ABSTRACT
In older diesel engines , a distributor-type injection pump ,regulated by the engine ,supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine’s combustion chamber. In common rail system the distributor injection pump is eliminated. Instead, a high-pressure pump pressurizes fuel at up to 1500 bar in a ‘common rail’. The common rail is a tube that branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid valve piezoelectric actuators. These systems are capable of high pressures. One of the function of the CRDI system is to decouple noises by keeping the pressure inside the injection pipes constant and adjustable. Injection pressure and timing can be regulated independently of each other by control unit.

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TABLE OF CONTENTS
CHAPTER TITLE PAGE NO:
1 INTRODUCTION 5
2 WHAT IS A COMMON RAIL SYSTEM ? 6
3 FUNCTIONS 7
4 FEATURES 8
5 INJECTION 9
6 INJECTION SYSTEMS 12
7 PRINCIPLES 15
8 COMPONENTS OF CRDI SYSTEM 17
9 WORKING 22
10 EMISSIONS 24
11 APPLICATIONS 27
12 CONCLUSION 28
13 REFRENCES 29





TABLE OF FIGURES
FIGURE NO: NAME OF FIGURE PAGE NO
2.1 Common Rail System 6
5.1 CRDI System 9
5.2 ECU, COMMON RAIL WITH INJECTORS, HIGH PRESSURE PUMP 10
6.1 DIRECT & INDIRECT INJECTION 12
6.2 Common Rail Injection System 13
7.1 Solenoid Valve 15
8.1 Parts Of CRDI System 17
8.2 CRDI System 18
8.3 High Pressure Pump 19
8.4 Pressure Control Valve 20
8.5 Common Rail 20
8.6 Fuel Injector 21
9.1 CRDI System 22
10.1 Catalystic Converter 25
10.2 Particulate Filter 26



CHAPTER-1
INTRODUCTION
The common rail system prototype was developed in the late 1960’s by Robert Huber of Switzerland. After that the technology was further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, later of Ganser-Hydromag AG (estb. 1995) in Oberageri. The CRDI systems are capable of high pressures. One of the function of CRDI systems is to decouple injection noises by keeping the pressure inside the injection pipes constant and adjustable. Maximum pressure is available from the beginning. The injection pressure and timing can be regulated independently of each other by the control unit. This system is applicable to the passenger car Diesel Engines with direct injection, also truck engines.

CHAPTER-2
WHAT IS A COMMON RAIL SYSTEM ?



FIGURE2.1 COMMON RAIL SYSTEM

Common rail refers to a small accumulation tank called Rail where the pressure of the fuel remains almost constant and always available in order to supply the electronic injectors and therefore for an optimum injection. The protection of the environment, the need to reduce the consumption of fuel and to make the diesel engines more silent and better performing are the key factors that determined the study and development of the Unijet common rail system. Born as a project from Marelli in 1987, it was afterwards acquired by Fiat’s research centre in Bari who set it up and tested it on a vehicle in 1992. The project was transferred to Bosch Group for the final industrialisation process in 1994. The first vehicles with Unijet Common Rail installation were introduced into the market in 1997.

CHAPTER-3
FUNCTIONS
A pump inhales the fuel from the tank (ELECTRONIC PUMP) and continuously sends the quantity of requested fuel towards a second pump (HIGH PRESSURE PUMP) by making it pass first through the fuel filter that purifies it from any impurity which would cause a premature wear of its components. The high-pressure pump compresses the fuel at a pressure of 1350 bar and transfers it through a connection pipe to the high-pressure accumulation duct (Rail). This tank develops the function of mitigating the pressure oscillations caused by the opening and closing of the injectors and by the continuous discharges of the pump. The fuel is then transferred from the Rail through some connection pipes to the electronic injectors, which - instructed by an electromagnetic valve –inject the correct amount of fuel directly into the combustion chamber of the engine.
The fuel in excess, required for the opening of the nozzles, is sent back to the tank along with the leakages of fuel coming from the pressure regulation valve and from the high pressure pump itself. In this type of system, the quantity of injection is being established by the driver through the accelerator pedal while the initial stage and the pressure of injection are calculated and controlled by the electronic control unit (EDC). Through the accelerator pedal’s sensor, the electronic control unit registers the driver’s intention while, thanks to other sensors, it registers the exercising conditions of the engine and vehicle and – according to the information acquired – it carries out the intervention for the engine regulation.
The power supply of the fuel is divided into low-pressure circuit and high-pressure circuit. The low-pressure circuit is made of:
- auxiliary immersed electronic pump
- diesel filter;
- leakage manifold
The high-pressure circuit is made of:
-pressure pump;
- repair collector
CHAPTER-4
FEATURES
1. Very high injection pressures of the order of 1500 bar
2. Complete control over start , and end of injection
3. Injection pressure is independent of engine speed
4. Ability to have pilot, main and post injection
5. Variable injection pressure



CHAPTER-5
INJECTION
Diesel engines are not throttled. Instead, the combustion behaviour is affected by these variables:
• Timing of start of injection
• Injection duration
• Injector discharge curve
Since the use of electronically controlled common rail injection allows these variables to be individually controlled, we’ll briefly look at each.


FIGURE5.1 CRDI SYSTEM



5.1 TIMING OF START OF INJECTION
The timing of the injection of fuel has a major affect on emission levels, fuel consumption and combustion noise. The optimal timing of the start of injection varies with engine load. In car engines, optimal injection at no load is within the window of 2 crankshaft degrees Before Top Dead Centre (BTDC) to 4 degrees After Top Dead Centre (ATDC). At part load this alters to 6 degrees BTDC to 4 degrees ATDC, while at full load the start of injection should occur from 6 – 15 degrees BTDC. The duration of combustion at full load is 40 – 60 degrees of crankshaft rotatio Too early an injection initiates combustion when the piston is still rising, reducing efficiency and so increasing fuel consumption. The sharp rise in cylinder pressure also increases noise. Too late an injection reduces torque and can result in incomplete combustion, increasing the emissions of unburned hydrocarbons

FIGURE5.2 ECU, COMMON RAIL WITH INJECTORS, HIGH PRESSURE PUMP
5.2 INJECTION DURATION
Unlike a conventional port fuel injected petrol engine, where the amount of fuel injected can be considered to be directly proportional to the injector opening time, a diesel injector will vary in mass flow depending on the difference between the injection and combustion chamber pressures, the density of the fuel (which is temperature dependent), and the dynamic compressibility of the fuel. The specified injector duration must therefore take these factors into account.
5.3 DISCHARGE CURVE
Diesel fuel injectors do not add the fuel for a combustion cycle in one event, instead they operate in up to four different modes. The first is pre-injection, a short duration pulse which reduces combustion noise and Oxides of Nitrogen (NOx) emissions. The bulk of the fuel is then added in the main injection phase, before the injector is turned off momentarily before then adding a post-injection amount of fuel. This post-injection reduces soot emissions. Finally, at up to 180 crankshaft degrees later, a retarded post-injection can occur. The latter acts as a reducing agent for an NOx accumulator-type catalytic converter and/or raises the exhaust gas temperature for the regeneration of a particulate filter.
The injection amounts vary between 1 cubic millimetre for pre-injection to 50 cubic millimetres for full-load delivery. The injection duration is 1-2 milliseconds.











CHAPTER-6
INJECTION SYSTEMS
The CR system is an injection system used in Direct-Injection (DI) engines. It is common to differentiate between Direct-Injection (DI) engines and Indirect-Injection (IDI) engines. In IDI the fuel is injected into a prechamber in which the combustion is initiated. In DI engines the fuel is injected directly into the cylinders combustion chamber. DI engines feature fuel savings of up to 20 percent compared with IDI engines, but the latter generates less noise than the former. The advantage of the CR System is the high pressure in the rail, which makes it possible to use precise and highly flexible injection processes.

FIGURE6.1 DIRECT & INDIRECT INJECTION


The CR System system can be divided into three different functional groups
• The high pressure circuit
• The low pressure circuit
• The ECU (Engine Control Unit) with sensors


FIGURE6.2

6.1 THE HIGH PRESSURE CIRCUIT
The high pressure circuit contains a high pressure pump, a pressure-control valve, a high pressure accumulator (the rail) with a rail pressure sensor, high pressure connection lines and injectors. This part of the CR system is responsible for generating a stable high pressure level in the rail and for injecting the fuel into the engines combustion chambers. The high pressure pump forces the fuel into the rail and generates a maximum pressure . There is one injector for each cylinder and injectors contain a solenoid valve which receives a current signal as an ‘open’ command from ECU at the time for injection. Every time an injection occurs, fuel is taken from the rail. The pressure control valve attempts to keep the pressure at the desired level. This control is based on measurements from the rail pressure sensor.
6.2 THE LAW PRESSURE CIRCUIT
The low pressure circuit provides the high pressure part with fuel. The fuel is drawn out of the tank by a pre-supply pump and forced through the lines and through a fuel filter to the high pressure pump in the high pressure circuit. Uninjected fuel from the rail is led back to the tank through the pressure control valve

6.3 THE ECU WITH SENSORS
The ECU evaluates signals from different sensors and supervises the correct functioning of the injection system as a whole. The main tasks for the ECU in the CR systems are to keep the pressure in the rail at a desired level by controlling the pressure control valve, and to start and terminate the actual injection processes. Some of the quantities that the ECU calculates from the sensor measurments (e.g. rail pressure, engine speed, accelerator-pedal position and air temperature) are the correct quantities for the fuel injections and the optimal start and duration of injections .












CHAPTER-7
PRINCIPLES
Solenoid or piezoelectric valves make possible fine electronic control over the injection time and amount, and the higher pressure that the common rail technology makes available provides better fuel atomisation. In order to lower engine noise, the engine's electronic control unit can inject a small amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting, and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.

FIGURE7.1 SOLENOID VALVE

ommon rail engines require no heating up time, and produce lower engine noise and lower emissions than older systems.
In older diesel engines, a distributor-type injection pump, regulated by the engine, supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine's combustion chamber. As the fuel is at low pressure and there cannot be precise control of fuel delivery, the spray is relatively coarse and the combustion process is relatively crude and inefficient.
In common rail systems, the distributor injection pump is eliminated. Instead an extremely high pressure pump stores a reservoir of fuel at high pressure up to 2,000 bar (200 MPa) in a "common rail", basically a tube which in turn branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid. Driven by a computer (which also controls the amount of fuel to the pump), the valves, rather than pump timing, control the precise moment when the fuel injection into the cylinder occurs and also allow the pressure at which the fuel is injected into the cylinders to be increased. As a result, the fuel that is injected atomizes easily and burns cleanly, reducing exhaust emissions and increasing efficiency.
Most European automakers have common rail diesels in their model lineups, even for commercial vehicles. Some Japanese manufacturers, such as Isuzu, Toyota, Nissan and recently Honda, have also developed common rail diesel engines. Some Indian companies have also successfully implemented this technology, notably Mahindra & Mahindra for their 'Scorpio-CRDe' and Tata Motors for their 'Safari-DICOR'.










CHAPTER-8

COMPONENTS OF CRDI SYSTEM

FIGURE8.1 PARTS OF CRDI SYSTEM
1. fuel tank
2. overall immersed pump complete with level indicator command
3.fuel introduction pipe
4. multifunctional valve
5. cartridge for diesel filter
6. pressure pump
7. high pressure connecting pipe
8. allotment collector 9. electronic injectors
10. electronic injectors recycle
11. return collector (low pressure)
12. pressure regulator
13. fuel temperature sensor
14. fuel pressure sensor
15. diesel heater
16. heat switch


FIGURE8.2 CRDI SYSTEM

This figure indicates various flows. The light arrows indicate diesel at high pressure (discharges). The dark arrows indicate diesel at low pressure (return to tank and discharges from primer pump).
8.1 ELECTRONIC PUMP TANK
The main trigger pump of fuel is situated in the tank inside a sump containing a filter with and a sensor for the level of fuel. It is a volumetrically type with a roller impeller and its function is to fill up the circuit and to supply the high-pressure pump. It has two valves: a non-return one in order to prevent the emptying of the circuit and a safety one which limits the pressure to a maximum value of 5 bar in case of obstruction of the diesel circuit. The electronic pump is feeded at 12V from the special relay, which is instructed – at its turn – from the EDC control unit. It guarantees a minimum flow of 0.5 litres/minute and with lot pressure of about 0.5 bar.


8.2 HIGH PRESSURE MECHANICAL PUMP
The high pressure is obtained from the action of three small pistons being arranged in radial position (radialjet) at an angular distance of 120° and thanks to their action; they generate a pressure from a minimum of 150 bar to 1350 bar and even more among the pumps of latest generation.
The pump is dragged by the engine through the toothed distribution belt at about half speed. The pump does not require the phasing since the instant and time of injection are being entrusted to the control unit, which manages the opening of the injectors. The alterning movement of the three small pistons is assured by a triangular cam connected to the pump’s shaft and every pumping group is characterised by a suction valve and by a discharging one, the first having a clay shape and thesecondasphericalone.

FIGURE8.3 HIGH PRESSURE PUMP
8.3 FUEL FILTERS
The fuel could contain impurities or combined water (emulsion) or non-combined water (for example: condensation formation due to an change of temperature), which may cause corrosion and wear damages to the components of the pumps and injectors. For this reason, the system needs a fuel filter with a water-collecting compartment, which must be periodically emptied.
8.4 PRESSURE CONTROL VALVE
The fuel pressure control valve comprises a fuel-cooled solenoid valve. The valve opening is varied by its solenoid coil being pulse width modulated at a frequency of 1 KHz. When the pressure control valve is not activated, its internal spring maintains a fuel pressure of about 100 Bar. When the valve is activated, the force of the electromagnet aids the spring, reducing the opening of the valve and so increasing fuel pressure. The fuel pressure control valve also acts as a mechanical pressure damper, smoothing the high frequency pressure pulses emanating from the radial piston pump when less than three pistons are activated.

FIGURE8.4 PRESSURE CONTROL VALVE
8.5 FUEL RAIL
The fuel rail feeds each injector. It is made sufficiently large that the internal pressure is relatively unaffected by fuel being released from the injectors. As indicated earlier, the rail is fitted with a fuel pressure sensor. To guard against dangerously high fuel pressure, a fuel pressure relief valve is also fitted.

FIGURE8.5 FUEL RAIL

8.6 FUEL INJECTORS
The fuel injectors superficially look like the injectors used in conventional petrol injection systems but in fact differ significantly. This diagram shows a common rail injector. Because of the very high fuel rail pressure, the injectors use a hydraulic servo system to operate. In this design, the solenoid armature controls not the pintle but instead the movement of a small ball which regulates the flow of fuel from a valve control chamber within the injector.

FIGURE8.6 FUEL INJECTOR

The life of a common rail diesel fuel injector is certainly a hard one. Bosch estimates a commercial vehicle injector will open and close more than a billion times in its service life.







CHAPTER-9
WORKING

FIGURE 9.1 CRDI SYSTEM
1. High pressure pump
2. Sensor
3. Common rail
4. Fuel rail control valve
5. Injectors
6. Fuel filter
7. Fuel tank
8. ECU
9. Engine speed sensor
10. Camshaft position sensor
11. Accelerator pedal travel sensor
12. Boost pressure sensor
13. Intake air temperature sensor
14. Engine coolant temperature sensor
The common rail injection system has a high pressnre pump which operates continuously and charges a high pressure rail or reservoir or accumulator. Fuel is led from this rail to the injector mounted on the cylinder head through lines. The injector is solenoid operated. It received pulses from the ECU to open the same.
The engine directly drives the pump of the common rail system. It is generally of the multi-cylinder radial piston type. The generated pressure is independent of the injection process unlike conventional injection systems. The rail pressure pump is generally much smaller that conventional pumps and also is subjected to lesser pressure pulsations. The injection occurs when the solenoid is energized. The quantity of fuel injected is directly dependent on the duration of the pulse when the injection pressure is constant. Sensors on the crankshaft indicate its position and speed and so the timing of injection and its frequency can be controlled. A typical layout of the common rail fuel injection system is indicated in Fig.10.18. Fuel from the tank is lifted by a low pressure pump and passed through a filter. The pump is generally run by an electric motor independent of the engine speed. The maiu pumping element can be a conventional gear pump or of the roller cell type. The roller cell pump has a rotor with radial slots. These slots house rollers which are always in contact with the inner surface of the housing due to fuel pressure arid centrifugal forces. The space between the rotor and the housing varies as the rotor turn and this is responsible for the suction and delivery.








CHAPTER-10
EMISSIONS
Five major approaches are taken to reducing diesel exhaust emissions
10.1 DESIGN
Within the engine itself, the design of the combustion chamber, the placement of the injection nozzle and the use of small droplets all help reduce the production of emissions at their source. Accurate control of engine speed, injection mass, injection timing, pressures, temperatures and the air/fuel ratio are used to decrease emissions of oxides of nitrogen, particulates, hydrocarbons and carbon monoxide.
10.2 EXHAUST GAS RECIRCULATION
Exhaust gas recirculation, where a proportion of the exhaust gas is mixed with the intake charge, is also used to reduce oxides of nitrogen emissions. It does this by reducing the oxygen concentration in the combustion chamber, the amount of exhaust gas passing into the atmosphere, and the exhaust gas temperature. Recirculation rates can as high as 50 per cent
10.3 CATALYTIC CONVERTER
Diesel oxidation-type catalytic converters can be used to reduce hydrocarbon and carbon monoxide emissions, converting these to water and carbon dioxide. So they rapidly reach their operating temperature, this type of catalytic converter is fitted close to the engine
NOx accumulator-type catalytic converters are also used. This type of design breaks down the NOx by storing it over periods from 30 seconds to several minutes. The nitrogen oxides combine with metal oxides on the surface of the NOx accumulator to form nitrates, with this process occurring when the air/fuel ratio is lean (ie there is excess oxygen). However, the storage can only be short-term and when the ability to bind nitrogen oxides decreases, the catalytic converter needs to be regenerated by having the stored NOx released and converted into nitrogen. In order that this takes place, the engine is briefly run at a rich mixture (eg an air/fuel ratio of 13.8:1)

FIGURE10.1 CATALYTIC CONVERTER
Detecting when regeneration needs to occur, and then when it has been fully completed, is complex. The need for regeneration can be assessed by the use of a model that calculates the quantity of stored nitrogen oxides on the basis of catalytic converter temperature. Alternatively, a specific NOx sensor can be located downstream of the accumulator catalytic converter to detect when the efficiency of the device is decreasing. Assessing when regeneration is complete is done by either a model-based approach or an oxygen sensor located downstream of the cat; a change in signal from high oxygen to low oxygen indicates the end of the regeneration phase.
In order that the NOx storage cat works effectively from cold, an electric exhaust gas heater can be employed.
10.4 SELECTIVE CATALYTIC REDUCTION
One of the most interesting approaches to diesel exhaust treatment is Selective Catalytic Reduction. In this approach, a reducing agent such as dilute urea solution is added to the exhaust in minutely measured quantities. A hydrolysing catalytic converter then converts the urea to ammonia, which reacts with NOx to form nitrogen and water. This system is so effective at reducing NOx emissions that leaner than normal air/fuel ratios can be used, resulting in improved fuel economy. The urea tank is filled at each service.
10.5 PARTICULATE FILTERS
Exhaust particulate filters are made from porous ceramic materials. When they become full, they can be regenerated by being heated to above 600 degrees C. This is a higher exhaust gas temperature than is normally experienced in diesels and to achieve this, retarded injection and intake flow restriction can be used to increase the temperature of the exhaust gas.








FIGURE10.2 PARTICULATE FILTERS












CHAPTER-11
APPLICATIONS
1. BMW’s D-engines
2. Fiat Groups ( Fiat, Alfa Romeo and Lancia)
3. Honda Groups
4. Hyundai Groups
5. Ships
6. Tata’s Dicor
7. Toyota’s D-4D












CHAPTER-12
CONCLUSION
Common rail systems are capable of high pressures. Due to the high pressure in the system and the electromagnetically controlled injectors it is possible to inject correct amount of fuels at exactly right movement. This implies lower fuel consumption and less emissions.















REFRENCES
1. INTERNAL COMBUSTION ENGINE – V.GANESAN (PAGE 342 TO 355)
2. AutoSpeed - Common Rail Diesel Engine Management, Part 1.mht
3. Common rail - Wikipedia, the free encyclopedia.mht
4. Application of CFD Methodology to Air Intake System of CRDI Engine.mht
5. Philippines Handyman DIY Portal - Diesel Quality and CRDI Engines.mht
6. INTERNAL COMBUSTION ENGINES – MATHUR & SHARMA
7. Feature Spotlight.mht
8. Diesel injection systems, diesel fuel injection, diesel injection, diesel fuel injection pumps, diesel injection pumps.mht
9. Common rail.pdf
10. Common rail system.pdf
11. Diesel engine – Wikipedia
12. injection system.pdf