Study of inline-slot ejector diffuser under varying ambient conditions: A passive infrared suppression device for ships

Passive infrared (IR) suppression device, commonly known as ejector diffuser, is an integral part of the defence system of a ship. The definitive role of passive IR suppressor to counter the IR tracking and locking of the ship has made them indispensable for any combat marine. The gas turbine exhaust gases are the leading heat source on a ship. The exhaust temperature of the gases ranges between 650K-850K. At such temperatures, the ship can be easily detected by the enemy through IR imaging. The role of the ejector diffuser is to (i) lower the gas turbine exhaust gases temperature to the limits (< 450K) such that the IR locking of the marine can be avoided, and (ii) recover static pressure such that the engine performance of the gas turbine is not affected. Ejector diffuser has the ability to entrain ambient air and allow mixing it with the exhaust gases thereby, lowering the temperature of the exhaust gases. However, the mixed exhaust gases temperature depends on the ambient air temperature which under extreme conditions can fluctuate from 273K to 323K. This temperature range can affect the temperature characteristics of an ejector diffuser. The present study undertakes the effect of ambient temperature on the performance of inline-slot ejector diffuser. The ambient temperature (T0) has been varied in the range 273K ≤ T0 ≤ 323K in the step of 10K. It has been found that the mass entrainment increases (≈ 8%) as the ambient temperature decreases. The core temperature at the exit decreases, from 457.58 K to 417.75K, with a decrease in the ambient temperature. However, no significant changes in static pressure recovery.