Energy-exergy analysis of a diesel engine running on preheated SVO (straight vegetable oil)

Abstract

Vegetable oils are emerging as promising fuel substitutes to the conventional petroleum fuels from the viewpoint of the energy crisis and emission problems. These seem to be attractive substitute of diesel fuels. Vegetable oils have the advantage of being geographically widely produced, in a variety of products and are renewable in nature and thereby not contributing to the net atmospheric concentrations of green house gas carbon dioxide. However, higher viscosity and low volatility are identified as the main reasons for the unsuitability of straight vegetable oils as the substitute of diesel fuel. Researchers have reported that the problem of high fuel viscosity can be overcome by using esters, blending and heating. In this study, attempts have been made to evaluate the possibility of using vegetable oils as diesel f!lel substitute by modifying their properties by means of preheating. Engine performance evaluation has been carried out on the basis of both the first and the second laws of thermodynamics. The first law of thermodynamics has been employed to give a general macroscopic performance evaluation. In order to render a critical look into the performance of the engine using preheated soybean oil fuel, the second law of thermodynamics is also utilized. Although conventional performance analysis shows an improvement in engine performance (especially, brake thermal efficiency) due to preheating of soybean oil, the second-law analysis (known as 'availability analysis' or 'exergy analysis') reveals rather a different picture. It shows that the second-law efficiency (known as 'availability efficiency') of the engine running on. preheated soybean oil fuel is somewhat less than the brake thermal efficiency of the same. Availability analysis also pinpoints the leakages of major energy losses in terms of 'availability destruction' or 'availability loss' that is a strong tool to ensure the best utilization of the energy input.