Response functions of HMX and RDX burning rates with allowance for melting

Experimental values of the burning rate with variations in pressure and initial temperature are given, and identity of gasification laws in the wave for RDX and HMX is demonstrated. Differential parameters (sensitivities) of the burning rate and surface temperature are found. Based on these parameters, response functions of the burning rate to pressure oscillations are calculated. The calculations are performed with and without allowance for condensed phase melting. Allowance for melting is shown to reduce the amplitude of the real part of the response functions, while the thickness of the melted layer does not produce any significant effect on the response functions. Errors of calculating the response functions are presented. The calculated response functions are compared with experimental data. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 72–82, May–June, 2007.     

Characteristics of RDX combustion zones at different pressures and initial temperatures

The RDX burning rates and temperature profiles in the combustion wave are measured with the pressure and initial temperature varied within wide limits. Parameters of combustion waves are found. The gas phase of RDX is demonstrated to have a single-zone structure. Two regimes of RDX combustion are found: a basic regime at p > 0.1 MPa and a special regime at p ≤ 0.1 MPa. The main characteristics of these regimes are obtained, and the wave regions responsible for the burning rate are determined. Both regimes are characterized by wide reaction zones in the gas phase. The processes of vaporization and decomposition of the condensed phase proceed simultaneously on the burning surface. The fraction of thermal expansion in the reaction layer of this phase is estimated. Laws of RDX gasiffication (pyrolysis) in the combustion wave are found, which turn out to be the same as those for HMX. Distributions of the heat-release rate in the combustion wave (in the reaction layer of the condensed phase and in the gas phase) are obtained. Sensitivity of the burning rate to the initial temperature is measured. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 32–45, September–October, 2006.     

Ammonium perchlorate-based composite solid propellant formulations with plateau burning rate trends

This paper presents burning rates as a function of pressure of several propellant formulations based on ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene cured by isophorone diisocyanate, many of which exhibit significantly low (nearly zero or negative) values of the pressure exponent of the burning rate in distinct pressure ranges, termed as plateau burning rate trends. The propellants contain a bimodal distribution of AP particles with the size of the coarse and fine particles within narrow ranges whose mean values are widely separated. Two mean sizes of fine particles were considered for the propellant formulations in the present work, namely, 5 and 20 μm. These choices are based on the mid-pressure extinction behavior exhibited by the matrix of fine AP and binder contained in the propellants but when tested alone over a wide range of fine AP size and pressure. The propellants that include the fine AP/binder matrixes exhibiting a mid-pressure extinction, in turn, exhibit the plateau burning rate trends within the corresponding pressure ranges. A plateau is also observed at elevated pressures in the burning rates of some formulations, which is related to the diminishing relative importance of the near-surface leading-edge region of the oxidizer/fuel diffusion flame in the gas-phase combustion zone. The choice of the coarse AP size influences the exact pressure range within the mid-pressure extinction domain of the matrix where the propellant exhibits the plateau burning rate trends. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 73–81, July–August, 2007.     

On the threshold nature of erosive burning

A physical explanation for the existence of the threshold of erosive burning is proposed. It is shown that this type of combustion occurs when the thickness of the laminar sublayer in the turbulent boundary layer becomes smaller than the thickness of the laminar combustion zone. In this case, turbulent flame in the gas phase is formed. Relations are obtained linking the critical (threshold) velocity of the blowing flow and the critical Vilyunov number to the properties of the propellant and the gas resulting from propellant decomposition. Simple exponential dependences on the blowing velocity are found for the burning rate. The simplest representation of the erosive burning rate is obtained using the Bulgakov-Lipanov number, whose threshold value is equal to unity. A new mechanism for the occurrence of negative erosion is proposed, according to which the burning rate decreases during blowing because the boundary layer is displaced, resulting in a decrease in the heat flux from the flame zone to the solid-phase decomposition surface. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 61–71, May–June, 2008.     

Effect of the equivalence ratio on the effectiveness of inhibition of laminar premixed hydrogen-air and hydrocarbon-air flames by trimethylphosphate

This paper reports results of an experimental study and numerical simulation of the effect of the equivalence ratio (φ = 0.6–1.6) on the burning velocity of laminar, premixed atmospheric methane-air and propane-air flames without additives and with 0.06% trimethylphosphate (TMP). The effect of the equivalence ratio (φ = 0.7–4.5) on the burning velocity of hydrogen-air flames without additives and with 0.1% TMP was studied by simulation. The experimental and simulation results show that, in hydrocarbon flames doped with TMP, the inhibition effectiveness decreases sharply with a growth in φ from 1.2–1.3 to 1.4–1.6 and in hydrogen-air flames, the inhibition effectiveness increases with a rise in φ from 1.5 to 4.5. The reactions determining the dependence of the inhibition effectiveness on the equivalence ratio were found by analyzing the flame velocity sensitivity coefficients to changes in reaction rate constants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 14–22, March–April, 2008.     

Effect of the addition of ultrafine aluminum powders on the rheological properties and burning rate of energetic condensed systems

The effect of small additives (1.25–5.00%) of ultrafine aluminum powders (UFAP) on the rheology and combustion of model four-component energetic condensed systems is studied. It is found that the addition of UFAP decreases the temperature of HMX decomposition. Small additives of UFAP increase the burning rate of model energetic condensed systems and decrease the exponent ν in the burning rate law without deteriorating the rheological characteristics of the model propellants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 54–59, January–February, 2007.     

Critical diameter and transverse waves of powder combustion

A critical review is given of the problem of powder extinction with a decrease in the sample diameter due to heat release. The results of our experimental studies of the critical combustion diameter are presented. A comparison of the experimental data on the critical diameter as a function of burning rate is shown to be the most informative. These functions follow a power law with an exponent of −1.15 to −1.17. The relations between the sizes of the cells (hot spots) formed by the set of transverse waves on the burning surface and the burning rate follow the same law. The sizes of the cells are 2.1–2.3 times smaller than the critical combustion diameter. It is also found that the transverse wave decays if its curvature exceeds a critical value. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 72–78, March–April, 2007.     

Cross-flow effect on combustion of a solid propellant with harmonically varying pressure

The response function of the burning rate of a solid propellant to periodically varying pressure is found with allowance for the cross-flow (erosion) effect in the linear approximation of the phenomenological theory of nonsteady combustion. Numerical results are obtained for the simplest propellant model with the minimum number of parameters. An elementary acoustic perturbation (planar monochromatic traveling acoustic wave) is considered. The role of steady-state and nonsteady cross-flow components at low and high values of the erosion ratio is elucidated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 66–72, July–August, 2007.     

Combustion characteristics of a hydroxylammonium nitrate based liquid propellant. Combustion mechanism and application to thrusters

A new composition of hydroxylammonium nitrate based solution containing ammonium nitrate, methanol, and water was developed for monopropellant in a reaction control system (RCS) as an alternative to conventional hydrazine. In comparison with hydrazine, this solution has a 20% higher specific impulse, 1.4 times higher density, and lower freezing point and toxicity. The linear burning rate of the solution is moderate at the operating pressures of RCS thrusters. It was found that the linear burning rate had some characteristics whose mechanisms had not been understood. The combustion mechanism of this solution was investigated. The burning behavior was observed using a medium speed camera, and a temperature profile for the combustion wave was measured with a 2.5 μm diameter thermocouple. From these results, the instability of the liquid-gas interface may trigger a sudden increase in the burning rate, and methanol was found to be effective in reducing the bubble growth rate in the solution. The reactivity of several catalysts was evaluated in an open-cup test, and the S405 catalyst for hydrazine showed the best performance among them. Thruster tests were conducted using the S405 catalyst with variation in the propellant mass flow rate, catalyst bed configuration, and length-to-diameter ratio of the combustor. As a result, parameters were determined that ensured long operating time. The model thruster operated stably for up to 100 sec with a specific impulse I _sp = 240 sec, which corresponds to a 90% efficiency. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 109–120, July–August, 2009. An erratum to this article can be found at     

Modeling of controlled combustion of high-energetic materials on structured catalysts

A mathematical model of combustion of high-energetic materials on structured catalysts is developed. Numerical studies are performed for combustion of a typical material: aminoguanidine nitrate. An increase in catalytic activity, as well as an increase in the thermal conductivity of the catalyst, is found to expand the range of real-time controlling of the burning rate of the condensed substance. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 45–53, September–October, 2008.     

Combustion of pressed specimens of heterogeneous systems subjected to a constant axial mechanical load

The growth dynamics of the height of burning pressed specimens with the specimen ends subjected to a compressive force of constant magnitude is studied using the heterogeneous Ti+C+20% TiC system as an example. It is found that in the examined range of compressive forces 0.1–2 kg/cm², the growth of the height of the burning specimens with time obeys a linear law; under a compressive force of ≈0.1 kg/cm², the specimen height increases by ≈100%, and under a force of ≈2 kg/cm², it increases by about 25%. The method used to measure the growth dynamics of the specimen height during combustion proved a useful tool for the experimental determination of both the burning time of the specimens and the delay in the transfer of combustion through an obstacle. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 103–109, May–June, 2007.     

Erosive burning. Modeling problems

Existing models for the erosive burning of homogeneous energetic materials ignore the fact that the burning regime can be changed radically by exposure to a hot gas blowing over the burning surface. In other words, transition can occur from the gasification regime at very high blowing rates (where the burning rate is determined primarily by the heat transfer from the flow core) to the self-heating regime of the condensed phase at low or zero blowing if the heat release in the condensed phase is sufficient to heat it to the surface temperature. A possible method for solving this problem is proposed. The approach proposed provides a plausible explanation for the experimentally observed singular (kinked) dependence of the magnitude of the negative erosion effect on the initial temperature. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 47–58, May–June, 2007.     

Nonlinear response functions of the burning rate of ballistite powders

Second-order nonlinear response functions to pressure oscillations are calculated for a group of ballistite powders with additives, based on results of microthermocouple measurements. A unified law of gasification of ballistite powders is refined. A classification of nonlinear response functions is proposed: viscous, normal, and critical response functions are identified. More than half of the burning regimes of these powders are demonstrated to have a viscous response type with a weak dependence on frequency and with a weakly expressed maximum in the case of a resonance. The effect of the powder composition on the nonlinear response functions is analyzed. Specific features of the nonlinear response as a function of a new parameter (phase shift between the interacting modes) are considered. It is shown that the errors in determining the nonlinear response functions depend on the response type and have low values for the majority of the burning regimes. Arguments in favor of the process one-dimensionality in the reactive layer of the condensed phase are given. A hypothesis of the near-critical state of some products of decomposition in this layer is proposed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 44–59, July–August, 2008.     

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.     

Properties of the surface layer and combustion behavior of metallized solid propellants

The properties of the surface layer of burning metallized solid propellants are analyzed on the basis of available experimental data. A general physical concept of processes in the surface layer is developed. The structure called a skeleton layer is shown to play a key role in combustion. The factors influencing the properties of the skeleton layer are determined, and the effect of these of properties on the properties of condensed combustion products and the propellant burning-rate law is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 156–165, July–August, 2009.     

Study on Dynamic Burning Rate Equation of Propellant

Aiming at the difficulty that the actual burning law of propellant in the gun bore couldn't be described exactly by static burning rate equation in the closed‐bomb, propellant dynamic burning rate equation and its acquisition method were established in the paper, which are based on static burning rate equation and considering burning gas flow and loading density influence factors in bore. A numerical code for interior ballistic two‐phase flow was successfully developed. And corresponding firing tests were also carried out. The comparison of simulations with interior ballistic code and firing test results show that the propellant dynamic burning rate equation makes the maximum errors of muzzle velocity and pressure in breech decreased from 2.97 % to 0.75 % and from 6.68 % to 0.38 %, respectively. This method not only improves simulation precision of gun muzzle velocity and pressure significantly, but also provides a means to improve the design accuracy for interior ballistic performance.     

Correlating Aluminum Burning Times

Characteristics of aluminum combustion are summarized in an overview of the subject, focusing on the burning time of individual particles. Combustion data from over ten different sources with almost 400 datum points have been cataloged and correlated. Available models have also been used to evaluate combustion trends with key environmental parameters. The fundamental concepts that control aluminum combustion are discussed, starting from a discussion of the D ⁿ law. The exponent in the D ⁿ law is shown to be lower than two, with nominal values of ≈1.5 to 1.8 being typical. The effect of the ambient medium on the burning time is considered, oxygen as an oxidizer being twice as effective as water and about five times more effective than carbon dioxide. The effect of pressure and initial temperature is minor. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 55–69, September–October, 2005.     

碳硼烷类燃速催化剂的研究进展

综述了国内外碳硼烷类燃速催化剂的研究情况,介绍了各种碳硼烷类催化剂的性能特点,指出碳硼烷类燃速催化剂是适用于高燃速和超高燃速推进剂配方的燃速催化剂,具有显著提高推进剂燃速的作用,对压强指数的影响依据配方组成的不同而有区别.     

Combustion of Energetic Materials in an Acoustic Field (Review)

The review summarizes the long-term experience in theoretical research of combustion of gasifying condensed systems with periodically varied pressure. Most results are obtained within the framework of the Zel'dovich-Novozhilov theory. The main properties of the linear function of the burning rate response to harmonically varied pressure are discussed. The concept of nonlinear response functions is introduced, which is illustrated by the explicit form of a number of second-order response functions. A new phenomenon is described: bifurcations of response functions with a varied amplitude or frequency of pressure oscillations. For the simplest gunpowder model containing three parameters only, the sequence of bifurcations of doubling of the burning rate oscillation period is studied, which finally leads to a random combustion regime. An analytical relation between the linear response functions to harmonically varied pressure and to an oscillating radiant heat flux is noted. An example of calculating the response function with allowance for thermal inertia of the gas phase is presented. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 116–136, November–December, 2005.