Convertion from CO2 Vol to "g/km"

[markbmw]

How does one work out the CO2 result from volume to grams per kilometre? The problem is that test machines only give the C02 result in volume. So for old cars manufactures do not specifices the g/km. I have a 1991 BMW 320i SE and I need to find its CO2 in g/km as this is need by the governement for licensing perposes or else I have to pay a huge license fees. The government does not accept CO2 results in vol.

The test shows that this car produces 14.99% Volume of CO2. We know that this car consumes from 9 to 11 litres of petrol per 100 KM = 0.9 to 0.11 litre per 1 km. I need the FORMULA to work our the g/km. BMW cannot help me. Does anyone know who could?

[markbmw]

I want to add all the test results as follows:

ppm HC = 19
%vol COc = 0.009
%vol CO = 0.009
%vol CO2 = 14.99%
%vol O2 = 0.76
Lambda = 1.035

Machine use is BOSCH ETT 008.63

[warthog1984]

Since I do not know the total volume of air sampled:

1 mol of gas = 22.4L at Standard temp & pressure. Weight of 1 mol of CO2 = (12.01g + 15.99g + 15.99g) = 43.99g

short version: CO2 weighs 1.96g/L at STP

[ILAveo]

I think you need to run the calculation off the L/100 km figure. Burning a liter of gas makes 2360 g of CO2 This came up before so I don't claim credit. Check the linked thread for calculation instructions.

[phoebeisis]

This is how I would calculate it.

I would use 10 liters fuel per 100 KM.
10 LITERS OF FUEL HAS ABOUT 7500 GRAMS OF MASS. Look this up to get a more precise mass for one gram of gasoline-a better density or specific gravity number will be easy to find.

Use this formula to get the correct moles for fuel used and CO2 produced.I used CH2 as the formula for gasoline- it is a decent enough approximation for this.

2CH2 +3O2 > 2CO2+H20

One mole of CH2 is 14
One mole of CO2 is 44 grams

7500 grams X 1mole/14 grams =536 moles Ch2 used per 100 KM
536 Moles of CH2 produce 536 moles of CO2 -2 moles of CH2 produce 2 moles CO2

536 MOLES OF CO2 produced per 100 km.
536 moles X 44 GRAMS/MOLE= 23571 GRAMS PER 100 km
or 23571grams per 100 KM= 236 grams per KM.

I get about 236 grams/KM if you use 10 liter per 100 KM.

The formula

Liters used per 100km X density of fuelx1000 X 1/18 x44X 1/100= grams per KM.

10 liters X1000 G/L X .7G/ml X 1/14 x44 X 1/100=236 grams/km

I think this is right.Never bothered to do it before. Maybe someone can check it- 236 grams per KM seems high!! One mile would produce about 0.8 lb of CO2!!

Charlie

ps I know gasoline-say octane is-
C8H18 but for this purpose CH2 is close enough.
The .75 g/ml IS STRICTLY A GUESS.Search for a better density number. .75 is close, but a guess.

[Tochatihu]

Gasoline 0.72 g/mL per wiki

[phoebeisis]

Tochatihu,

Thanks- that would drop it to 72/75 X 236=227GRAMS/km

Still is that correct-227 grams per KM?? Wow, that is a lot.

Charlie

[phoebeisis]

IF YOU DO IT THE HARD WAY-pretending gasoline is all octane with 114 mole wt. We just look up how much CO2 a liter of gasoline produces-but that would be too easy.

8 C8H18 + 25 O2 > 16CO2 + 18H20

You get 222 grams/KM

Charlie

[Ptero]

Interesting question. I have a 1990 750il. I'll see if I can identify the proceedure that Cal EPA uses.