Quote:
Originally Posted by Daox
I'd have to politely disagree with a few statements of yours. 
1) This is not completely true. At WOT, engines run in open loop and enrich the air/fuel mixture to function fine. This kills efficiency.
2) These engines are specifically designed to run lean. Engines designed to run EGR could do the same thing. Perhaps not to the extent of lean burn, but it can be used in a similar fashion and without the NOx problems that lean burn causes. I'm not saying all engines do do this (especially older ones), but some definitely do.
Sorry, a bunch of published SAE papers would disagree. |
1) So, for point one, you are saying that since modern high compression engines are run with a fatter mix, they don't detonate? That's inaccurate. While the risk of detonation is high at peak BMEP, high power mixes, it's lowest at very lean of peak mixes. In fact, detonation is near impossible with very lean mixtures. I know we've all been led to believe otherwise. But, it's only a disgustingly overly rich mix that can quell deto and that, of course relates to this forum in a very negative way, economy.
2) No they are not. In fact, the manufacturers prohibit, discourage or simply don't mention lean of peak operation. Yet, it works. Come fly with me sometime and I'll demonstrate what can be done with a Lycoming IO-360A1B6, with 25 degrees timing (a fuel injected, high compression, big piston, low RPM, 2 sparkplug eng). You'll be impressed. It's the simple fact that these engines were equipped with adjustable props, mixture and throttle (not a single power lever) AND modern instrumentation that makes the difference. Maybe I'll put up a YouTube video to demonstrate. My point is that these engines are world class efficient when operated like this. Testing with EGR under similar conditions does not help economy. And, that testing has been going on since the 40's. FWIW, piston engine aircraft can teach us quite a bit about high power levels and BSFC.
CAFE Foundation
3) I've not read all the papers SAE has published. I'd love to read some of these where high power, lean burn and peak BSFC numbers all come together, and do some personal testing. If you have some info, please share!