Chapter Eight - Irreversible engines—Open cycles

Abstract

In many practical applications, an engine operates in an open cycle that is driven by fuel combustion. This chapter shows that in combustion-driven power cycles, the thermal efficiency inversely correlates with specific entropy generation defined as the total entropy generation rate per unit flowrate of the fuel burned. A mathematical proof will first be presented demonstrating that a design based on maximum thermal efficiency is identical to that of minimum specific entropy generation. The power cycles to be examined include simple gas turbine cycle, regenerative gas turbine cycle, and combined cycle. The application of organic Rankine cycles to produce power from low-grade heat such as the exhaust of a regenerative gas turbine will also be discussed.