Energy, exergy and emission analysis of CI engine fueled with Croton macrostachyus biodiesel-diesel blends

Growing energy demand associated with population increase and industrial expansion is contributing to the rapid depletion of fossil fuel reserves and the rise in emission related pollution. In response, attention has shifted toward sustainable energy sources, where biodiesel is recognized as a renewable, environmentally benign, and biodegradable alternative to traditional fuels. However, evaluating engine performance alone is insufficient, as it does not account for inefficiencies and irreversibility that contribute to energy losses in diesel engines. This study aims to evaluates the energy, exergy, and emission characteristics of a compression ignition (CI) engine fueled with Croton macrostachyus methyl ester (CMB) biodiesel blends. It also synthesis a CaO–Al 2 O 3 composite heterogeneous catalyst via calcination method and characterize the fuel properties. The biodiesel was produced through transesterification using a novel hybrid calcium–aluminum oxide (CaO–Al 2 O 3 ) heterogeneous catalyst. Five fuels pure diesel (B0) and blends CMB10, CMB15, CMB20, and CMB25 were tested on a single-cylinder, four-stroke diesel engine under full load conditions at varied speeds of 800, 1400, 2000, and 2600 rpm. Results showed that CMB20 achieved the best overall balance among the blends, with a 5.85% lower brake thermal efficiency (BTE) and 3.86% higher brake specific fuel consumption (BSFC) than diesel. CMB25 reduced CO 2 emissions by 1.55%, though NOx emissions increased by 8.6%. At 2600 rpm, CMB20 slightly raised the exhaust gas temperature (EGT) by 6.14%, while CMB25 exhibited 18.02 and 13.1% higher exhaust energy and exergy losses, respectively. Cooling water energy and exergy losses rose by 19–31.6% and 6.67–23.8% at lower engine speeds. CMB20 demonstrated 15.4% lower exergy destruction, and the maximum exergy efficiency (20%) was observed for CMB15. Overall, Croton macrostachyus biodiesel blends exhibited higher exhaust energy losses but lower exhaust exergy losses than diesel. At low to moderate speeds, CMB20 delivered improved thermodynamic performance and reduced emissions, indicating its potential as an environmentally favorable diesel substitute requiring optimization at higher speeds.