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The effects of an increasing boost pressure, a high EGR rate and a high injection pressure on exhaust emissions from an HSDI (High Speed Direct Injection) diesel engine were examined. The mechanisms were then investigated with both in-cylinder observations and 3DCFD coupled with ϕT-map analysis. Under a high-load condition, increasing the charging efficiency combined with a high injection pressure and a high EGR rate is an effective way to reduce NOx and soot simultaneously, which realized an ultra low NOx of 16ppm at 1.7MPa of IMEP (Indicated Mean Effective Pressure). The flame temperature with low NOx and low soot emissions is decreased by 260K from that with conventional emissions. Also, the distribution of the fuel-air mixture plot on a ϕT-map is moved away from the NOx and soot formation peninsula, compared to the conventional emissions case.

The aim of this work is to investigate the possibility of heat insulation by “Temperature Swing”, that is temperature fluctuation, on combustion chamber walls coated with low-heat-conductivity and low-heat-capacity materials. Adiabatic engines studied in the 1980s, such as ceramic coated engines, caused constantly high temperature on combustion wall surface during the whole cycle including the intake stroke, even if it employed ceramic thermal barrier coating methods. This resulted in increase in NOx and Soot, decrease in volumetric efficiency and combustion efficiency, and facilitated the occurrence of engine knock. On the other hand, “Temperature Swing” coat on the combustion chamber walls leads to a large change in surface temperature. In this case, the surface temperature with this insulation coat follows the transient gas temperature, which decreases heat loss with the prevention of intake air heating, and also which is expected to prevent NOx and Soot from increasing.