calculate diesel fuel consumption

Hi

I found this helpfull doc: AVR-Based Fuel Consumption Gauge

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Now I want to calculate the consumption of my diesel car. I think this should be possible with the help of the engine load and speed (or other values?). Unfortunately I do not know the calculation method. Can someone help me?

Reply to
Florian Schaeffer
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The method won't work for a diesel since fuel consumption is independent of airflow (unlike a gasoline engine).

Reply to
John_H

John_H schrieb am 19.12.2006 22:59:

I know this facts. Therefore I look for another method. It must go, how one sees at ScanGauge

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Reply to
Florian Schaeffer

Florian Schaeffer schrieb am 19.12.2006 09:18:

I must ask again, because no one knows the answer. :-( Is it possible to calculate the consumption with the engine speed (rpm) and the knowing about the count of cylinders and the cylinder capacity? Is the injected fuel quantity all times the same? And how much fuel was injected in each cylinder on a 2500 ccm engine for example?

Thank you

Reply to
Florian Schaeffer

Do you think the same amount of fuel is needed to keep the engine at

2500 RPM in neutral as when climbing a hill at 2500 RPM, or driving on a highway in the highest gear at 2500 RPM?

Don't you notice that you have to press the pedal differently in these situations?

Are you stupid???

Reply to
Kaz Kylheku

Kaz Kylheku schrieb am 22.12.2006 15:49:

*plonk*
Reply to
Florian Schaeffer

There is no 'calculation' for that.

The only way to test it is to fill it up until you see the fuel, drive it for most of the tank and fill it up to the same place as before. You then see how many miles that took you and how many gallons of fuel was used for this mileage.

That will give you the mileage for 'that' particular tank full. Each tank full will vary radically according to even simple things like a headwind or tailwind.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

I've found that my car gives remarkably consistent fuel consumption figures - as long as I drive in the same way - not varying by more than +/-

2 mpg from one tankful to the next. Some of that variation may be due to not always filling up to the same point on successive tankfuls - different pumps cut out at different levels in the filler pipe. Out of sympathy for cyclists and motorbikes, I don't fill up so full that I can see the fuel in the pipe, because spilled diesel is *slippy*. (I did once drove behind a car that was gushing fuel from its filler cap on every left turn. The driver seemed utterly indifferent when I flashed him and pointed out that spilled diesel - if it was diesel rather than petrol - is a skidding hazard, that spilled petrol is a fire hazard and that anyway he was wasting fuel, which is not to be recommended at inflated UK prices.)

(All these figures are miles per UK gallon: multiply by 4/5 to get miles per US gallon)

40 mpg stop-start driving in heavy traffic: maximum 30 mpg but with frequent stops and starts from rest or crawling forward in traffic jams 45 mpg local journeys - max 15 miles, many T junctions, roundabouts (traffic circles, rotaries) and traffic lights 52 mpg long motorway journeys (fairly constant 60-80 mph) 58 mpg long journeys around 50-60 mpg with few junctions or stops

My car (Peugeot 306 HDi) has averaged 50 mpg over its severn-year,

104,000-mile life so far. And thankfully the consumption shows no sign of getting worse with age - once it levelled out ofter the car was run-in, it's been remarkably constant since then.

Is the thread suggesting that there is no easy way of calculating instantaneous fuel consumption with a diesel-engined car? Or is it that you need to measure the rate at which diesel fuel is being consumed, rather than inferring it from other parameters like engine revs, speed, gear? Because I've driven plenty of diesel cars (eg VW Golf, Citroen C5) which have a second-by-second display of fuel consumption and can also average this over a journey.

Reply to
Martin Underwood

That means something when it doesn't come from a pitiful moron.

Reply to
Kaz Kylheku

Martin Underwood schrieb am 22.12.2006 19:23:

Thanks. That's what I know. By this way I get the average consumption for the car.

This is what I want to know: How to calculate a continuous (approximated) value for the driving situation just in this time? As said like the ScanGauge.

Reply to
Florian Schaeffer

Well I presume that these cars have a fuel flow meter. I hadn't realised that you could get the instantaneous fuel consumption in a petrol/gasoline engine *without* having a fuel flow meter.

From the information about ScanGauge it looks as if many cars have some sort of information socket under the dashboard that devices such as ScanGauge can connect to. I wonder if the cars which have it use a flow meter.

Reply to
Martin Underwood

petrol/gasoline

A fuel-injected engine is run by a management which determines the instantaneous amount of fuel to squirt via the fuel injectors, based on inputs such as airflow and the concentration of oxygen in the exhaust.

Reply to
Kaz Kylheku

Martin Underwood schrieb am 22.12.2006 23:13:

I think ScanGauge only connects to the OBD II plug and calculate with the available values. There is no value of a fuel flow meter in the data set. Only the first 32 PIDs:

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Also the X-Gauge:
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Reply to
Florian Schaeffer

Yes, but the amount of fuel flowing past a fixed point (eg in the line between the tank and injectors) will be the same as the sum of the amounts going down all the injectors - fuel doesn't get created or destroyed!

Presumably you *have* to use a flow meter if you have a carburettor engine or a mechanical injection engine, and you *can* use either flow meter or per-injector fuel-flow data from the engine-management system with electronically-controlled injection (and the answers should be identical in either case).

If you know the rate at which fuel is being consumed (millilitres/second) and the speed of the car (miles/hour), then dividing one by the other gives distance per unit volume (miles/gallon) or volume per unit distance (litres/100 km).

When I drove a diesel car with a fuel consumption readout, I was surprised at how little the consumption varied depending on what gear the car was in - is this normal with diesel rather than petrol engines?

Reply to
Martin Underwood

No.

No.

That depends on the load and the "throttle" position, among other things.

Reply to
Steve

I borrowed a diesel Volvo for a couple of weeks and found that the indicated MPG varied ENORMOUSLY with the gear, the accelerator, etc.

Loping along calmly, I got an indicated 70 mpg (and that is an American gallon). With heavy accelerator pressure, it would drop instantaneously to the teens or so. (This was not a turbo diesel).

Basically, the car averaged about 40 mpg, as measured by fuel in the tank versus mileage. Not bad, for a turd car like this Volvo.

Reply to
<HLS

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