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Water and diesel fuel emulsions containing 13% and 26% water by volume were investigated in a modern diesel engine with relatively early pilot injection, supercharging, and cooled EGR. The heat release from the pilot injection with water emulsions is retarded toward the top dead center due to the poor ignitability, which enables larger pilot and smaller main injection quantities. This characteristic results in improvements in the thermal efficiency due to the larger heat release near the top dead center and the smaller afterburning. With the 26% water emulsion, mild, smokeless, and very low NOx operation is possible at an optimum pilot injection quantity and 15% intake oxygen with EGR at or below 0.9 MPa IMEP, a condition where large smoke emissions are unavoidable with regular unblended diesel fuel. Heat transfer analysis with Woschni's equation did not show the decrease in cooling loss with the water emulsion fuels.

Combustion and exhaust gas emissions of alcohol and vegetable oil blends including a 20% ethanol + 40% 1-butanol + 40% vegetable oil blend and a 50% 1-butanol + 50% vegetable oil blend were examined in a single cylinder, four-stroke cycle, 0.83L direct injection diesel engine, with a supercharger and a common rail fuel injection system. A 50% diesel oil + 50% vegetable oil blend and regular unblended diesel fuel were used as reference fuels. The boost pressure was kept constant at 160 kPa (absolute pressure), and the cooled low pressure loop EGR was realized by mixing with a part of the exhaust gas. Pilot injection is effective to suppress rapid combustion due to the lower ignitability of the alcohol and vegetable oil blends. The effects of reductions in the intake oxygen concentration with cooled EGR and changes in the fuel injection pressure were investigated for the blended fuels.

The main objectives of this research are to establish the practical use of DME (Dimethyl ether) diesel engine with high performance and clear the emission regulation in urban area by securing a stable DME supply system and the engine durability and reliability. In this research, the fuel injection system including a fuel supply system that provides a long-term stable engine operation was developed. The effect of thermal efficiency improvement using larger EGR (Exhaust gas recirculation) was not found by changing injection parameter. The decrease of suction temperature by cooling the EGR was the most effective in thermal efficiency improvement at the target NOx (Oxides of nitrogen) of 100 ppm (13%O2 conversion). With DME, the amount of PM (Particulate matter) with EGR was extremely low compared with diesel fuel. The endurance test was conducted for a continuous operation of 5000hrs and the engine and fuel system durability were achieved.