Ignition and emission analysis of a hydrogen-assisted diesel engine fueled with waste Sapota seed biodiesel

Abstract This research presents an innovative dual-fuel methodology that incorporates hydrogen fumigation at a sustained flow rate of 1.0 L/min in conjunction with biodiesel synthesized from waste Sapota (Achras zapota) seed oil, aiming to improve the operational efficiency and environmental efficacy of a compression-ignition engine. The synthesis of Sapota seed oil methyl ester (SOME) was accomplished through the transesterification process of Soxhlet-extracted oil, resulting in a yield of 91.5%. The biodiesel produced demonstrated a calorific value of 39.1 MJ/kg, a kinematic viscosity of 4.5 mm2/s, and a flash point of 148°C, in compliance with ASTM D6751 specifications. An experimental analysis was conducted on a 5.2 kW single-cylinder diesel engine utilizing diesel–SOME blends (B10, B20, and B30). Among the evaluated blends, the B20 configuration with hydrogen fumigation exhibited the most favorable outcomes, enhancing brake thermal efficiency from 28.4% (baseline diesel) to 33.2% and decreasing brake-specific fuel consumption by 6.4%. Significant reductions in emissions were also recorded, with carbon monoxide diminishing by 38%, unburned hydrocarbons by 34%, and smoke opacity by 25%. Conversely, nitrogen oxide emissions escalated by 9.6% due to increased in-cylinder temperatures attributed to the elevated flame speed of hydrogen, underscoring the necessity of integrating aftertreatment systems such as exhaust gas recirculation or selective catalytic reduction. This study represents the inaugural report on the amalgamation of SOME with hydrogen fumigation within a compression-ignition engine framework, demonstrating a technically feasible strategy for waste valorization and the generation of low-emission, high-efficiency energy without necessitating modifications to the engine. The findings provide significant contributions to the progress of sustainable and cleaner internal combustion technologies.