Авіаційно-космічна техніка та технологія (Aug 2019)
TO THE QUESTION OF THE THERMODYNAMIC DESIGN OF THE LRE CHAMBER
Abstract
Analysis of the thermodynamic and thermophysical properties of combustion products (CP) in the liquid rocket engine (LRE) chamber shows that their dissociation degree depends on temperature T, gas expansion degree ε, etc. Practically, CP’s are always chemically active working fluid, therefore the number of moles N of the products varies along the length of the LRE chamber in the entire reaction mixture. The local values of the parameters T and N depend on the specific physical conditions. Therefore, the distribution of local numbers of moles of the components of the gas mixture and its heat capacities can be represented as dependencies N~f(T) and c~g(T). For this purpose based on the numerical values of the moles and the heat capacities of the gas mixture components in the main sections of the LRE chamber are formed as corresponding empirical functions through interpolation. Analysis of changes in moles and weight fractions of gaseous and condensed СP’s components shows that, depending on the specific conditions (α, Km, pc, ε), the number of moles of one group of individual substances increases, while these parameters of the other group decrease. These changes are alternating in nature and lead to the formation of new centers -sources of chemical and thermal energy along the length of the LRE nozzle. Thus, for different conditions (α, Km, pc, ε), the design of the LRE chamber should be carried out taking into account the nature of the change in N, cp, cv, and γ. Therefore, from energy conversion, the number of moles of the i-th CP component can be represented as a function Ni = f(Ti) or Ni = f(x,y). Numerical studies show that, based on the Ni values in the main sections of the LRE chamber with a given length, it is possible to form linear or nonlinear empirical functions in the form Ni= f(x) by interpolation. Depending on the specific tasks, one of the interpolation functions can be taken into account in the formulas for calculating the specific heats of CP. In this case, to form the refined geometry of the LRE chamber, the thermo-gas-dynamic calculation is repeated taking into account new indicated dependencies. Consequently, the system of equations for the thermodynamic calculation of an LRE is solved taking into account new functions. This approach allows forming the optimal contour of the LRE chamber at the preliminary stage of engine design and improving the results of gas-dynamic calculation and profiling of the nozzle using a modified method of characteristics. In the framework of the presented studies, to obtain an optimal geometry for the LRE nozzle, are compared values of the velocities, which obtained using the solutions of the direct and inverse problems. Thus, the correct consideration of changes in the basic parameters along the nozzle length allows us to organize the correct operation of the LRE chamber by changing the thermal properties of CP along the nozzle length in all flight conditions of the flight vehicle. This circumstance requires some improvement of the principles and schemes of regulation systems of the LRE operation, which leads to the conduct of extensive researches in this direction.
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