A twin cylinder, constant speed, direct injection CI (diesel) engine was run on jatropha biodiesel and diesel fuel blends. The engine was directly coupled to a hydraulic dynamometer whose load was varied by adjusting load wheel on the top of the engine. The test results were recorded for pure diesel, pure biodiesel (B100) and different diesel/biodiesel blends. The performance characteristics shows that brake specific fuel consumption (BSFC) decreases rapidly with increase of load up to 4.0 to 4.5 kW (55% to 62% of full load) and then decreases slowly. This result also indicates that BSFC increases when the percentage of biodiesel in the blends is increased. Brake thermal efficiency also increases from high biodiesel blends to pure diesel fuel. Each fuel curve shows maximum efficiency reaches at the load range of 5.0 to 5.5 kW (68% to 75% of full load). Pure diesel has maximum efficiency 29.6%, where as pure biodiesel has maximum efficiency of 21.2%. The exhaust gas temperature increases with the load for all fuel blends. Pure biodiesel gives higher exhaust temperature (320°C) than pure diesel (260°C). The exhaust gas temperature increases with the higher percentage of biodiesel blends in different fuel blends. The probable reason for that is biodiesel contains oxygen atoms which make the combustion process complete and hence more energy is released. In respect of emission characteristics, carbon mono-oxide (CO) and hydrocarbon emissions are improved with the addition of biodiesel to diesel. But these emissions increase with the increase of load for all fuel blends. NOx emission increases with load as well as percentage of blending of biodiesel in the diesel fuel.

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