# "Liquid Piston" rotary engine with 75% thermal efficiency



## PStechPaul (May 1, 2012)

I just got this link in my email today:
http://www.gizmag.com/liquidpistol-...aign=b07dede3b3-UA-2235360-4&utm_medium=email

Seems like a perfect fit for a hybrid or an EV range extender.


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## DawidvC (Feb 14, 2010)

If it can be brought to production, it will be great. I was thinking of a wankel-powered apu for longer range, having worked on a French-derived version in my far distant youth, but this would be so much better.


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## Duncan (Dec 8, 2008)

Great Idea - then I read 75% efficient

Sorry guys its not possible - it is a heat engine - modern diesels get within 90% of the theoretical maximum using modern materials

75% efficient with zero losses and zero friction implies

(Temp IN - Temp OUT) / Temp IN = 0.75

Temp Out - has to be above 300degrees Kelvin (or you can't reject the heat) 
So temperature IN has to be above 1200 degrees Kelvin - 927C

That is the *average* inlet temperature during the combustion - several things happen at those temperatures
Aluminium melts
Steel loses 90% of it's strength
And most importantly - all of your thermal losses go through the roof! 

Its the same as the guy promising to pack 2000 liters of water into a 200 liter container


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## PStechPaul (May 1, 2012)

I don't know if it's possible or not, and my knowledge of thermodynamics is minimal, but the engine uses parts of the Otto cycle as well as the Diesel and Atkinson cycle.









The figure above compares air-standard efficiency as a function of compression ratio. the three curves compare HEHC, Otto (typical for a gasoline engine) and Diesel thermodynamic cycles.

More information may be found here:
http://en.wikipedia.org/wiki/Liquidpiston
http://www.liquidpiston.com/technologycycle/tid/4.html
http://patentscope.wipo.int/search/en/detail.jsf?docId=WO2012135556&recNum=1&tab=PCTClaims&maxRec=1&office=&prevFilter=&sortOption=&queryString=FP%3A%28liquidpiston%29


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