Quote:
Originally Posted by some_other_dave
That is still a low throttle setting to my way of thinking. I really don't think I understand what you are saying...
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What happens is the 25-30 hp point is on a steep part of the power required curve. Any slight rise or additional drag requires the engine to run up that curve into higher consumption and even more inefficient power settings:
The areas of peak engine efficiency are marked by the small, red dots. You'll notice the 25-30 hp curve fall right under the last of them. Any higher power demands push the engine into inefficient, lower BSFC regions.
So it is a combination of two effects:
- steep power slope - so any local variance in power demand will rapidly go into much higher power regions
- upper limit of high efficiency - anything over 30 hp is going to have lower BSFC than the 25-30 hp region.
I've thought about making a cruise control device that limits the peak HP setting, just using the ICE rpm of say 2,600 rpm AND a maximum speed. The car would slow down going up a hill but it would stay in a fuel efficient mode. But it in an actual design, I would allow excursions up to 3,400 rpm to handle hills. If any more is needed, the accelerator would be used.
Bob Wilson