The characteristics of a combustor operating under submerged conditions are affected by the two phase interaction of exhaust gas jet from the combustor with surrounding liquid. The characteristics of combustion gases are simulated with air and helium to represent combustor operation under different conditions. The exhaust gas signatures under submerged conditions are examined using different nozzle exit cross-sections (circular, square, triangular and elliptical with aspect ratio of 1.5 and 2.5) for their effect on sound pressure levels and pressure fluctuations in the combustion chamber. High-speed cinematography is used to examine the two-phase region and the associated instabilities by the gas jet. Dynamic pressure sensor is used to study the effect of submerged jet on the pressure fluctuations in the upstream gas chamber. The sound pressure level from the elliptical nozzle is found to be lower than the circular, square and triangular nozzles. The frequency of jet instabilities is observed to increase with increase in gas jet momentum but independent of nozzle exit cross-section. The pressure fluctuation in the gas chamber is closely coupled with two phase instabilities downstream of the jet region. At lower jet momentum bubbling regime is present but it transitions to more jet like behavior with increase in the jet momentum, representing deep water and shallow water propulsion applications, respectively. These studies provide valuable fundamental information for range of applications in energy systems extending from underwater propulsion, evaporator, heater, desalination and waste water treatment. (C) 2011 Elsevier Ltd. All rights reserved.