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This paper describes the progress of IDI diesel engine for passenger car. There are two options of direct-injection(DI) and indirect-injection(IDI) type for diesel engines. IDI-engines have been mainly used for diesel passenger car for a long time. In recent years, in order to reduce CO2 and fuel consumption, DI engine for passenger car have been developed. Convential IDI engine have, generally speaking, 15 percent worse fuel economy while it has better potential of exhaust emissions, combustion noise and cabin heater performance than DI engines for passenger car. The possibility of fuel economy (CO2) improvement in IDI diesel engine has been persued in a single cylinder engine. It was found that high pumping rate of injection system gives excellent fuel economy at high engine speed because of shorter injection duration without increase of exhaust emissions, though it gives a slightly worse fuel economy and HC at low speed.

During our investigations using an ion-gap, we observed a rise of the ion-current before the injection event. We then tried to trap some portion of the fuel spray in the swirl-chamber to cause early ignition in the next cycle in order to get the effect of pilot injection. As a result, a very smooth pressure rise was attained and the objectionable knocking noise at idling was eliminated. However, we had to make compromises when taking advantage of this combustion mechanism, as there was a trade-off between noise level and HC emission.