Motor vehicle comprises a combustion engine with internal combustion of fuel and/or cold-flame product for driving the motor vehicle and thereby producing exhaust gas and an auxiliary power unit comprising an external burner and an expansion machine. A fuel tank with fuel provides energy to the burner and the combustion engine. The motor vehicle has a cold-flame-reactor with means for feeding the fuel from the fuel tank to the cold-flame reactor, and at least a portion of the fuel is pre-combusted to a cold-flame product in the cold-flame reactor.