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In recent years, trans-esterified vegetable oils have been widely applied to diesel engine in order to suppress greenhouse gas emissions. However, “neat” vegetable oils are expected to be directly used to resolve some difficulties faced in their use, such high viscosity and slightly high fuel consumption. In this study neat linseed oil has been investigated as a neat vegetable oil. It was found to show higher fuel consumption than diesel fuel, however at the same time it showed lower indicated fuel consumption than diesel fuel. These results suggest some increase in engine friction loss in a neat biofuel diesel engine. Studies have been extensively investigated the difference in friction loss and a newly developed “improved deceleration method” has been applied.

NO, OH, and soot in combustion flame produced from burning at high temperature and pressure diesel fuel spray issuing from a single-hole injection nozzle was measured by laser induced fluorescence (LIF) and laser induced incandescence (LII) methods. The LIF images of OH showed that OH radical, distributed in a band-like zone outside the region of the flame luminescence observed, would persist even after the extinction of flame luminescence. The LIF images of NO showed that NO was located slightly outside the flame luminescence zone and that its region was almost the same as that of OH and would tended to increase in the latter period of the combustion process. Also, the LII images showed that the formation of soot would take place near the flame central zone coincident with the flame luminescence zone.

To reduce exhaust emissions and fuel consumption, the effect of high pressure fuel injection was investigated with in-cylinder fuel spray observation and single cylinder engines. Spray impingement on the cavity wall promotes mixing with air and reduction in the nozzle area extends this wall impingement as a result of increasing both fuel injection pressure and injection period. There exists an optimum range for the injection period. Increased injection pressure by modifying injection rate of fuel pump and nozzle area, improves smoke and fuel consumption at low and medium speeds in particular. To extend these effects of high pressure injection, more optimized combustion system and minimized injection equipment drive torque must be required. To resolve the problem of high pressure injection such as higher combustion noise and increase in NOx emissions, the combination with pilot injection must be one of the most effective ways.