Theoretical And Experimental Study On The Working Process Of The Solid Fuel Scramjet Combustor

In order to research the performance of the solid fuel scramjet combustor, on the basisof the two-dimensional numerical flow field results, a quasi-one-dimensional numericalmethod was established. A solid fuel regression rate model was coupled into the quasi-onedimensional flow equation that contains the area increment, the mass increment, the frictionbetween the flow and the wall, and the heat increments. The solid fuel regression rate wasset as a function of flow paremeters of the combustor and the mass increment of the flowequation was set as a function of fuel regression rate as well. Then the flow parameters andthe fuel regression rate could be calculated together. According to the regression rate andthe combustor diameter in previous moment, the combustor diameter of the next momentcould be acquired. The unsteady combustion and flow matter in the combustor wassimplified into a steady calculation of every moment by solving the boundary condition atdifferent moment independently. The numerical results was compared to actualexperimental data from the literature, and it was consistent with the experiment well. Thismethod can be used to analysis and design the solid fuel scramjet combustor quickly.Base on the characteristics of the solid fuel scramjet combustor and basic rules of thesupersonic combustion, an initial design theory of the solid fuel scramjet combustor wasput forward. There are three major elements of this theory: one is that the combustonr couldself-ignite and the flame can be held; the second one is that the fuel/air ratio should beappropriate; the last one is that the combustor wouldn’t be choked and the Mach numbershouldn’t be overlarge to decrease the total pressure loss as much as possible. Using thequasi-one-dimensional numerical code, a quasi-one-dimensional design method of thecombustor was fiured out. And then an engineering design method was established bysimplifying the combustion and flow of the solid fuel scramjet to the one-dimentional heatpipe flow.A methane-burning vitiated air heater was designed and made to simulate the flightenvironment of high Mach number and high altitude. This air heater has three advantages:start quickly, work steady, few pollutants. Then the ability of self-ignite and flame holding and the fuel regression rate of each moment and the average fuel regression rate of thecombustor were got by the experiments. It was found that the locations of largest fuelregression rate were at the junction of the cavity and the straight combutor and the junctionof the straight combustor and the expanding combustor. Moreover, the changing rule of thecombustor structure and other paramaters were researched using both numerical andexperimental methods. It was found that: during the working process, the cavity will bebigger and deeper, but the form of the cavity changes little and the flame can be held by thecavity; the rear segment of the straight combustor will be disappeared and will be integratedwith the expanding combustor; the expansion ratio of the expanding combustor will bedecreased; the fuel regression rate in the cavity is small and increase along the axis; beforethe junction of the straight combustor and the expanding combustor disappeared, the fuelregression rate of the straight combustor first decrease and then increase, but after thejunction disappeared, the fuel regression rate decrease along the axis; the fuel regressionrate in the expanding combustor decrease along the axis; the local fuel regression rate at aspecific position decreases gradually with time; as the combustion area increase with time,the mass flow rate at the combustor exit and the fuel/air ratio is relatively steady; the Machnumber in the combustor increase due to the diameter of the combustor increasing; the totalpressure recovery coefficient and the specific impulse of the combustor declines gradually.The influence of inlet airflow parameters on the combustor performance wasresearched at the last section. It can be found that: under the premise of a certain flightconditions, enhancing the total pressure or enlarging the total tempreture or decreasing theMach number could increase the fuel regression rate and minish the length of thecombustor and increase the specific thrust; the total temperature had the greatest influenceon the properties of the combustor. Then the influence of cavity sizes on the combustorperformance was researched too. It was found that: in under the premise of an acertaincombustion efficiency, enlarge the the relative diameter of the cavity outlet will increase theMach number and total pressure loss, will decrease the fuel regression rate and increase thelength of the combustor, will decrease the specific thrust; however, the changing of thedepth and length of the cavity influence the pefermance of the combustor little. At last the influence of flight environment on the property of the solid fuel scramjet was studied. Itwas found that: with the increasing of flight Mach number, the specific thrust first increaseand then decrease and the biggest specific thruse appear at the designed working point; thespecific of the inpulse decrease; with the increasing of the flight altitude, the specificinpulse first increase and then decrease and the biggest specific inpulse appear at thedesigned working point too; but the specific present a small increasing.