Isothermal combustion for improved performance in air-breathing engines

Abstract

This theoretical effort proposes and explains in detail the concept of isothermal combustion. The concept involves combustion at constant total temperatures in order to realize isothermal heat addition to the working fluid in typical powerplants. It is rendered practical by extracting a precise amount of work from the flowing/expanding gases; the heat addition due to combustion will be balanced out to keep the total temperature constant. In an oversimplified description, it might be said that this involves burning in the turbine stages, or burning during the expansion stroke. Isothermal heat addition enables the thermodynamic cycle to approach the Carnot cycle more closely than the state-of-the-art Bray ton, Otto, or diesel cycles. A closed-form analytical expression is derived to explicitly show the cycle efficiency in terms of the pressure ratio and the overall temperature ratio. Thirty to forty percent efficiency increases are seen over the Brayton efficiency for the same overall temperature ratio. Practical aspects are qualitatively mentioned. Future prospects are outlined.