This study investigates the combustion performance, efficiency, and emission characteristics of four fuel blends—B7 (7% biodiesel), B100 (pure biodiesel), B100E5 (95% biodiesel + 5% ethanol), and B100E10 (90% biodiesel + 10% ethanol)—in a light-duty diesel engine. Experiments were conducted on an engine dynamometer and a chassis dynamometer under varying loads (84, 112, and 140 Nm) and speeds (1600, 1800, and 2000 rpm) to assess in-cylinder pressure, temperature, engine efficiencies, and emissions. The results demonstrate that the oxygenated B100Es blend achieves superior combustion performance, exhibiting higher peak in-cylinder pressures and temperatures than conventional B7, attributable to enhanced oxygen availability, which promotes more complete fuel oxidation. This translates to an improvement in indicated thermal efficiency despite its lower calorific value relative to B7. B100 demonstrates distinct advantages in mechanical efficiency at higher engine speeds, attributed to its superior lubricity. The study provides quantitative evidence that a strategic blend of biodiesel with ethanol can effectively balance the often-competing objectives of combustion efficiency and emission reduction in modern diesel engines. The average brake thermal efficiencies of B7, B100, B100E5, and B100E10 are approximately 35.8, 36.4, 37.7, and 37.2%, respectively. Additionally, the average smoke intensities of B7, B100, B100E5, and B100E10 are approximately 0.211, 0.075, 0.042, and 0.038%/kW, respectively. • Among the ethanol-biodiesel fuels, B100 primarily improves lubricity and reduces mechanical losses, whereas ethanol mainly enhances combustion efficiency. • The average brake thermal efficiencies of B7, B100, B100E5, and B100E10 are approximately 35.8, 36.4, 37.7, and 37.2%, respectively. • Additionally, the average smoke intensities of B7, B100, B100E5, and B100E10 are approximately 0.211, 0.075, 0.042, and 0.038%/kW, respectively.
Suteerapongpun et al. (2026) studied this question.