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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.

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.

The authors developed a new method to calculate engine exciting forces by solving equations of motion using measured angular velocity fluctuation at the flywheel of the engine. Vibration response of a powerplant to the calculated engine exciting forces can be obtained by rigid body frequency response analysis with NASTRAN program using the measured value of the powerplant moment of inertia and the mount rubber characteristics. Calculated acceleration levels of a powerplant by this method were in close agreement with the measured ones. This method can be applied to estimate a powerplant vibration mode and levels when such parameters as engine mount locations are changed. As examples, the effect of reciprocating mass and cylinder-to-cylinder variation of fuel delivery were quantitatively discussed.

The generation mechanism of the knocking-like, characteristic engine noise in a swirl-chamber-type, automotive engine was investigated. This characteristic engine noise was particularly dominant in cold weather and at idling conditions. It was found that in cold weather, cylinder pressure pulsations of significant amplitude can be induced in the main chamber by the cavity resonance of the swirl chamber and throat, but the pulsations distribute non-uniformly on the piston top surfaces. Collisons between the pistons and the cylinder liners were induced by the pulsating, non-uniformly distributed cylinder pressure, therefore engine structure noise was generated.

Several techniques have thus far been scrutinized for the estimation of machine vibration originated with the engine. Nevertheless, there has existed no other way available than to conduct experiments to know the vibration level quantitatively, since such techniques available today are not accurate enough. Authors have thus pursued research and succeeded in working out a simulation method that is capable of estimating, at design stage, the vibration attributable to engine exciting force on machine structure, especially on the low frequency vibration, that in consequence caused the oft-occurrence of problems such as noise through the vibroaction of panels, as the engine is mounted on the vehicle frame via mounting rubbers. Authors then applied such method to selective engine mounts and validated a good agreement with the results obtained from the simulation and the life-test, even with the use of mount rubbers of varying characteristics.

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.

This report describes the process and the result of captioned development. At first, the process of understanding the end user's requirement for farm tractors are described, then the technical factors for fulfilling the requirement are described. By these process we have achieved to satisfy the OEM requirement in many aspects especially the highest torque and horsepower among 1.5L class diesel engines.