K24A4-i-VTEC fuel consumption at idle?

I have an '05 Accord LX 5M, and I am looking for URLs that give some
idea about fuel consumption at idle (gallons per hour?) with minimal
accessories.

Anyone ever done a web calculator with BSFC @ load and RPM with other
factors like frictional losses, mechanical / volumetric efficiency, etc?

Many of the dyno plots I see are for the engine with various mods for
performance. I don't know how to read them to get the fuel consumption
info at idle.

The reason I'm looking for this info is not just to figure out how much
it costs to sit idling the car in traffic, but also to approximate
potential savings in fuel by letting the vehicle coast if the grade is
favorable.

I encounter places where I can let the car coast at 35mph for up to a
mile on a slight downhill grade, as opposed to leaving the car in gear
at part-throttle operation for the same distance.

I am guessing that the fuel economy while coasting will be something
like the fuel economy while idling, and with that as a baseline, you
could get some kind of idea about the savings per mile coasted versus
powered.

I think the drag coefficient on the '05 LX is something like .30, and my
experience thus far has been that it seems to want to coast forever even
on level ground.
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it's hard to calculate because it varies. oil temperature alone makes a
big difference to idle fuel consumption.

with an injected car, coasting in gear with rpm's above a given limit,
say 2,000 rpm, means the injectors are shut off completely. hence,
coasting in gear consumes less than coasting out of gear where the
injectors are squirting fuel to keep the motor from stalling.

that's all about engine braking, not fuel consumption.

if you want to save gas on coasting out of gear, you'd need to shut the
engine off completely. and that would be illegal because your vacuum
operated brakes would be disabled. not to mention your increased
eligibility for a darwin award.

 

To simplify, I would just consider idling at normal operating
temperature.

When I leave the car in gear, then take my foot off the
accelerator, the speed drops much more rapidly than when the
stick is in neutral.

Since the car would come to a stop much sooner than I'd like in
this condition, isn't this beside the point?

If you have info on the brake horsepower for this engine, that
would be great.

http://en.wikipedia.org/wiki/BSFC

What I'm looking for is observed fuel flow at idle. If I
happened to have the brake horsepower I think I'd be a long
way towards figuring BSFC.

I really don't know how these comments are helpful.

I'm interested in burning the least about of fuel for distance
traveled, by taking advantage of the momentum (mass) stored in
the moving vehicle.

Fuel consumption while decelerating rapidly (engine braking, in
gear) for a short distance does not interest me. I think you
can only compare coasting in gear versus coasting out of gear by
adjusting for distance traveled, which would be a very
significant difference.
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but that varies...

you don't understand. engine braking is the energy to turn an engine
through it's 4-cycle process without benefit of gasoline assistance.
since the injector system shuts off ALL gasoline when coasting above a
given rpm, coasting in gear will brake you.

dude, you're very very confused. brake horsepower is a measure of power
production, not consumption. brake specific fuel consumption is simply
efficiency - it's got nothing to do with slowing down.

bottom line, if you want to measure consumption at idle, calibrate your
injectors [volume vs. time], then scope your injector pulse widths over
an extended period to get average "open" timing. then calculate volume
of gasoline used accordingly.

because it's illegal and dangerous! you're welcome to remove yourself
from the gene pool, but don't do it on a public road in case you kill an
innocent in the process.

what part of "the injector system shuts off fuel when coasting above a
given rpm" don't you understand? that's when you're not using /any/
gas. coasting in neutral uses gas because fuel is used to keep the
motor idling.

then your stated objective is conflicted.

eh? dude, you're /way/ confused.

 

http://en.wikipedia.org/wiki/Brake_horsepower

This is a confusing subject as there have been many different
measures of horsepower over the years, and I don't mind admitting
that I can be confused by it.

After rereading things, I think that "friction horsepower" at a
given RPM would be a useful number. Frictional losses plus
plus pumping losses / cavitation -- some combination of these
describe the power required to turn the engine over at a given RPM
without benefit of combustion.

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

If you knew the horsepower requirement above, and knew the engine's
efficiency (BSFC is a measure of efficiency) then you could in theory
calculate the pounds per hour of fuel required to keep the engine
turning at idle for an hour.

Suppose for a moment that spinning the engine at 900 RPM with
minimal accessories required five horsepower. Then suppose your
BSFC value was .53 pounds of fuel per hour per horsepower.

You would be looking at something like something like:

5 * .53 = 2.65 pounds of fuel

Converting pounds to gallons you need the weight per gallon of fuel:

http://www.faqs.org/qa/qa-21281.html

This seems like a reasonable answer ...

(the weight) "Depends on the API gravity of the gasoline, which
varies by grade and refinery.

"Usually, regular unleaded gasoline has a gravity of around 58
and a weight per gallon of 6.216 pounds per gallon.

"Premium gasoline may have a gravity of 54, or 6.350 pounds per
gallon."

Using 6.2 pounds per gallon for regular, we would then get
something like:

2.65 / 6.2 = .43 gallons of fuel consumed to make five horsepower
at idle for one hour.

Of course the two numbers that I don't know are horsepower and
BFSC at a given idling RPM.

This would be a great shortcut to the above. Do you know the
answer using this formulation? Can you point me to the answer
using this formulation? Anything else is unhelpful.

It's obvious that I have no intention of turning off the ignition
while the car is going down the road. I never suggested this.
This is a straw man that you built for some purpose other than
being helpful.

Your previous answer seemed to suggest that this only happend
while the car was in gear. Are we talking about coasting in gear
(decelerating rapidly) or coasting in neutral?

This is a key distinction.

And you're coming to a stop fairly quickly.

I don't have a problem with this idea at all. But the objective is to
go a specific distance, as opposed to any distance.

Objective: While traveling at 40 mph in 4th gear, to travel an
additional one mile on a 1% downgrade using the lowest possible
amount of fuel.

Qualification: Any method of operation which doesn't get you the
full 1-mile is a failure.

Option one: Car in gear traveling a constant 40mph with engine
operating at part throttle, apply brakes to stop at destination.
This consumes quantity of fuel "X".

Option two: Leave car traveling in gear, the driver takes his
foot off the accelerator closing the throttle, and the car coasts
to a stop with engine stalling far short of the one mile mark.

(By definition a failure.)

Option three: Placing the car in neutral, the engine speed
decreases from 2100rpm (approx) to 900rpm (approx) idle, and
the car's momentum along with the slight downgrade keep the car
moving forward overcoming drag and rolling resistance with some
braking at the end of the one mile mark, using quantity of fuel
"Y".

I don't understand what part of this objective you think is
conflicted.

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why on earth would you bother with "difficult" unknowns when you can
directly measure an "easy" known, the amount of gas injected? what
you're suggesting is like measuring the length of a piece of string by
measuring earth's gravity field distortion that it creates. it's
possible, but hard and expensive. especially when a ruler will give you
the answer much more quickly.

figure out how much your injectors flow in gallons per hour. then add
up the injector pulse widths. it's real simple from there.

dude, you ask something self-contradictory, i point out the only
circumstances under which what you want is possible, and that it happens
to be dangerous and illegal. but now your objective is my fault?

read what i said!!!

doesn't happen because the injector system operates again once revs drop
below treshold.

ok, but illegal in many states.

aren't you the one that wanted to figure out "approximate potential
savings in fuel by letting the vehicle coast if the grade is
favorable"??? do the math. you've been told how. all /you/'ve done so
far is get confused over the word "brake" and perform the logical
equivalent of driving down the block to the gas station via both poles
and delhi, india.

 

The big problem is that the engine efficiency varies widely. A major source
of inefficiency is the reduction in combustion temperature, since heat
engines are affected by the "Carnot ratio" - the ratio of temperature at
which heat is added to the temperature at which it is exhausted from the
engine. If the combustion temperature is, say, 1500 degrees Rankine (about
1000 F) and the exhaust is 1000 degrees R (about 500 F), the theoretical
efficiency is (1 - 2/3 = 33%). As the combustion temperature drops, the
way it does at idle, the efficiency also drops. I'd be amazed if the idle
efficiency is as high as 10%. IIRC the theoretical maximum efficiency of an
Otto cycle engine - like our gasoline engines - is about 65% at an infinite
compression ratio, due to the poor elasticity of air.

Mike

 

Jim, I've got WRENCHES in my toolbox. I don't have ODBII meters,
scopes or anything else fancy.

How do I measure what you're talking about? I have no idea how
to:

"figure out how much your injectors flow in gallons per hour.
then add up the injector pulse widths. it's real simple from
there"

I don't have the gallons per hour number for the injectors on the
K24A4 engine. I don't know the "pulse widths" or the pressures
(you didn't mention), and I imagine all this changes at RPM and
load.

I'm asking here because I don't know how to "figure it out".

Telling me to "figure it out" doesn't help me.

But from the volume of posts that you answer, and the way you
seem to attack people that ask questions, it is my sense that you
really aren't interested in helping people.

You just like to call them them "dude".

Much as you might like to twist questions into something
contradictory so that you could make fun of them, there is
nothing inherent in the questions so far that have been
contradictory.

to revisit the relevant question:

CL>> I am guessing that the fuel economy while coasting will be
CL>> something like the fuel economy while idling, and with that
CL>> as a baseline, you could get some kind of idea about the
CL>> savings per mile coasted versus powered.

jb> if you want to save gas on coasting out of gear, you'd need
jb> to shut the engine off completely. and that would be
jb> illegal because your vacuum operated brakes would be
jb> disabled. not to mention your increased eligibility for a
jb> darwin award.

YOU are the one that mentions shutting off the engine
completely. I never did. Not coasting in gear. Not
coasting in neutral. Nada.

If the car is in 4th, and you take your foot off the
throttle, the car will decelerate and the engine will
eventually STALL. This assumes throttle is not being
otherwise applied (cruise control), which would defeat the
purpose of the test.

Once again, you assert something without providing any link
to support your claim. I don't doubt that ANYTHING is
illegal SOMEWHERE, but if you would like to provide a list
of states where this is illegal, and the link to the
statutory prohibition, that would be just dandy.

Or are you just too lazy?

No. You've told me how I could figure it out if I knew a lot
more things about injectors and fuel metering that I don't know,
and I think you don't know either, at the very least not for this
specific engine.

I've repeatedly invited you to post relevant URLs supporting your
opinions or pointing to relevant resources that would give me
what I've asked for, and you simply won't or can't do it.

Ahh, we're back to that now. I confuse brake and friction
horsepower once and you can't let it go. I admitted I was wrong
about that and I'm over it.

Have any of the posts with which you deluge this newsgroup ever
admitted that you could possibly be confused or wrong about
anything? If so I haven't seen them.

Spoken like a true Troll.

Is there any chance at all that you would just go ahead and put
me in your *plonk* file and / or just ignore my posts?

I'll bet not.
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| Charles Lasitter | Mailing/Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
+-----------------------------------------+

 

do you know what R-E-N-T-A-L is???

find out what your injectors are and look up the specs /or/ pull one and
have it calibrated at an injector shop. don't want to spend the time on
google or spend the money? sorry, can't help you bud.

dude, at this point, it's clear that you don't have enough clue to
actually want "help", you simply want to be spoon fed. and even then,
despite being told the answer 3 times, you're disputing what you hear.
bizarre. if you're serious about answers, you'll now go to the library
or better yet, go to school, but i'm not holding my breath on either
one. bye.

 

So now I'm "bud"? Great.

Well, Jimbo, my posts have provided many URLs from many
searches on related topics for the K24A4 engine.

But I guess you, bubba, couldn't be bothered to consult any
authority other than yourself, because your posts contain no
such references.

Gee Billy Bob, I didn't know that asking for web references
constituted being "spoon fed". I guess it does seem like a
lot of effort coming from someone that can't be bothered to
find the "SHIFT" key when he starts a sentence.

But in the context of being helpful, what's wrong with
asking a question in a forum like this where someone likely
already has the answer and can save you from pulling parts
off your engine and running around town with them?

It's this simple: Any question you don't have the answer
for must be unworthy, and any question you DO have the
answer for is usually ... unworthy.

I'm so glad that I don't need your permission to ask
questions, and I'm even happier that most of the folks here
are inherently friendlier than you are.

Bye!
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| Charles Lasitter | Mailing/Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
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