<p>In the present work, the energy and exergy analysis was carried out for a diesel engine fueled with soybean oil biodiesel and its blends at different temperatures and two speeds (1200 and 1600&#xa0;rpm). To simulate the combustion process, a single-zone combustion model was developed. A comprehensive MATLAB-based simulation tool incorporating multiple combustion by-products was developed to perform detailed energy and exergy evaluations. Simulated in-cylinder pressure profiles for pure diesel fuel were benchmarked against experimental observations, demonstrating strong correlation and reliability. The model also provided insights into both instantaneous and cumulative forms of energy and exergy at various crank angles for three biodiesel blend ratios—B20, B40, and B100. The results indicate that the total exergy of B100 is approximately 50% lower than that of B20 and B40. At the same time, the accumulative irreversibility decreases considerably. Additionally, despite similar fuel exergy inputs, B100 significantly improves performance, achieving higher thermal (53.2%) and exergy efficiency (50.5%) compared to B20 and B40, while substantially reducing heat exergy losses. An increase in engine speed, a comparison between 1200 and 1600, results in a decrease in total exergy and irreversibility of 5%. In addition, the indicated work exergy shows a slight reduction, while the heat loss exergy decreased significantly by almost 16% to 33%. Furthermore, the increase in the inlet mixture temperature from 400 to 490 caused an increase in total exergy and heat loss exergy (by 5% at 120⁰ CAD), whereas the indicated work exergy and irreversibility decreased between 10 and 15%.</p>