| Direct-connected air heater of low total temperature is mainly applicable for directconnect testing of scramjet, and the key technology is the guarantee of easy ignition,stable combustion, high quality of the outlet, as well as reliable thermal protectionmeasures in the surface of combustion chamber. A certain air heater based on thecombustion chamber of liquid rocket engine (LRE) is investigated by numericalsimulation and experiment to study the process of atomization and combustion, besides,acquire effects of structural or operating parameters on performances of the air heater.First of all, the atomization performance of tripropellant coaxial shear injectorsapplied in the air heater was investigated through the atomization experiment; moreover,influences of injector configurations and operation parameters on the discharge andatomization characteristics were analyzed in detail. Research results show that: thedischarge coefficient of injector is affected synthetically by the shear of gases, thepressure drop of air, the recess of injectors and the fluid viscosity. The gaseous phaseobviously improves the atomization effect, and increases the spray cone angle, while therecess of injectors and the circular seam area of air basically have no impact on thespray cone angle. Similarly, the Sauter Mean Diameter(SMD) of particle is influencedby the pressure drop of gases, the recess of injectors and the circular seam area of air,and the SMD in the same section increases with the accretion of pressure drop of gaswithin a certain range, whereas the SMD increases first and then decreases along withthe increase of the recess, furthermore, the SMD decreases with the increase of circularseam area of air. The distribution of the particle size agrees well with theRosin-Rammler function.Secondly, a numerical simulation model and calculation method suitable in spraycombustion of the air heater was developed, which was based on the existing theoreticalmodel to simulate the flow field of internal combustion, moreover compared with theresults of thermodynamic calculation and the test after validating the grid independenceunder the same conditions, which validated the correctness of the numerical calculation.Furthermore, effects of structural or operating parameters on the flow field ofcombustion were studied in thesis, and based on which, effects of the installation ofplug, as well as various positions of installation on performance of air-heater were putforward, simultaneously simulated. The results show that: the flow filed of combustionwith first/second precision nearly show no difference, and the quality of the outletindicated high; thermal protection of gas pipes improved by reducing the inclination ofmixing holes and increasing the number of mixing holes in single row; the state ofpropellant directly affects the structure of the flow field and the uniformity of the outlet;different injector configurations may affect the thermal protection of injection panel and the combustion performance of air-heater; the installation of plug is conducive to theuniformity of the flow field, while this effect varies with installation position of plug.Finally, hot-fire tests of air-heater were performed, and the distribution of totaltemperature on the outlet was measured by the designed rake of total temperature,additionally, effects of different flow ratio of air and aperture of clapboard on theignition characteristics, the combustion efficiency, as well as the uniformity of the outletwere investigated. Furthermore, cases involved in firing tests of air-heater were studiedthrough the method of numerical simulation. The investigation indicates that: theperformance of air-heater basically can meet the designed requirements, and there existsan area with low pressure in the upstream of mixing chamber; an optimal ratio existedbrings the highest combustion efficiency; combustion performance of air-heaterimproved by increasing the aperture of clapboard appropriately. |
PDF Full Text Request