A detailed thermodynamic analysis of a diesel engine at different compression ratios

Abstract

This study investigates experimentally effects of compression ratio (CR) on the combustion, energy, and exergy characteristics of a diesel engine. A four–stroke, naturally aspirated, water–cooled, direct–injection, single–cylinder diesel engine with variable CR capacity was employed. Experiments were conducted at a constant speed of 1500 rpm under various loads, with CRs set to 15:1, 16:1, and 17:1. The software in the experimental setup calculates the arithmetic mean of ten cycles to minimize the effects of cycle–to–cycle variations and enhance the accuracy of the results. A detailed thermodynamic analysis was carried out to examine the combustion, energy, and exergy characteristics of the tested CRs using data obtained from the experiments. The results demonstrated that CR has a significant influence on combustion, energy, and exergy characteristics. Combustion parameters such as mass burned fraction, heat release rate, cylinder pressure, and gas temperature increased with rising CR. Similarly, performance indicators including efficiency, fuel consumption, and the overall energy and exergy performance of the engine also tended to improve as CR increased. Among the tested CRs, a CR of 16 provided the most favorable exergetic outcomes. Specifically, exergy efficiency, exergy performance coefficient, and sustainability index improved by 9.9–22.1 %, 45.3–110.9 %, and by 0.6–6.9 %, respectively, depending on engine load for CR of 16.