Abstract
Numerical simulations of the flowfield in a hybrid rocket engine are carried out with a multispecies chemically reacting Reynolds-averaged Navier–Stokes (RANS) solver which includes detailed gas–surface interaction (GSI) modeling based on surface mass and energy balances. The oxidizer is gaseous oxygen which is homogeneously fed into single-port cylindrical grains. The modeling of GSI already developed and validated for pyrolyzing fuels such as hydroxyl-terminated polybutadiene (HTPB), is extended to the case of liquefying fuels, such as paraffin wax. A simplified two-step global reaction mechanism is considered for the gas-phase chemistry to model the combustion process inside the chamber. Numerical simulations performed at different gas/melt-layer interface temperatures and oxygen mass fluxes show a considerable increase of fuel regression rate, in the range of 3 up to 5 times, for the liquefying fuel with respect to the pyrolyzing one. Results show that the regression rate enhancement is significant only when the gas/melt-layer interface of the liquefying fuel is close to the melting temperature. At increasing gas/melt-layer interface temperatures, the regression rate decreases following an inverse power law and gets close to that of a pyrolyzing fuel for the same operating conditions. Finally, regression rate behavior at varying oxygen mass flux of liquefying fuels is not substantially altered from that of pyrolyzing fuels as the oxidizer flux exponent remains rather constant.
Highlights
The intrinsic properties of hybrid propellant rockets in terms of performance, simplicity, safety, reliability, low development cost, reduced environmental pollution, and §exibility make them one of the envisaged future generation propul-© The Authors, published by EDP Sciences
The results presented here are restricted to single-phase system; in case of liquefying fuels, the entrained fuel liquid droplets are not modeled and the fuel is directly injected in a gaseous state from the gas/melt-layer interface. This is an approximation of the real phenomena as the liquid droplets do not vaporize directly at the surface but are rather transported inside the §ow¦eld and, they should not contribute to the blockage eect, which is typical of pyrolyzing fuels
The results show an increase of the para©n wax regression rate enhancement with respect to hydroxyl-terminated polybutadiene (HTPB) at increasing oxygen mass §ux
Summary
The intrinsic properties of hybrid propellant rockets in terms of performance, simplicity, safety, reliability, low development cost, reduced environmental pollution, and §exibility make them one of the envisaged future generation propul-. © The Authors, published by EDP Sciences. There are some technical challenges to be overcome before achieving the same level of maturity as solid and liquid traditional systems, such as low regression rate, reduced combustion e©ciency, and combustion instability. The hybrid rocket engine development requires deeper understanding of the physico-chemical phenomena that control the combustion process and of the §uid dynamics inside the motor. The knowledge of the complex interactions among §uid dynamics, solid fuel regression, oxidizer atomization and vaporization, mixing and combustion in the gas phase, nozzle thermochemical erosion, particulate formation, and radiative characteristics of the gas and the §ame can only be improved by combined experimental and numerical research activities
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