Fuel calcs
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- LQFP112 - Up with the play
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Re: Fuel calcs
I am wrong and I stand corrected - thank you for the information
Re: Fuel calcs
Bump, restored one post :
http://www.diyefi.org/forum/viewtopic.p ... 2255#p2255
If anyone notices any other posts removed by disgruntled persons well after the fact, please let me know so I can track it down and replace it in a similar fashion.
Thanks,
Fred.
http://www.diyefi.org/forum/viewtopic.p ... 2255#p2255
If anyone notices any other posts removed by disgruntled persons well after the fact, please let me know so I can track it down and replace it in a similar fashion.
Thanks,
Fred.
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Re: Fuel calcs
Restored 2 more :
http://www.diyefi.org/forum/viewtopic.php?p=2266#p2266
http://www.diyefi.org/forum/viewtopic.php?p=2280#p2280
Strange character bob was.
Thanks for clearing up that post MotoFab/Jim, most appreciated.
Fred.
http://www.diyefi.org/forum/viewtopic.php?p=2266#p2266
http://www.diyefi.org/forum/viewtopic.php?p=2280#p2280
Strange character bob was.
Thanks for clearing up that post MotoFab/Jim, most appreciated.
Fred.
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Re: Fuel calcs
I've been doing a bit of searching and thought I would post my results here :
http://en.wikipedia.org/wiki/MAP_sensor ... ue_is_used
Which says :
Engine Mass Airflow Rate = (VE * RPM * MAP) / Temperature
http://en.wikipedia.org/wiki/Ideal_gas_law
Which says :
Where
P is the absolute pressure of the gas,
V is the volume of the gas,
n is the number of moles of gas,
R is the universal gas constant,
T is the absolute temperature.
Solving for moles of gas :
n = (P * V) / (R * T)
n = (100kPa * 0.5 Litres ) / (8.314472 * 353 Kelvin)
n = 0.0170357251 moles of air
The mean molar mass of air is 28.97 g/mol
so we have 0.493524957 grams of it in our 500cc cylinder with 100% VE
If we use pure octane to check this for realism :
density = 0.703 g/ml, liquid
14.7 grams of air to 1 gram of octane
gives us 0.0335731263grams of fuel per cycle per cylinder.
If we then take a typical injector for a 2.0/4cyl of 300cc/minute we have 5cc/second and an open (and flowing) time of 0.00671462526 seconds or 6.7ms
http://www.google.com/search?hl=en&safe=off&q=(1+%2F+(5+%2F+(((100++*+0.5)+++%2F+(8.314472+*+353)+*+28.97)+%2F+14.7)))+*+1000&btnG=Search
and HOORAY, it all works :-)
Tomorrow kids I'll reduce this to our known variables and resolutions and try to do some worst case calculations.
Fred.
http://en.wikipedia.org/wiki/MAP_sensor ... ue_is_used
Which says :
Engine Mass Airflow Rate = (VE * RPM * MAP) / Temperature
http://en.wikipedia.org/wiki/Ideal_gas_law
Which says :
Where
P is the absolute pressure of the gas,
V is the volume of the gas,
n is the number of moles of gas,
R is the universal gas constant,
T is the absolute temperature.
Code: Select all
R = 8.314472 J·mol−1·K−1
= 8.314472 m3·Pa·K−1·mol−1
= 8.314472 kPa·L·mol-1·K-1
= 0.08205746 L·atm·K−1·mol−1
= 62.36367 L·mmHg·K−1·mol−1
= 10.73159 ft3·psi·°R−1·lb-mol−1
= 53.34 ft·lbf·°R−1·lbm−1 (for air)
n = (P * V) / (R * T)
n = (100kPa * 0.5 Litres ) / (8.314472 * 353 Kelvin)
n = 0.0170357251 moles of air
The mean molar mass of air is 28.97 g/mol
so we have 0.493524957 grams of it in our 500cc cylinder with 100% VE
If we use pure octane to check this for realism :
density = 0.703 g/ml, liquid
14.7 grams of air to 1 gram of octane
gives us 0.0335731263grams of fuel per cycle per cylinder.
If we then take a typical injector for a 2.0/4cyl of 300cc/minute we have 5cc/second and an open (and flowing) time of 0.00671462526 seconds or 6.7ms
http://www.google.com/search?hl=en&safe=off&q=(1+%2F+(5+%2F+(((100++*+0.5)+++%2F+(8.314472+*+353)+*+28.97)+%2F+14.7)))+*+1000&btnG=Search
and HOORAY, it all works :-)
Tomorrow kids I'll reduce this to our known variables and resolutions and try to do some worst case calculations.
Fred.
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Re: Fuel calcs
More references I used :
http://en.wikipedia.org/wiki/Earth's_atmosphere
http://en.wikipedia.org/wiki/Density_of_air
http://en.wikipedia.org/wiki/Air-fuel_ratio
http://en.wikipedia.org/wiki/Octane
Fred.
http://en.wikipedia.org/wiki/Earth's_atmosphere
http://en.wikipedia.org/wiki/Density_of_air
http://en.wikipedia.org/wiki/Air-fuel_ratio
http://en.wikipedia.org/wiki/Octane
Fred.
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Re: Fuel calcs
Interesting stuff isn't it, Fred?Fred wrote:n = (P * V) / (R * T)
n = (100kPa * 0.5 Litres ) / (8.314472 * 353 Kelvin)
Just wondering about something. How was 353°K selected? I mean, that's pretty warm. Is it just an arbitrary value to show the equation?
- Jim
Re: Fuel calcs
LOL, good spotting! Arbitrary and chosen for coolant temp instead of air temp! woops! lol. Of course, 293 would have been more appropriate :MotoFab wrote:Just wondering about something. How was 353°K selected? I mean, that's pretty warm. Is it just an arbitrary value to show the equation?
http://www.google.com/search?hl=en&safe=off&q=(1+%2F+(5+%2F+(((100++*+0.5)+++%2F+(8.314472+*+293)+*+28.97)+%2F+14.7)))+*+1000&btnG=Search
which yields 8.08ms pulse which is even more accurate.
Thanks for pointing that out ;-)
Fred.
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Re: Fuel calcs
Sure Fred. It's still accurate though. If it ever happens to be 176°F outside it's good to know that the EMS is still on the job.Fred wrote:LOL, good spotting!
Re: Fuel calcs
LOL, exactly. I was just confused between coolant and air because I'd been working on both... I thought "What's a reasonable running temperature" and forgot which variable I was aiming for ;-)MotoFab wrote:Sure Fred. It's still accurate though. If it ever happens to be 176°F outside it's good to know that the EMS is still on the job.Fred wrote:LOL, good spotting!
Thanks.
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Re: Fuel calcs
time = (((((molar mass of air * ((P * VE * V) / (R * T))) / (AFRStoich * Lambda )) * density of fuel) * 1000 for mls) / (injector CC/min / 60))
time = ((((( 28.97gm/mol * ((100kPa * 100% * 0.5 Litres ) / (8.314472xyz/mol * 353 Kelvin)) ) / (14.7 * 1.0)) * 0.703) * 1000) / (300 / 60))
pw time = 4.72038156 ms fuel per cycle per cylinder
Given that the answer changed I think some brackets are misplaced.
pw / 0.0008 = timer units!
pw * 1250 = timer units
= 5900.47695 timer units
= 5900 timer units (for both round and truncate)
Next time I'll sort out the brackets and factor out the constants and variables and do some work on the scaling aspect of it all.
Edit : 5900!!
((((( 28.97 * ((100 * 100% * 0.5) / (8.314472 * 353)) ) / (14.7 * 1.0)) * 0.703) * 1000) / (300 / 60)) / 0.0008
Fred.
time = ((((( 28.97gm/mol * ((100kPa * 100% * 0.5 Litres ) / (8.314472xyz/mol * 353 Kelvin)) ) / (14.7 * 1.0)) * 0.703) * 1000) / (300 / 60))
pw time = 4.72038156 ms fuel per cycle per cylinder
Given that the answer changed I think some brackets are misplaced.
pw / 0.0008 = timer units!
pw * 1250 = timer units
= 5900.47695 timer units
= 5900 timer units (for both round and truncate)
Next time I'll sort out the brackets and factor out the constants and variables and do some work on the scaling aspect of it all.
Edit : 5900!!
((((( 28.97 * ((100 * 100% * 0.5) / (8.314472 * 353)) ) / (14.7 * 1.0)) * 0.703) * 1000) / (300 / 60)) / 0.0008
Fred.
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