Sustainable biodiesel production and engine performance: A study on microwave‐assisted synthesis and its impact on <scp>CRDI</scp> diesel engine emissions and energy efficiency

Abstract The rapid depletion of fossil fuel reserves and increasing global energy demand necessitate the development of sustainable alternative fuels and advanced combustion strategies to support clean energy and climate action goals (SDG 7 &amp; 13). In this study, biodiesel derived from Simmondsia chinensis oil was synthesized via alkali‐catalyzed transesterification and subsequently stabilized using pyrogallol antioxidant to enhance oxidation resistance and fuel durability. The synthesized biodiesel was blended with diesel to prepare D70SCOME30, D50SCOME50, and a ternary antioxidant‐enriched blend (D50SCOME30PY20, denoted as DBPY20). Experimental investigations were conducted on a modified CRDi diesel engine by varying compression ratios (16, 18, and 20:1) and exhaust gas recirculation (EGR) rates (10%, 15%, and 20%) at a fixed injection timing of 25° CA. Among all operating conditions, the ternary blend at CR 20:1 with 15% EGR exhibited the highest BTE, showing a 2.31% improvement compared to baseline diesel. A reduction of 29% in NO x emissions was achieved. Smoke opacity decreased by 16.2% at CR 20 and 15% EGR compared to conventional diesel operation. However, HC and CO emissions increased at lower CRs and higher EGR rates due to incomplete combustion. Energy balance analysis indicated that diesel transferred more heat to the cooling water and brake power, whereas biodiesel blends exhibited relatively higher exhaust and unaccounted heat losses. Overall, the antioxidant‐enhanced ternary biodiesel blend demonstrated improved combustion efficiency and emission reduction under optimized CR and EGR conditions, highlighting the significance of integrated fuel synthesis and engine parameter optimisation for sustainable diesel engine operation.