Measurement and Modelling of Pyrotechnic Time Delay Burning Rates: Application and Prediction of a Fast Burning Delay Composition

A predictive numerical model was implemented for a time delay based on the Si+Pb₃O₄ system. The reaction kinetic parameters were estimated by comparing predicted surface temperature profiles with experimental data acquired with an infrared camera. Fair agreement between the modelled and measured burning rates was achieved. The burning rate is predicted to increase by 9.4 % for every 50 °C increase in ambient temperature. The core diameter was found to have a slightly larger impact on the burning rate than the wall thickness. The effect of using different wall thickness materials was evaluated and indicated that the burning rate is significantly influenced by the wall material when the thermal conductivity is increased and the volumetric heat capacity is reduced. The shape of the combustion front was found to widen with a long tail for materials with a low thermal conductivity and a narrower combustion front with a short tail for materials with high thermal conductivity. Preheating occurred for pyrolytic graphite‐ and diamond‐based elements but no radial combustion was observed. The external heat transfer parameters (convection and radiation) did not affect the burning rate of the fast delay composition. It is concluded that the ambient temperature, volume fraction solids, molar heat of reaction, core and outer diameter are the factors that most significantly influence the burning rate of the Si+Pb₃O₄ composition in long cylindrical elements.     

Unsteady combustion of a binary gasless mixture ignited by a hot wall

The effect of phase-transition parameters and chemical conversion kinetics on unsteady combustion of gasless systems with a melting reagent is studied. It is found that the change in the kinetic law and in the chemical reaction rate constant resulting from the emergence of the liquid phase in the system destabilizes the combustion. The mean front velocity in the self-oscillatory mode with an adiabatic burning temperature close to the melting point exceeds the front velocity in the steady-state mode. In this case, the front stability improves with an increase in the rate of heat withdrawal from the system and with a decrease in the burning temperature.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 2, pp. 45–50, March–April, 2005.     

Effect of mechanochemical activation and microgrinding on the intensity of combustion of solid fuel

The effect of mechanochemical activation and microgrinding on the intensity of combustion of solid fuel particles was studied. As applied to the rapid process of the combustion of solid fuel particles, mechanochemical activation was simulated within the framework of nonequilibrium thermodynamics with the expansion of the classical dependence of the local entropy of state of the reacting system on relaxation phenomena. The dependences of the intensity of burning (mass loss time) of deformed organic solid fuel particles on the relaxation processes of the momentum transfer of their excited states and on the mutual orientation of shear stresses and the first difference in normal stresses (a steric factor), which compensate for temperature power consumption, were established. The rate of combustion is determined by the size of burning particles, their density, and a ratio between the elastic and dissipative scattering of mechanical energy in the particles, which increases the diffusion mobility of burning components with a decrease in the time of their burning. The ranges of variation in the parameters of the burning system in which the particle size or mechanoactivation exerts a considerable effect on the combustion time of fuel particles were recognized. Experiments on the torch combustion of coal-dust fuel as the cumulative combustion of its particles confirmed the effect of mechanoactivation.     

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.     

The use of a simplified mathematical model for prediction of burn out of non-uniform sprays

A simple one-dimensional mathematical model is developed which is used to calculate the burning rate of a spray of droplets with an initial Rosin—Rammler size distribution. The model is based on experimental observations of the influence of temperature, partial pressure of oxygen, and droplet size on the burning rate of a single droplet. In addition, balance equations are employed to determine the time dependent parameters of the rate equation. The model is used to show the significance of various input parameters on the combustion rate (i.e. evaporation rate) of the spray. The validity of the model is examined by comparing predicted changes in combustion efficiency with those obtained previously from a single tubular turbojet combustor operating with liquid iso-octane over a range of inlet oxygen concentrations.     

Influence of Particle Size and Mixing Technology on Combustion of HMX/Al Compositions

In this work, two widely used components of high‐energy condensed systems – HMX and aluminium – were studied. Morphology, thermal behaviour, chemical purity and combustion parameters of HMX as a monopropellant and Al/HMX as a binary system were investigated using particles of different sizes. It was shown that in spite of the differences in composition and particle size, combustion velocities are almost identical for micrometer‐sized HMX (m‐HMX) and ultrafine HMX (u‐HMX) monopropellants under pressure from 2 to 10 MPa. Replacement of the micrometer‐sized aluminium with ultrafine one in the system with m‐HMX leads to a burning rate increase by a factor of 2.5 and the combustion completeness raise by a factor of 4. Two mixing techniques to prepare binary Al/HMX compositions were applied: conventional and ‘wet’ technique with ultrasonic processing in liquid. Applying wet mixing results in a burning rate increase of 18% compared to the conventional mixing for systems with ultrafine metal. The influence of the component's particle size and the composition microstructure on the burning rate of energetic systems is discussed and analysed.     

基于一维气相稳态反应流的燃速预估软件研究

在一维气相稳态反应流模型的基础上,总结了适用于双基推进剂、改性双基推进剂、复合固体推进剂燃速预估的修正因子,拓宽了燃烧理论模型的适用范围.采用Visual C++和Microsoft Access为开发工具,完成了基于组分化学键结构参数的固体推进剂燃速预估软件(SPRS)编制.该软件基于Windows XP系统,界面友好,使用方便,具有数据更新和信息查询功能.用户不仅能根据推进剂的化学组成(配方)和给定压强计算燃速、压力指数等参数,还可根据给定的燃速和压力指数等调整推进剂配方组成,对缩短固体推进剂研制周期和节约研制成本具有重要意义.     

Method of the model equation in the theory of unsteady combustion of a solid propellant

A model equation for the unsteady burning rate of a solid propellant is proposed and justified. In the frequency range of interest for practice, the proposed model agrees with the phenomenological theory of unsteady combustion, but it is even more convenient for applications because it reduces to an ordinary differential equation of the second order with respect to the burning rate. A parametric study of the transitional process in the solid-propellant rocket motor is performed with variations of the nozzle throat area in a wide range of solid propellant parameters. The model predicts oscillatory combustion regimes and propellant extinction in the case of a decrease in pressure. The boundary of stability of the transitional process in the coordinates “sensitivity of the burning rate to changes in pressure—sensitivity of the burning rate to changes in initial temperature.” It is demonstrated that the calculations performed with the use of this model are in qualitative and quantitative agreement with experimental data for a full-scale solidpropellant rocket motor.     

Transient group combustion of the pulverized coal particles in spherical cloud

A transient group combustion model for the pulverized coal particles in a spherical cloud is developed to predict the transient group combustion characteristics. The submodels, which account for the detailed combustion process of both homogeneous and heterogeneous reactions, are also applied for the pulverized coal particles. The numerical simulation of the collective behaviors of ignition and its subsequent burning were carried out. The ignition mechanism is characterized by the heterogeneous process of the dilute cloud and the homogeneous process of the dense cloud. Two dominant flame structures are observed: one flame penetrating inside the cloud and the other moving outside the cloud. The effects of various parameters (i.e., radiation heat transfer, group combustion number, air temperature, air oxygen concentration, particle size distribution, and particle number density) on the particle mass burning rate and on the overall performance of the group combustion are examined. The results are in good agreement with existing experimental data.     

一种新型高燃速推进剂的燃烧性能

介绍了一种新型推进剂的多孔结构和燃烧性能．并重点讨论了在发动机中不同装填参数下所产生的平行层燃烧。选择不同燃烧类型．可获得不同压力下的燃速及其他参数．为该推进剂的应用打下了良好的基础。     

DAGQ发射药膛内静态和动态燃烧性能

为了研究DAGQ发射药在膛内的燃烧性能,以经典内弹道理论为基础,建立了发射药膛内燃烧测试系统和处理方法,通过密闭爆发器燃烧试验和微波干涉法发射药膛内动态燃烧性能试验,研究了DAGQ发射药的静动态燃烧规律及不同温度下的动态燃烧特性。结果表明,所建立的试验系统和处理方法,能够很好地获得弹丸在膛内的运动过程。DAGQ发射药的静动态燃速都存在转折现象,静态燃速在转折点前压力指数大于1,转折点后压力指数都远小于1,动态燃速压力指数基本都小于1。在膛内燃烧过程中,由于高速气流对发射药的燃面冲刷,使得膛内的动态燃速要大于密闭爆发器内的静态燃速,并且随着膛内压力的增大,燃速相差越来越大。     

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     

A Study of Solid Propellant Containing Titanium Hydride

The burning rate characteristics of the propellant containing TiH₂ have been examined in order to understand the effect of TiH₂ addition on the combustion wave structure. The burning rate increases and the pressure exponent of burning rate decreases as the addition of TiH₂ increases. Using very fine thermocouples which were embedded within the propellant samples, the heat transfer process in the combustion wave was determined. The results indicate that the heat flux feedback from the gas phase to the burning surface increases when TiH₂ is mixed within the propellants.     

Effects of fuel devolatilisation on the combustion of wood chips and incineration of simulated municipal solid wastes in a packed bed

Detailed mathematical simulations as well as experiments have been carried out for the combustion of wood chips and the incineration of simulated municipal solid wastes in a bench-top stationary bed and the effects of devolatilisation rate and moisture level in the fuel were assessed in terms of ignition time, burning rate, reaction zone thickness, peak flame temperature, combustion stoichiometry and unburned gas emissions at the bed top. It is found that devolatilisation kinetic rate has a noticeable effects on the ignition time, peak flame temperature, CO and H₂ emissions at the bed top and the proportion of char burned in the final stage (char burning only) of the combustion. However, it has only a minor effect on the other parameters. Reaction zone thickness ranges from 20 to 55 mm depending on the moisture level in fuel and an increase in the moisture level causes a shift of the combustion stoichiometry to more fuel-lean conditions.     

Local Fluctuations of Physicochemical Parameters in Condensed System Combustion

Using the 3Zr + 2WO₃ system as an example, it is shown that fluctuations of physicochemical parameters in the combustion wave of a condensed system in both loose and pressed forms can be recorded by means of two parallel wires placed in the burning system. It is established that changes in the initial density of the system and its burning rate results in corresponding changes in the fluctuation frequency. The relationship between these three parameters can be expressed, as a first approximation, by a fairly simple analytical relation.     

Simulation of the Erosion Burning of a Granular Propellant

For combustion of axisymmetric propellant grains under blowing conditions, a mathematical model is proposed and numerical simulation is performed. The effects of incoming–flow parameters (velocity, pressure, and temperature) and surface dimensions and geometry on grain–burning rate are studied. Physical patterns of flow around burning propellant grains are presented.     

Combustion of NaN3 Based Energetic Pyrolants

The burning rate of pyrolants composed of NaN₃ and metal oxides was investigated in order to gain information on their combustion characteristics. The metal oxides mixed with NaN₃ were Fe₂O₃, CoO, Co₃O₄, and CuO. The effect of the addition of whiskers and fibers was also examined. The test results indicated that the burning rate was highly dependent on the type of ingredients and the mixture ratio of the ingredients. The pyrolant composed of NaN₃/CuO (61/39) appeared with the highest burning rate, 50 mm/s at 7 MPa, throughout the burning rate experiments. The residue of the combustion products of each sample was examined to evaluate the effectiveness of the gas generation.     

Theoretical Analysis of Plasma Enhancement of Propellant Burning Rate

A theoretical model of the combustion of a nitramine solid propellant in the presence of a plasma jet is proposed. Unlike standard double‐base compositions, nitramine propellants exhibit experimental evidence that plasma induces a burning rate enhancement. The model is based on heat transfer considerations and proposes a closed‐form solution of the enhancement of the propellant burning rate as a function of the thermophysical parameters of the system. The model provides a good qualitative agreement with experimental results.     

Fuel size effect on pinewood combustion in a packed bed

In this paper, particle size effect on pinewood combustion in a stationary packed bed was investigated. Mass loss rate, temperature profile at different bed locations and gas compositions in the out-of-bed flue gases were measured at a fixed primary air flow rate. Pinewood cubes was fired with size ranging from 5 to 35 mm. A unique numerical model applicable to thermally thick particles was proposed and relevant equations were solved to simulate the non-homogeneous characteristics of the burning process. It is found that at the operating conditions of the current study, smaller particles are quicker to ignite than larger particles and have distinctive combustion stages; burning rate is also higher with smaller fuel size; and smaller fuels have a thinner reaction zone and result in both higher CO and CH₄ concentrations in the out-of-bed flue gases; on the other hand, larger particles produced a higher flame temperature and result in higher H₂ concentration in the flue gases. Larger particles also cause the combustion process becoming more transient where the burning rate varies for most part of the combustion process.     

Energetic Solid Fuels for Ducted Rockets (II)

The combustion characteristics of variable-flow ducted rockets were evaluated in order to obtain optimum design parameters of the gas generators. The energetic solid fuels used for the gas generators were glycidyl azide polymer (GAP) with burning rate catalysts. The burning rate of GAP based energetic fuels was much higher than that of composite and double-base based fuel-rich propellants. The pressure exponent of the burning rate was high enough to obtain a wide range of variable-flow rat. Two types of combustion test were conducted: a semi-free jet and a direct connect flow. The pressure-time response in the primary combustor obtained by the use of a throttable nozzle was evaluated.