The Dearman engine
The Dearman engine is a novel piston engine powered by the phase-change expansion of liquid air or liquid nitrogen. In principle it works just like a steam engine only 300°C colder. It was invented by Peter Dearman, a classic British 'garden shed' inventor, and is being developed by the Dearman Engine Company (DEC) to perform a variety of roles.
Because it produces both power and cooling from the same unit of 'fuel', the Dearman engine can serve as an efficient and zero-emission transport refrigeration engine to replace the highly polluting secondary diesel units used on trucks today. The Dearman refrigeration engine is now in on-vehicle trials with MIRA, and will go into commercial field trials in 2015 and larger-scale international trials in 2016. Modelling shows the engine would repay its investment within three months.
Because liquid air boils at -194°C (and liquid nitrogen at -196°C), its work output can be raised by the addition of waste heat from another source. This means the Dearman engine can be combined with a diesel engine or hydrogen fuel cell to form a 'heat hybrid', where waste heat and cold are exchanged between the engines to increase the efficiency of both and reduce fuel consumption. Modelling suggests this arrangement would turn waste heat into extra power at practical conversion efficiencies approaching 50%, and reduce bus and truck diesel consumption by 25%. A consortium including DEC, Air Products, MIRA, Cenex, TRL, The Manufacturing Technology Centre and The Proving Factory has been awarded nearly £2 million by Innovate UK to build a heat hybrid prototype by 2016 while further developing and testing is being undertaken at the Birmingham Centre for Cryogenic Energy Storage.
In the future, the Dearman engine could also be used as a stand-alone propulsion engine for smaller, shorter distance vehicles such as auto-rickshaws ('tuk tuks') in developing countries, where the exhaust of clean cold air would provide 'free' air conditioning. It could also be used as a static back-up electricity generator to replace highly polluting diesel gen-sets.
Cryogenic expansion engines have existed for over a century, but the Dearman engine is novel because it uses a heat exchange fuid (made of water and glycol – just like conventional radiator fuid) to promote rapid and efficient re-gasification inside the engine cylinder.
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