Plot of Engine Speed vs. Fuel Consumption

I am looking for a plot of engine speed vs. fuel consumption. Is one
available anywhere? I am not at all picky about what specific engine.

 

ecarecar4/12/08 16:

While each vehicle reaches its optimal fuel economy at a different speed (or
range of speeds), gas mileage usually decreases rapidly at speeds above 60
mph.

As a rule of thumb, you can assume that each 5 mph you drive over 60 mph is
like paying an additional $0.20 per gallon for gas. Quote from the feds.

Graph here:
http://www.fueleconomy.gov/feg/driveHabits.shtml
--
Pickleman

Please remove "yourpants" to reply
1998 Civic HX MT with 142K
2000 CRV EX MT with 98K

 

I have seen that graph. From where did the data come?

 

ecarecar4/12/08 21:

The URL says it all. The suffix .gov means it was published by a government
agency. In this case it means the US Dept. of Energy with cooperation of the
Dept of Energy Efficiency and Renewable Energy AND the EPA.
--
Pickleman

Please remove "yourpants" to reply
1998 Civic HX MT with 142K
2000 CRV EX MT with 98K

 

Such a graph must be stupid, of course consumption rises
with rpm

| gas mileage usually decreases rapidly at speeds above 60 mph.
Not necessarily fr 60 mph, big factors incl
exhaust*manifold : cheapo 4-1 short branch * can give
¾ of maximum torque @ low rpm <1000, but gives <½
of maximum torque @>3000 rpm, & even less @ higher
rpm
[ii] voltage & ampere from small single coil ( esp if hot )
drop fast @>3000 rpm : sparks will be too small to
ignite enough fuel before pistons reach b-d-c, esp where
only cheapo carbon core cables are used
[iii] cheapo mineral oil's coarseness are apparent only @ high
rpm when only the most slippery oil ( e.g. synthetic with
fullerene ) can produce high torque.
[iv] gear ratios & axle (tyre) height

 

Just throwing in some other good discussions for the
archives:

Optimal speed by model (compact, mid-size, van, etc.)
http://auto.howstuffworks.com/framed.htm?parent=question477.htm&url=http://tqjunior.thinkquest.org/4116/Trip_Planning/speed.htm

Discussion of how resistance (especially wind resistance)
causes fuel mileage to plummet at high (55+ mph) speeds:
http://auto.howstuffworks.com/question477.htm

 

Needless to say, this guy is wacko. By far the biggest factor in poor
fuel economy at high speeds is wind resistance. Many vehicles (e.g.
big SUVs) run less than 3000 rpm at speeds above 60 mph and get much
reduced fuel economy due to their barn door aerodynamics.

Of the above, only iv. will have any noticeable effect on fuel
economy. To the extent that i. reduces power at high speeds it may
actually reduce fuel consumption.

 

Is there something not-too-expensive I could plug in to get the data for
myself?

 

c'mon dude - you need to be much more precise with your questions to get
meaningful answers.

1. do you mean engine speed or vehicle speed?
2. what kind of engine?
3. what kind of fuel?

there's more, and it's a long list of highly significant variables.

as for plug-ins, yes, you can use obd output data to compute
consumption, if you know some other data, but it's a non-trivial
exercise, and without knowing a /lot/ more detail, you're pretty much
stuck with getting gas station receipt data, recording mileage between
each fill-up, then driving different speeds.

 

I suspect Universities that compete in building very fuel efficient
vehicles (esp. hybrids) would have this information available to the
public.

Marine applications may be a source, too.

Maybe Briggs & Stratton has that info. for their lawn mower engines.

 

You would think, but, actually, no. They may have it, but it isn't public.

After years - literally YEARS - of searching, I found information that
served my purposes.

This will get you from 0 km/hr to 60 km/hr
http://www.jari.jp/pdf/rt2005/09Fu_eng.pdf

This will get you from 50 km/hr to 140 km/hr
http://www.greencarcongress.com/2006/05/fuel_consumptio.htm

The first, as you might have guess, is from Japan. The second is from
Germany.

 

Here is a plot of Brake Specific Fuel Consumption vs. rpm for a VW TDI
engine.

http://forums.tdiclub.com/showthread.php?t=208125

BSFC is the measure of how much fuel is being consumed per unit power
generated - a true fuel efficiency measurement. To get an absolute
fuel consumption rate, you could multiply the BSFC by power at a given
rpm. Of course this all assumes wide open throttle. If you are
running at a lower power setting, the absolute fuel consumption will
be lower. I would guess that BSFC might be higher or lower depending
on the way the engine is set up.


Maybe the OP could tell us exactly what he wants to know.

 

This second link doesn't work for me. Even after correcting obvious
spelling errors. Could you try again?
Thanks.

 

"www.greencarcongress.com/2006/05/fuel_consumptio.html"

 

This is WOT? Therefore, it is also full throttle ignition advance?
The bottom of the curve is quite narrow.

 

Well actually it is a diesel so there is no throttle (my bad) and no
ignition. What I should have said is that I assume this curve is for
maximum power setting.

Again, it is not clear exactly what you are trying to show/learn here.
For example, are you interested in fuel consumption at various engine
speeds or car speeds?

 

By laws of aerodynamics, air drag is proportionate to the square of
the object's velocity. If the speed is doubled, then it requires a
quadrupled energy to overcome the drag. At the same time, the object
travels twice the distance. Spending four times the amount of energy
to propel the object twice the distance means the energy efficiency is
cut in half.

Likewise, if the object's velocity is trippled then energy efficiency
is reduced to one third.. and so on...

In automobile, rolling friction is also a factor but it's a linear
drag, while air drag is a quadratic drag. The combined result is
closer to the air drag only model.

In layman terms, if you've got a car that does 30 mpg at 60 mph, then
you can expect 15 mpg at 120 mph. It can be more or less, depending on
the efficiency of the engine's combustion chambers, and its own
internal friction at higher rpm

 

That works!! And so does the other one now if I edit an 'L' where needed.
It didn't work before.

Thanks again.

 

I don't know which chart you mean. Not all the cars in the top chart at

www.greencarcongress.com/2006/05/fuel_consumptio.html

are diesel.

 

Actually, it is a quadrupling of the force.