Experimental Investigations On Outlet Combustion Flow Field Of RBCC Engine By Using TDLAS Technique

Rocket Based Combined Cycle(RBCC) engine combines rocket with ramjet together, and also combines the high thrust to weight with the high specific impulse efficiency advantages. It can work at the wide Mach number through the modal transition, which has a promising prospect for development and application.Enormous challenges come along with the rapid development of research of RBCC engine, as the research gradually focuses on the detailed combustion mechanism, more advanced measurement and combustion diagnosis methods are needed to get more accurate combustion flow field parameters. Tunable Diode Laser Absorption Spectroscopy(TDLAS) technique has the advantages of non-contact measurement, high time resolution, wide measurement range and so on, it can meet the needs of parameters measurement of RBCC engine combustion flow field. But large numbers of carbon particles generate during the combustion of kerosene fuel RBCC engine which produce strong flame radiation. Thus the application of TDLAS on RBCC engine is influenced.In present study, the theoretical basis of TDLAS is introduced at first, two direct-absorption-spectroscopy techniques and their parameters measurement principles in detail. Problems occur when the TDLAS system is used for the measurement of outlet flow field of kerosene-fueled RBCC engine and are solved by some optimized schemes. The TDLAS system is finally successfully used for the combustion diagnosis of outlet flow field of RBCC engine.Then the optimized TDLAS system is used for the temperature measurement of the outlet flow field of RBCC engine with pylon injection at the Mach number of 5.5. H2 O absorption spectrum is obtained in this case, and temperature-time curve is calculated based on the TDLAS temperature measurement principle. The temperature measurement of the 120 g/ s fuel-injection case agrees well with the CFD result. Temperature measurements of outlet flow field of RBCC engine are carried out for different cases. Though the comparative analysis of TDLAS measurement results and flame states of different stages and experiments, references are provided for the combustion optimization and the fuel injection law.In addition, the limitations of TDLAS cross-beam velocity measurement method based on the Doppler effect is analyzed. A velocity measurement method which combines TDLAS with the cross-correlation method is put forward, and is used for the velocity measurement of outlet flow field of RBCC engine at the Mach number of 6. The result shows that this method can realize velocity online measurement of outlet flow field of RBCC engine effectively.