Experimental insights into injection timing effects upon VCR diesel engine fuelled with injected waste cooking oil ethyl ester-diesel blends and induced biogas operated in dual fuel mode

This study investigates the dual-fuel operation of a single-cylinder, four-stroke, 5.2 kW variable compression ratio (VCR) diesel engine fueled with a 20 % blend of waste cooking oil ethyl ester (WCOEE_20) and diesel as pilot fuel, and biogas (1.2 kg/h) as the inducted secondary fuel. The study aims to integrate renewable fuels into conventional diesel engines, promoting both efficiency and ustainability. Biogas was introduced through the intake manifold, while WCOEE_20 was directly injected into the combustion chamber. Experiments were performed at 1500 rpm and a compression ratio of 17.5:1, across varied injection timings (21◦, 23◦, 25◦, and 27 ◦CA bTDC) to identify the optimal operating condition for enhanced combustion, performance, and emission
behavior. Among all test cases, WCOEE_20+DFM25 ◦CA exhibited the best performance with a brake thermal efficiency (BTE) of 27.55 %—an improvement of 10.51 % over WCOEE_20+DFM23◦, while 7.61 % lower than
diesel operated in natural aspirated mode. This onfiguration reduced brake specific fuel consumption (BSFC) by 15.33 %, and exhaust gas temperature (EGT) increased by 3.28 %, compared to WCOEE_20+DFM23◦ while,34.77 % increase in BSFC and 2.24 % decrease in EGT observed for plain diesel, respectively. Emission analysis showed reductions in CO (15.79 %), HC (16.0 %), NOx (17.41 %), and smoke opacity (28.49 %) relative to diesel fuel. Compared to WCOEE_20+DFM23◦, smoke opacity decreased by 5.52 %, while NOx increased slightly by 9.67 %. Combustion analysis revealed that WCOEE_20+DFM25◦ caused a 0.83 % and 2.27 % increase in ignition delay period (IDP) over diesel and WCOEE_20+DFM23◦, respectively, and combustion duration (CD) increased by 6.97 % and decreased by 2.76 %. Heat release rate (HRR) and cylinder pressure (CP) were found to be 3.58 % and 13.22 % higher than WCOEE_20+DFM23◦, while 1.88 % lower and 10.02 % higher than normal diesel fuel in natural mode of aspiration. These findings demonstrate the potential of WCOEE_20+DFM25◦ as a cleaner and efficient alternative for diesel engine operation, supporting the United Nations Sustainable Development Goals (SDG) 7 (Affordable and Clean Energy) and SDG 13 (Climate Action)