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Development status of small direct Injection diesel engine at Isuzu Motors Ltd. is reviewed. There is much difficulty in combustion optimization of small DI engines, due to small combustion chamber volume, large surface to volume ratio, wide engine speed range and so on, Novel ideas in the area of injection system, combustion chamber and induction swirl were tried to solve these problems and their effects are presented here. Our prototype DI engines which adopted some of these ideas has turned out to have better fuel economy by about 15 percent, 2-3 dB(A) higher noise level than IDI and almost the same power output performance as IDI. As to exhaust emissions, they have a possibility to conform to ′86 California emission standards, in inertia weight classes up to 2625 LBS. The remaining problem areas are noise emission, durability of injection pump and cabin heater performance.

Isuzu Motors Ltd. & Jidosha Buhin Kogyo Co., Ltd. have newly developed 1.0 & 1.4 lit direct injection 3 cylinder diesel engines, named K-Series, for industrial application. The 1.0 lit engine is one of the smallest displacement class per cylinder in vertical water-cooled DI engine category. Design concept is to improve said disadvantage of DI such as white smoke, black smoke, and noise level, involving the original characteristics of DI such as high output, low fuel consumption, and easy startability. Those characteristics are incompatible factors, therefore our development efforts have been concentrated to optimize the combustion system. These concept has been achieved by adoption of relatively high compression ratio, square cavity combustion chamber with squish lip, high effective volume ratio, high induction swirl, and matching of fuel injection system.

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.