Analysis of entropy generation and exergy loss during combustion

Abstract

The analysis of entropy generation and exergy loss is used for optimizing the performance of energy conversion systems such as gas turbines. Exergy loss in the combustor of 20%–30% is the largest of all component losses in the gas turbine systems. The sources of the large exergy loss during the combustion process can be evaluated by analyzing local entropy generation of irreversible processes. Multicomponent flow with chemical reactions such as combustion involves four irreversible processes: viscous dissipation, heat conduction, mass diffusion, and chemical reaction. In this study, we analyzed local entropy generation and exergy loss due to these processes in premixed and diffusion flames in order to clarify the reasons for large exergy destruction during combustion processes, taking into account detailed chemical kinetics and multicomponent diffusion. The effects of fuels, equivalence ratio, and inlet fluid temperature on local entropy generation and exergy loss were evaluated for premixed flames. Chemical reaction is the dominant process for exergy loss in premixed flames, and the fraction of it changes in relation to the flame structure modification and temperature. On the contrary, for diffusion flames, heat conduction instead of chemical reaction is the major process for exergy loss.