Slippery:
The loss of efficiency due to pumping losses are comparatively small. The biggest loss of efficiency in an engine with poor VE is because of a drop in effective compression ratio. For example, if an engine can only suck in half a cylinder full of air because of intake/exhaust restrictions or throttle position - a 10:1 compression ratio engine is actually only effectively producing a 5:1 compression against atmospheric pressure. I still don't think VE is important in the question of the OP.
You are indeed slippery! That sounds suspiciously like what I said to begin with: 'The goal is to get maximum charge into a given combustion chamber. That is, basically, volumetric efficiency'. You're meant to be arguing against it because you said:
the answers given about volumetric efficiency have nothing to do with your question about thermodynamic efficiency of an engine.
However, with your new post you have now introduced some more errors:
if an engine can only suck in half a cylinder full of air because of intake/exhaust restrictions or throttle position - a 10:1 compression ratio engine is actually only effectively producing a 5:1 compression against atmospheric pressure
You have to remember that the fuel metering system will have reduced the fuel so as to maintain the desired mixture. Therefore what you have described is a loss of torque or power, not a loss of efficiency per se. Meanwhile, the "comparatively small" pumping losses you mention are big enough to explain the efficiency difference between diesel and petrol engines.
Exactly. This is exactly what I said. A higher compression ratio adds the heat to a hotter air charge, so once the engine reaches BDC the higher compression engine "fluid" will be cooler. By "absorb less heat", I meant at the end of the cycle the fluid has absorbed less total heat during the cycle (not saying it's cooler at the point of ignition - it is, in fact, hotter as you said).
I don't really understand where you are coming from there. If the working fluid absorbs less heat its pressure will rise less. Less work will be done on the piston.
The difference in percentage of unburnt fuel between a low and high compression engine is quite small - trust me - I've done it on a lab dyno at university.
It's not about unburnt fuel so much as flame front speeds and a few other things that a chemical engineer might discuss. Essentially the flame propagates faster at high temp which has benefits under the heading 'timing' I can't be bothered to explain, but which the mechanical engineer and engine tuner inside me finds useful.
You can't get more "umph", plus hotter exhaust gases too - where is all this extra energy coming from?
Strawman. I have never said that.
A diesel engine is approximately 30-35% more efficient at the same RPM and fuel flow. Let's assume 30%.
So that's 30% more power from 11% better fuel. If you take the 11% off to even the playing field of fuel energy density, that's 19% more efficient.
Are you trying to tell me that 19% effciency gain comes about solely because of more complete combustion and "mixing"?
No I'm not! The difference is mainly to do with pumping losses. I did mention them in my previous post but you decided they are "comparatively small". The diesel doesn't have a throttle it just fills the cylinder with maximum air each time and varies the power by injecting less fuel. No throttle restriction = less pumping losses. Which renders the rest of your latest post redundant.
More energy is transferred to useful work because less heat is wasted heating the fluid. It's that simple
This is just wrong. If you don't put the heat in the fluid you can't expand the fluid against the piston. Perhaps you could just explain how you're going to expand the fluid without heating it?