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Author Topic: Something is puzzling me  (Read 4025 times)

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TheBoy

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Something is puzzling me
« on: 29 November 2011, 19:56:19 »
Sure somewhere along the line, I've got it all arse about face....


Our 3.0l cars have, obviously, a displacement of 3.0l. Any one piston will fire every other revolution. So 1.5l of 'firing' displacement per revolution?

Petrol to air ratio is approx 1:14.5?

So by my maths, uses 1500/14.5 = approx 100ml petrol per revolution. Or 1l per 10 revs, or 10l per 100 revs.

So at 600 rpm idle, uses 60l a minute.


My maths is rubbish somewhere, but where?
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albitz

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Re: Something is puzzling me
« Reply #1 on: 29 November 2011, 19:58:31 »
Everyratherwhere by thelook of that. :D ;D ;D
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TheBoy

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Re: Something is puzzling me
« Reply #2 on: 29 November 2011, 19:59:55 »
Its amazing the crap that goes through your mind when sat in the little boys room, pondering life...
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MutantCav

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Re: Something is puzzling me
« Reply #3 on: 29 November 2011, 20:02:42 »
Maybe 14.5/1500??
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dad1uk

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Re: Something is puzzling me
« Reply #4 on: 29 November 2011, 20:04:06 »
Going by the info screen my 2.5 uses 0.2l per hour on tickover, so I fink you got something wrong ;D
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the alarming man

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Re: Something is puzzling me
« Reply #5 on: 29 November 2011, 20:05:19 »
or may be 60 millilitres?? :y
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cem_devecioglu

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Re: Something is puzzling me
« Reply #6 on: 29 November 2011, 20:15:30 »
as far as I know 14.7 grs of air and 1 gr of fuel..  14.7 gr of air must be converted to volume in related temperature but cant remember the related formula .. something like pv=nrt etc :-\
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Debs.

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Re: Something is puzzling me
« Reply #7 on: 29 November 2011, 20:16:31 »
 ::) "Men and Maths.....

......know your place!" :P

 ;D


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cem_devecioglu

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Re: Something is puzzling me
« Reply #8 on: 29 November 2011, 20:18:54 »
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cem_devecioglu

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Re: Something is puzzling me
« Reply #9 on: 29 November 2011, 20:20:48 »
Quote from: Debs. on 29 November 2011, 20:16:31
::) "Men and Maths.....

......know your place!" :P

 ;D

dont tar ..... ;D :P
 
I'm a bit rusted as its more trhan 20 years but I was good at chemistry.. but these rpm maf readings mess up my mind :-\ 
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dbug

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Re: Something is puzzling me
« Reply #10 on: 29 November 2011, 20:23:49 »
Its 42 TB - that's the meaning of life  :) ;)
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Kevin Wood

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Re: Something is puzzling me
« Reply #11 on: 29 November 2011, 20:24:42 »
2 things missing:

Your calculation of air volume assumes 100% volumetric efficiency. That won't be achieved because the engine won't suck its' complete swept volume in each induction stroke, especially at idle, because the cam timing, intake design, etc. isn't optimised for running at 600 RPM. The throttle is also almost closed, which doesn't help. ;)

You are comparing volumes of air/fuel when the stoichiometric mixture you have quoted by mass, as said.
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cem_devecioglu

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Re: Something is puzzling me
« Reply #12 on: 29 November 2011, 20:26:19 »
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cem_devecioglu

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Re: Something is puzzling me
« Reply #13 on: 29 November 2011, 20:32:48 »
and of course this 14.7 changes , so not easy to calculate
http://www.fuelairspark.com/Products/Documentation/C-Com/Help/targetaf.htm
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Entwood

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Re: Something is puzzling me
« Reply #14 on: 29 November 2011, 21:08:03 »
Okies .. to "redo" TB's calculations ... as best I can and hopefully I've got it right .....

1500 cc of air per revolution @ 600 rpm (idle) = 900000 = 900 ltrs air /minute

Relative density of air is 0.0013 kg/ltr

so 900 X .0013 =1.17 kg of air /minute

"perfect" ratio of 14.7:1

so 1.17 / 14.7 = .07959 kg fuel/minute

Relative density of petrol is 0.72 kg/ltr

.07959 / 0.72 = .11054 l/min

.11054 l /min = 6.6326 l/hr = 1.46 galls/hr

HTH  :)


This is the "theoretical case" as it assumes a full swept volume and a 14.7 ratio ... as Kevin says .. this just won't happen ....

In reality less volume will pass the MAF so less fuel needed, but ratio will be lower so more fuel needed .... :(
« Last Edit: 29 November 2011, 21:10:17 by Entwood »
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