A new formulation of the thermodynamic limits on the performance of chemical and nuclear engines

The upper limits have not been established on the performance of engines that use chemical fuel or a heat source such as a nuclear reactor, but do not reject heat to the environment. Important examples of such engines are simple open-cycle gas turbines, ideal internal combustion engines, and either chemical or nuclear fueled jet and rocket engines. Many cycles for such engines have been analyzed in the literature and the performance determined. This paper defines the thermodynamic limits for such systems in the same sense as Carnot established the limiting efficiency for heat engines, or Gibbs, the maximum work, obtainable from a chemical reaction. The maximum specific work or specific impulse available from the chemical engine is shown to depend upon the initial and final conditions and the enthalpy and free energy change of the reaction involved. Results for the nuclear engines show that the maximum values of specific impulse are considerably greater than that obtained by an adiabatic expansion of the propellant from the temperature of the heat source.