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Jan Kalin
science forum beginner

Joined: 19 Jul 2006
Posts: 3

Posted: Wed Jul 19, 2006 11:26 am    Post subject: Estimating the ammount of water relased by burning petrol

Hi everyone. I was wondering if anyone here can give me an estimate of how
much water is produced when petrol is burned in a internal combustion
engine.

The background for my question: in a local forum we're discussing the
effects of hydrogen powered cars. One (not very technically inclined)
person believes that the water emissions from H2 powered cars will be a
problem - rising humidity in cities, more precipitation, greenhouse
effect,...

I tried convincing him that in my estimate this will not be a problem, by
calculating the ammount of water that 1E9 cars running 100kW engines at
full power for 24 hours a day will produce. The result is 3.5g of water
per second for one car and 3E11kg per day for all cars. This ammounts to
0.002% of total water content of the atmosphere.

Running the engines for a more realistic 2.4 hours per day drops that by a
factor of 10 (not to mention that no engine is run at full power all the
time and that an average of 100kW - 136HP - is probably an overestimate).
He still insists that it will be a problem.

In a DUHHH moment I remembered that burning of petrol also produces water.
If I can show that the ammount released by a petrol engine is similar to
the one released by an H2 engine, that should probably convince him.
However, when I tried to estimate the ammount, I found out that the
calculations are rather complicated, due to the petrol being a mixture.
Whilst in principle I could do them (and will if I need to), I wanted
to ask here first if anyone has done that or has any idea where I could
find such an estimate. Googling has not produced anything useful.

Cheers!

--
/"\ Jan Kalin (male, preferred languages: Slovene, English)
\ / http://charm.zag.si/eng/, email: "name dot surname AT zag dot si"
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Frank11
science forum beginner

Joined: 21 Aug 2005
Posts: 45

Posted: Wed Jul 19, 2006 12:32 pm    Post subject: Re: Estimating the ammount of water relased by burning petrol

Jan Kalin wrote:
 Quote: Hi everyone. I was wondering if anyone here can give me an estimate of how much water is produced when petrol is burned in a internal combustion engine. The background for my question: in a local forum we're discussing the effects of hydrogen powered cars. One (not very technically inclined) person believes that the water emissions from H2 powered cars will be a problem - rising humidity in cities, more precipitation, greenhouse effect,... I tried convincing him that in my estimate this will not be a problem, by calculating the ammount of water that 1E9 cars running 100kW engines at full power for 24 hours a day will produce. The result is 3.5g of water per second for one car and 3E11kg per day for all cars. This ammounts to 0.002% of total water content of the atmosphere. Running the engines for a more realistic 2.4 hours per day drops that by a factor of 10 (not to mention that no engine is run at full power all the time and that an average of 100kW - 136HP - is probably an overestimate). He still insists that it will be a problem. In a DUHHH moment I remembered that burning of petrol also produces water. If I can show that the ammount released by a petrol engine is similar to the one released by an H2 engine, that should probably convince him. However, when I tried to estimate the ammount, I found out that the calculations are rather complicated, due to the petrol being a mixture. Whilst in principle I could do them (and will if I need to), I wanted to ask here first if anyone has done that or has any idea where I could find such an estimate. Googling has not produced anything useful.

I'd just take n-octane as representative of gasoline and use that as
basis for calculations.
This reminds me of some functional, technically illiterate official in
New England spouting off that a gallon of gasoline give off about 20
pounds of pollutants, where he was obviously inventorying water and
carbon dioxide as pollutants.

Frank
Richard J Kinch
science forum beginner

Joined: 26 May 2005
Posts: 36

Posted: Wed Jul 19, 2006 5:18 pm    Post subject: Re: Estimating the ammount of water relased by burning petrol

Jan Kalin writes:

 Quote: Hi everyone. I was wondering if anyone here can give me an estimate of how much water is produced when petrol is burned in a internal combustion engine.

If you can't compute that high school chemistry problem, then you have no
business discussing the topic.
somebody@compusmart.ab.ca
science forum beginner

Joined: 18 Jun 2006
Posts: 2

Posted: Thu Jul 20, 2006 4:22 am    Post subject: Re: Estimating the ammount of water relased by burning petrol

nobody@noknown.domain (Jan Kalin) wrote:

 Quote: However, when I tried to estimate the ammount, I found out that the calculations are rather complicated, due to the petrol being a mixture.

The fact that it is a mixture is irrelevant for this calculation. Just
use the wt% hydrogen in the fuel. All of it will turn into water, no
matter from which hydrocarbon it came.

Roger
Herman Family
science forum Guru Wannabe

Joined: 14 Jun 2005
Posts: 173

Posted: Thu Jul 20, 2006 5:58 am    Post subject: Re: Estimating the ammount of water relased by burning petrol

<somebody@compusmart.ab.ca> wrote in message
news:pq0ub25c4evisi62qqs139lgh2pn4uf9q6@4ax.com...
 Quote: nobody@noknown.domain (Jan Kalin) wrote: However, when I tried to estimate the ammount, I found out that the calculations are rather complicated, due to the petrol being a mixture. The fact that it is a mixture is irrelevant for this calculation. Just use the wt% hydrogen in the fuel. All of it will turn into water, no matter from which hydrocarbon it came. Roger

After the water is exhausted from the vehicle, it will probably be mostly
condensed in short order as it cools down. A cool evening would also get
rid of a lot of the water. Indeed, some will make it to the upper
atmosphere. We might see a very slight increase in precipitation, which
could help many areas.

CO2 on the other hand does not precipitate. It pretty much sticks around
until it is converted to sugar by some tree.

Michael
N:dlzc D:aol T:com (dlzc)
science forum Guru

Joined: 25 Mar 2005
Posts: 2835

Posted: Thu Jul 20, 2006 1:08 pm    Post subject: Re: Estimating the ammount of water relased by burning petrol

Dear Herman Family:

"Herman Family" <ecalptsudwaseht.in.reverse@frontiernet.net>
wrote in message news:aYEvg.5959\$Oh1.398@news01.roc.ny...
....
 Quote: CO2 on the other hand does not precipitate. It pretty much sticks around until it is converted to sugar by some tree.

The ocean is also a net consumer of CO2.

David A. Smith
Jan Kalin
science forum beginner

Joined: 19 Jul 2006
Posts: 3

Posted: Thu Jul 20, 2006 1:30 pm    Post subject: Re: Estimating the ammount of water relased by burning petrol

In article <Xns9805876BC5CB9someconundrum@216.196.97.131>, Richard J Kinch
wrote:
 Quote: Jan Kalin writes: Hi everyone. I was wondering if anyone here can give me an estimate of how much water is produced when petrol is burned in a internal combustion engine. If you can't compute that high school chemistry problem, then you have no business discussing the topic.

Thank you for the very useful advice, but apparently you have not read the
last paragraph where I wrote:

Whilst in principle I could do them (and will if I need to), I wanted
to ask here first if anyone has done that or has any idea where I could
find such an estimate. Googling has not produced anything useful.

--
/"\ Jan Kalin (male, preferred languages: Slovene, English)
\ / http://charm.zag.si/eng/, email: "name dot surname AT zag dot si"
X ASCII ribbon campaign against HTML in mail and postings.
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Jan Kalin
science forum beginner

Joined: 19 Jul 2006
Posts: 3

Posted: Thu Jul 20, 2006 1:41 pm    Post subject: Re: Estimating the ammount of water relased by burning petrol

In article <1153312324.555771.257990@i3g2000cwc.googlegroups.com>, Frank
wrote:
 Quote: Jan Kalin wrote: Hi everyone. I was wondering if anyone here can give me an estimate of how much water is produced when petrol is burned in a internal combustion engine. The background for my question: in a local forum we're discussing the effects of hydrogen powered cars. One (not very technically inclined) person believes that the water emissions from H2 powered cars will be a problem - rising humidity in cities, more precipitation, greenhouse effect,... I tried convincing him that in my estimate this will not be a problem, by calculating the ammount of water that 1E9 cars running 100kW engines at full power for 24 hours a day will produce. The result is 3.5g of water per second for one car and 3E11kg per day for all cars. This ammounts to 0.002% of total water content of the atmosphere. Running the engines for a more realistic 2.4 hours per day drops that by a factor of 10 (not to mention that no engine is run at full power all the time and that an average of 100kW - 136HP - is probably an overestimate). He still insists that it will be a problem. In a DUHHH moment I remembered that burning of petrol also produces water. If I can show that the ammount released by a petrol engine is similar to the one released by an H2 engine, that should probably convince him. However, when I tried to estimate the ammount, I found out that the calculations are rather complicated, due to the petrol being a mixture. Whilst in principle I could do them (and will if I need to), I wanted to ask here first if anyone has done that or has any idea where I could find such an estimate. Googling has not produced anything useful. I'd just take n-octane as representative of gasoline and use that as basis for calculations.

Thanks for the tip!

In case anyone's interested, the result comes out as 1.7g of water per car
per second, i.e., about half of the amount from the equivalent hydrogen
engine.

--
/"\ Jan Kalin (male, preferred languages: Slovene, English)
\ / http://charm.zag.si/eng/, email: "name dot surname AT zag dot si"
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