Unconventional engines -Thermal engines with external combustion

Original ideas for replacing the usual kinematics of a combustion engine's connecting rod-crank motion transformation are regularly put forward. Some of these concepts, conceived as far back as the 1900s, are re-emerging at the beginning of the 21st century, and a better grasp of the technologies involved could help reactivate some of them as part of the energy transition. However, they often lead to the development of complex technologies with varying levels of reliability.

Two types of motor with external heat supply were invented as early as the 1800s. The Stirling engine was patented by Robert Stirling in 1816, and was first produced by Philips in the Netherlands in the 1830s. The Ericsson motor, whose first model dates back to 1833, was produced from 1889 to 1900.

The concept of the external combustion hot gas engine (Stirling, Ericsson, Rankine, Hirn and other derivative applications in steam engines) is enjoying a resurgence of interest in the 21st century in the field of low-power decarbonized and hybridized thermal machines.

The aim of this article is to re-establish the intrinsic link between the genesis of these hot gas machines and their current sustained revival in today's low-carbon context. A range of modestly-powered, but very real, combined energy production and waste energy recovery solutions is making a comeback in sectors as varied as housing, mobile telephony, solar power, military applications and space.

Similarly, there is renewed interest in micro-cogeneration applications and the production of electricity in remote locations. The conversion of solar energy and the use of biomass, for their part, require heat recovery systems that facilitate additional heat storage. Finally, the use of high-efficiency hybrid solar systems is also becoming a reality, with reliability now at a high level, i.e. longer life and reduced maintenance.