  Engineering Thermodynamics has been the core course of many science and
engineering majors at home and abroad, including energy and power, mechanical
engineering, civil engineering, aerospace, cryogenic refrigeration, food
engineering, chemical engineering, and environmental engineering, among which
gas power cycle is one of the important contents. However, many Engineering
Thermodynamics textbooks at home and abroad focus only on evaluating the
thermal efficiency of gas power cycle, while the important concept of specific
cycle net work is ignored. Taking an ideal Otto cycle and an ideal Brayton as
examples, the optimum compression ratio (or the pressure ratio) and the maximum
specific cycle net work are analyzed and determined. The ideal Otto and the
ideal Brayton cycles, and also other gas power cycles, are concluded that the
operation under the optimum compression/pressure ratio of the engine, instead
of under the higher efficiency, is more economic and more reasonable. We
concluded that the two very important concepts, i.e., the maximum specific
cycle net work and the optimum compression (or pressure) ratio for the gas
power cycles, should be emphasized in the Engineering Thermodynamics teaching
process and the latter revised or the newly edited textbooks, in order to
better guide the engineering applications. In the end, general T-s diagram is
proposed for the gas power cycles.
