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Cooling heat loss is one of the most dominant losses among the various engine losses to be reduced. Although many attempts to reduce it by insulating the combustion chamber wall have been carried out, most of them have not been successful. Charge air heating by the constantly high temperature insulating wall is a significant issue, because it deteriorates charging efficiency, increases the emissions of soot and NOx in diesel engines, and promotes the knock occurrence tendency in gasoline engines. A new concept heat insulation methodology which can reduce cooling heat loss without heating the charging air has been developed. Surface temperature of insulation coating on the combustion chamber wall changes rapidly, according to the quickly changing in-cylinder gas temperature in each engine stroke. During the compression and expansion stroke, the surface temperature of the insulation coating goes up rapidly, and consequently, the heat transfer becomes lower by the reduced temperature difference between the surface and the gas. During the intake stroke, the surface temperature goes down rapidly, and it prevents intake air heating from the wall. To realize the above-mentioned functionality, a thin coating layer with low thermal conductivity and low heat capacity was developed. It was applied on the pistons of diesel engines, and showed improvement in thermal efficiency. It also showed a reduction of unburnt fuel emission in low temperature engine starting condition. The energy balance analysis showed reduction of cooling heat loss and, on the contrary, increase in the brake power and the exhaust loss.

A series calculation method from injector nozzle internal flow to in-cylinder combustion in diesel engines has been developed. In this study, the calculation results of in-cylinder pressure, heat release rate, and NO concentration are compared with experimental results for conventional combustion conditions as well as an advanced combustion condition, which combines a high exhaust gas recirculation (EGR) rate, high boost pressure, and high pressure injection. The calculated pressure and heat release rate histories are in reasonable agreement with those of experiments, but the NO concentration is underestimated especially on the higher EGR rate condition. Therefore, an investigation to improve the quantitative accuracy of NO concentration is performed. The probability density function (PDF) method is one way to estimate the accurate mean reaction rate containing the reaction rate fluctuation by turbulence. In this study, the PDF method only applied for NO calculation is developed to balance the calculation accuracy and the computational cost. The result shows that the reaction rate fluctuation, on NO formation, has a small effect on conventional combustion conditions, but increases with decreasing combustion temperature.

The effects of aromatic components in fuel on ignition and combustion of intermittent spray were examined experimentally. Four types of fuel with different aromatic components, and with similar cetane number and calorific value were used in this study. Fuels were injected into the high-temperature and high-pressure vessel with the injection pressures of 100 MPa and 60 MPa using an electronically controlled fuel injection system developed by the authors. Injection rate shaping applied to the experiments was rectangular, which is a typical injection rate shaping of a common rail type injection system. Images of spray flames were captured using an ICCD camera under ambient conditions corresponding to a turbo-charged diesel engine, 6.1 MPa and 1030 K. A two-color pyrometry technique was applied to the images of spray flame to quantify two-dimensional distributions of flame temperature and soot in flame. Through systematic experiments, it was explored that the aromatic components have little effects on ignition delay and combustion period. However, the aromatic components have significant effects on flame temperature and soot formation. The flame temperature and the amount of soot in flame become higher as the aromatic components in fuel increase. The injection pressure has a great effect on spray combustion, i.e., shorter combustion period and rapid soot oxidization with high injection pressure. However the effects of aromatic components on combustion were not changed qualitatively by the increased injection pressure.