# Calculating CV of Fuel/Air Mixture @ 25°C

• Andy86
In summary, the fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butene (C4H8) by volume. It is to be fed to the combustion chamber in 10% excess air at 25°C, where it is completely burnt to carbon dioxide and water. The flue gases produced are to be used to generate 5 bar steam from water at 90°C.
That's the incorrect number of total mols in the mix, total ,mols is 33.8 > 34 Mols

OK. So 2580/33.8=76.3 kJ/mole

The volume per mole is 0.0245 m^3/mole

So, 76.3/0.0245 = 3115 kJ/m^3 of fuel mixture = 3.12 MJ/m^3 of fuel mixture

OK. So 2580/33.8=76.3 kJ/mole

The volume per mole is 0.0245 m^3/mole

So, 76.3/0.0245 = 3115 kJ/m^3 of fuel mixture = 3.12 MJ/m^3 of fuel mixture

Chestermiller said:
OK. So 2580/33.8=76.3 kJ/mole

The volume per mole is 0.0245 m^3/mole

So, 76.3/0.0245 = 3115 kJ/m^3 of fuel mixture = 3.12 MJ/m^3 of fuel mixture

It doesn't look right that the CV is 3.12 MJ / m^3 as the gross CV is 108.1 MJ M^3, my calculated NET CV of 103.2 MJ M^3 looks more realistic?

Andy86 said:
It doesn't look right that the CV is 3.12 MJ / m^3 as the gross CV is 108.1 MJ M^3, my calculated NET CV of 103.2 MJ M^3 looks more realistic?
The stream is diluted by a factor of 33,9

Chestermiller said:
The stream is diluted by a factor of 33,9

Meaning?

Andy86 said:
Meaning?
You have 1 mole of actual fuel and 32,9 mioles of nitrogen and oxygen that dilute the heating value. Just take your 100MJ and divide by 33.9. What do you get?

NET CV BY VOL = 103.2MJ / M^-3

103.2 / 33.8 = 3.05MJ / M^-3

Andy86 said:
NET CV BY VOL = 103.2MJ / M^-3

103.2 / 33.8 = 3.05MJ / M^-3
Pretty close, huh?

VERY! :-)

So.....

NET CV BY MASS

n = PV / RT = 100000 * 1 / 8.314 * 298 = 40.3 MOL = 0.0403 KMOL

CV = MK M^-3 / KMOL
= 3.05 MJ M^-3 / 0.0403 KMOL
= 75.6 MJ KMOL^-1

?

Last edited:
Andy86 said:
VERY! :-)

So.....

NET CV BY MASS

n = PV / RT = 100000 * 1 / 8.314 * 298 = 40.3 MOL = 0.0403 KMOL

CV = MK M^-3 / KMOL
= 3.05 MJ M^-3 / 0.0403 KMOL
= 75.6 MJ KMOL^-1

?
You're going in a circle. You already had the CV per mole.

Andy86 said:
VERY! :-)

So.....

NET CV BY MASS

n = PV / RT = 100000 * 1 / 8.314 * 298 = 40.3 MOL = 0.0403 KMOL

CV = MK M^-3 / KMOL
= 3.05 MJ M^-3 / 0.0403 KMOL
= 75.6 MJ KMOL^-1

?
You're going in a circle. You already had the CV per mole.

Ok Great, thanks for all your help Chester I really appreciate it.

Andy

Chestermiller

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