is low.
At full load, as the GDI engine operate with throttle, only a small reduction of fuel
consumption can be obtained to the PFI engine. There is the more fuel economy potential at
part load. At compression stroke, since air is given the cylinders without throttle for
stratified charge mode, pumping losses of the GDI engine is minimum at part loads, Fig.1
(Baumgarten, 2006). The improvements in thermal efficiency have been obtained as a result
of reduced pumping losses, higher compression ratios and further extension of the lean
operating limit under stratified combustion conditions at low engine loads. In the DI
gasoline engines, fuel consumption can be decreased by up to 20%, and a 10% power output
improvement can be achieved over traditional PFI engines (Fan et al., 1999).
Fig. 1. Reduction of throttle losses in the stratified-charge combustion (Baumgarten, 2006).
The CO2 emissions, which are one of the gases, bring about the global warming. To decrease
CO2 emitted from vehicles, it is required to decrease fuel consumption. Downsizing
(reduction of the engine size) is seen as a major way of improving fuel consumption and
reducing greenhouse emissions of spark ignited engines. In the same weight and size,
significant decreases in CO2 emissions, more power and higher break mean effective
pressure can be obtained. GDI engines are very suitable for turbocharger applications. The
use of GDI engine with turbocharger provides also high engine knock resistance especially
at high load and low engine speed where PFI turbocharged engines are still limited
(Lecointe & Monnier, 2003; Stoffels, 2005). Turbocharged GDI engines have showed great
potential to meet the contradictory targets of lower fuel consumption as well as high torque
and power output (Kleeberg, 2006).
4 Fuel Injection
In GDI engine, by using twin charging system drive comfort, engine torque and power can
be increased for the same engine size. For example, Volkswagen (VW) has used the dual
charging system in TSI (twin charged stratified injection) engine. The system includes a
roots-type supercharger as well as a turbocharger. The supercharger is basically an air
compressor. A mechanical device driven off the engine's crankshaft, it employs rotating
vanes which spin in opposite directions to compress air in the engine's intake system. The
high and constant torque is obtained at wide range speed by activate supercharger at low
speeds and turbo charger at high speeds (Anon, 2006).
In Table 1, it is given specifications of the two different engines belonging to the 2009 model
VW Passat vehicle, for example. TSI engine urban driving fuel economy is 18% lower than
that of PFI engine. CO2 emission is 12% lower than that of PFI engine. Although TSI engine
swept volume is lower than PFI engine, power and torque is higher by 20% and 35%,
respectively (Table 1). As engine torque is maximum at interval 1500-4000 1/min, shifting is
not necessary at the acceleration and thus drive comfort increase (Anon, 2009).
2.2 Exhaust Emissions of the GDI Engine
CO emission is very low in GDI engine. CO varies depending on air /fuel ratio. CO is high
at rich mixtures. Since GDI engines operate with lean mixture at part loads and
stoichiometric mixture at full load, CO is not a problem for these engines. In GDI engine,
due to the wetting of the piston and the cylinder walls with liquid fuel, HC emission can
increase. Hydrocarbon (HC) emissions are a function of engine temperature and, therefore it
can rise during cold start. The cold starts characteristics vary depending on the fuel
distribution

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