Abstract
Gasoline direct injection was introduced in Europe and Japan primarily to reduce fuel consump-tion.
Direct injection also offers a large potential for fuel economy improvement with simultaneous in-crease of the power output. The first production direct injection engines used wall-guided combustion processes to achieve a stable combustion process. The disadvantage of these wall-guided combustion processes are high hydrocarbon emissions due to the poor mixture preparation with a cold engine as well as the deferred combustion of a part of the injected fuel caused by a delayed vaporization of the fuel from the combustion chamber walls. Even further developments such as wall-/air-guided combustion processes solve only a part of these problems. The result was that the fuel economy and power improvements were below the initial expectations.
Spray-guided combustion processes avoid the disadvantages of wall-guided and wall-/air-guided combustion processes and thus achieve both improved exhaust emissions and a further improvement of fuel consumption. Due to the smaller distance between spark plug and injector, however, demands concerning the mixture formation are much higher. The stability of the injection spray must be ensured irrespectively of the back-pressure. The spark plug must not be hit directly by the main spray. For a stable combustion in stratified operation the transport of fuel vapor and very small fuel droplets from the main spray to the spark plug must be ensured.
An outward opening injector with very good mixture preparation and large working flow range fits best to the requirements from spray guided combustion systems and the fueling demands of high performance engines.