Hi Oggers.
I'll say it one more time, and if you can't understand it after that, then I will consider
to stop wasting my breath.
Flame front speeds have absolutely nothing to do with it. You simply CAN NOT burn the fuel "faster" to get more energy out of it. You seem to have a fundamental problem understanding this. You can burn the fuel as quickly or as slowly as you like, and it produces the same amount of energy. 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.
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.
This is exactly right - YOU DON'T UNDERSTAND. The comment about the fluid absorbing less heat is once the fluid is returned to atmospheric pressure. I'll now write it very, very simply for you:
The change in heat between the air which enters the engine (at standard atmospheric pressure) and the air which leaves the engine (one it is returned back to atmospheric pressure) is what I am talking about here. If you fail to understand that, and keep incorrectly assuming I'm saying cylinder pressures and temperatures at TDC are lower, you will never understand this most basic of principles.
The fluid pressure and temperature are both HIGHER at ignition than in a low compression engine. 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.
It's really not that hard.
Meanwhile, the "comparatively small" pumping losses you mention are big enough to explain the efficiency difference between diesel and petrol engines.
Completely disagree. Are you telling me a gasoline engine uses 19% of it's energy (say, 30hp in a standard car) to suck the air in and blow it out? Hahaha, you've got to be joking.
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.
So what you are trying to tell me here that an engine which is effectively only compressing the air to 5x the atmospheric pressure rather than 10x, is still able to extract the same amount of energy per unit of fuel? Give me a break! If this were true, then high compression and low compression engines would have identical thermodynamic efficiency, and we wouldn't be discussing the differences between the two.
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?
See above. It's about the total fluid heat change from start to finish. It is lower in a high compression engine. You need to stop assuming this means less absolute pressure/temperature at TDC. It doesn't.