| Doing some back of the envelope stuff...
I read that you can usually drive 180-200 miles on 1 full CNG tank in the CNG Honda...so I will use that as a basis.
190 miles in a car getting 30 mpg conventional gasoline will emit about 125 pounds of CO2.
If one tank of CNG is worth about 8 GGE (and assuming natural gas is only methane), then driving on one tank (about 190 miles) will emit about 110 pounds of CO2.
This seems reasonable....natural gas does have a lower carbon content than other fuels, but it still results in a lot of CO2 emissions. The CNG cars will certainly result in less emissions of other kinds...but when it comes to global warming arguments, you only get an 8% improvement in CO2 emissions at the tailpipe. If the CO2-cost of extracting, transporting, compressing, etc. the natural gas is less than the CO2-cost of similar processes for gasoline, then this improvement could be a bit more than 8%. |