>>13548368Air volume is plain wrong.
The basic calculation is about converting every carbon atom into carbon dioxide and trace elements. Carbon atomic mass is 12.011 and Oxygen is 15.9994, if every carbon grabbed two oxygen, then the resulting weight of the molecule is approximately 44. This is 11/3 as much. Take the starting weight of gas and you have to isolate out what percentage of it is carbon mass. Hydrogen doesn't have too much mass at approximately 1.01 with a ratio of 1.87 Hydrogen per carbon atom. Taking the ratio of carbon mass to both hydrogen and carbon mass present gets about 85.6% of the mass is Carbon.
6.1lbs(0.856)(11/3) gets 19.2lbs.
Not all of the gas is converted to carbon dioxide and some small amount of fuel will exhaust.
http://web.mit.edu/2.61/www/Lecture%20notes/Lec.%2004%20Comb%20&%20thermochemistry.pdf 
