History and Development 6
Supersession of carburetor 10
Basic function 13
Fundamentals of fuel injection 15
Various injection system 18
I was commuting with my friends back from college one evening when one of them asked me: What is an MPFI Engine? 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 (also called fuel-injection system) [pic]
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.
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
• 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...