Suppressing the Infrared Signatures of Marine Gas Turbines

The exhaust plumes and visible areas of the engine exhaust ducting associated with marine gas turbines are major sources of infrared (IR) radiation on ships. These high-radiance sources make excellent targets for IR-guided threats. In recent years significant efforts have been made to reduce or eliminate these high-radiance sources to increase the survivability of naval and commercial ships when sailing in high-risk areas of the world. Typical IR signature suppression (IRSS) systems incorporate film cooling of visible metal sources, optical blockage to eliminate direct line-of-sight visibility of hot exhaust system parts, and cooling air injection and mixing for plume cooling. Because the metal surfaces radiate as near black bodies, every attempt is made to reduce the temperatures of the visible surfaces to near ambient conditions. The exhaust gases radiate selectively and therefore do not have to be cooled to the same degree as the metal surfaces. The present paper briefly describes the motivation for incorporating IRSS into the exhaust systems of marine power plants. IRSS hardware developed in Canada by the Canadian Department of National Defence and Davis Engineering Limited is presented along with details of their operating principles. A typical installation is presented and discussed. Design impacts on the ship are described with reference to engine back pressure, noise, and weight and center of gravity effects.