Читать книгу Internal Combustion Engines - Allan T. Kirkpatrick - Страница 33

Revolutionary changes have taken place with engine controls and fuel delivery systems in recent years and the progress continues. The ignition and fuel injection systems of the engine are now controlled by computers. Conventional carburetors in automobiles were replaced by throttle body fuel injectors in the 1980s, which in turn were replaced by port fuel injectors in the 1990s. Port fuel injectors are located in the intake port of each cylinder just upstream of the intake valve, so there is an injector for each cylinder. The port injector does not need to maintain a continuous fuel spray, since the time lag for fuel delivery is much less than that of a throttle body injector.

Direct injection spark‐ignition engines are available on many production engines. With direct injection, the fuel is sprayed directly into the cylinder during the late stages of the compression stroke. Compared with port injection, direct injection engines can be operated at a higher compression ratio, and therefore will have a higher theoretical efficiency, since the combustion knock limitations are reduced. They can also be unthrottled, resulting in a greater volumetric efficiency at part load. The evaporation of the injected fuel in the combustion chamber will have a charge cooling effect, which will also increase volumetric efficiency.