omega0684
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| posted on 2/7/09 at 08:37 AM |
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one for the brainiaks
How do you work out how much fuel is being used, every minute, at these 2 idle speeds, 900rpm & 1000rpm?
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coozer
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| posted on 2/7/09 at 08:39 AM |
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Feed the system with a small (1 litre) tank and record the time taken to use the fuel up.
Do both at the different rpm speeds and you have the data you require....
1972 V8 Jago
1980 Z750
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omega0684
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| posted on 2/7/09 at 08:44 AM |
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i was thinking more along the lines of a theoretic explanation, if you can work out how much fuel is going it, by having injector opening times, fuel
pressure, air volume etc
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smart51
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| posted on 2/7/09 at 08:46 AM |
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Loosely speaking (for the pedantics) the volume of your engine is the amount of air fuel mixture it draws in every 2 revs. This is multiplied by your
throttle opening, which might be around 5% at idle.
The density of air is about 1.2 grammes per litre near sea level. Your air / fuel ratio will be about 14:1, so from a 2 litre engine drawing in 5% of
1.2g of air per rev, it will draw in 4.286mg of fuel per rev.
The density of petrol varies with temperature but 0.75 g/ml is a good figure. your 4.286 mg = 5.714 micro litres.
At 900 RPM that is 5.14 ml per min or 0.3 litres per hour. At 1000 RPM that is 5.71 ml per min or 0.34 litres per hour.
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MikeRJ
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| posted on 2/7/09 at 08:46 AM |
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Far too many variables to even hazard a guess. The maths would be horrendous to try and model this.
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MikeRJ
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| posted on 2/7/09 at 08:48 AM |
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quote:
Originally posted by smart51
Loosely speaking (for the pedantics) the volume of your engine is the amount of air fuel mixture it draws in every 2 revs. This is multiplied by your
throttle opening, which might be around 5% at idle.
The density of air is about 1.2 grammes per litre near sea level. Your air / fuel ratio will be about 14:1, so from a 2 litre engine drawing in 5% of
1.2g of air per rev, it will draw in 4.286mg of fuel per rev.
The density of petrol varies with temperature but 0.75 g/ml is a good figure. your 4.286 mg = 5.714 micro litres.
At 900 RPM that is 5.14 ml per min or 0.3 litres per hour. At 1000 RPM that is 5.71 ml per min or 0.34 litres per hour.
Now introduce the parasitic losses at the two different speeds and the differences in volumetric and thermal efficiency.
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Mr Whippy
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| posted on 2/7/09 at 08:51 AM |
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fit a fuel flow meter, then you can get all depressed in real time
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smart51
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| posted on 2/7/09 at 08:52 AM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by smart51
Loosely speaking (for the pedantics) the volume of your engine is the amount of air fuel mixture it draws in every 2 revs. This is multiplied by your
throttle opening, which might be around 5% at idle.
The density of air is about 1.2 grammes per litre near sea level. Your air / fuel ratio will be about 14:1, so from a 2 litre engine drawing in 5% of
1.2g of air per rev, it will draw in 4.286mg of fuel per rev.
The density of petrol varies with temperature but 0.75 g/ml is a good figure. your 4.286 mg = 5.714 micro litres.
At 900 RPM that is 5.14 ml per min or 0.3 litres per hour. At 1000 RPM that is 5.71 ml per min or 0.34 litres per hour.
Now introduce the parasitic losses at the two different speeds and the differences in volumetric and thermal efficiency.
Now read the first 5 words again. I understand that pumping losses through a 5% open throttle butterfly will almost certainly mean that a figure
other than 5% of the ultimate air flow will reach the engine and that valve timing and engine temperature and a million other things will affect the
numbers. There's nothing wrong with using the basic numbers to give you an order of magnitude type calculation. The answer is about 1/3 litre
per hour.
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02GF74
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| posted on 2/7/09 at 09:05 AM |
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I was gonna post mucvh along the lines of what smart1 says - that is how you would go about calculating although there are still unknowns.
not sure the throttle opening would be 5 %, I' d thought it be less but that would need to be measured or calclated - also the cmputation misses
out that at 900 rpm, the thjrottle will be a bit more open that at 800.
Not sure how acurate the answer would be but would give a ball pack figure.
Best way is to feed in known amount of fuel and time how long the engine runs or be able to measure the fuel flow.
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dinosaurjuice
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| posted on 2/7/09 at 11:09 AM |
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fit a diesel engine and never worry about fuel consumption ever again
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MikeR
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| posted on 2/7/09 at 11:16 AM |
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sounds like you want 100ml of fuel and start the engine .... see if its still running after 20 minutes.
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brianthemagical
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| posted on 2/7/09 at 01:35 PM |
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If using MS, open Tuner studio, and run the engine at the two idle speeds, after a bit of tweaking to get them perfect, then note pulsewidth. The
ratio of the two will give the difference in fuel used. to gain a specific value you'll need to know the injector flow rate, which can easilly
be empirically derived and at the same time you can perfect the dead time.
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clairetoo
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| posted on 2/7/09 at 05:56 PM |
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quote:
Originally posted by Mr Whippy
fit a fuel flow meter, then you can get all depressed in real time
Or a fuel gauge like mine ............ 
Its cuz I is blond , innit
Claire xx
Will weld for food......
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paulf
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| posted on 2/7/09 at 09:29 PM |
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Megalog viewer can give a fuel flow figure.
Paul
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02GF74
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| posted on 3/7/09 at 09:31 AM |
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quote:
Originally posted by clairetoo
quote:
Originally posted by Mr Whippy
fit a fuel flow meter, then you can get all depressed in real time
Or a fuel gauge like mine ............
I have 2 in the landy (v8) so get doubly depressed
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