Discussions of gas power cycle performance analysis method in the course of Engineering Thermodynamics

TL;DR

This paper emphasizes the importance of analyzing specific cycle net work and optimal compression ratios in gas power cycles, advocating for their inclusion in thermodynamics education to improve engineering applications.

Contribution

It introduces the concepts of maximum specific cycle net work and optimal compression ratio analysis for gas power cycles, enhancing thermodynamics teaching and textbook content.

Findings

Optimal compression ratio leads to more economical operation.

Maximum specific cycle net work occurs at specific pressure ratios.

Revised teaching should include these concepts for better engineering guidance.

Abstract

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.