Quote:
Originally Posted by dcb
Problem is extracting the additional heat energy without undue back-pressure (which makes the pistons not want to come back up).
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I'm not sure if a bit more backpressure really matters. I used to think it does, but not anymore. Any modern diesel engine with a variable geometry turbocharger can have upwards of 50 psi (yes, 50 psi) of exhaust manifold pressure at full load. You would think 50 psi is ridiculously high, especially compared to a naturally aspirated engine with almost zero exhaust manifold pressure, but this pressure is miniscule when compared to the other pressures that make things "go." Combustion pressure can be 2800 psi +. Compression pressure can be 800 psi + at TDC at full load with 35 psi of boost. I'm not sure that a relatively small 50 psi of backpressure means a lot.
I think what killed the piston engine in the airplane wasn't a lack of power and efficiency, but unreliability, complexity, expensive maintenance, and the inability to do high altitude well.