Polyurethane–urea elastomers as working substances in rubber heat engines

The possibility of using synthetic elastomers as working substances in a rubber heat engine was investigated at the laboratory and pilot scale. Two polyurethane–urea elastomers were subjected to expermental heat engine cycles at a variety of strains and temperature differences. It was found that optimum power and thermal efficiency were obtained at small strain perturbations where the elastomers were close to mechanical equilibrium. Crystallization of the rubbery phase during large strain perturbations is a nonequilibrium process which should be avoided. Quasi‐ideal rubber behavior is approached in the pilot‐scale heat engine which supports these conclusions.