Burning Rate Law Research Articles

Features of the mechanism of pasty propellants burning

The composition of a pasty propellant for small-sized space engines has been proposed. For this propellant, a research of the burning process was carried out. This research included the determination of the burning rate law, the characteristics of the agglomeration process, and the properties of the surface layer. The presence of an intermediate structure, a skeleton layer, during the burning of such propellants, and the nature of the influence of pressure, additives, and the size of oxidizer particles on this structure, have been established. The determining influence of this structure on the burning process is shown. Composition solutions that provide control over the burning rate law of such propellants are determined. These solutions make it possible to change the absolute value of the burning rate, as well as its dependence on pressure. Regularities of the agglomeration process have been established. These regularities are associated with the features of the formation of the skeleton layer, which depend on the structure of the propellant, pressure, and the presence of additives.

Effect of Al–Li Alloy on the Combustion Performance of AP/RDX/Al/HTPB Propellant

Aluminium–lithium alloy (Al–Li alloy) powder has excellent ignition and combustion performance. The combustion product of Al–Li alloy powder combined with ammonium perchlorate is gaseous at the working temperature of solid rocket motors, which greatly reduces the loss of two-phase flow. Experimental investigations were thoroughly conducted to determine the effect of the Al–2.5Li (2.5 wt% lithium) content on propellant combustion and agglomeration based on thermogravimetry-differential scanning calorimetry, heat combustion, laser ignition, combustion diagnosis, a simulated 75 mm solid rocket motor and a condensed combustion products (CCPs) collection device. The results show that the exothermic heat and weight gain upon the thermal oxidation of Al–Li alloy is obviously higher than those of Al powder. Compared with the reference propellant’s formulation, Al–2.5Li leads to an increase in the burning rate and a decrease in the size of the condensed combustion products of the propellants. As the Al–2.5Li alloy content gradually increases from 0 wt% to 19 wt%, the burning rate increases from 5.391 ± 0.021 mm/s to 7.244 ± 0.052 mm/s at 7 MPa of pressure; meanwhile, the pressure exponent of the burning rate law is changed from 0.326 ± 0.047 to 0.483 ± 0.045, and the d43 of the combustion residue is reduced from 165.31 ± 36.18 μm to 12.95 ± 4.00 μm. Compared to the reference propellant’s formulation, the combustion efficiency of the HTPB propellant is increased by about 4.4% when the Al–2.5Li alloy content is increased from 0 to 19%. Therefore, Al–2.5Li alloy powder is a promising fuel for solid propellants.

Theoretical and Experimental Research on Gun Propellant Burning

The paper presents a method to determine the burning rate law and the progressivity coefficient of the fine-grained propellants shape. To achieve the objective of this paper, a series of tests were performed in a closed vessel. The results obtained from these tests were processed to determine experimentally the burning rate and the progressivity coefficient of the propellant shape starting from the premise that the burning surface has identical values for the same value of the volume fraction of burned propellant in two closed vessel tests at different loading densities. The experimental determination of the progressivity coefficient of the propellant shape shows that irregularities of the shape of the fine-grained propellants and gradual ignition lead to values completely different from the theoretical ones.

Experimental study on the combustion characteristics of aluminized nitrate ester plasticized polyether solid propellant under high pressure

Aluminized Nitrate Ester Plasticized Polyether high-energy solid propellant demonstrates bright application prospects due to its high-density specific impulse and satisfactory mechanical properties. The high-pressure experiment study were conducted on aluminized Nitrate Ester Plasticized Polyether to quantitatively investigate the burning rate characteristics at 1–7 MPa, and qualitatively analyse the agglomeration characteristics at 7 MPa. The burning rate experiment results indicate that the relationship between burning rate and pressure basically conforms to Vielle's burning rate law. When the ammonium perchlorate partice size decreases from 298 to 142 μm, the burning rate coefficient increases by 9.1% and the pressure index decreases by 7.6%. With the octogen particle size increasing from 15 to 150 μm, the burning rate coefficient and pressure index increases by 15.0% and 9.8%, respectively. When the aluminum particle size decreases from 30 to 16 μm, the burning rate parameters remain unchanged. While the aluminum particle size decreases from 16 to 2 μm, the burning rate coefficient increases by 20.5% and the pressure index decreases by 18.6%. The burning rate is significantly affected by octogen particle size and aluminum particle size has the vital influence on burning rate coefficient and pressure index. The agglomeration process and second mergence phenomenon at 7 MPa were observed for the first time and the agglomeration process mainly happens on the burning surface and above the burning surface under high pressure. Qualitative analysis shows that high pressure reduces the retention time of agglomerates on the burning surface and intensifies the combustion process of agglomerates, and coarse octogen can effectively reduce the agglomeration particle size at 7 MPa. The conclusions can provide insights into the influence of Nitrate Ester Plasticized Polyether composition on burning rate and the effect of high pressure on the agglomeration process in the motor.

Characterization of Aluminum Powders: IV. Effect of Nanometals on the Combustion of Aluminized Ammonium Nitrate‐Based Solid Propellants

AbstractThis study is devoted to the investigation of the energetic properties of two types of aluminized solid propellants with inert and active binders modified by additives of six different metal nanopowders. The substitution of an inert binder for the active one resulted in significant improvement of energetic properties. However, burning rate regulation become more complicated because the pressure exponent in burning rate law was increased as well. The DSC analysis revealed that the most significant catalytic effects were observed while using Zn, Cu, and Mo powders. Combustion of compositions based on an inert combustible binder and ammonium nitrate was studied in the pressure range 0.1–10.0 MPa. Due to the low combustion rate, no dispersion of burning aluminum particles was observed. During combustion, a single agglomerate of aluminum particles was formed, the mass of which was about 96 % of the initial aluminum mass in the formulation. A comparative analysis of nanosized metal additive effect on the propellant's combustion process was performed. It had been found that the activity of the metal nanopowders depends on the propellant formulation. It had been shown that Al and Zn did not affect the combustion rate of propellant with inert binder but they were effective in compositions with an active binder. Cu and Ni were found to be a good catalyst for the ammonium nitrate and active binder decomposition.

НЕСТАЦИОНАРНОЕ ПОВЕДЕНИЕ ЗАРЯДА ТТ БЕССОПЛОВОГО РДТТ ПОД ДЕЙСТВИЕМ ГАЗОДИНАМИЧЕСКОЙ НАГРУЗКИ

The numerical solution to a conjugate problem of an unsteady flow of combustion products in a flow path of the nozzleless solid rocket motor (SRM) and the oscillation of a solid propellant charge under the action of the forces directed from combustion products is considered. The Navier-Stokes equations for a compressible viscous gas are used to mathematically describe the flow of the combustion products. To model the charge oscillations, the equations of solid mechanics are applied, which take into account the propellant hyperelasticity. Pressure distributions and the propellant burning rate along the charge channel are presented for different models of the propellant burning rate. It is revealed that at the stage of SRM design, the use of the burning rate law, determined by pressure in the head of the combustion chamber, is more preferable in order to assess the internal ballistic characteristics. The solution to the conjugate problem shows that in the nozzleless SRM with the propellant having low Young's modulus, resonance can occur, which causes uncontrolled charge oscillations.

Method for determining parameters of the high energy materials burning rate law

Method for determining parameters of the burning rate law including combustion of high energy material samples in a manometric bomb is proposed. This method is based on solving the inverse problem of internal ballistics in an integral formulation. Unlike the prior versions embodiments of the experimental setup, the principle of ignition of a HEM sample by a heated spiral is used herein. In the prior versions, the ignition of the sample was carried out with black powder, which introduced errors due to gas formation during the burning of the powder. In addition, heat-insulated inserts are installed on inner walls of manometric bomb to prevent heat losses. The results of the method verification for model high energy material are discussed. Verification of the proposed method for identifying the parameters of the burning rate law was carried out for the model HEM composition with known values of thermophysical and ballistic characteristics. The integral method allows determining parameters of the burning rate law u 1, v with the error of not more than 3-4% by experimental dependence p(t) measured with a random error of 10%. At the same time errors of determination u 1, v by the differential method is 14-32%.

On the Effectiveness of Using the Real Law of Solid Propellant Burning Rate As a Function of Solid Rocket Motor Pressure

This paper presents a comparative analysis of the maximum possible solid rocket motor pressures obtained using the exponential and real laws of the propellant burning rate as a function of pressure. It is shown that at high exponents in the burning rate law, there is a large (tens of percent) difference between the maximum motor pressure obtained by the above two methods. In the case where the exponent is in the range 0.3–0.4, the exponential burning rate law overestimates the motor pressure by only 2–3%.

Numerical simulation on the pressure wave in a 30 mm electrothermal-chemical gun with the discharge rod plasma generator

Abstract An axisymmetric two-dimensional (2D) internal ballistic model including the transient burning rate law is used to simulate the 30 mm electrothermal-chemical (ETC) launch with the discharge rod plasma generator (DRPG). The relationship between the pressure wave and the initial parameters, such as input electric power, discharging timing sequence, loading density and propellant web thickness, is researched through the change of initial parameters in the model. In the condition of synchronous discharging, the maximum of the pressure wave can be controlled while the ratio of the input electric energy to the propellant chemical energy (electric energy ratio) is less than 0.11. If the electric energy ratio is larger than 0.11, the maximum of the pressure wave increases rapidly with the electric energy ratio. With the increasing of the electric energy ratio, the change of the first negative amplitude value can be ignored. In the condition of timing sequence discharging, the allowed input electric energy ratio to control the pressure wave is proportional to the current pulse duration. At the high electric energy ratio, the maximum of the pressure wave is inverse proportional to the current pulse duration. The pressure wave increases with the increasing of the loading density. But the allowed electric energy ratio to control the pressure wave and the variation trend of the first negative amplitude wave value doesn't change. During the discharging of the DRPG, the influence of changing propellant web thickness in ETC launch can be ignored.

Formation of solid residues in combustion of boron-containing solid propellants

Boron-containing solid propellants are promising propellants for ducted rockets. The experimental data show that combustion of boron-containing propellants is accompanied by an intense conglomeration of the boron particles near the burning surface. As a result, the boron particles conglomerates which are the branched coral structures composed of sintered boron particles are formed in combustion of boron-containing solid propellants. This results in decrease in combustion efficiency of ducted rockets. To calculate the ignition and combustion of a conglomerate in the secondary combustor of a ducted rocket, it is necessary to know the size, structure and shape of the boron particle conglomerates that can significantly affect these processes. In this paper, we consider a model and a method for calculating the boron particles conglomeration in combustion of the boron-containing solid propellants. The process of the boron particles conglomeration is considered as a result of competition between two main processes: the formation of adhesive bonds between the contacting boron particles and rupture of these bonds under the action of the aerodynamic detached force from the side the flow of gaseous combustion products of solid propellant. The criterion of formation of residues (slag) on the burning surface of boron-containing propellants is considered. It is shown that depending on the propellant burning rate law, two different types of propellants with different conglomeration behavior can exist. The results of calculations of the boron particles conglomeration which demonstrate the slag formation are shown.

Study on the analysis method on ballistic performance of deterred propellant with large web size in large caliber artillery

As for the characteristics of combustibility of deterrent propellant with large web size which is used in large-caliber gun and interior ballistic performance, the combustion characteristics of deterrent propellant are obtained by using closed-bomb experiments. The combustion law of deterrent propellant and the classic interior ballistic model of composite charge are given. By simulation and analysis the results of the artillery firing test, the burning rate variation law and the interior ballistics simulation parameters of propellant A are determined, and the burning rate relationship between propellant A and propellant B obtained from closed-bomb, then the ballistic performance of propellant B is predicted. The results show that the predicted results are in good agreement with the experimental results. The study shows that the burning rate law of deterrent propellant with large web size can be obtained by closed-bomb experiment. Using the method provided in this paper can accurately predict the interior ballistic performance and provide an important basis for improving the accuracy of interior ballistic calculation.

Boron particle agglomeration and formation of solid residues in combustion of boron-containing solid propellants

The model of the boron particles agglomeration in combustion of boron-containing solid propellants is suggested. The process of the boron particles agglomeration is considered as a result of competition between two main processes: the formation of adhesive bonds between contacting boron particles and rupture of these bonds under the action of gaseous combustion products. The criterion of solid residues formation and dependence of their relative mass on pressure are obtained. It is shown that depending on the propellant burning rate law, two different types of propellants with different behavior of the agglomeration process at pressure change can exist.

Correlation of parameters in the burning rate law and its influence on intraballistic characteristics of a rocket motor

Experimental data demonstrating the correlation of parameters in the power-law dependence of the burning rate of composite solid propellants on pressure are reported. The reasons for changes in the burning rate due to changes in propellant mixing conditions are discussed. The deviation of the pressure in the combustor of a solid-propellant rocket motor is analyzed with due allowance for the correlation of parameters in the burning rate law. It is shown that the relative deviation of the burning rate depends on pressure at which propellant combustion occurs. Moreover, for each propellant, there exists a pressure level at which the burning rate deviation is theoretically equal to zero, regardless of the differences in propellant compositions and properties.

Propellant Grain with Maximum Combustion Efficiency of Metal

This paper reports on the ways of allocating the metal particles in the propellant grain of tube cross-sectional type to provide maximum combustion efficiency of metal. Two-dimensional flow field and the burning rate law govern a transport of the burning metal particles. The analytical correlation for the optimum allocation of metal particles in the case-bounded propellant grain of tube cross-sectional type under the assumption of equilibrium two-phase flow is deduced.

Correlation of Parameters in the Burning Rate Law and Its Influence on Intraballistic Characteristics of a Rocket Motor

Correlation of Parameters in the Burning Rate Law and Its Influence on Intraballistic Characteristics of a Rocket Motor

Application of transient burning rate model of solid propellant in electrothermal-chemical launch simulation

A 30mm electrothermal-chemical (ETC) gun experimental system is employed to research the burning rate characteristics of 4/7 high-nitrogen solid propellant. A modified 0D internal ballistic model is established to simulate the ETC launch. According to the measured pressure and electrical parameters, a transient burning rate law including the influence of enhanced gas generation rates (EGGR) coefficient by electric power and pressure gradient (dp/dt) is added into the model. The EGGR coefficient of 4/7 high-nitrogen solid propellant is equal to 0.005MW-1. Both simulated breech pressure and projectile muzzle velocity accord with the experimental results well. Compared with Woodley’s modified burning rate law, the breech pressure curves acquired by the transient burning rate law are more consistent with test results. Based on the parameters calculated in the model, the relationship among propellant burning rate, pressure gradient (dp/dt) and electric power are analyzed. Depending on the transient burning rate law and experimental data, the burning of solid propellant under the condition of plasma is described more accurately.

Cast composite solid propellants with different combustion stabilizers

The effect of four different compounds as the combustion stabilizers of composite solid propellants based on the AP/HTPB/IPDI has been presented in this paper. Except that, various total solid content, ammonium-perchlorate bimodal and trimodal combination of particle sizes ratio have been made by preparing the eleven formulations. For all of them, the burning rate law's parameters and temperature sensitivity, uniaxial mechanical characteristics, apparent viscosity of uncured propellants and physic-chemical and energetic values have been determined and compared.

Effect of Aluminum-Boron Powders Mechanical Mixtures on the Combustion of High-Energy Materials at Subatmospheric Pressures

This paper presents the results of an experimental study of the high-energy materials combustion at subatmospheric pressures. Systems containing powders of micron-sized aluminum, ultrafine aluminum, boron and their mechanical mixtures were investigated. Effect of the replacement of aluminum by aluminum-boron mixtures in propellant systems on the burning rate law was determined.

Specifics of the combustion of aluminum-water mixtures

Experimental studies of the combustion of mixtures of micron-sized flaky aluminum powder with unthickened water in different conditions at atmospheric and high pressure in nitrogen and argon are performed. The density and composition of the mixture are varied. The regularities of the combustion have been established. A filtration wave of hot hydrogen ahead of the combustion front in samples with high porosity has been revealed. For the combustion under a nitrogen atmosphere, the pressure exponent in the burning rate law is close to 0.47 in a wide range of pressures. For the combustion under an argon atmosphere at pressures above 50 atm, the pressure exponent becomes zero or negative. Aluminum powder is demonstrated to be able to burn under conditions of a separated charge, where the fuel (aluminum) and oxidizer (water) are separated by a thin partition or brought in direct contact. The fast convective burning of aluminum-water mixtures in a semiclosed volume is discovered.

Measurement and Analysis of the Burning Rate of HAN-Based Liquid Propellants

A new device for measuring the linear burning rate of liquid propellants at high pressures is reported. High-pressure environments were generated by the combustion of solid propellants. The coated propellants, which burn progressively, were introduced to maintain the approximate constant-pressure environments. By use of ion probe transducers, measurements were made of the spread velocity of the flame surface, i.e. the apparent linear burning rate of the HAN-based liquid propellant LP1846 (HAN =hydroxylammonium nitrate) was measured quantitatively at pressures from 6 to 28 MPa. The results show that it follows the exponential burning rate law. The burning rate coefficient and exponent were fitted by least-squares methods. Based on the experiment, a simplified model of the linear burning rate of HAN-based liquid propellants at high pressures was developed. The numerical simulation is found to be in good agreement with the experimental data.