Editing Watt steam engine (section)

== Recent developments ==
Watt's Expansion Engine is generally considered as of historic interest only. There are however some recent developments which may lead to a renaissance of the technology. Today, there is an enormous amount of waste steam and [[waste heat]] with temperatures between {{Convert|100 and 150|C|4=-1}} generated by industry. In addition, solarthermal collectors, geothermal energy sources and biomass reactors produce heat in this temperature range. There are technologies to utilise this energy, in particular the [[Organic Rankine cycle|Organic Rankine Cycle]] (ORC). In principle, these are steam turbines which do not use water but a fluid (a refrigerant) which evaporates at temperatures below {{Convert|100|C}}. Such systems are however fairly complex. They work with pressures of {{Convert|6 to 20|bar|kPa psi}}, so that the whole system has to be completely sealed.

The Expansion Engine can offer significant advantages here, in particular for lower power ratings of 2 to 100&nbsp;kW: with expansion ratios of 1:5, the theoretical efficiency reaches 15%, which is in the range of ORC systems. The Expansion Engine uses water as working fluid which is simple, cheap, non-toxic, non-flammable and non-corrosive. It works at pressure near and below atmospheric, so that sealing is not a problem. And it is a simple machine, implying cost effectiveness. Researchers from the University of Southampton / UK are currently developing a modern version of Watt's engine in order to generate energy from waste steam and waste heat. They improved the theory, demonstrating that theoretical efficiencies of up to 17.4% (and actual efficiencies of 11%) are possible.<ref>{{Cite journal|last=Müller|first=Gerald|year=2015|title=Experimental investigation of the atmospheric steam engine with forced expansion|url=https://eprints.soton.ac.uk/381695/1/Revised%2520manuscript%2520Muller%252022_06_2014.pdf|access-date=5 March 2018|journal=Renewable Energy|volume=75|pages=348–355|doi=10.1016/j.renene.2014.09.061|bibcode=2015REne...75..348M }}</ref> 
[[File:25 Watt Condensing Engine Model 2016.jpg|thumb|The 25 Watt Experimental Condensing Engine built and tested at Southampton University|alt=]]

In order to demonstrate the principle, a 25 watt experimental model engine was built and tested. The engine incorporates steam expansion as well as new features such as electronic control. The picture shows the model built and tested in 2016.<ref>{{Cite web|url=https://the-condensing-engine-project.com/technology/model-tests/|title=Model tests, Mk 1|date=2016-10-08|website=The Condensing Engine Project|language=en|access-date=2019-08-25}}</ref> Currently, a project to build and test a scaled-up 2&nbsp;kW engine is under preparation.<ref>{{Cite web|url=https://the-condensing-engine-project.com/crowd-funding/|title=Crowd funding|date=2016-10-09|website=The Condensing Engine Project|language=en|access-date=2019-08-25}}</ref>