| OK, Paul, let's review the issue.
Compression ratio: The higher CR WILL ALWAYS result in a lower EGT/TIT if all else is held constant. Why? Boyle's Law. PV = nRT. As the volume expands, the gas temperature goes down. More expansion; more temp loss = lower EGT.
RPM: Higher RPM move the EFFECTIVE timing closer to TDC. This results in more expansion = lower EGT.
There are many factors, but those two account for a lot.
The FF is set by the pilot and is meaningless as a comparison. You must only use peak TIT as the comparison or all FF values between engines are pretty meaningless.
This is basic physics and if the experiment is properly done, it will always result in the same answer! <g>
Walter
If you are asking for confirmation that the above is true, ANY text on combustion, and all of the data collected at any one of the existing engine test facilities will confirm.
Walter Walter: I understand the theory and am confident you have many Ada test runs to quote. I am however a curmudgeon test pilot who had been fooled by well meaning engineers for years and like to see FLIGHT data when ever possible. There are many ways to effect egt in flight and most are easier than putting in new pistons. Additionally most of the flight conditions I have seen posted here by TSIO-550-8.5 flyers have had LOP fuel flows nearer 19gph than 7.5 to achieve 200ish KIAS so that is a curiosity. Lastly you also point out that the higher CR engines have retarded timing, and of course lower boost--so it is more than just a piston change and flight experience is worth reviewing. paul |