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Old 08-17-2008, 02:43 PM   #9 (permalink)
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Join Date: Apr 2008
Location: Anaheim, CA
Posts: 129

LR3 - '06 Land Rover LR3 HSE
90 day: 21.13 mpg (US)
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This is a very difficult problem. The data on the linked site above is convincing for the vehicle and conditions tested, but EOC isn't a viable option for me in my LR3.

Why is it difficult? You'd think that it would be a matter of running at the most fuel efficient portion of the engine map (for the poster above, BSFC is "brake specific fuel consumption," see here for a pretty good article) up to the intended speed, presumably that which yields best fuel economy.

But the wild card is the fact that, when accelerating, you're using fuel both to overcome external resistance (drag, rolling resistance) and to add kinetic energy. It's easy to show that the more slowly you accelerate, the greater distance covered in the process of adding a fixed amount of kinetic energy (the kinetic energy of the vehicle at the selected final speed). So, there are three considerations: slowly adding kinetic energy, spending as much time as possible at the most efficient speed, and operating in the most efficient portion of the engine map.

I've rigged a "generic" engine map (they all kind of look similar) and used known points for my engine to try to use optimization techniques to find the most efficient acceleration but, mathematically, it's a difficult problem. Especially for an old fart like me (math is a young person's game). But if and when I reach a conclusion, I'll post it.

Man, that's a long post for no particular conclusion, but I did want to point out the kinetic energy aspect, which I don't see anyone considering in discussing this issue.

Last edited by PA32R; 08-17-2008 at 02:46 PM.. Reason: punctuation
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