Abstract: The problems involved for using vegetable fuel as an alternative to diesel fuel are(1) carbon or gum deposits on chamber, injection nozzle tips and injector coking, (2) serious contamination of the lubricating oil and (3) the difficulty for starting the engine.The carbon and gum deposits mainly caused by the high viscosity of the vegetable fuels which is more than ten times as high as that of the diesel fuel. The high viscosity leads to poor atomization and inefficient combustion of the fuel. Also residues of partly combusted fuel remained in the engine to form deposits or to contaminate the lubricating oil.The purposes of the research are to change the properties of vegetable fuel throuhh heating the fuel as the main measure, to improve the poor atomization and imcompletcd combustion of the fuel and furthermore to reduce the deposits and lubricating oil coutamination of the D.I.engine.The paper analyzed the improvement on tne properties of injection, atomization, combustion performance of the D.I.engine by heating the fuel.The E.M.A.Test Cycle have been conducted with both heated (80℃) and no heated (20℃) oils.The result is that the method to heat oil is feasible in reducing deposits accumlating in the combustion chamber and on the injection nozzle tips was observed when heated fuel was used. The E.M.A.Test Cycle provided a promising result that heated fuel could improve the duribility of the D.I.engine.By the way of experimental design of regression analysis,this research established a mathematic model between the specific consumption of the fuel and the injection advance angle, injection pressure and fuel temperature. The potimum solution obtained are injection advance angle: 27°, injection pressure: 175kg/cm² and temperature: 80℃. The results indicate that it is effective to use the exhausted heat of engine to heat the vegetable oil to increase the duribility of engine.