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The present review aims to study the prospects and opportunities of introducing vegetable oils and their derivatives as fuels in diesel engines. A survey of recent studies and research on vegetable oil based fuels is given within the historical context. Fuel related properties are reviewed and compared with conventional diesel fuel. The use of neat vegetable oil (edible and/or non-edible), biodiesel and its blends in a diesel engine has been discussed. Performance and emission characteristics are highlighted. Suitability of different combustion chambers for diesel engine operation with vegetable oils is outlined. Techniques to decrease viscosities are discussed. Current developments on the use of vegetable oils and its blends, biodiesel and its blends in diesel engines are examined.

The reduction of NOx without the degradation of soot emission and/or fuel economy necessitates the grasp of the in-cylinder temperature behavior, since NOx is mainly generated within localized high temperature regions in the cylinder of diesel engines. Therefore, a split injection method to reduce NOx has been proposed. In this method, injection is divided into two steps, the main injection of larger quantity and the sub-injection of smaller quantity. The sub-injection is practiced late into the flame of the main injection fuel. The moment of flame tip approaches the nozzle hole, the sub-injection is practiced, and the sub-injection spray folded in the flame. This attempted to control the localized high temperature regions by promoting the mixing of in-cylinder gases owing to supplementary fuel injection energy. Thus split injection suppresses the formation of nitrogen oxide.