Slippers...
"Regarding my agreement with Chris Weston, my posts have ALWAYS related to the thermodynamic efficiency of higher combustion ratios, and not the question which was in the subject line of the OP until now."
In post #63 CW answered that very question: "why compress - to release more energy to do useful work per unit time within the engine (be it piston or turbine)." But in the very next post you quoted him and replied: "It's so that less heat is added to the air over the entire cycle" and then went on about efficiency again. And so on, throughout the thread. It's clear to me you have shifted position, however, I'm not interested in a subjective exchange so I'll move along.
"I will happily admit that my explanation in my first post was not ideal, but then it wasn't meant to be."
I wouldn't say "not ideal". I would say wrong.
"It certainly wasn't supposed to be taken so literally, and after you chipped me on it, I clarified what I meant in subsequent posts (temperature change over the entire cycle)."
[BTW, small point but temp change over the entire cycle is zero in both cases. Has to be if the engine is in a steady state because internal energy is a state variable. I only mention that because you said "argue all you like, but I have a physics degree and the principles of thermodynamics have been unchallenged for a few hundred years"
]
I assume this was your clarification from the post after I first "chipped you" on it:
"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)."
Yes, we know the exhaust is cooler. That's a given if we consider increased efficiency in an idealised cycle. The question is why is it cooler? So back to what you wrote originally:
"A high compression ratio engine will ignite a hotter air/fuel charge which will absorb less heat. Less energy wasted as heat = more energy transferred to the crank. When the ignition occurs, a lower compression ratio engine will have a cooler air/fuel charge in the cylinder - and so it will absorb more energy (which is wasted as exhaust gas heat)."
Three questions for you:
1. If that wasn't an attempt to explain
why the exhaust ended up cooler, where in that first post is it?
2. Where in any of your posts do you clarify that what you wrote above isn't meant to suggest that 'a hot charge absorbs less heat during the combustion process and vice versa'?
3. If that's not what you were getting at, why write this:
"consider two cups of water - 1x 50 degrees celsius, 1x 100 degrees celsius... if you put them over a flame of 200 degrees for exactly one second, the cooler cup of water will absorb more heat (because the temperature split between the two is larger)."
...and by post #31 you were still reiterating the point:
"The DIFFERENCE between the fluid temperature and the burning temperature of the fuel at the point of ignition is LOWER in a high compression engine."
?
What I'm getting at is - despite what you may say now - you were definitely writing that by increasing CR, the working fluid would absorb less heat during the heat addition phase.
Finally:
"The fact remains that EVERY FN TIME you refuse to answer my question about two different compression turbines with the same fuel flow and the difference in their thermodynamic efficiencies. How many times have you avoided this now? I've asked AT LEAST 5 TIMES now how your "better mixing, flame front speeds" BS applies in this situation, but you simply refuse to answer."
I'll leave the finer points of combustion in a turbine for someone else. I'll just say this: you chose the piston engine as your original example and no matter how these factors relate to a turbine it doesn't change the fact they are critical in a piston engine, unless you limit your knowledge to an idealised approximation of the cycle. In the real world no such ideal engine exists.