Stirling engines are classed as external combustion engines. They are sealed systems with an inert working fluid, usually either helium or hydrogen. They are generally found in small sizes (1 - 25 kW) and are currently being produced in small quantities for specialized applications.
Stirling-cycle engines were patented in 1816 and were commonly used prior to World War I. They were popular because they had a better safety record than steam engines and used air as the working fluid. As steam engines improved and the competing compact Otto cycle engine was invented, Stirling engines lost favor. Recent interest in DER, use by the space and marine industries, has revived interest in Stirling engines and as a result, research and development efforts have increased.
Photo Source: WhisperTech Ltd.
Stirling Engine Overview
<1 kW - 25 kW
Natural gas primarily but broad fuel flexibility is possible