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In recent years, although experiment technologies on real engines and simulation technologies has been improved rapidly, the tribology contributing factors have not been quantitatively well evaluated to reveal critical lubrication failure mechanisms. In this study the oil film thickness of the main bearings in multicylinder diesel engines was measured, and the data was analyzed using response surface methodology, which is a statistical analysis methods used to quantitatively derive the factors affecting oil film thickness and the extent of their contribution. We found that the factor with the strongest effect on minimum oil film thickness is oil pressure. Lastly, as a verification test, bearing wear on the main bearings was compared under various oil pressure conditions. Clear differences in bearing wear were identified.

A new concept for diesel combustion has been investigated by means of engine experiments and combustion observations in order to realize a simultaneous reduction of NOx and particulate emissions. The concept is based on pre-mixed compression ignition combustion combined with multiple injection. In this method, some part of fuel is injected at an early stage of the process to form a homogeneous lean pre-mixture, then the remaining fuel is injected at around the TDC in the same manner as a conventional diesel injection. The emissions, ROHR (rate of heat release), and combustion pictures of conventional combustion, pilot injection combustion, and this new combustion concept were compared and analyzed. Engine tests were carried out using a single cylinder research engine equipped with a common rail injection system.

A new concept for diesel combustion was investigated by means of numerical simulation, engine experiment, and combustion observation in order to realize a simultaneous reduction of NOx and particulate emission. This concept (HiMICS: Homogeneous charge intelligent Multiple Injection Combustion System) is based on pre-mixed compression ignition combustion combined with multiple injection. Combustion characteristics of HiMICS concept was investigated by comparing with both a standard single injection and a pilot injection. In HiMICS concept, the pre-mixture is formed by a preliminary injection performed during a period from the early stage of the induction stroke to the middle stage of the compression stroke. Modified KIVA-II code was used to predict engine performances and emissions of each injection method. The simulation results show a capability of considerable improvement in the trade-off relation between NOx emissions and fuel consumption of HiMICS.

In a diesel engine, the mixing of the fuel spray and in-cylinder air controls rate of beat release during combustion, namely it will determine the thermal efficiency, maximum output and gas or noise emission, etc. Therefore, it is important to measure the droplet size and its volume density distribution in diesel fuel sprays. The optical measuring method, which includes a light scattering and holographic technique, seems the only feasible method for analysing these unsteady characteristics of fuel sprays. The light scattering technique described herein was based upon Mie scattering theory, and the droplet size and volume density distribution of fuel sprays were calculated from the combination of the light extinction and the forward-to-backscattering ratio of Mie scattering intensity. The volume density and droplet size distribution of fuel sprays were obtained from the light intensity distribution on a photograph of fuel sprays.

Recently the analysis of air-fuel mixing and combustion has become important under the stringent emissions regulations of diesel engines. In the case of gasoline engines, the KIVA computer program has been developed and used for the analysis of combustion. In this paper, the calculations of combustion phenomena in DI diesel engines are performed by modifying the KIVA program so as to be applicable to multi-hole nozzles and arbitrary patterns of injection rate. The thermophysical and ther-mochemical properties of gasoline are altered to those diesel fuel. In order to investigate the ability of this modified program, the calculations are compared with the experiments on single cylinder engines concerning the pressure, flame temperature and mass change of chemical species in cylinders. Furthermore, the calculation for the heavy duty DI diesel engine is performed with this diesel combustion program.