Ballistic Evaluation Motor Research Articles

Cold-Crafted KNSu Mechanically Pressed Burning Rate for Combustion Pressure Ranging from 0.9 to 7.7 bar

ABSTRACT Potassium nitrate/sucrose propellant (KNSu) is a common solid propellant, which can be cold or hot crafted, employed in amateur and experimental model rockets. There is limited burning rate data available for the KNSu, particularly for the cold-crafted one. In this study, KNSu composed of 65% potassium nitrate and 35% sucrose was prepared through cold crafting and by pressing with a hydraulic press. For such a particular crafting method, we did not find any experimental data on the burning rate versus combustion pressure. Therefore, we experimentally determined the cold-crafted KNSu burning rate for pressure levels ranging from 0.9 to 7.7 bar. We employed a ballistic evaluation motor with varying nozzle diameters to obtain the desired combustion pressure. We demonstrate that the cold-crafted KNSu burning rate lies in the range of available data for the hot-crafted version. The burning rate is not sensitive to combustion pressure levels lower than 2 bar, and the combustion temperature is 98.7% of the theoretical value. We also explain the estimation the combustion pressure from the thrust-plotted curve or by using the engine burning video.

Conjugate Analysis of Silica-Phenolic Charring Ablation Coupled with Interior Ballistics

Because of its excellent insulation capability, the usage of a silica-phenolic charring ablator as a nozzle liner is a common practice in the solid rocket motor industry. During the design of a solid rocket motor employing a silica-phenolic nozzle liner, it is desired to conduct an accurate analysis yielding in-depth thermal response and recession characteristics. As the interior ballistics and nozzle recession rate mutually interact, the best practice is to perform a coupled solution to both. Commonly used one-dimensional analysis tools with empirical approaches for estimation of convective heat transfer rate and blowing effect generally lack sought accuracy and do not model the transient shape-change phenomenon, which affects the nozzle performance. This Paper considers governing equations for charring, including pyrolysis gas injection and surface energy balance for melting ablation, along with a boundary condition governed by interior ballistics, and demonstrates a framework in which these equations are solved with governing equations for the nozzle flowfield in a coupled manner. Development and validation of a one-dimensional material response solver based on the same governing equations is also demonstrated. Also, results from a static firing test conducted with a small-scale ballistic evaluation motor employing a silica-phenolic nozzle insert are provided. Results from both investigations are compared and discussed.

Ballistic and mechanical characteristics of paraffin-based solid fuels

In a hybrid rocket, paraffin-based fuels are characterised by high regression rates and zero chemical explosion potential. However, paraffin wax is a brittle material and exhibits poor mechanical strength. The production of large-scale paraffin motors is a challenging task because of the poor structural performance of such motors. The addition of polymers and metallic additives to paraffin wax can considerably enhance mechanical performance. In this study, three different paraffin-based fuels, namely paraffin–aluminium (P–Al), paraffin–boron (P–B), and paraffin–carbon black (P–CB), were prepared using polyethylene (PE) polymer additive. The effects of these additives on the thermal, mechanical, and ballistic performance of the paraffin-based fuels were examined. The mechanical strength of these fuels was evaluated using compressive tests. Differential scanning calorimetry (DSC) experiments were performed to study the thermal decomposition of these paraffin-based fuels. A lab-scale ballistic evaluation motor was used to study the regression rates in a gaseous oxygen environment. The results revealed that the addition of the polymer and metallic additives improved the mechanical strength of fuels. The DSC results demonstrated that the addition of the additives accelerated oxidation and improved the heat release rate during combustion. The oxidation enthalpies for the P–Al, P–B, and P–CB samples were 291, 274, and 268 J/g, respectively. Finally, the ballistic results indicated that the regression rate decreased when 10 wt% PE was added to the paraffin wax, and such depreciation of regression rate due to polymer addition was compensated by the addition of the Al, B, and CB additives.

Acceleration methods for multi-physics compressible flow

In this work we investigate the Runge–Kutta (RK)/Implicit smoother scheme as a convergence accelerator for complex multi-physics flow problems including turbulent, reactive and also two-phase flows. The flows considered are subsonic, transonic and supersonic flows in complex geometries, and also can be either steady or unsteady flows. All of these problems are considered to be a very stiff.We then introduce an acceleration method for the compressible Navier–Stokes equations. We start with the multigrid method for pure subsonic flow, including reactive flows. We then add the Rossow–Swanson–Turkel RK/Implicit smoother that enables performing all these complex flow simulations with a reasonable CFL number. We next discuss the RK/Implicit smoother for time dependent problem and also for low Mach numbers. The preconditioner includes an intrinsic low Mach number treatment inside the smoother operator. We also develop a modified Roe scheme with a corresponding flux Jacobian matrix. We then give the extension of the method for real gas and reactive flow. Reactive flows are governed by a system of inhomogeneous Navier–Stokes equations with very stiff source terms. The extension of the RK/Implicit smoother requires an approximation of the source term Jacobian. The properties of the Jacobian are very important for the stability of the method. We discuss what the chemical physics theory of chemical kinetics tells about the mathematical properties of the Jacobian matrix. We focus on the implication of the Le-Chatelier's principle on the sign of the diagonal entries of the Jacobian. We present the implementation of the method for turbulent flow. We use a two RANS turbulent model – one equation model – Spalart–Allmaras and a two-equation model – k–ω SST model. The last extension is for two-phase flows with a gas as a main phase and Eulerian representation of a dispersed particles phase (EDP). We present some examples for such flow computations inside a ballistic evaluation rocket motor.The numerical examples in this work include transonic flow about a RAE2822 airfoil, about a M6 Onera wing, NACA0012 airfoil at very low Mach number, two-phase flow inside a Ballistic evaluation motor (BEM), a turbulent reactive shear layer and a time dependent Sod's tube problem.

Observation in Ballistic Evaluation Motor Static Firing: Cracking in Graphite Nozzle

Observation in Ballistic Evaluation Motor Static Firing: Cracking in Graphite Nozzle

Evaluation of Nanoaluminum in Composite Propellant Formulation Using Bicurative System

The incorporation of nanoaluminum in an 86% solid composite propellant formulation poses processing problems when following conventional methods. Therefore, to accommodate an optimum percentage of nanoaluminum in such formulations, a new bicurative system was introduced. Summarizing in the present study, a bicurative system consisting of toluene diisocyanate and isophorone diisocyanate was chosen to enable incorporation of 18% nanoaluminum powder (93 nm) in place of 18% micrometer-sized Aluminum powder. The developed compositions were studied in detail for their mechanical, thermal, sensitivity, and ballistic properties. The mechanical properties data, such as tensile strength, modulus, and percentage elongation, are almost on par with the values obtained with micrometer-sized aluminum powder using a developed bicurative system. The results of thermal properties reveal that, as the percentage of nanoaluminum increases in the composition, the onset decomposition temperature decreases. The impact and friction sensitivity data indicate that the sensitivity of the propellant formulation increases in comparison to micrometer-sized aluminum powder propellant. The ballistic properties, such as burning rate and ballistic evaluation motor data, reveal that there is more than a 110% increase in burning rate and a gain in specific impulse on the order of 6 s in comparison with propellants using micrometer-sized aluminum powder.

A Study of Basic Aluminized Propellants Characteristics

There were very limited number of references published discussing the burning characteristic of aluminized propellant without any additive substance. This paper describes the performance characteristics of basic formulations of aluminized ammonium perchlorate based propellant. Four sets of propellant formulations namely by p60, p66, p74 and p80 had been formulated and manually prepared without adding any additives. The propellant consists of ammonium perchlorate (AP) as an oxidizer, aluminum (Al) as fuel and hydroxy-terminated polybutadiene (HTPB) as fuel/binder. For each mixture, HTPB binder composition was fixed at 15% per-weight. By varying AP and Al, the effect of oxidizer-fuel (O/F) ratio on the whole propellant can be determined. The propellant strands were manufactured using press-molding method and burnt in a strand burner over a range of chamber pressure from 6 atm to 31 atm. Based on theoretical evaluation using NASA CEC71 program, p66 has been selected for testing in ballistic evaluation motor (BEM) to ascertain its characteristics performance. The results from burning rate test shows that the increasing of O/F ratio and combustion pressure lead to the increase in burning rate. The highest burning rate achieved was 12mm/sec at combustion pressure of 31atm for propellant p80 which has O/F ratio of 4.0. While for the BEM, the propellant efficiency obtained for p66 was 95.44%.

Parametric Studies on Star Port Propellant Grain For Ballistic Evaluation

Star port propellant grains have been extensively studied for their operating as well as geometrical parameters. It is observed that reduced tail-off and better neutrality cannot be achieved simultaneously in a configuration. Parametric study is conducted to know the effect of various parameters of star-shaped propellant grains for ballistic evaluation motor. For reduced tail-off, higher characteristic velocity, lower outer diameter of the star, and lower value of angular fraction is preferred. Star angle, burning rate, and throat diameter have negligible effects on the tail-off factor. For better neutrality, higher value of angular fraction, higher star outer diameter, and star angle near to neutrality, is needed. An alternate configuration is suggested using this parametric study to ascertain least tail-off and enhanced neutrality.

A Study on the Effect of Additives on Temperature Sensitivityin Composite Propellants

The hydroxy-terminated polybutadiene (HTPB) based composite propellants without any metal additive and with varying concentration of metal additives such as iron oxide, copperchromite, strontium carbonate and lithium fluoride have been cast and cured. These propellants have been characterized for density and calorimetric value (cal-val). Further, their temperature sensitivity has also been determined from the burning rates calculated from the P-t profiles obtained on static evaluation of Ballistic Evaluation Motor (BEM) after conditioning at different temperatures. The data indicate that iron oxide is best to enhance burning rates and at the same time, to reduce temperature sensitivity.

Determination of Pressure Dependence of Burning Rate in Solid Motors Using Ultrasonic Technique

The instantaneous burning rate of an aluminized composite solid propellant in a ballistic evaluation motor was measured continuously using an ultrasonic pulse-echo technique. The motor was designed to operate over a range of pressure from 2.5 to 4.5 MPa during its burning period. Hence, the burning-rate data could be obtained at different pressures directly from a single motor Ž ring itself, and the data were used to determine the pressure dependence of the burning rate. Thus, the technique is shown to overcome the need for carrying out several strand tests or ballistic evaluation motor tests, each at a different pressure, for characterizing a solid propellant burning rate.