An auxiliary power unit includes an autothermal reformer for producing a reformate from fuel; a turbine; a combustor for burning the reformate to power the turbine; a recuperator for obtaining thermal energy to improve the efficiency of the auxiliary power unit; a steam generator for using thermal energy from the recuperator to produce steam from a water supply; a condenser for recovering the water from turbine exhaust; and an electrical generator coupled to the turbine for producing electrical power. Recovered heat and water are used with the autothermal reformer to produce rapid and complete combustion of the fuel with a relatively low concentration of emissions.