Energy and exergy analysis of compressed air engine systems

Abstract

In the past decade, compressed air vehicles have attracted much attention because of their zero pollution, high efficiency, environmental friendliness and relative maturity. To further explore the potential of compressed air technology in vehicles, three-stage and four-stage compressed air engine systems are optimized in present study by analyzing the energy and exergy distribution from a technological viewpoint. Their characteristics are compared in terms of shaft work, coolth, overall efficiency, and exergy distribution. Stage expansion ratios differ under maximum work output. The shaft work and coolth of both systems are increased with the increase of working pressure, turbine inlet temperature, or stage efficiency. Three-stage compressed air engine systems have a lower work output and coolth than four-stage compressed air engine systems at given operation condition. The overall efficiencies of these two systems are comparable to those of conventional diesel engines and fuel cell vehicles. Exergy losses of the two systems are composed by the exergy loss in the turbines, heat exchangers, and exits. The analyses suggest that increasing the number of stages, improving stage efficiency, and utilizing coolth to reduce the exergy loss in heat exchangers are effective ways to decrease the total exergy loss and improve the work output and overall efficiency of the compressed air engine systems.

Keywords

• Energy analysis
• Exergy
• Exergy analysis
• Compressed air
• Engine