Stirling Engine question

I started penning a response to this, but it quickly became clear that it would approach book like proportions. So suffice it to say that the limiting efficiency of any thermodynamic cycle is determined by the temperature at which heat is added to and rejected by the system. This is called the Carnot efficiency and is calculated by T(hot) - T(cold) / T(hot). So for a cycle to which heat is added at 900K and which rejects it at 300K, the Carnot efficiency would be 900-300/900 = 0.67 (67%). Theoretically the regenerative stirling cycle is capable of approaching this ideal much more closely than any internal combustion cycle but there are many practical difficulties which prevent this from being fully realised.

Probably the shining light in the stirling world at the moment is the Whispergen - a micro combined heat and power system - and in this application it is not primarily the potential for high efficiency of the stirling engine which appeals (in a CHP system waste energy is used to heat water) but its civilised nature in terms of noise, vibration and exhaust pollutants which make it attractive for use in a domestic environment.

There is loads of information (and misinformation!) about stirling engines on the internet and I would suggest you look in that direction for further reading.

""Paul E. Bennett"" wrote (snip):-

Sure does. But even if you could make an engine which could utilise those extremes of temperature, you would probably use more energy producing your plasma and liquid helium than would be recovered at the end of the day!

Probably a thick question but I'll ask anyway (only to be first to ask it).

Does this calculation you show us above mean that if we could heat the hot end to 10 million K (like in a Fusion Plasma) and keep the cold end at 4k (by supplying huge quantities of Liquid Helium) we would have a 99.999% efficient engine. Cool, no hot, no cool, doh! ;>.

There was a sectionalised one on view at Kew Bridge Steam Museum on (at the Stirling Engine Rally) Sunday.

There are also some useful books on the topic and the Stirling Engine Society at

PO. Box 5909 Chelmsford CM1 2FG.

Membership costs UKP10 per year (UKP12 for overseas members). The society have a web site but I will have to dig a bit for the URL (buried it in a massive intersystem data move).

When one has fusion plant at ones disposal......

Actually, at present you are correct about the cost of producing hot plasmas. The current systems still use more energy input than they return out. That will change soon enough though as the new generation of fusion plant is constructed.