Another consideration is the amount of CO2 emitted into the atmosphere by the fuel you burn. Of the three fuels discussed here, oil is by far the worst, at 161.4 lbs. of CO2 per million Btus produced. Propane is considerably better, creating 139.05 lbs. of CO2 per million Btus. Natural gas is best, at 117 lbs. of CO2 per million Btus.
The maximum burning velocity of hydrogen-air mixtures is about eight times greater than for methane-air and propane-air mixtures and occurs at about 40 vol% hydrogen in air. The high burning velocity of hydrogen is an indication of its high explosive potential and the dificulty of confining or arresting hydrogen flames and explosions.
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