Multi-objective optimization of performance and emission characteristics of a CRDI diesel engine fueled with sapota methyl ester/diesel blends

Abstract

This study examines the combined effect of compression ratio (CR) and exhaust gas recirculation (EGR) on combustion, performance, and emissions characteristic of a common rail direct injection (CRDI) engine fueled by sapota methyl ester (SME) and diesel blend. Biodiesel extracted from sapota fruits waste seeds through the transesterification process. This work utilised diesel-biodiesel blend B50% blend (D50SME50 by vol.), and the engine was run with different compression ratios (16, 17.5, and 19) and EGR rates (0%, 10%, and 20%) to evaluate engine outcome parameters. The result found that the ignition delay was reduced with an increased compression ratio. The high heat release rate (HRR) was ascertained with the CR 16 and EGR 10% rate, about 6.01% higher than diesel fuel. The highest in-cylinder pressure was observed with the CR 19 and EGR 0% rate, about 2.02% higher than diesel. The thermal brake efficiency (BTE) for CR 16 and EGR, 0% rate, is higher than other test conditions but 11.21% lower than neat diesel. The nitrogen (NOx) emission oxides for all the test conditions were lower than neat diesel. The highest NOx emission reduction was achieved in CR 16, and EGR 20% rate about 61.91% lower than diesel operation. The smoke opacity increased by increasing the EGR rate. The CR 17.5 and EGR 0% rate displayed lower smoke opacity, about 2.5% lower than diesel operation. The hydrocarbon (HC) emission was lower than neat diesel at all operating parameters. The CR 17.5 and EGR, 0% rate, displayed the lowest HC emission, about 44.82% decreased than neat diesel operation. The carbon monoxide (CO) emission displayed lower for the EGR 0% rate at all the compression ratios. The CR 16 and EGR 0% rate displayed the lowest HC emission, about 10.77%, than diesel operation. The energy analysis noted that the fuel energy input and energy for brake power and energy flown through the exhaust gases are higher in diesel fuel than biodiesel blend. The unaccounted losses were low in diesel than biodiesel blend. Finally, the TOPSIS optimization study was carried out to find the optimum input conditions to improve combustion, performance, energy, and reduced emissions. The B50% blend with CR 16 and EGR 20% at full load achieved 1st rank with 0.809 relative closeness value. So, this operating condition was projected as the best prospect for applying in a CRDI diesel engine.