Approximate estimates of the characteristics of propellant ignition using radiant flux through shields with various properties

An analytical solution to the problem of propellant ignition using radiant flux is presented in a conjugate statement. The solution generalizes and supplements the results obtained earlier. The cases of ignition through absolutely transparent and opaque shields are considered. Approximate formulas for estimation of the time and temperature of the chemical-reaction onset and the time and temperature of the loss of quasi-stationary equilibrium in different limiting cases are obtained. Estimates of the influence of heat transfer into the environment (by the conductive mechanism) on the ignition characteristics are given. A comparison of the ignition characteristics of the propellant and shields is made.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 26–41, January–February, 1996.     

Regimes of ignition of a porous body using a heat flux

The ignition of a semiinfinite porous body using a heat flux is studied numerically. The influence of the gas flow from the surrounding medium into the pores and of the heat exchange among the phases inside the body on the ignition regimes is studied. A critical condition is found that distinguishes the regimes of ignition and explosionless heating. The dependence of the ignition delay and coordinate of the ignition point on the system parameters is analyzed.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 20–25, January–February, 1996.     

Experimental Investigation on Laser Ignition and Combustion Characteristics of NEPE Propellant

The ignition and combustion property of solid propellant is the main content in internal ballistic research, which has a great significance for propulsion application and combustion mechanism. In this study, the detailed gas‐phase reaction mechanism of Nitrate Ester Plasticized Polyether Propellant (NEPE) was developed. It is helpful to understand the intricate processes of solid‐propellant combustion. The factors which may have influences on ignition delay time and temperature distribution of propellant surface was analyzed by laser ignition experiment. Using high‐speed camera and an infrared thermometer, the ignition and combustion process and the surface temperature distribution of NEPE propellant under laser irradiation were measured. Laser heat flux, ambient pressure and initial temperature of NEPE propellant have an influence on the ignition delay time and the surface temperature. Results show that the ignition delay time decreases with the increase of laser heat flux, ambient pressure and initial temperature of NEPE propellant. At the same time, with the increase of laser heat flux, the influences of ambient pressure and initial temperature on the ignition delay time decrease. Besides, laser irradiation, ambient pressure and initial temperature have significant influences on the surface temperature distribution of the propellant.     

环境气体氧含量对NEPE推进剂激光点火过程的影响

为研究环境气体氧含量对硝酸酯增塑聚醚(NEPE)推进剂激光点火过程的影响,采用CO2激光辐射点火并利用高速摄影仪记录NEPE推进剂的点火过程,讨论了环境气体氧含量对NEPE推进剂初焰位置与点火延迟时间的影响。结果表明,当环境气体氧含量小于NEPE推进剂热解产物中氧化性气体含量时,NEPE推进剂点火的气相反应发生在推进剂热解产物的分散区,初焰紧靠NEPE推进剂表面,环境气体氧含量变化不影响NEPE推进剂的点火延迟时间;当环境气体氧含量大于NEPE推进剂热解产物中氧化性气体含量时,NEPE推进剂点火的气相反应发生在推进剂热解产物与环境气体的扩散区,初焰远离NEPE推进剂表面,此时由于扩散区氧含量高于NEPE推进剂热解产物分散区氧含量,NEPE推进剂的点火延迟时间减小。     

Effect of Radiant Heat Transfer on the Minimum Spark–Ignition Energy of Gas Suspensions

A mathematical model of spark ignition of a gas suspension is constructed on the basis of a two–temperature thermal diffusion model of gas–suspension combustion and the radiant heat transfer is modeled in a diffusion approximation. The dependences of the minimum ignition energy on the parameters which describe the disperse phase and the domain of the disperse–phase parameters in which the radiant heat transfer affects greatly the minimum spark–ignition energy is determined by solving the problem numerically. The analytical formula that was obtained for determination of the critical spark–ignition energy of the gas suspension and that takes into account the radiant heat transfer in the gas suspension gives values different from numerical results by not more than 30% in a broad range of determining parameters of the problem. The theoretically obtained values of the minimum spark–ignition energy of a gas suspension of coal dust agree satisfactorily with experimental data.     

Ignition of a heterogeneous cloud of particles by a radiant flux

The paper deals with the ignition of a heterogeneous cloud of a gas suspension of reacting particles by an external radiant flux. Depending on the parameters of the problem, the ignition and bulk inflammation regimes are distinguished. An increase in the external-flux intensity and dispersed-phase particle size favors transition of bulk inflammation to ignition. The inflammation coordinate is independent of the mass concentration of the dispersed phase. Allowance for heat radiation by particles leads to an insignificant shift of the inflammation coordinate inside the cloud and to an increase in the induction period of inflammation.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 4, pp. 19–24, July–August, 1996.     

Ignition of a porous layer with a flow of heat carrier

Thermal ignition of a porous layer of finite thickness with a moving heat carrier has been studied. The asymptotic character of the critical conditions at high velocities of the heat carrier has been established. A nonmonotonic dependence of the ignition delay on the heat carrier velocity has been observed. Possible ignition regimes and their characteristics are described.Tomsk State University, 634050 Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 2, pp. 3–7, March–April, 1994.     

Composite Propellant Ignition and Extinction by CO2 Laser at Subatmospheric Pressure

Aspects of the heating, ignition and extinction of an AP/HTPB(86/14) composite propellant, induced by means of a CO₂ laser energy pulse, are investigated in the subatmospheric pressure range to determine the influence of the operating conditions on these processes. Measurements of the ignition delay time and ignition temperature for any operating condition have been done by microthermocouples able to record the temperature history of the irradiated surface and of the gas phase. Determinations of the boundaries location, defining the propellant behavior after the external energy removal, by the go-nogo techniques, have permitted to evaluate the minimum exposure time which assures to avoid the propellant extinction after the propellant ignition. Combustion transients have been studied to determine the burning propellant response to the laser energy pulse and to define the pulse features which yields the propellant extinction for different working pressure. Laser Doppler Velocimetry(LDV)technique, able to measure the velocity of the gas coming out from the burning propellant surface, was used to follow the whole combustion transient giving a precise picture of the phenomenon. Comparisons between data obtained studying the ignition and extinction by laser energy pulse phenomena show that the operating pressure has opposite effects on the propellant response to the external energy input having the same characteristics.     

Destruction of the surface layer of nitroglycerin powder during ignition at various initial temperatures

Destruction of the surface of nitroglycerin powder during ignition was detected experimentally. It was shown that the degree of destruction depends on the power of the external source, initial temperature, and exposure time. A model of ignition of a solid propellant is proposed which takes into account the occurrence of stresses and deformations in the surface layer during initiation of the chemical reaction. The characteristics of ignition and the degree of destruction are estimated. The results agree qualitatively with experimental data.Tomsk State University, Tomsk 634050. Research Institute of Applied Mathematics and Mechanics, Tomsk 634050. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 10–19, July–August, 1995.     

The primary zone in the combustion of solid propellants containing catalysts

Using a scanning electron microscope and an x-ray microprobe analyzer, we investigated the structure and composition of the combustion surface of the N propellant containing catalysts (PbO₂, CuO, PbO₂+CuO) which was extinguished at various pressures. Based on the obtained results, the heat-transfer coefficient was calculated for the layer above the catalyzed propellant combustion surface and found to be greater than that of the gas by factors ranging from 1.5 to 15. The calculation of the C-phase heat balance for the N propellant with additives showed that the rise in the combustion rate is caused by the increased quantity of heat entering into the C-phase from the zone above the combustion surface. Thus, the driving stage in the combustion of catalyzed propellants is the zone above the combustion surface and not the C-phase reaction layer, as in the case of the propellants without any catalysts.D. I. Mendeleev Russian Chemical Methodology University, 125190 Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 32–40, March–April, 1995.     

Influence of radiation on the critical heat-and mass-transfer conditions in parallel reactions at the surface of a particle

Analytical expressions are derived for the critical diameters bounding the region of high-temperature heat and mass transfer in parallel reactions at the surface of a particle. It is found that radiation with a large initial particle diameter leads to increase in the critical diameter of ignition with increase in the initial particle temperature. Formulas relating the combustion temperature and the particle diameter are derived. The influence of the prevailing conditions on the critical particle diameter at which spontaneous (induced) extinction and ignition occur is investigated in detail. An expression is obtained for the limiting gas temperature and oxidant content below which particle combustion is impossible. Degeneracy of the critical parameters of heterogeneous particle ignition and damping is investigated.State University, Odessa 270074. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 63–74, July–August, 1994.     

Modification of Thermal Theories to Solid Propellant Ignitibility

The conventional thermal theories are inventively modified for analyzing the ignition behaviors of solid propellants. Based on the modification of the thermal theory with the boundary condition of constant heat flux, the effects of heat flux, pressure, threshold of heat flux and absorbability on the radiant ignition of solid propellant are elaborated. The innovations of theoretical analyses are consistent with most of experimental results depicted in literatures. That the increase of hot gas velocity increases the ignition time of solid propellant is verified to be attributable to the decrease of hot gas temperature, ascertaining insight of the thermal theory with the boundary condition of flowing hot gas. In addition, a tentative estimation of pressurization rate effect on ignition time of solid propellant is proposed.     

Two-stage ignition of energetic materials with a liquid surface layer

Two-stage ignition regimes of energetic materials with a liquid surface layer were revealed by mathematical modeling of transient combustion processes. First, under the action of a radiant flux, the regime of forced gasification of a condensed phase with a degree of its surface depletion of 0.1–0.3 was observed. Gas-phase combustion occurs in the blow-off regime. As the radiant flux decreases, the gas flame approaches the surface and becomes determining, and the degree of condensed-phase depletion decreases.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 3, pp. 140–142, May–June, 1996.     

丁羟复合推进剂的辐射点火

采用CO2激光点火装置,对丁羟复合推进剂的点火过程进行了实验研究,利用描述固体推进剂物化现象的一维传热模型对复合推进剂的辐射点火特性进行了理论分析。通过最小二乘法拟合实验数据得到了丁羟复合推进剂的点火准则。结果表明,丁羟复合推进剂的点火过程主要包括惰性加热及气相点火过程,惰性加热时间和点火延迟时间随热流密度的增大而减小,且随着热流密度的增大,热流密度的影响逐渐降低。固相传热数学模型能够比较准确地描述复合推进剂的辐射点火特性。     

Hot-Spot Ignition of a Reactive Gas in an Inert Porous Medium

The main stages of development of hot-spot ignition of a reactive gas in a high-porous medium with high values of the Peclet number under conditions of natural gas filtration and limited internal heat transfer between the phases are determined. Gas ignition in a U-shaped hot spot is considered within the framework of an asymptotic analysis with high values of the temperature difference and Frank-Kamenetskii parameter. The critical relation of parameters separating the regimes of gas ignition and gradual cooling of the hot spot is determined. The dependence of the ignition time on parameters of the process is found and analyzed. A strong effect of interphase heat transfer on the ignition limit and time is demonstrated. An example of calculating the critical parameters of hot-spot ignition of methane in processed rocks is given. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 41–48, September–October, 2005.     

Numerical simulation of transients in the ignition of two-component propellants by intense heat fluxes

An ignition model is developed for quasi-homogeneous propellants consisting of two perfectly mixed compnents which decompose independently in the condensed phase and then react in the gas phase. The model describes the heat propagation in the condensed and gas phases as well as the diffusion of components in the gas phase. The transition processes from ignition to self-sustaining combustion under pulsed irradiation are studied numerically for the simplest case of a monopropellant. It is shown that the critical value of heat flux for stable ignition of monopropellant and the shape of the stable ignition peninsula in the exposure time-heat flux coordinates depend on the extinction criterion.Tomsk. Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 16–20, May–June, 1993.     

Ignition of a radiating gas by an incandescent surface

Conclusions The fundamental regularities of ignition of a radiating and absorbing gas by an incandescent surface are examined. In the case of an optically thin medium characteristic for high-temperature ignition, the problem is solved in the traditional stationary and nonstationary formulations [8]. It is shown that radiant heat transfer plays an essential part in the gas ignition process, in particular, the process can be accelerated and retarded in an optically thin gas medium because of radiant heat exchange. The case of an optically dense gasl _kb/l _o corresponds to radiant heat conduction, and therefore, does not result in a change in the ignition time but only to an increase in the scale of the lengthl _o. For intermediate values ofl _kb/l _o the dependence of on parameters governing the energetics of radiant heat transfer is complex in nature and can only be analyzed numerically in each specific case. The development of a suitable model of radiation heat exchange is the fundamental difficulty here.Minsk. Translated from Fizika Goreniya i Vzryva, Vol. 26, No. 1, pp. 15–21, January–February, 1990.     

Heating and ignition of aerosol particles in a gas by intense optical radiation

Conclusion We have theoretically investigated the heating and ignition of aerosol particles in a gas by intense optical radiation, determined the threshold radiation intensities for ignition of single particles of magnesium in air and obtained satisfactory agreement with experimental data. We have shown that particle concentration has an appreciable influence on the ignition process.Minsk. Translated from Fizika Goreniya i Vzryva, Vol. 24, No. 3, pp. 60–67, May–June, 1988.     

Chemical transformation mechanism and combustion regimes in the system silicon-carbon-fluoroplastic

The combustion mechanism and regimes are studied for the mixture Si–C–(–C₂F₄–)_ir Experimental curves are given for dependences of combustion wave parameters for the mixture on the ratio of original components, inert atmosphere pressure, ignition source temperature, and specimen diameter. It is shown that depending on these parameters the process may occur in two steady-state regimes: low-temperature, when there is only formation of silicon fluorides, and high-temperature, when there is successive formation of silicon fluorides and carbides.Erevan. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 77–81, November–December, 1991.     

Ignition of condensed systems interacting through a layer of high-melting product

The functional dependence of the ignition delay time on the main parameters of the problem is determined for condensed systems interacting through a layer of high-melting product by a power law. A formula for determining the ignition temperature from the equality between the external heat flux and integral heat evolution in a chemical reaction in a stationary combustion wave with temperature equal to the ignition temperature is proposed and substantiated. It is shown that at a surface temperature below the ignition temperature the heating can be considered inert and the duration of this stage makes up the bulk of the delay time.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka 142432. Tranalated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 3–9, July–August, 1995.