Optimization, fuel characterization, and variable compression ratio diesel engine performance and emission of biodiesel from three different nonedible seed oils

Abstract The present study investigates the engine compatibility of biodiesel derived from three non‐edible second‐generation feedstocks, Gossypium hirsutum (GHO), Hevea brasiliensis (HBO), and Pongamia pinnata (PPO), under identical operating conditions. The biodiesels were evaluated in a single‐cylinder variable compression ratio diesel engine at compression ratios of 16–20 using B20, B30, B40, B60, and B100 blends, with conventional diesel (B0) as the reference fuel. Engine performance, combustion characteristics, and exhaust emissions were systematically examined to identify suitable blend‐compression ratio combinations. The results showed that the optimum operating condition depended on the feedstock. GHO and HBO achieved their highest brake thermal efficiencies of 35.17% and 32.17%, respectively, at B30‐CR19, accompanied by minimum specific fuel consumptions of 0.217 and 0.253 kg/kWh. In contrast, PPO exhibited its highest brake thermal efficiency of 30.97% and a specific fuel consumption of 0.244 kg/kWh at B20‐CR18. These results indicate that moderate biodiesel blending combined with an appropriate compression ratio provides a more favorable balance between thermal efficiency and fuel consumption than either increasing the biodiesel fraction or the compression ratio alone. Increasing the biodiesel fraction and compression ratio generally reduced CO, HC, CO 2 , and smoke emissions, while NOx increased because of the oxygenated nature of biodiesel and higher in‐cylinder temperatures. This study demonstrates that the suitable operating condition varies with feedstock properties and that GHO‐B30/CR19, HBO‐B30/CR19, and PPO‐B20/CR18 provide favorable performance‐emission combinations under full‐load operation.