Abstract: An apparatus is provided for controlling gas temperature during compression or expansion. The apparatus comprises a chamber for containing gas, a piston for changing the volume of gas in the chamber, a plurality of atomisers for spraying liquid into the chamber and means for delivering liquid to the atomisers. Each atomiser comprises a spray aperture and means defining a flow path for imparting rotary motion to the flow of liquid about the axis of the aperture so that on leaving the aperture the liquid divides into a conical spray. Spray apertures are positioned adjacent one another and the axes of adjacent spray apertures are oriented such that their respective sprays intersect at a position proximate at least one of the respective adjacent spray apertures.

Abstract: A gas compressor is provided comprising a chamber (9) to contain gas to be compressed, a piston (12) and the chamber (9) and an apparatus to drive the piston into the chamber (9) to compress the gas. The compressor also comprises another apparatus (5) to form a spray of liquid in the chamber (9) to cool the gas on compression therein, so that the gas may be compressed approximately isothermally. Valve (17) are provided to allow compressed gas to be drawn from the chamber. The apparatus to drive the piston (12) comprises another apparatus to deliver driving energy stored in the fluid directly to the piston. In one embodiment, the driving energy is provided by a combustible fuel. The heat of compression is rejected at the lowest temperatures and the hot exhaust gas from the combustion process may be used to preheat the isothermally compressed gas.