Analytical Approach to the Exergy Destruction and the Simple Expansion Work Potential in the Constant Internal Energy and Volume Combustion Process

The exergy destruction due to the irreversibility of the combustion process has been regarded as one of the key losses of an internal combustion engine. However, there has been little discussion on the direct relationship between the exergy destruction and the work output potential of an engine. In this study, an analytical approach is applied to discuss the relationship between the exergy destruction and efficiency by assuming a simple thermodynamic system simulating an internal combustion engine operation. In this simplified configuration, the exergy destruction during the combustion process is mainly affected by the temperature, which supports well-known facts in the literature. However, regardless of this exergy destruction, the work potential in this simple engine architecture is mainly affected by the pressure during the combustion process. In other words, if these pressure conditions are the same, increasing the system temperature to reduce the exergy destruction does not lead to an increase in the expansion work; rather, it only results in an increase in the remaining exergy after expansion. In a typical internal combustion engine, temperatures before combustion timing must be increased to reduce the exergy destruction, but increasing pressure before combustion timing is a key strategy to increase efficiency.