hypermiling technique, driving with load
hypermiling technique, driving with load
(OP)
The hypermilers have this technique they call driving with load DWL.
In a nutshell the technique is to hold a constant load on the climb, keeping the fuel consumption constant while allowing the speed to drop.
http://ecomodder.com/forum/EM-hypermiling-driving-...
http://www.cleanmpg.com/forums/glossary.php?s=&...
I'm trying to understand the fundamentals with this, but I think if one is trying to optimize the trade off between time and fuel consumed then I don't think this makes sense. Since most of the losses are aero, which is proportional to v^2, if you want to arrive at your destination in a certain elapsed time, the most efficient speed would be constant, not increasing and decreasing. So instead of slowing down on the hill it would be more efficient to slow down a bit on the flat sections and hold that speed constant on the climb. I don't think there is anything about the engine efficiency that would negate the increased losses due to aerodynamics incurred by varying the speed.
Am I missing something?
Sorry if this is too off topic for this forum.
In a nutshell the technique is to hold a constant load on the climb, keeping the fuel consumption constant while allowing the speed to drop.
http://ecomodder.com/forum/EM-hypermiling-driving-...
http://www.cleanmpg.com/forums/glossary.php?s=&...
I'm trying to understand the fundamentals with this, but I think if one is trying to optimize the trade off between time and fuel consumed then I don't think this makes sense. Since most of the losses are aero, which is proportional to v^2, if you want to arrive at your destination in a certain elapsed time, the most efficient speed would be constant, not increasing and decreasing. So instead of slowing down on the hill it would be more efficient to slow down a bit on the flat sections and hold that speed constant on the climb. I don't think there is anything about the engine efficiency that would negate the increased losses due to aerodynamics incurred by varying the speed.
Am I missing something?
Sorry if this is too off topic for this forum.





RE: hypermiling technique, driving with load
It's not off topic, my first serious job was working out such things. On graph paper. With a calculator.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: hypermiling technique, driving with load
Most people don't drive with the intent to arrive at their destination in a certain elapsed time. Generally, you decide it will take X amount of time so you leave X amount of time early. You really get there in Y amount of time. You hope Y < X so you are not late.
RE: hypermiling technique, driving with load
The rollercoaster highway (Lionel's example) may be a special case where it makes sense. Most of the hills that I drive on are not like that.
I should probably run some calcs on this, but it seems to me that if the aero losses are greater by varying your speed, & you don't gain anything with increased engine efficiency or reducing other losses then its a net loss. The only gainer I can see is if you hit the top of a hill at a low speed, you can regain that energy on the downhill for free by coasting.
RE: hypermiling technique, driving with load
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: hypermiling technique, driving with load
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RE: hypermiling technique, driving with load
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: hypermiling technique, driving with load
http://www.youtube.com/watch?v=MmQhKsHcOOQ
RE: hypermiling technique, driving with load
http://scholar.google.com/citations?user=gDW8CxoAA...
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
No wind, on the flat, constant speed, obviously.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: hypermiling technique, driving with load
However, that does not mean that what you claim is technically untrue. If an auto with a conventional IC engine and MT must drive at 50mph in low gear to operate the engine at the WOT and low rpm conditions that give best BTE, then I would agree with you. But this not true for most automobiles.
RE: hypermiling technique, driving with load
- Steve
RE: hypermiling technique, driving with load
The first rule of hypermiling is to slow down. But I think your point is that it's rather difficult to determine how much of the savings is due to going slower up the hill vs using less throttle to climb the hill.
Who believes everything that is published by manufacturers? Being in Canada, all the published fuel economy literature is complete BS. There are class action suits due to the overinflated fuel economy claims and many vehicles that would never achieve their published economy unless they were pushed off a cliff.
I will repeat myself worded differently. People do not drive with the intent to make the trip within a exact time or to drive at an exact average speed. I was assuming this is what was meant by the use of "certain time". Are you really meaning to arrive within an approximate time or drive at an approximate average speed?
certain
adjective
1.known for sure; established beyond doubt.
2.specific but not explicitly named or stated.
approximate
adjective
1.close to the actual, but not completely accurate or exact.
RE: hypermiling technique, driving with load
Near the low point for BSFC, in other words ... from my experience on a hybrid vehicle design team in college, most stock production cars had a peak fuel economy point at around 40-50mph. This corresponded to loading the engine as much as you could to get near min BSFC with whatever transmission was in the vehicle, while not wasting too much energy due to aero drag. Lower speeds would have given a better figure if the engines had been much smaller - but at 45mph you're looking at an engine load of 17-ish horsepower to move down the road, which is really not much load and not an efficient operating point. Running faster than ~60 mph starts to eat a whole lot of fuel compared to 45mph.
If you could alternately run the engine and shut it off completely (speed up then coast), you'd probably see that average speeds lower than 45mph look attractive.
RE: hypermiling technique, driving with load
https://en.wikipedia.org/wiki/File:Fuel_economy_vs...
Looks like I was wrong in some cases.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
Basically car engines are so powerful that you cannot get near the max efficiency point for the engine at the low speeds you would otherwise want.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
Or, for a fleeting moment in 4th non-OD below 33 mph.
http://volvoamazonpictures.se/documents/mish/M004_...
The e-brake was capable of 0.37 g stops
RE: hypermiling technique, driving with load
It sounds like what they're trying to do is minimize the time spent operating with part throttle enrichment due to a drop in manifold vacuum, ideally (to them) not invoking it at all.
Norm
RE: hypermiling technique, driving with load
I agree with you on that point. Due to the design compromises that production auto drivetrains demand to make them acceptable to the general public, the engines and transmissions are never optimized for the maximum fuel economy possible. Instead they are designed to provide the best compromise in fuel economy over the entire range of driving conditions of the typical buyer.
RE: hypermiling technique, driving with load
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
the mix is usually (intended to be) richer at higher throttle openings, and maybe at idle, but leaner at part throttle, right?
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: hypermiling technique, driving with load
The term may be a bit archaic.
Norm
RE: hypermiling technique, driving with load
A power enrichment mode when the engine runs with the fuel richer then stoimetric ratio or with lambda < 1.0.
People will often say with the air fuel ratio < 14.7:1, but that's not necessarily true. Different fuel blends require different air fuel ratios.
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
RE: hypermiling technique, driving with load
The hypermilers generally don't want to invoke downshifts (higher revs) either.
Norm
RE: hypermiling technique, driving with load
Holley suggests selecting a power valve that opens about half way between manifold vacuum at idle and zero.
http://www.holley.com/TechService/FAQ.asp?category...
Stoichiometric is the target (what we are stuck with) for cars with O2 sensors and demanded by catalysts needing to meet NOX emissions limits.
http://ect.jmcatalysts.com/images-upload/air-fuel-...
I think in the old days running leaner than stoi was attempted as there are some BSFC and unburned HC advantages to doing so.
The Chrysler lean burn system of the late 70s said this -
"The control system is particularly advantageous when used in an engine which uses a leaner fuel-air mixture (17-18:1, for example) in comparison to presently used mixtures (15-16:1). Improvement accrues by way of reduction in exhaust emission products and better fuel economy.”
Original is at The Chrysler Lean Burn engine control system http://www.allpar.com/mopar/lean-burn.html#ixzz2oO...
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RE: hypermiling technique, driving with load
I think maybe there is a terminology difference here. To me "enrichment" means increasing the proportion of fuel in the charge (ie, changing the air-to-fuel ratio in the direction of being "richer", or having more fuel). Using that definition, there is no need to reduce AFR to increase power output. When the throttle opens wider, more air gets through, so more fuel is added (per unit time) to maintain the air-to-fuel ratio at roughly the same level. More fuel is used, but the mixture does not become more rich. Using my terms, there would be no "enrichment" at part load. At/near full load, having excess fuel can reduce the peak temperature in the cylinder and help to keep hot parts from exceeding relevant limits, so temporary enrichment (increasing of the amount of fuel relative to air) is used under the highest-load conditions. Most of the time the three-way-catalyst needs to be near stoich to do its job, and its job must be done to meet emissions requirements.
RE: hypermiling technique, driving with load
Operation outside the range of rpm and load that covers emissions testing need not operate at stoic, and from what I understand about OE fueling they may intentionally be set to run a little fat at higher rpms and loads to protect the converter(s) from overheating.
Within emissions certification load and rpm for a car requiring it you would of course want to remain close to stoic, and closed loop operation with O2 sensor feedback ensures that you stay there.
http://www.bing.com/images/search?q=EFI+fuel+maps&...
Norm