Experimental Inert Characterization of an Exhaust System Downstream of a CVC

Nowadays, multiple research institutes focus their interest on the Pressure Gain Combustion Cycles (PGC) due to their superior theoretical performance compared to the traditional Joule cycle. On the contrary of the quasi isobaric conventional burners, a PGC cycle achieves increment of total pressure during the combustion process by utilizing either the detonation mode or the deflagrative isochoric combustion. As a result, PGC integrated in a Gas Turbine cycle can offer larger inlet stagnation pressure and temperature for the work extraction by the subsequent turbine module significantly elevating the theoretical cycle efficiency. Under this context, a prototype Constant Volume Combustor (CVC) has been developed operating with a mixture of liquid iso octane and air. With the help of inlet outlet rotary valves and a spark plug ignitor, sequential isochoric combustion events are accomplished. The current work aims at experimentally investigating the peculiar outflow of this combustor. CFD optimization techniques provided a transition duct that can be mounted downstream of the CVC to integrate it with a High Pressure Turbine (HPT) stage. The profile of the transition duct was designed and manufactured to serve the demands of the experimental test rig. The outlet of this component is followed by a converging diverging circular nozzle. On the top and lateral side of the transition duct are inserted windows to allow for penetration of a laser sheet and the visual inspection of the transition duct. Particles of silicon oil are seeded upstream of the CVC chamber. Hence, PIV analysis is conducted in the exhaust part. In addition, pressure sensors monitor the evolution of the pressure in the chamber, the inlet and the outlet of the transition duct. This experimental campaign is considered inert as no injection or ignition is performed inside of chamber. The valve motion provide strong pressure fluctuation to the outtake system. The transition duct outlet is able to alleviate any vertical distortion in the velocity profile which is imposed by the exhaust valves. As a result, a smooth acceleration is achieved for every moment of the cycle. These results are promising for the integration of this peculiar PGC with a subsequent turbine, as the benefits of the CVC operation will not be deteriorated by excessive pulsating outflow towards the HPT.