Different types of fuel injection systems

You must have often heard of terms like MPFI, DI, SFI etc pertaining to car fuel intake systems. But what are these and how do they function? MPFI, DI, SFI, TBI are all types of fuel injectors or fuel injection systems read what is fuel injection here and are extensively employed in modern age cars for enhanced performance and increased fuel economy. How does each of them function? We explain it to you.

Throttle body or Single Point Injection aka TBI

This is the simplest and the foremost fuel injection system which was employed in cars as a replacement for carburetors. This employs either one or two fuel injectors in the throttle body which delivers the apt ratio of fuel-air mixture to every fuel intake manifold in the engine. The drawback if this system is that cylinders closest to the fuel injectors would get a better mixture than the ones away from them. The reason why TBI replaced carburetors was because these would easily adjust according to air density and altitude, and were independent of the vacuum manifold.

Multi-point fuel injection or Port injection aka MPFI

The term MPFI is widely used by car manufacturers as a USP for their cars.  As the name suggests the multi point fuel injector denotes one fuel injector for every cylinder - the fuel is misted at the intake manifold. If an engine has six cylinders then it will have six fuel injectors - one for each cylinder located at the intake port of the manifold. Since the fuel is misted so closed to the intake manifold, it ensures the complete amount is used for combustion, making it more efficient than TBI, hence aiding in enhanced fuel economy as well.   

Multi-port fuel injectors fire fuel all at the same time, with the fuel sitting at the intake manifold till the time it’s needed. This happens for a split second, even during engine idling. MPFI allows for more even fuel distribution.

Sequential fuel injection aka SFI

Sequential fuel injection system is a type of MPFI. While in an MPFI all the injectors are fired at the same time, in SFI they are fired according to the intake timing of the respective cylinder i.e. just before the intake valve of that particular cylinder opens. This timing is matched according to the camshaft and though it may seem as a minor change it has helped improve efficiency and emissions.

Direct Injection aka DI

Direct injection is one of the most advanced fuel injection systems. More commonly seen on diesel engines, this technology is now making way in petrol engines. In a direct injection system the fuel is injected directly in the combustion chamber i.e the cylinder. The advantage of this system is that there is no wastage of fuel or any carbon deposit at the intake valve. The sensors monitor the exact amount of fuel needed by the vehicle and supply the same to the chamber. In direct injection fuel metering is more precise than any other system.