Feasibility study of crude rice bran oil as a diesel substitute in a DI-CI engine without modifications

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Oil extracted from the inner husk of rice, termed rice bran oil (RBO), promises to be a low-cost, renewable substitute for petroleum-derived diesel as a compression ignition (CI) engine fuel. While rice is a major crop in India, RBO is underutilized. This research work concentrates on the study of the prospect of using unrefined RBO as a diesel engine fuel without any modifications. Like other vegetable oils, crude RBO faces the problem of high viscosity and hence blending RBO with diesel is attempted in this work. Tests were conducted in a naturally aspirated direct injection (DI) four-stroke 4.4 kW stationary diesel engine with pure RBO and blends of RBO with diesel. It is observed that specific energy consumption (SEC) of RBO is higher than that of all the fuels at all loads and for 25% RBO, it is very close to that of diesel. As an oxygenated fuel, RBO reduces emission of pollutants like CO and unburnt hydrocarbon (UBHC) by supplying additional oxygen from the fuel. At no-load condition the delay period for RBO and its blends were slightly higher than for diesel. As the load increased the delay periods were shorter than for diesel. The maximum heat release rates of RBO and its blends were lower than that of diesel. The peak pressures for RBO and its blends were slightly higher and occurred earlier than that of diesel. In general blended fuels result in lower viscosity, better combustion and lesser emission than RBO and 25% RBO shows better results than RBO and other blends of RBO.