A combustion system comprising a combustion chamber fed by fuel and oxidant delivery lines. The oxidant line has an oxidant tank pressurized by a compressor. The fuel delivery line has a fuel source and a fuel feed mechanism. An ignition device ignites the oxidant and fuel mixture in the combustion chamber. The coolant line is adapted to inject cooling fluid directly into the combustion chamber. An energy production device is disposed downstream a combustion chamber exhaust valve for converting energy from both exhausted combustion gases and coolant gases exhausted from the combustion chamber. In some embodiments the coolant is the oxidant, while in other embodiments the coolant is another fluid introduced from a separate coolant delivery line.