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

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.

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

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.

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wrote:

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

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!!!

ok
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.

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

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.
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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! +-----------------------------------------+ | Charles Lasitter | Mailing/Shipping | | 401/728-1987 | 14 Cooke St | | cl+at+ncdm+dot+com | Pawtucket RI 02860 | +-----------------------------------------+
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<big snip>

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
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