This paper investigates non-edible straight vegetable oils of Putranjiva, Jatropha and Karanja to find out the most suitable alternative diesel by a chemical processing. Degumming is an economical chemical process that is done by concentrated phosphoric acid. This process is applied to the above-mentioned non-edible oils to remove the impurities for the improvement of viscosity, cetane number and better combustion in the diesel engine upto certain blend of diesel and non-edible vegetable oils. Ten percent, 20%, 30% and 40% blends of degummed non-edible oils and diesel are used in a Ricardo variable compression engine to study and compare the performance and emission characteristics. it is observed that the non-edible oil of Jatropha gives the best results related to the performance and emissions at high loads and 45 degrees bTDC injection timing. (C) 2008 Elsevier Ltd. All rights reserved.