To provide an engine, capable of reducing the consumption of the oxygen in the air, suppressing the rate of generation for carbon dioxide gas and emitting a large output with smollee amount of fuel by using ammonium nitrate as a main oxygen source, as compared with the arrangement where oxygen in the air is utilized chiefly.

From an air/ammonium nitrate supply valve 12, air and ammonium nitrate spherical particles 19 are supplied to a main combustion chamber 5. When a mixture gas f the fuel and air in an aux. combustion chamber 1 is ignited by an ignition plug 3, the mixture gas undergoes combustion to produce a high-temperature gas which is injected into the main combustion chamber 5 from a jet 4, and the ammonium nitrate captured by a dimple 8 is pyrolyzed to result in generation of oxygen. With this oxygen generated from ammonium nitrate, the uncompensated fuel is combusted, and the combustion gas generated moves a piston 7. With the piston motions, the power is taken out from a crank 16.