Natural gas deserves to be a primary fuel for automotive engines because of the abundant supply in the world. As a gaseous fuel, natural gas differs from liquid petroleum and biofuels fundamentally in combustion. The primary constituent of natural gas, methane (CH4), is a very stable species that is difficult to burn completely. The activation energy for methane oxidation is much higher than most other hydrocarbon fuels. Therefore, a high flame temperature is generally required to oxidize methane completely.