POWERTRAIN SYSTEM

Provided is a power train system provided with a novel fuel reforming device capable of improving fuel economy by adjusting an operating state of an internal combustion engine depending on components of an auxiliary fuel synthesized from hydrogen and carbon dioxide which is emitted from the internal combustion engine. The auxiliary fuel including methane, as a main component, is synthesized from hydrogen and carbon dioxide which has been separated from the exhaust gas using a methane conversion catalyst 24. The auxiliary fuel is mixed with a main fuel to be burnt in an internal combustion engine 20, and a combustion start timing is adjusted by an ignition plug 39 of the internal combustion engine depending on the temperature of the methane conversion catalyst 24 or a combustion period is adjusted by a tumble generation valve 43. As a result, the operation of the internal combustion engine is appropriately controlled depending on the components of the auxiliary fuel to be synthesized to improve the thermal efficiency, thereby improving the fuel economy.