What are the co2 emissions (in lbs per gallon) of a CNG bus?
Posted on November 29th, 2009 by admin
I cannot find this for the life of me. I know that typically 19.4 lbs of co2 are released for every gallon of gasoline, but I need to know how much compressed natural gas (CNG) produces!!!
CNG or compressed natural gas, (CH4) is a compressed gas and not a liquid. It is not typically measured in gallons. Liquids that are stable at room temperature and pressure are measured in gallons. LNG (liquid natural gas) is a liquid because it has been compressed and cooled.
In this article: http://www.triplepundit.com/2006/11/askpablo-clean-natural-gas/ you will find a very careful discussion of gasoline and CNG emissions. It turns out that CNG produces less particulate matter and about 70% of the CO2 that would be required from a gasoline powered vehicle.
November 29th, 2009 at 4:15 pm
It depends on the pressure of the CNG.
You see, a liquid like gasoline has a certain number of molecules in each gallon, which burn to produce a certain quantity of CO2.
However for a gas like CNG, the number of molecules in a gallon is dependent on the pressure of the system. A highly pressurized system will contain more fuel per gallon and will emit more CO2 per gallon.
References :
November 29th, 2009 at 5:04 pm
CNG or compressed natural gas, (CH4) is a compressed gas and not a liquid. It is not typically measured in gallons. Liquids that are stable at room temperature and pressure are measured in gallons. LNG (liquid natural gas) is a liquid because it has been compressed and cooled.
In this article: http://www.triplepundit.com/2006/11/askpablo-clean-natural-gas/ you will find a very careful discussion of gasoline and CNG emissions. It turns out that CNG produces less particulate matter and about 70% of the CO2 that would be required from a gasoline powered vehicle.
References :
November 29th, 2009 at 5:18 pm
CO2 is released when burning methane CH4 at a rate proportionate to the number of Carbons on each side of the Chemical balance of
CH4 + 2 *O2 = CO2 + 2 *H2O or 1 mole of CH4 makes 1 mole CO2.
1 mole (lb-mole) of CH4 weights 16 pounds and will make 44 pounds of CO2 or 2.75 pounds CO2/lb CH4.
As stated above you have to define a gallon of CNG at a set pressure and temperature.
Now lets look at your gasoline value. Gasoline is a whole bunch of different molecules but, we can assume gasoline is Octane C8H18.
C8H18 + 12.5 *O2 = 8 *CO2 + 9 * H2O, so 114 pounds of octane will make 352 pounds of CO2 .or 3.08 pounds of CO2 per pound of C8.
since all hydrocarbons have about the same energy per pound. methane will produce 2.75/3.08 or 90%. If you do take into account the slight BTU/lb difference, it works out that CNG produces 18% less CO2 per energy unit than gasoline.
References :