Fuel calcs

[shameem]

I am wrong and I stand corrected - thank you for the information

[Fred]

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.

[Fred]

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.

[Fred]

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.

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)

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.

[Fred]

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.

[MotoFab]

n = (P * V) / (R * T)

n = (100kPa * 0.5 Litres ) / (8.314472 * 353 Kelvin)

Interesting stuff isn't it, Fred?

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

[Fred]

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?

LOL, good spotting! Arbitrary and chosen for coolant temp instead of air temp! woops! lol. Of course, 293 would have been more appropriate :

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.

[MotoFab]

LOL, good spotting!

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]

LOL, good spotting!

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.

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 ;-)

Thanks.

[Fred]

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.