My dear friend Oggers,
Your attempt at ignoring the main point of my last post (which I repeated a myriad of times) is noble, but not unnoticed. I will AGAIN post it here for you to consider
It's about the total fluid heat change from start to finish (once the fluid is returned to atmospheric pressure). It is lower in a high compression engine. You need to stop assuming this means less absolute pressure/temperature at TDC. It doesn't.
I'm listening.
I also wrote this
Even if gasoline fuel burns "slowly" or "quickly", the ignition timing is simply adjusted to ensure the maximum pressure in the cylinder is occuring at TDC. This has been happening for the past 20 years with electronic ignition control, and for the 30 years before that, with centrifugal spark advance. Welcome to the 1960s.
And then you accused me of not understanding timing with this...
But you have to realise that in an engine, having got the heat into the fuel you then have convert it to work on the piston during the limited time available on the power stroke. This is where timing comes in.
I guess they missed that bit out when you were doing physics at uni
Oops, guess you didn't read (or understand) what I'd already written.
19% is your figure from the back of a fag packet.
Nope, that's calculated from the chemical energy density of the fuels (MJ/L gasoline vs. diesel) and the proven efficiency of diesel engines. The 30% I assumed as the difference between gasoline/diesel engines is actually 30-35%, so it could have actually been as high as 24%.
Poor volumetric effficiency is a consequence of not operating at it's most efficient (small throttle settings), not the thermodynamic efficiency of the cycle which was the question in the OP (posted here for your benefit).
Also why is it that both the piston engine and the turbine engine can have their efficiencies increased by increasing the pressure ratio (compression ratio for piston)? Is there some sort of simple thermodynamic explanation for this?
