Beyond constant-temperature reservoirs: A Stirling cycle with constant heat-generation rate.

Abstract

Conventional heat-engine models typically assume two reservoirs at fixed temperatures, whereas radioisotope power systems provide heat at a constant generation rate rather than a constant temperature. We develop a theoretical framework for finite-time heat engines operating between constant heat-generation-rate hot sources and constant-temperature cold reservoirs, establishing a universal relation between average power and efficiency that is independent of engine cycle or working substance. As an illustrative example, we analyze a finite-time Stirling cycle with different control protocols, and find the match between our predicted efficiency and that of practical data. We also quantify the long-term performance degradation due to radioactive decay. This work introduces a new prototype for heat-engine theory and offers guidance for analyzing and designing radioisotope power systems.