EcoModder Forum Why is 'driving with load' better than constant speed

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Quote:
 Originally Posted by bikenfool Minor nit: you are misusing the term acceleration, "In physics, acceleration is the rate at which the velocity of a body changes with time" https://en.wikipedia.org/wiki/Acceleration. Of course, you are correct the engine doesn't know the difference.
No, I don't believe I am... the wiki page you linked discusses g as acceleration as well... in order to rise vertically at a steady speed, you will need an upward force that directly counteracts the downward pull of gravity, or, since F = ma, you would need ma = mg and since mass is equal, a = g. I don't know how that is a misuse of the term?

I would suggest removing the arbitrary flat section (how much of a flat section? what is the total travel time / total travel distance?); this just muddles things. Just focus in on the hill section only, base to crest. There are already more than enough variables in that short section. If you assume the starting and ending speed are the same, which approach is better. Then what if you assume the average speed from bottom of hill to crest is the same (which would mean Method 2 starts out slower), which approach is better. I don't have the answer, but that's how I would constrain it.

From my own perspective, I wouldn't drive differently on the flats just because I *might* choose DWL or choose P&G when I encounter a hill. I would wait until I encounter the hill then choose what I believe to be the best method depending on the size of the hill, the grade, and the current conditions (traffic, etc). Heck, I might even change from "pulse" to DWL in the middle of my climb and then back to "pulse" depending on changing conditions. All of that would be SOP (seat of pants) because I'm sure as heck not going to stop, measure the parameters of the hill, plug them into a formula or script and then use the approach that calculates out to a 0.001% (or whatever) fuel savings.

And with a different car, I would probably do it differently. As they say, YMMV.

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Quote:
 Originally Posted by NachtRitter No, I don't believe I am... the wiki page you linked discusses g as acceleration as well... in order to rise vertically at a steady speed, you will need an upward force that directly counteracts the downward pull of gravity, or, since F = ma, you would need ma = mg and since mass is equal, a = g. I don't know how that is a misuse of the term?
I don't want to argue that in this thread since it doesn't matter to this subject.
Quote:
 Originally Posted by NachtRitter I would suggest removing the arbitrary flat section (how much of a flat section? what is the total travel time / total travel distance?); this just muddles things. Just focus in on the hill section only, base to crest. There are already more than enough variables in that short section. If you assume the starting and ending speed are the same, which approach is better. Then what if you assume the average speed from bottom of hill to crest is the same (which would mean Method 2 starts out slower), which approach is better. I don't have the answer, but that's how I would constrain it.
If you remove the flat section, & the total time is not the same then you're answering the question "which is the lowest fuel cost method to get up the hill". This is a good question for a hypermiler & I'd like to know the answer too, & I agree the answer probably won't be constant speed, but my question is more practical. In the real world most of us trade off fuel consumption with time, so fixing the time variable, what is the most fuel efficient way to drive?
The starting and ending speed must be the same or it isn't a relevant test.
There are a lot of inputs, such as the length of the flat section, & the length & grade of the climb, but I don't see a way to eliminate the flat section and have a good comparison.

Quote:
 Originally Posted by NachtRitter From my own perspective, I wouldn't drive differently on the flats just because I *might* choose DWL or choose P&G when I encounter a hill. I would wait until I encounter the hill then choose what I believe to be the best method depending on the size of the hill, the grade, and the current conditions (traffic, etc). Heck, I might even change from "pulse" to DWL in the middle of my climb and then back to "pulse" depending on changing conditions. All of that would be SOP (seat of pants) because I'm sure as heck not going to stop, measure the parameters of the hill, plug them into a formula or script and then use the approach that calculates out to a 0.001% (or whatever) fuel savings. And with a different car, I would probably do it differently. As they say, YMMV.
All true, & traffic typically forces the issue anyway. But if you knew what the best solution was for a typical grade wouldn't you at least try it?

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Quote:
 Originally Posted by bikenfool Perhaps you guys are right and I'm an idiot, perhaps it works for some cars, or some conditions. For now, I remain skeptical.
You've ended up here, so you're not

You may be skeptical, it's a good attitude, but these things have been tested over and over by people here and elsewhere on fuel-efficiency forums

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Quote:
 Originally Posted by euromodder You've ended up here, so you're not You may be skeptical, it's a good attitude, but these things have been tested over and over by people here and elsewhere on fuel-efficiency forums
Great, point me to the tests!

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Quote:
 Originally Posted by bikenfool There are a lot of inputs, such as the length of the flat section, & the length & grade of the climb, but I don't see a way to eliminate the flat section and have a good comparison.
OK

Quote:
 Originally Posted by bikenfool All true, & traffic typically forces the issue anyway. But if you knew what the best solution was for a typical grade wouldn't you at least try it?
If your question here is related to the two methods you describe, which include an arbitrary length of flat section and an arbitrary fixed amount of time to cover both the flat section and the hill, then my answer would be no. If instead you are asking only about the best method (which in this context means getting the best FE) for getting up a grade from base to crest, then I think it would be interesting academically but my intuition tells me that there wouldn't be enough of a difference to change my behavior. I would still do what feels right at the time based on the conditions (choosing between P&G and DWL), since I know either approach will be better than using cruise control or flooring the pedal to maintain speed uphill.

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Quote:
 Originally Posted by Old Mechanic since engine braking consumes no fuel,
which vehicles are you referring to, please?

 01-04-2014, 02:21 PM #57 (permalink) Master EcoModder   Join Date: Aug 2010 Location: Philippines Posts: 2,173 Thanks: 1,739 Thanked 587 Times in 401 Posts I'm pretty sure that's just about everything with computerized fuel injection. There are those that still inject a miniscule amount during engine braking, but it's a tiny percentage of what you use while idling.
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Quote:
 Originally Posted by 3-Wheeler Driving with load allows the gas engine to run in a more efficient regime. If you can find it, look for a fuel consumption map for your particular engine. HTH, Jim.
So where does one find this map??

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Quote:
 Originally Posted by zingaro So where does one find this map??
In general, they are not available. There's a thread &a wiki page on this site with the best collection of them.

 01-17-2014, 07:32 PM #60 (permalink) The PRC.   Join Date: Oct 2009 Location: Elsewhere. Posts: 5,304 Thanks: 285 Thanked 535 Times in 384 Posts Question. In your challenge you seem to suggest an either/or choice of DWL vs P&G ? Is that correct ? In your scenario I would use P&G on the flat part and then use an extra strong Pulse just before the hill Once the speed bleeds off I would then maintain a minimum until the top and I would expect to gain again on the following flat or descent. If it has been a long journey or I feel lazy then I would maintain a minimum speed / MPG combination on the flat as that requires less effort but still speed up just before the hill to get a push and then again maintain a minimum speed. The instrumentation available - built in or add in - isn't accurate enough to determine which is better in one run or a collection of runs really but they give a guide, better than nothing. __________________ [I]So long and thanks for all the fish.[/I]