NOVELTY - A hybrid engine system (20) for producing energy from hydrocarbon fuel, includes internal combustion engine in communication with source of oxidizing fluid and source of hydrocarbon fuel; and heat exchanger providing heat exchange relationship between output of fuel cell cathode before or after cathode output passes through the oxidizer and portion of oxidizing fluid for preheating oxidizing fluid before the oxidizing fluid enters the cathode.    USE - The hybrid engine system is used for producing energy from a hydrocarbon fuel (claimed).    ADVANTAGE - The system is highly efficient in producing energy from a hydrocarbon fuel while maintaining low polluting emissions. The overall system efficiency is 35-50%.    DETAILED DESCRIPTION - A hybrid engine system for producing energy from hydrocarbon fuel, comprises:    (1) an internal combustion engine (21) in communication with a source of oxidizing fluid and a source of hydrocarbon fuel (24) producing power and an exhaust gas from the combustion of the hydrocarbon fuel and at least some of the oxidizing fluid, a fuel cell (50) producing power, the fuel cell and having an anode (51) in communication with a source of synthesis gas including hydrogen gas and a cathode in communication with at least some of the oxidizing fluid and having an anode output and a cathode output;    (2) an optional reformer (30) which if present is in selective communication with a portion of the exhaust gas from the internal combustion engine and in selective communication with a portion of the oxidizing fluid from the source and in communication with at least some of the hydrocarbon fuel for producing a synthesis gas including hydrogen as an input to the fuel cell anode;    (3) an oxidizer (60) in communication with exhaust gas from the fuel cell anode and in selective communication with the exhaust gas from the internal combustion engine and in selective communication with at least some of the oxidizing fluid before or after it passes through the cathode and having an output gas either as an input to the cathode or vented to the atmosphere after passing in heat exchange relationship with oxidizing fluid to preheat oxidizing fluid before the oxidizing fluid is introduced to the cathode;    (4) a heat exchanger providing heat exchange relationship between the output of the fuel cell cathode before or after the cathode output passes through the oxidizer and at least a portion of the oxidizing fluid for preheating oxidizing fluid before the oxidizing fluid enters the cathode; and    (5) a proportioning mechanism (70) connected to the output gases from the internal combustion engine and the source of oxidizing fluid to adjust the composition of gases entering the fuel cell anode and cathode to accommodate both lean burn conditions in which the air to fuel equivalence is greater than 1 and rich burn conditions in which the fuel to air equivalence ratio is greater than 1 in the internal combustion engine while providing a reducing atmosphere in the reformer if present and the anode and an oxidizing atmosphere in the oxidizer and the cathode to reduce internal combustion engine pollutants including emissions of nitrogen oxide (NOx), carbon monoxide (CO), and unburned hydrocarbons while achieving high overall system efficiency.    DESCRIPTION OF DRAWING(S) - The figure is a schematic illustration of the direct fired reforming heat engine-bottoming fuel cell hybrid.    Hybrid engine system (20)    Internal combustion engine (21)    Source of hydrocarbon fuel (24)    Reformer (30)    Fuel cell (50)    Anode (51)    Oxidizer (60)    Proportioning mechanism (70)