[aerohead]

There has been some mention of the Stirling engine and here is what I have so you all don't think it's some new savior technology:

The Stirling Cycle is,as is the Erricson Cycle,given a theoretical enthalpy efficiency,as the Carnot Cycle,80%.
In 1955,GM Research Labs were investigating the engine.
In 1973,with the Arab Oil Embargo and 'energy-crisis,' interest was renewed.
GM,Ford,Philips Research Laboratories,Holland,and NASA were all doing R&D with it.
When crude prices fell,so did interest for some.Ford quit it after umpteen millions of dollars spent on it.
GM had achieved BSFCs of 0.418-0.358 pounds/Bhp-hr ( 39% enthalpy efficiency ).
When Reagan/Bush cut 90% of alternate energy research funding in 1983,NASA dropped out.
NASA had developed a Mod 1 engine and was poised for Mod 2 when the money dried up.
Hydrogen embrittlement of metals operating at elevated temperatures required the use of exotic,extremely expensive,strategically critical materials to withstand the rigors of the extreme delta-Ts encountered within the engine.
SAE Transactions,Volume 687,1960,pp.665-684 is the only source I have as a reference to actual lab data.

As a comparison for efficiency,the 2010 Honda Insight, with CVT and Chevrolet Volt,with constant-speed serial hybrid engine,both should achieve enthalpy efficiencies on the order of 40% due to high-load/fixed-rpm operation.

These current-day technologies may dampen enthusiasm for expenditures for continued investigation of the more exotic Carnot-type engine technologies.