Development of Engine Intake Anti-Icing Systems for LCAC

Abstract

US Navy ships operating in cold weather require the protection of an engine intake air anti-ice system to prevent blockage of combustion airflow during snow and icing conditions. This requirement does not present any unusual design demands on large displacement type ships because there is more available space, an abundance of usable thermal energy, and lastly their design allows engine weather intakes to be placed in relatively protected locations. However on small craft such as the Navy’s Landing Craft Air Cushion (LCAC), intake air anti-icing presents a unique design challenge. This is due to the spray generated by venting of the craft’s pressurized air cushion during normal over-water operations that results in significant carry-over of this spray onto the cargo deck, from which it is subsequently ingested into the engine intakes. LCAC is also powered by gas turbines that require large quantities of inlet combustion air for power generation. Because of these considerations the thermal energy required for intake anti-icing on LCAC are significantly higher than for large displacement type ships. Adding to this challenge are the facts that on-board space in an air cushion vehicle is at a premium, and power for thermal energy must be obtained from existing sources whose primary function is other than anti-icing. This paper will trace the development and evolution of LCAC’s engine intake anti-ice systems from the craft’s initial design, through to the present systems used in the fleet. It will present the tradeoff issues that effected selection of the anti-ice systems, such as energy availability, cold weather criteria, and craft design constraints.