Quote:
Originally Posted by aerohead
A very dated SAE paper dealt with acceleration/MPG.Their reference acceleration was 6- feet- per- second- per -second."jack-rabbit" acceleration of 12-ft-per-sec-per-sec showed a dramatic drop in MPG.Halving the acceleration to 3-ft-per-sec-per-sec,showed a dramatic improvement in mpg.I'll dig out the paper if you wish.These findings fly in the face of research by BMW,who advocate much more lively acceleration (presumably in one of their BMWs) explaining that the waste came within the "transient" period,so get up to speed and hold your speed,and don't fart around getting there.
I think the BMW article is in my Phil Knox aerodynamic photos album,under "good news for jack-rabbit starts".
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I'd love to see both of those articles. I've posted quite a few times on this subject and brought up an issue that HAS to play into the optimization question: the adding of kinetic energy. The fuel burned (and not wasted as heat, friction, etc.) goes to two things: overcoming the total resistive force (externally, these are aerodynamic drag and rolling resistance) and adding kinetic energy (we'll ignore potential energy by assuming level ground). It's quite easy to show that to add the kinetic energy to get the vehicle mass up to, say, 55 m.p.h., all else being equal, accelerating 1/2 as fast will get you twice as far in the process of adding that kinetic energy. This argues for the slowest possible rate of acceleration. But the m.p.g. as a function of m.p.h. curve and the engine map argue for a different protocol. I haven't yet concluded how to optimize these conflicting factors.