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In this study, effects of nozzle hole diameter and EGR ratio on flame temperature (indication of NO formation) and KL value (indication of soot formation) were investigated. Combustion of a single diesel fuel spray in the cylinder of a rapid compression machine (RCM) was analyzed. Three nozzles with different hole diameter were used corresponding to present, near term and long term heavy duty diesel engine specifications. EGR was simulated through 2%vol. CO2 addition to the inlet air and by increase of in-cylinder surrounding gas temperature. Various types of fuels were used in this. The ignition and combustion processes of diesel fuel spray were observed by a high-speed direct photography and by indicated pressure diagrams. Flame temperature and KL factor were analyzed by a two-color method. With larger nozzle hole diameters there are larger high temperature areas. With smaller nozzle hole diameters there is more soot formed. Introduction of 2% vol.

High pressure fuel injection and a micro-hole nozzle were used with a rapid compression machine to study soot and nitrogen oxide reduction by creating a uniform and lean fuel distribution in the combustion chamber. The rapid compression machine was optically accessible, which allowed high-speed photography and subsequent two-color flame temperature and soot concentration measurements to be made. In addition, band spectrum radical luminescence images were also observed.

In order to clarify the reason why NOx emissions factor becomes higher at vehicle acceleration at intersections etc, two freight vehicles, that have EGR system for the reduction of NOx, were tested by an on-board NOx measurement system. Higher NOx emissions factor was observed in operations in lower-gear operation for each vehicle. Since the engine speed change was higher in the operation of lower gears, NOx emissions characteristics were analyzed in view of engine torque, NOx mass emissions and EGR rate, considering engine speed change. It was found that lower-gear operations made the engine speed change higher and the EGR rate lower. This seems to be one of the factors to engender the intensive NOx pollution at roadsides.