Studies on vegetable oils as fuel in CI engines

Abstract

Bioenergy options to replace fossil fuels have attracted worldwide attention as they are renewable and environment friendly. The search for a renewable diesel fuel alternative is often directed towards vegetable oils and the trans-esterification of vegetable oils has been emerged as the most promising technology. Coconut is the major oil crop of Kerala and an investigation on the use of coconut oil in comparison with other vegetable oils as fuel in compression ignition engines was carried out which included a study of the fuel properties of the vegetable oils, their methyl esters (biodiesels) and different blends. Two different methods were examined for trans- esterification of vegetable oils. Engine tests were then undertaken with the different fuels and fuel blends. It was observed that the fuel properties viz. specific gravity and viscosity were unsuitable for use of straight vegetable oils where as their methyl esters exhibited comparable viscosities with diesel fuel. Among the two methods of trans- esterification studied, the procedure proposed by Gupta, 1994 was superior over the method proposed by Kumar et al. (2003).There was a considerable reduction in the smoke density while using biodiesel in CI engines when compared to diesel. Coconut oil methyl ester showed the lowest smoke density compared to other methyl esters at all loads. All proportions of coconut oil methyl ester with diesel exhibited considerable reduction in smoke densities compared to diesel at all loads except at no load which confirmed the pollution reduction ability of coconut oil biodiesel. The 1: 1 blend of coconut oil methyl ester with palm oil methyl showed a smoke density very close to that from coconut oil methyl ester. The specific fuel consumptions of biodiesels and their blends were higher than diesel at all loads. Coconut oil methyl ester and palm oil methyl ester showed the highest specific fuel consumptions. Engine tests with straight coconut oil - diesel showed that the smoke densities were higher than diesel at loads higher than 20 %. The study indicated that coconut oil biodiesel is a better fuel than diesel for CI engines, except for its high specific fuel consumption. Blending coconut oil biodiesel with diesel resulted in a considerable reduction in pollution and hence its potential as an anti pollutant additive for diesel is noteworthy.