SIE Metering and Manifold Phenomena

The fuel injection system for conventional spark ignition engine injects the fuel into the engine intake system. The intake manifold delivers air to the engine through pipes to each cylinder, called runner.
The fuel is injected into the intake port of each engine cylinder. Thus these systems require one injector per cylinder (plus, in some system, one or more injector to supplement the fuel flow during starting and warming up).
There are both mechanically injection system and electronically controlled systems. The advantages of port fuel injection system are increased power and torque through improved volumetric efficiency and more uniform fuel distribution, more rapid engine response to change throttle position and more precise control of the equivalence ratio during cold start and engine warm up.
Fuel injection allows the amount of fuel injected per cycle, for each cylinder, to be varied in response to input derived from sensors which define the actual engine operation conditions. Two basic approaches have been developed. The major difference between them is the method used to determine the air flow rate.