Mech,
Thanks for another illuminating post! I agree fully that simplicity is king for a new concept. Indeed my biggest problem often is that, having had a good simple idea I will then 'bolt-on' all sorts of extra systems in the hope of making it work!
Your (so-called lunatic) points about steam are actually most valid - being a technology that has fallen by the wayside, but is by no means out of the running.
Have you come across this design:
Cyclone Power Technologies - How It Works
It appears a good, workable idea that could be scaled to work as an auto-engine.
The biggest hang up with steam (as with all external heat engines) is the start up time - as drivers want to jump in & go...
Of course with hybrids some of those arguments go away. Indeed if compressed air can be used to test boilers, etc - It can certainly run pistons for a short time during 'heat-up'.
The big plus with all piston drives is they develop max torque at zero revs - so goodbye gearbox!
Free piston engines via one or other type of fluid drive still strikes me as an elegant solution, especially with the averaging effect of an accumulator.
I, too, have come across the INGOCAR design and have been similarly impressed with its clever simplicity. HCCI is, as you say, going to bring technology jumps at least on a par with those realised through the introduction of fuel injection, only at the cost of even more intense reliance on computer control (with a slight feeling of regret for the tinkerers amongst us!).
I still find the animation of the engine/pump difficult to follow in terms of the gas path through the engine. I also wonder if there would be even more advantage to adding turbo-charging or other exhaust power recovery in this configuration than in a traditional engine.
I think the lesson in all these pursuits, is there is still room for the little guy in pushing tomorrow's ideas! I hope to see yours on the streets real soon!
Cheers, Tom