28-12-2010, 11:46 AM
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INTRODUCTION
You must have seen cars with specifications which mention words like MPFI and CRDI or CRDE. To an automotive engineer or enthusiast, it means something, but for a common man, it may not make much sense.
MPFI means – Multi-point Fuel-Injection
The term MPFI is used to specify a technology used in Gasoline/petrol Engines. For Diesel Engines, there is a similar technology called CRDI. MPFI System is a system which uses a small computer to control the Car’s Engine. A Petrol car’s engine usually has three or more cylinders or fuel burning zones. So in case of an MPFI engine, there is one fuel –injector installed near each cylinder, that is why they call it Multi-point (more than one points) Fuel Injection.
In plain words, to burn petrol in an Engine to produce power, Petrol has to be mixed with some air, ignited in a cylinder (also called combustion chamber), which produces energy and runs the engine.
Before MPFI system was discovered, there was a technology called “Carburetor”. Carburetor was one chamber where petrol and air was mixed in a fixed ratio and then sent to cylinders to burn it to produce power. This system is purely a mechanical machine with little or no intelligence. It was not very efficient in burning petrol; it will burn more petrol than needed at times and will produce more pollution. But with the advancement of technology this was about to change.
Based on various inputs from the sensors, the computer in the MPFI system decides what amount of fuel to inject. Thus it makes it fuel efficient as it knows what amount of petrol should go in. To make things more interesting, the system also learns from the drivers driving habits. Modern car’s computers have memory, which will remember your driving style and will behave in a way so that you get the desired power output from engine based on your driving style. For example, if you have a habit of speedy pick-up, car’s computer will remember that and will give you more power at low engine speeds by putting extra petrol, so that you get a good pick-up. It will typically judge this by the amount of pressure you put on accelerator.
So the cars of today are really intelligent, well not as intelligent as drivers but fairly intelligent to keep pollution under control and saving the fuel.
Objectives
The functional objectives for fuel injection systems can vary. All share the central task of supplying fuel to the combustion process, but it is a design decision how a particular system will be optimized. There are several competing objectives such as:
• power output
• fuel efficiency
• emissions performance
• ability to accommodate alternative fuels
• reliability
• driveability and smooth operation
• initial cost
• maintenance cost
• diagnostic capability
• range of environmental operation
• Engine tuning
History and Development
Herbert Akroyd Stuart developed the first system laid out on modern lines to meter out fuel oil at high pressure to an injector. This system was used on the hot bulb engine and was adapted and improved by Robert Bosch for use on diesel engines.
The first use of direct gasoline injection was on the Hesselman engine invented by Swedish engineer Jonas Hesselman in 1925. Hesselman engines use the ultra lean burn principle; fuel is injected toward the end of the compression stroke, and then ignited with a spark plug. They are often started on gasoline and then switched to diesel or kerosene. Fuel injection was in widespread commercial use in diesel engines by the mid-1920s. Because of its greater immunity to wildly changing g-forces on the engine, the concept was adapted for use in gasoline-powered aircraft during World War II, and direct injection was employed in some notable designs like the Junkers Jumo 210, the Daimler-Benz DB 601, the BMW 801, the Shvetsov ASh-82FN (M-82FN) and later versions of the Wright R-3350 used in the B-29 Superfortress.
Mechanical
The term Mechanical when applied to fuel injection is used to indicate that metering functions of the fuel injection (how the correct amount of fuel for any given situation is determined and delivered) is not achieved electronically but rather through mechanical means alone.
In the 1940s, hot rodder Stuart Hilborn offered mechanical injection for racers, salt cars, and midgets.
One of the first commercial gasoline injection systems was a mechanical system developed by Bosch and introduced in 1952 on the Goliath GP700 and Gutbrod Superior 600. This was basically a high pressure diesel direct-injection pump with an intake throttle valve set up. This system used a normal gasoline fuel pump, to provide fuel to a mechanically driven injection pump, which had separate plungers per injector to deliver a very high injection pressure directly into the combustion chamber.
Another mechanical system, also by Bosch, but injecting the fuel into the port above the intake valve was later used by Porsche from 1969 until 1973 for the 911 production range and until 1975 on the Carrera 3.0 in Europe. Porsche continued using it on its racing cars into the late seventies and early eighties.
Chevrolet introduced a mechanical fuel injection option, made by General Motors' Rochester Products division, for its 283 V8 engine in 1956 (1957 US model year). This system directed the inducted engine air across a "spoon shaped" plunger that moved in proportion to the air volume. This system was not a "pulse" or intermittent injection, but rather a constant flow system, metering fuel to all cylinders simultaneously from a central "spider" of injection lines. The fuel meter adjusted the amount of flow according to engine speed and load, and included a fuel reservoir, which was similar to a carburetor's float chamber. With its own high-pressure fuel pump driven by a cable from the distributor to the fuel meter, the system supplied the necessary pressure for injection. This was "port" injection, however, in which the injectors are located in the intake manifold, very near the intake valve. The highest performance version of the fuel injected engine was rated at 283 bhp (211.0 kW) from 283 cubic inches (4.6 L). This made it among the early production engines in history to exceed 1 hp/in³ (45.5 kW/L), after Chrysler's Hemi engine and a number of others.
During the 1960s, other mechanical injection systems such as Hilborn were occasionally used on modified American V8 engines in various racing applications such as drag racing, oval racing, and road racing. These racing-derived systems were not suitable for everyday street use, having no provisions for low speed metering or even starting. However they were a favorite in the aforementioned competition trials in which essentially wide-open throttle operation was prevalent.
Electronic
The first commercial electronic fuel injection (EFI) system was Electrojector, developed by the Bendix Corporation and was to be offered by American Motors (AMC) in 1957. A special muscle car model, the Rambler Rebel, showcased AMC's new 327 cu in (5.4 L) engine. The Electrojector was an option and rated at 288 bhp (214.8 kW). With no Venturi effect or heated carburetor (to help vaporize the gasoline) AMC's EFI equipped engine breathed easier with denser cold air to pack more power sooner and it reached peak torque 500 rpm quicker. This was to have been the first production EFI engine, but Electrojector's teething problems meant only pre-production cars were so equipped: thus, very few cars so equipped were ever sold and none were made available to the public. The EFI system in the Rambler was a far more-advanced setup than the mechanical types then appearing on the market and the engines ran fine in warm weather, but suffered hard starting in cooler temperatures.
Chrysler offered Electrojector on the 1958 Chrysler 300D, Dodge D500, Plymouth Fury, and DeSoto Adventurer, arguably the first series-production cars equipped with an EFI system. It was jointly engineered by Chrysler and Bendix. The early electronic components were not equal to the rigors of underhood service, however, and were too slow to keep up with the demands of "on the fly" engine control. Most of the 35 vehicles originally so equipped were field-retrofitted with 4-barrel carburetors. The Electrojector patents were subsequently sold to Bosch.
Bosch developed an electronic fuel injection system, called D-Jetronic (D for Druck, German for "pressure"), which was first used on the VW 1600TL/E in 1967. This was a speed/density system, using engine speed and intake manifold air density to calculate "air mass" flow rate and thus fuel requirements. This system was adopted by VW, Mercedes-Benz, Porsche, Citroën, Saab, and Volvo. Lucas licensed the system for production with Jaguar.
Bosch superseded the D-Jetronic system with the K-Jetronic and L-Jetronic systems for 1974, though some cars (such as the Volvo 164) continued using D-Jetronic for the following several years. The Cadillac Seville was introduced in 1975 with an EFI system made by Bendix and modeled very closely on Bosch's D-Jetronic. L-Jetronic first appeared on the 1974 Porsche 914, and uses a mechanical airflow meter (L for Luft, German for "air") that produces a signal that is proportional to "air volume". This approach required additional sensors to measure the atmospheric pressure and temperature, to ultimately calculate "air mass". L-Jetronic was widely adopted on European cars of that period, and a few Japanese models a short time later.
In 1982, Bosch introduced a sensor that directly measures the air mass flow into the engine, on their L-Jetronic system. Bosch called this LH-Jetronic (L for Luftmasse and H for Hitzdraht, German for "air mass" and "hot wire", respectively). The mass air sensor utilizes a heated platinum wire placed in the incoming air flow. The rate of the wire's cooling is proportional to the air mass flowing across the wire. Since the hot wire sensor directly measures air mass, the need for additional temperature and pressure sensors is eliminated. The LH-Jetronic system was also the first fully-digital EFI system, which is now the standard approach. The advent of the digital microprocessor permitted the integration of all power train sub-systems into a single control module.
