Background: The impulse for the propulsion of a rocket engine is obtained from the combustion of propellant mixture inside the combustion chamber and as the plume exhausts through a convergent-divergent nozzle.At stoichiometric ratio, the temperature inside the combustion chamber can be as high as 3500K. Thus effective cooling of the thrust chamber becomes an essential criterion while designing a rocket engine.
Objective: A new cooling method of thrust chambers was introduced by Chiaverni, which is termed as Vortex Combustion Cold-Wall Chamber (VCCW). The patent works on cyclone separators and confined vortex flow mechanism for providing high propellant mixing with improved degree of turbulence inside the combustion chamber provides the required notion for the studies on VCCW.The flow inside a VCCW has a complex structure characterised by axial pressure losses, swirl velocities, centrifugal force, flow reversal and strong turbulence. Inorder to study the flow phenomenon, both experimental and numerical investigations are carried out.
Methods: Non-reactive flow analysis is conducted with real propellants like gaseous oxygen and hydrogen. The test is done to analyse the influence of mixture ratio and injection pressure of the propellants on the chamber pressure in a vortex combustion chamber. A vortex combustor is designed in which the oxidiser injected tangentially at the aft end near the nozzle spirals up to the top plate and forms an inner core inside the chamber. The fuel is injected radially from injectors provided near the top plate. The propellants mix in the inner core. This results in enhanced mixing and increased residence time for the fuel. More information on the flow behaviour is obtained by numerical analysis in Fluent. The test also investigates the sensitivity of the tangential injection pressure on the chamber pressure development.
Results: All the test cases showed an increase in chamber pressure with the mixture ratio and injection pressure of the propellants. The maximum chamber pressure is found to be 3.8 bar atPC1 and 2.7 bar at PC2when oxidiser to fuel ratio is 6.87. There is a reduction in chamber pressure of 1.1 bar and 0.7 bar at PC1and PC2 respectively in both cases when hydrogen is injected. A small variation in the pressure of the propellant injected tangentially made a pronounced effect on the chamber pressure and hence vortex combustion chamber is found to be very sensitive to the tangential injection pressure.
Conclusion: VCCW mechanism is found to be very effective for keeping the chamber surface with in the permissible limit and also reduce the payload of the space vehicle.