contd...

In the EFI systems, for control of fuel injection rate and  in turn the  air-fuel ratio, airflow to the engine is measured by a hot-wire or hot-film anemometer. Air-fuel ratio is more precise. Use of measured air flow rate data by the engine fuel management system results in an automatic compensation for changes in air flow resulting from variations in engine speed, load, exhaust back pressure or change in volumetric efficiency due to   valve adjustments, engine wear, deposit build-up etc.
The typical emissions from a car equipped with carburettor and  open loop PFI systems are compared in Fig. 5.4.  Use of port fuel injection alone provided 20- 30 % reduction in HC and 50 to 60% reduction in CO compared to carburettor when tested over the urban driving cycle. The NO_x however, increased by about 45% as for smooth engine operation overall a leaner mixture was used with PFI. In the closed loop controlled stoichiometric operation of the engine, the effect of PFI on NO_x would not be very significant, while lower CO and HC are obtained due to more uniform fuel distribution among the different engine cylinders.
Gasoline direct injection (GDI) system has been employed for the direct injection stratified charge (DISC) engines. During mid 1990s, Mitsubishi and Toyota introduced DISC engines on the production cars. The DISC engine operates as lean as 40: 1 air-fuel ratio and provides large reductions in engine-out emissions.  Now however, stoichiometric GDI engines are also being considered for production. These engines are discussed in detail later in the section on advanced engines.