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. Also, the operation with all the blended and reference fuels with optimized pilot quantities and suitable EGR rates was investigated over a wide range of IMEP 1.0 MPa. Silent, low NOx, and smokeless combustion is possible over a wide IMEP range with the alcohol and vegetable oil blended fuels here with optimized quantities of pilot injection and EGR rates. Premixed combustion with pilot injection occurs near TDC with the alcohol + vegetable oil blended fuels due to the poor ignitabilities, which make it possible to increase the quantity of pilot injection and reduce the after burning with the main injection, resulting in improvements in the indicated thermal efficiency due to the increase in the degree of constant volume heat release. Smokeless operation is possible with the alcohol and vegetable oil blends even at low injection pressure and large EGR rate conditions.
