Thermodynamic irreversibilities and exergy balance in combustion processes

The growing concern for energy, economy and environment calls for an efficient utilization of natural energy resources in developing useful work. An important thermodynamic aspect in gauging the overall energy economy of any physical process is the combined energy and exergy analysis from the identification of process irreversibilities. The present paper makes a comprehensive review pertaining to fundamental studies on thermodynamic irreversibility and exergy analysis in the processes of combustion of gaseous, liquid and solid fuels. The need for such investigations in the context of combustion processes in practice is first stressed upon and then the various approaches of exergy analysis and the results arrived at by different research workers in the field have been discussed. It has been recognized that, in almost all situations, the major source of irreversibilities is the internal thermal energy exchange associated with high-temperature gradients caused by heat release in combustion reactions. The primary way of keeping the exergy destruction in a combustion process within a reasonable limit is to reduce the irreversibility in heat conduction through proper control of physical processes and chemical reactions resulting in a high value of flame temperature but lower values of temperature gradients within the system. The optimum operating condition in this context can be determined from the parametric studies on combustion irreversibilities with operating parameters in different types of flames.