Unsteady combustion of solid propellants subject to dynamic external radiant heating

A theoretical and experimental investigation is conducted on the effect of a dynamic external radiant heat flux on the combustion of energetic materials. These studies have illustrated the need for including the effect of the mean radiant heat flux and in-depth absorption. Also, a method for obtaining the linear frequency response function over a range of frequencies from a single test using series of radiant pulses is demonstrated. Experimental results have been obtained for an AP/HTPB propellant.Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign. Published in Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 31–36, May–June, 1993.     

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.     

Gasification of silicone fluids under external thermal radiation. Part I. Gasification rate and global heat of gasification

Transient gasification rates and fluid temperatures were measured for polydimethylsiloxane fluids ranging in viscosity from 0.65 cS to 60 000 cS in a nitrogen atmosphere at external radiant fluxes from 20 kW/m² to 70 kW/m². A detailed energy balance for each fluid sample was conducted to determine its global heat of vaporization. Two major energy loss corrections were identified and quantified. The absorption of incident radiation by the volatile products from short chain oligomers was measured and found to substantially reduce the incident flux to the sample surface; the energy loss due to re-radiation was determined to be a substantial factor in reducing the net heat flux to the sample for long chain length fluids. Other energy losses, e.g. heat loss to the substrate, were observed but were less significant. The average gasification rate for each fluid increased linearly with increasing external radiant flux. The global heat of gasification increases with an increase in the chain length (molecular weight) for the siloxane oligomers. These agreed well with calculated values. The global heat of gasification for 50 cS fluid is about 1200 kJ/kg and its value remains nearly constant for all higher molecular weight dimethylsiloxanes. Pyrolysis rates for siloxane fluids are very sensitive to trace catalysts. Measurements of the global heat of gasification for ultra-clean polymers resulted in significantly higher values (3000 kJ/kg). The gasification of siloxanes occurs via two modes or combinations thereof: (1) volatilization of molecular species native to the polymer, and (2) volatilization of thermal degradation products. The former process dominates for low molecular weight siloxanes (η<10 cS) and the latter process dominates for high molecular weight siloxanes (η>1000 cS). For the intermediate molecular weight siloxanes, both volatilization and degradation processes occur. © 1998 John Wiley & Sons, Ltd.     

A theoretical basis for flammability properties

Theoretical formulations are presented for the fire growth processes under external radiant heating. They included ignition, burning and energy release rate, and flame spread. The behaviour of these processes with external heating is described along with the critical conditions that limit them. These include the critical heat fluxes for ignition, flame spread and burning rate. It is shown how these processes and their critical conditions depend on a limited number of properties measurable by a number of standard test methods. The properties include heat of combustion, the heat of gasification, ignition temperature and the thermal properties of the material. Alternatively, the properties could be related to parameters easily found from data; namely: (1) the critical heat flux (CHF) for ignition; (2) the slope of the energy release rate with externally imposed flux, defined as heat release parameter (HRP); and (3) the ignition parameter, defined as thermal response parameter (TRP). It is further shown that the flame heat flux differences between small laminar flame ignition sources and larger turbulent flames can affect flame spread due to heat flux and ignition length factors. Finally, it is found that the critical energy release rates theoretically needed for ignition, sustained burning, and turbulent upward flame spread are roughly 13, 52, and 100 kW/m², respectively, and independent of material properties. Copyright © 2005 John Wiley & Sons, Ltd.     

The simulation of an existing ethane/dehydrogenation reactor

This paper is concerned with the mathematical representation of an existing box-type furnace for the thermal dehydrogenation of ethane. The furnace is composed of a preheating convection section and a radiant heated section. The two models considering (i) the tube-side calculation and (ii) the radiant heat transfer in the combustion chamber are independent of each other. A study is made of the effects of pressure, heat flux level and “steam/hydrocarbon” ratio on the effluent composition. A significant improvement in reactor operation if a more uniform heat flux could be achieved is predicted. From the radiant heat transfer computations an unexpected variation in flame temperature in the furnace under study was detected.     

Ignition and extinction of homogeneous energetic materials by a light pulse

Numerical calculations using a model of unsteady combustion of melting energetic materials were performed to simulate the results of qualitative experiments on the ignition and quenching of energetic materials by a light pulse. The parameters of the model composition were chosen to correspond to combustion with the burning-rate control reaction in the gas phase to ensure the stability of self-sustained combustion after the cessation of irradiation. Regions of stable ignition in the coordinates “radiant flux amplitude-irradiation time” were obtained for compositions with different transparency for igniting pulses of three shapes: rectangular, linearly decreasing to zero, and exponentially decreasing. Extinction conditions of the steadily burning composition by a rectangular light pulse were calculated.     

An experimental facility for determination of steady flame spread rate of materials employing the Quasi-stationary flame front technique

An experimental facility based on the Quasi-stationary Flame Front Technique for determination of steady flame spread rate of materials at discrete levels of external radiant heat flux was developed. The method employs an external radiant heat source in front of which an element of a specimen of the material is positioned at a location corresponding to the desired level of external radiant heat flux. A specimen movement assembly, which can be operated manually, was designed for moving the specimen towards the stationary external radiant heat source such that the flame front could be maintained quasi-stationary. The experimental technique employed is simple in operation yet is capable of yielding reliable flame fornt displacement–time data. In the paper the design considerations of the experimental facility, details of its components, calibration and typical experimental results obtained are presented.     

Gasification of coal-derived chars in synthesis gas mixtures under intraparticle mass-transfer-controlled conditions

A model has been formulated to describe the quasi-steady-state gasification of coal-derived chars in gas mixtures where both the reactants carbon dioxide and steam, and the gasification products carbon monoxide and hydrogen are present. As such, these conditions reflect the situation found in most practical gasification systems.The model presented is applied under conditions where intraparticle mass transfer is rate-controlling. Intraparticle heat transfer is neglected. In view of the non-equimolar gasification reactions, the mass flux equations are derived from the continuum limit of the dusty gas model. These flux equations are combined with strongly non-linear Langmuir-Hinshelwood kinetics for the gasification reactions. The model accounts for local variations of the diffusive and convective permeability parameters, as well as variations in the reactive surface area, during burnoff of a char particle.The impact of the various relevant mass-transfer parameters, the gasification temperature and pressure, and the char particle size on the gasification behaviour is discussed. A comparison is made between the present model and existing models, and various modelling approaches are critically reviewed.     

Modeling of Gasification of Sewage Sludge for Phosphorus Recovery and Hydrogen Generation

Due to the amendment of sewage sludge ordinance in Germany, phosphorus must be recovered from sewage sludge in the future. Previously developed phosphorus recycling processes are not economically viable due to high material and energetic expenditures. Gasification of dried sewage sludge enables the energetic utilization of sewage sludge and provides the energy for phosphorus recovery. The present paper focuses on thermodynamic modeling of the gasification system to demonstrate the potential for holistic utilization of dried sewage sludge as phosphorus fertilizer. The results shows that an energy self-sufficient, optimized process can be realized for recovery of phosphorus by gasification and subsequent thermo-chemical treatment of dried sewage sludge.     

Role of the gas phase in the transition of condensed material to combustion on ignition by a radiation flux

A model of ignition and the transition to combustion in condensed material under the action of a pulse of radiant flux is outlined. Chemical reactions on both sides of the phase interface are taken into account. It is shown that taking account of the thermophysical and chemical properties of the phases has a significant effect on the limits of stable ignition. The dynamics of the basic characteristics of the process is studied with pulsed heating of gasifying condensed material.Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 4, pp. 7–12, July–August, 1991.     

煤气化工序中气化炉系统的节能分析与计算

煤气化工序消耗大量的原料煤,所以必然要作为一个重点能耗单元来进行细致分析、核算。文章通过煤气化工序中气化炉系统的节能分析与计算,利用实例对气化炉系统的物料平衡和热平衡计算评估过程做了阐述,介绍了节能分析与计算在实际操作中的应用。     

Non-dimensional heat of gasification measurements in the intermediate scale rate of heat release apparatus

Wall-fire spread models require heat of gasification or non-dimensional heat of gasification to calculate mass loss rate or rate of heat release from the wall material. An intermediate scale rate of heat release apparatus was used to measure all the parameters needed to calculate non-dimensional heat of gasification for wood materials. An infra-red pyrometer was used to measure surface temperature. The results of measurements on six wood materials indicate that non-dimensional heat of gasification, if plotted against mass remaining, does not change significantly with external heat flux, but is material dependent.     

Texaco煤气化工艺技术经济指标的评价方法与评价系统设计

目前Texaco煤气化工艺的技术经济指标评价多采用手工作业方式，工作量大而且繁琐。针对这一现状，在分析Texaco煤气化工艺流程的基础上，运用物料衡算、热量衡算方法，获得了Texaco煤气化工艺的碳转化率、冷煤气效率、比煤耗、比氧耗等指标的计算方法。通过具体计算这些评价指标，即可定性、定量地评价整个工艺系统的运行状况。在此基础上，采用VB6．0、Access7．0等开发工具，开发了Texaco煤气化工艺技术经济指标评价系统。该系统支持多用户、多数据库、多报表、多权限，界面友好，操作简单，具有很好的应用前景。     

基于遗传算法-综合计算法的生物质热解气化优化分析

生物质热解气化可实现碳基可再生能源的高效清洁利用。为准确预测生物质热解气化产率分布,贴合生物质热解气化真实转化过程,由生物质热解气化实测数据通过遗传算法（genetic algorithm, GA）对综合计算法模型进行改进,按照综合计算法中热解段和固定碳气化反应段建立Aspen Plus模型。 结果表明：在GA-综合计算法中,稻壳在热解段CO₂的氧为干基氧含量的32.02%,焦油产率为挥发分的8.32%, 平均热解组分误差为8.53%,平均合成气组分误差为5.37%;基于GA-综合计算法的Aspen Plus模型,热解过程组分和气化段固定碳转化率由GA-综合计算法得出,实现了GA-综合计算法和流程模拟的复合, 其合成气模拟值与实验值接近,较好地反映生物质热解气化流程,为生物质热解气化产率分布及流程参数优化提供指导。     

煤气化过程的模型和模拟与优化操作

介绍了煤气化过程的模型和煤气化过程采用机理模型的理由，固定床煤气化过程机理模型的建立以及模拟计算的结果，并探讨了固定床水煤气化炉和流化床水煤气炉制气过程优化操作参数的确定。开发的数学模型已用于制气炉的模拟计算，与实测数据比较符合，由气化过程的数学模拟气化过程不同条件下各种参数的变化规律，进而可得出气化过程的优化操作条件，其确定过程比试验法安全，省时，省料。     

Ignition of composite propellant at subatmospheric pressures by means of carbon dioxide laser

Ignition behavior of solid propellant composed of 25 wt% polybutadiene and 75% ammonium perchlorate under subatmospheric conditions has been studied using a carbon dioxide laser whose radiant flux is uniformalized. Data of ignition time in Ar, N₂ and He atmospheres, and critical radiant flux and pressures over which ignition might be achieved, were obtained. Moreover, the data were compared with theoretical values, taking account of variable heat conductivity for the ambient gases with a surface ignition hypothesis. It is concluded that these ambient gases participate in the pre- and post-ignition reactions and the ignition preventive behavior of He atmosphere is not predictable merely based on its high transport properties. The detailed observation of the ignition transient near the critical pressure revealed that the ignition in Ar atmosphere occurs in gas phase under less than 100 torr whereas in He atmosphere it occurs always at the condensed phase surface.     

AspenPlus软件应用于煤气化的模拟

用AspenPlus软件对煤气化过程进行模拟，同时考察操作条件的改变对煤气化性能的影响。计算时假定煤气化反应分成两部分：煤的热裂解和气化炉内进行的一系列化学反应。用CPD模型预测煤热裂解的产物分布，并假定所有反应遵循Gibbs自由能最小的原理。计算结果与气流床的煤气化反应结果比较符合。     

Errors and noise in laser-recoil measurements

A study of noise and error sources encountered during development of a laser-recoil test capability is reported. The laser-recoil technique is a method of evaluating the response of a burning energetic material to fluctuations of radiant heat flux, usually supplied by a laser. The technique involves measuring the extremely small recoil force imparted as the burning gases leave the surface. This technique offers the advantages of small sample size, reduced cost, and potentially improved accuracy over the existing acoustic T-burner technique but has the disadvantage of high sensitivity to noise because of the small magnitude of the recoil force to be measured. Noise sources identified include electrical ground loops, thermal drift, structural vibrations, acoustics, and low-frequency atmospheric pressure variations. Remedial changes reduced the overall noise level by a factor of five and extended the usable measurement range from 200 to 700 Hz. Tests and analyses of several potential errors are discussed, including demonstration of linear behavior at input heat-flux modulation levels up to 25%. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 1, pp. 31–42, January–February, 2000.     

考虑肋片与内外管壁辐射换热时肋片温度与散热量计算

建立了肋片与内外管壁的辐射换热方程及肋片的温度分布计算方程 ,分析了它们之间的辐射换热对肋片温度、散热量和外壁温度的影响