Exergetic analysis of compressed air for vehicular propulsion

Exergy analysis is a valuable tool for new combustion engine technologies evaluation. By combining both first and second laws of thermodynamics, the availability content of a control system can be precisely calculated, and maximum available work can be determined. One of the main features of exergy evaluation is that it can be performed without knowledge of intrinsic working details of the device being tested.

Compressed air vehicles have been studied in the latter years, and several commercial solutions are being developed. While each developer approaches the problem with a different setup, all must be constrained by the second-law analysis.

In this paper, a theoretical exergy analysis is performed for the compressed air engine, and the exergy content is determined as a function of the storage pressure. The exergy density of a typical compressed air tank is compared to those of hydrocarbons. It is shown that this technology isn't capable of supplying the necessary mileage for a typical light commercial vehicle, unless significant power saving procedures are implemented.