Full-scale Solid Rocket Motor Research Articles

Studies on Aluminum Agglomeration and Combustion in Catalyzed Composite Propellants

Composite propellants are tested using the quench particle collection bomb (QPCB) for the pressure ranging from 2 to 8 MPa to estimate the particle size distribution of aluminum agglomerates from quenched combustion residues emerged out from the burning surface. The major ingredients included in the propellants are ammonium perchlorate (AP), aluminum (Al), hydroxyl-terminated polybutadiene (HTPB), and toluene diisocyanate (TDI). Five propellant compositions are considered in this study; two of them are mixed with catalysts. Propellant formulation variables like the coarse AP/fine AP ratio, total solid loading, catalyst percentage, and aluminum content are varied to assess their effects on the aluminum agglomeration process at different pressures. Unburnt aluminum in agglomerates is continuously getting combusted as they move out from the propellant burning surface. Large agglomerates comprise both Al2O3 and unburnt aluminum. The majority of agglomerates are spherical in shape, and the sizes vary from 31 to 115 $$\mu$$ m for non-catalyzed propellants and from 28 to 136 $$\mu$$ m for catalyzed propellants over the tested pressure conditions. These results can give further insight into the aluminum agglomeration process of catalyzed and non-catalyzed propellants and also affect the choice of the propellant ingredient percentage aimed at reducing aluminum agglomeration, which causes two-phase flow losses of thrust and slag accumulation in full-scale solid rocket motors.

Nonlinear time-series analysis of thermoacoustic oscillations in a solid rocket motor

Recent applications of nonlinear time-series analysis have shown that thermoacoustic systems can exhibit self-excited behavior more complex than simple period-1 oscillations. Such behavior has been comprehensively explored in the Rijke tube and in gas turbines, but less so in rocket engines. In this experimental study, we examine the thermoacoustic oscillations of a full-scale solid rocket motor (SRM) by means of nonlinear time-series analysis, namely phase portraits, Poincaré maps and recurrence plots. In contrast to conventional linear tools based on the Fourier transform, these nonlinear tools can enable unambiguous identification of different dynamical states, such as period-k states, quasiperiodicity and chaos. In this study, these tools reveal limit-cycle dynamics not reported before in an SRM, such as transient mode switching between unstable attractors in phase space, with transitions between period-2 and period-3 states. In summary, this study constitutes the first experimental application of nonlinear time-series analysis to a full-scale SRM, demonstrating an alternative to conventional linear tools for the characterization of nonlinear thermoacoustic oscillations in rocket engines.

Influence of different propellant systems on ablation of EPDM insulators in overload state

This study examines the propellants used in full-scale solid rocket motors (SRM) and investigates how insulator ablation is affected by two propellant formulations (A and B) during flight overload conditions. An experimental study, theoretical analysis, and numerical simulations were performed to discover the intrinsic causes of insulator ablation rates from the perspective of lab-scaled ground-firing tests, the decoupling of thermochemical ablation, and particle erosion. In addition, the difference in propellant composition, and the insulator charring layer microstructure were analyzed. Results reveal that the degree of insulator ablation is positively correlated with the propellant burn rate, particle velocity, and aggregate concentrations during the condensed phase. A lower ratio of energetic additive material in the AP oxidizer of the propellant is promising for the reduction in particle size and increase in the burn rate and pressure index. However, the overall higher velocity of a two-phase flow causes severe erosion of the insulation material. While the higher ratio of energetic additive to the AP oxidizer imparts a smaller ablation rate to the insulator (under lab-scale test conditions), the slag deposition problem in the combustion chamber may cause catastrophic consequences for future large full-scale SRM flight experiments.

Influence of source level, peak frequency, and atmospheric absorption on nonlinear propagation of rocket noise

Nonlinear propagation effects in rocket noise have been previously shown to be significant [M. B. Muhlestein et al. Proc. Mtgs. Acoust. (2013)]. This paper explores the influence of source level, peak frequency, and ambient atmospheric conditions on predictions of nonlinear propagation. An acoustic pressure waveform measured during a full-scale solid rocket motor firing is numerically propagated via generalized Burgers equation model for atmospheric conditions representative of plausible spaceport locations. Cases are explored where the overall sound pressure level and peak frequency has been scaled to model engines of different scale or thrust. The predicted power spectral densities and overall sound pressure levels, both flat and A-weighted, are compared for nonlinear and linear propagation for distances up to 30 km. The differences in overall level suggest that further research to appropriately include nonlinear effects in launch vehicle noise models is worthwhile.

Carbon-Carbon Nozzle Erosion and Shape-Change Effects in Full-Scale Solid-Rocket Motors

The erosion of nozzle protection materials during solid-rocket-motor burning needs to be accounted for to get reliable performance predictions, especially for long-durationfirings.A study is conducted topredict carbon–carbon nozzle erosion behavior in full-scale solid-rocket motors for wide variations of motor operating conditions. The numerical model considers the solution of Reynolds-averaged Navier–Stokes equations in the nozzle, heterogeneous chemical reactions at the nozzle surface, ablation species injection in the boundary layer, variable multicomponent transport and thermodynamic properties, and heat conduction in the nozzlematerial. Two different ablationmodels are considered: a diffusion-limited approach and a finite-rate approach. The numerical model is used to study the erosion of carbon–carbon nozzle inserts for the secondand third-stage solid-rocket motors of the European Vega launcher. The effect of variable chamber pressure over the burning time and the effect of nozzle shape change on the erosion rate are taken into account in the numerical analysis. The obtained results show a very good agreement with the measured final eroded profile along the entire carbon–carbon nozzle throat insert for both motors. The shapechange effect is shown to be an important factor that has to be taken into account to get a goodprediction of the throat erosion for long-duration firings.

Rocket motor microphone investigation.

At ATK's facility in Utah, large full-scale solid rocket motors are tested. The largest is a five-segment version of the reusable solid rocket motor, which is for use on the Ares I launch vehicle. As a continuous improvement project, ATK and BYU investigated the use of microphones on these static tests, the vibration and temperature to which the instruments are subjected, and in particular the use of vent tubes and the effects these vents have at low frequencies.

Empirical Methods to Estimate Burn Rate Scale up Factor from Sub scale to Full Scale Solid Rocket Motors

Two empirical methods to estimate the burn time of full scale motors (FSMs) are presented. The static test data of sub-scale motors and other FSMs provide the necessary input for the use of these methods. The applicability of these methods was verified by comparing the predicted values with actual values which were found to match closely. Advantages and disadvantages of each method are discussed.