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The environmental pollution and global warming associated with the use of fossil fuels, has forced a search for alternative fuels in transportation. This paper presents a review of the use of biodiesel in CI engines and its environmental impacts. There is a significant reduction in the emission of unburned hydrocarbons, polyaromatic hydrocarbons and soot, particulate matters, carbon monoxide, carbon dioxide and sulfur dioxide with biodiesel. Smoke opacity also decreases, but the NO x emission is more with biodiesel. It is evident from the study that biodiesel can only replace conventional diesel to some extent due to economic, social and other constraints.

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.

Fast depletion of the conventional petroleum-based fossil fuel reserves and the detrimental effects of the pollutant emissions associated with the combustion of these fuels in internal combustion (IC) engines propelled the exploration and development of alternative fuels for internal combustion engines. Biodiesel has been identified as one of the most promising alternative fuels for IC engines. This paper discusses about the advantages and disadvantages of biodiesel vis-a-vis the conventional petro-diesel and presents the energetic performances and emission characteristics of CI engine using biodiesel and biodiesel-petrodiesel blends as fuels. An overview of the current research works carried out by several researchers has been presented in brief. A review of the performance analysis suggests that biodiesel and its blends with conventional diesel have comparable brake thermal efficiencies. The energy balance studies show that biodiesel returns more than 3 units of energy for each unit used in its production. However, the brake specific fuel consumption increases by about 9–14% compared to diesel fuel. But, considerable improvement in environmental performance is obtained using biodiesel. There is significant reduction in the emissions of unburned hydrocarbons, polyaromatic hydrocarbons (PAHs), soot, particulates, carbon monoxide, carbon dioxide and sulphur dioxide with biodiesel. But the NOx emission is more with biodiesel compared to diesel. A case study with Jatropha biodiesel as fuel and the current development status, both global and Indian, of biodiesel as a CI engine fuel have been included in the paper.