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Old 08-15-2008, 02:59 PM   #1 (permalink)
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Turtle Ideal rate of acceleration?

What is the ideal rate of acceleration, in regards to fuel economy?
I'm looking for statistics.


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Old 08-15-2008, 03:01 PM   #2 (permalink)
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crxMPG - Gas mileage never looked so good Acceleration and Fuel Economy Tested

But then there's so much variation from car to car and all
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Old 08-15-2008, 03:13 PM   #3 (permalink)
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Thanks man, this is perfect.
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Old 08-15-2008, 07:57 PM   #4 (permalink)
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You want to accelerate at whatever power output is best BSFC for your engine. Typically this is much faster acceleration than people think would give them the best FE. I call it "moderate" acceleration.
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Old 08-15-2008, 09:17 PM   #5 (permalink)
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I have read that BMW instructs drivers to accelerate at 75% engine load and shift when the engine's mean piston speed reaches 1200-1500 feet per minute. Mean piston speed is a function of engine stroke and RPM.


Vp= mean piston speed
RPM= engine speed
S= engine stroke length, inches

This keeps you in closed-loop operation (for EFI) at high volumetric efficiency with low frictional horsepower loss for as short a time as possible before you can achieve steady-state cruise and/or EOC. It is what I like to say is accelerating "smartly."
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Old 08-16-2008, 12:56 PM   #6 (permalink)
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MechEngVT: That's kind of funny... when I first started to try hypermiling, I tried to get my automatic to downshift below 2000 RPM (by letting up on the gas a bit), but it was kinda hard to do without lurching in my Protege, not to mention holding up people behind me in congested traffic. So I've gone to using 2000 to 2500 RPM as my downshift target. When I solve your equation for the 1200 to 1500 fps range I get .... 1988 to 2495 fps. Now I don't feel quite as guilty about letting the rev get up to 2400 to 2500. ;-)
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Old 08-16-2008, 01:13 PM   #7 (permalink)
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Interest info MechEngVT. Where did you find this info?
Current project: A better alternator delete
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Old 08-16-2008, 02:34 PM   #8 (permalink)
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I am trying to figure out the best way also. I have read easy acceleration. How easy is easy. The link above seems to suggest that going out fast is better than going out easy. I have ready to accelerate as fast as possible without going open loop. I have read that accelerating with a high LOD is the best way. The RPM stuff doesn't mean much to me since I drive an automatic and have little control over what RPMs the car shifts at. I have no clue what BSFC is.
Can someone post in easy to follow instructions the best way to accelerate for the best fuel efficiency. Pretend that I am kind of slow (um...yeah...pretend :P ).


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Old 08-17-2008, 03:43 PM   #9 (permalink)
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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 03:46 PM.. Reason: punctuation
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Old 08-17-2008, 04:40 PM   #10 (permalink)
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torque is the work . non-japanese inline four bangers find it naturally.
I made a funny. anybody get it?

your foot finds it for your car: the slowest rpm to get what you want. Screaming weirdos enignes don't understand and called it moderate to heavy acceleration...

a big diesel at 40 tons loaded is getting 224 mtpg (mile tons per gallon) all while never seeing much more than 2k rpm. The ultimate workers has no concept of this "perfect throttle".It is never a concern. all else who ask have pansy driveline. "Statistics" you seek will only reveal the most common driveline. Most likely that dumbo inline four cylinder...and those are in the moderate to heavy acceleration to get a thing called torque doing the work...
the concept of hypermiler would not exist if we had real engines....

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