Ultra-Efficient Hybrid Propulsion System Integrating Stirling Engines and PEM Fuel Cells: Thermodynamic Feasibility and Techno-Economic Assessment

This paper describes a thermally-coupled hybrid propulsion system that uses an alpha-type Stirling engine and a 100 kW Proton Exchange Membrane hydrogen fuel cell for mobile vehicles. The Stirling engine will work as part of the waste-heat recovery subsystem by transforming low-grade thermal energy from the PEMFC coolant into additional electric power. Corrected thermodynamic modeling shows that system efficiency reaches 54–58% in pure waste-heat mode, increasing up to 62% with auxiliary hydrogen combustion, which is 4–8% absolute better than conventional fuel-cell-only architectures. After considering a +95 kg weight penalty as well as realistic vehicle consumption (0.85–0.90 kg H₂/100 km), this system increases driving range by 12-18% (80-120 km). A techno-economic analysis has indicated more than 40-100 years of payback at expected hydrogen prices in 2030 ($5-8/kg), thus making it clear that mass market viability would only be possible with more than 70% cost reduction for Stirling or otherwise through niche deployment. An exergy analysis has confirmed small improvements in quality due to low temperature heat recovery. This study sets a realistic performance baseline and charts the course for experimental validation.