Computational Combustion and Emission Analysis of Biodiesel in a Variable Compression Ratio Engine

The aim of the present study is to analyse the combustion characteristics, performance and emission parameters of a variable compression ratio (VCR) diesel engine experimentally and numerically using soybean methyl ester (SME) biodiesel. Initially the engine is fed with diesel to capture the basic data, and then SME was tested as 20 % blend (B20), as 40% blend (B40) and as pure bio-fuel (B100). The experimental investigations are followed by a computational combustion and emissions analysis of diesel engine which is done by using the CFD software (ANSYS FLUENT 13). The combustion, performance and emissions parameters are evaluated by operating the engine at four different compression ratios of 15, 16, 17.5 and 19 and varying the load from 0 kW to 4.4 kW with 1.1 kW step. It is observed that peak pressure is closer to TDC when SME blends is increased. SME blend has earlier combustion start because of the advancement in the injection timing, shorter delay time. Increasing mixing ratio of biodiesel is found to decrease BTE slightly and increases the BSFC. Remarkable decrease in UHC and CO emissions as the ratio of SME is increased due to the complete combustion of biodiesel with presence of more oxygen in the combustion chamber. The measured BSN for B20, B40, and B100 SME was less than that of diesel fuel by 20.44%, 35.78%, and 48.3% respectively. It is inferred from the combustion analysis that as the compression ratio increases from 15 to 19 a decrease in smoke intensity, UHC, and CO, but it increases the emission of NOx. Both turbulent kinetic energy and turbulent dissipation rate were decreased as the percentage of SME increased by 10.84% and 2.01% respectively. The increase in compression ratio from 15 to 19 caused an increase in the peak pressure, density, combustion velocity, turbulence, peak temperature, NOx and a decrease in soot emissions. It can be assessed that the B20 SME is best suited to implement it into diesel engine without any effects. It has been founded from the results that 19 compression ratio has shown good performance and low emissions as compared to other compression ratios. The results obtained from the experimental investigation have been compared with the results of CFD analysis and are found to be in good agreement with each other with just slight deviation. © 2019 University of Al-Qadisiyah. All rights reserved