Which fuel contributes least to global warming per kj of heat produced? which fuel contributes least to global warming per of heat produced? propane methane octane?

Methane would contribute the least to global warming per kilo-joule of heat that is produced. This is because of the three hydrocarbons methane is the simplest. One molecule of methane has only 1 atom of carbon while propane has three and octane has eight. This means that methane will produce less carbon dioxide per mole burned, while propane will be next followed by octane.