Automotive Applications of Stirling Engines

Abstract

Stirling engines are heat engines receiving heat from an external source, chemical combustion, thermal storage, nuclear or solar, converting a fraction to work and rejecting the remainder as waste heat at low temperature.

They operate without noise, have low exhaust emissions, can operate on any liquid or solid fuel, have low cycle torque variation, a flat part-load characteristic and can be made as efficient and compact as internal combustion engines.

With this array of advantageous characteristics Stirling engines appears suitable for use as vehicle engines. Over the past decade, various vehicles have effectively demonstrated this capability.

Nevertheless Stirling engines are unlikely to pass into general automotive service so long as liquid fuels are available and internal combustion engines can be used. Stirling engines are inherently more expensive and more complicated than internal combustion engines. At high power densities they must use light gas (hydrogen or helium) working fluids at relatively high pressure and high speed with difficult sealing problems and a relatively high maintenance requirement. The cooling system must have twice the capacity of that required for a diesel engine of equivalent power. Moreover, there is no established production and use of Stirling engines in large numbers and little prospect of the massive capital and operating funds necessary to accomplish this.

Future automotive applications for Stirling engines operating with alternative fuels are foreseen including:

• a) the small commuter car with thermal storage/Stirling engine propulsion. The thermal battery may be recharged overnight with low cost electric energy or natural gas combustion. The combination would be half the size and weight of the lead acid battery/electric motor car.

• b) coal and biomass fired Stirling engines in the power range 0.5-5 MW for locomotives, marine propulsion, stationary power and the large, off-highway vehicles used in mining, construction, forestry and agriculture.

Many non-automotive applications for Stirling engines are established or are in prospect including miniature cryogenic refrigerators for missile guidance and night vision equipment, natural gas and propane fired drivers for refrigeration, heat pumps, cogeneration sets and irrigation pumps, trickle chargers and low, capacity generators for long term unattended operation in remote locations, underwater and space power systems, solar energy conversion, marine propulsion and yacht or recreational vehicle power generation.