ИСТИНА

Solid-fuel scramjet engines (SFScRE) are considered to be promising propulsion systems of unmanned aerial vehicles. A feature of the workflow in these engines is that the used solid fuels contain a minimum quantity of oxidizing components and incapable to self-sustained combustion. Solid fuel combustion occurs in a forced mode: due to heat supplied from the high-speed flow in the grain channel, the gasification (decomposition) of solid fuel occurs; the products of gasification enter the flow and burn out there, providing the thrust. In order to stabilize the solid fuel combustion in SFRE, the solid fuel grains with a profiled channel are used. It was established experimentally that the steady combustion of solid fuel in SFScRE is possible only at a certain shape and size of the flame holder, but the detailed mechanism of stabilization of combustion is not completely clear. In this study, polymethylmethacrylate (PMMA) was taken as the solid fuel. We consider the model of PMMA combustion and show that PMMA combustion can occur in different modes. The expression for mass rate of PMMA gasification has been obtained and used for calculation of the process in the solid-fuel scramjet combustor. The multicomponent gas mixture is described by the Reynolds-averaged Navier-Stokes equations (RANS) in the fully compressible formulation. Five mixture components are considered: , , , , . The temperature of gas mixture was determined from its total energy and composition by solving a corresponding nonlinear equation. Turbulence is described by the standard model, the gas-phase combustion rate is described by the Eddy Break-up (EBU). The heat flux from the gas phase onto the fuel surface required for calculation of the solid fuel gasification mass rate was determined from wall functions for the temperature. The governing equations are solved in the axisymmetric framework by an explicit finite-volume high-resolution scheme on a uniform Cartesian grid. The solid fuel surface, generally, does not coincide with cell boundaries of Cartesian grid. In this work, we apply the “embedded” sharp interface approach. The approach of “embedded” internal boundaries allows describing the shape change without the need to rebuild the mesh each time the solid fuel shape changes. Numerical simulations were carried out for the geometry which resembles closely the well-known experiments. The results of numerical simulations obtained for different initial conditions and different geometries on the combustor are discussed. We show that the model under consideration allows describing the instability of SFScRE operation and we investigate the range of the parameters of SFScRE which correspond to stability of solid fuel combustion in such a combustor.