十二氢十二硼酸双四乙基铵的点火与燃烧特性

为了探索十二氢十二硼酸双四乙基铵(Et_4N)_2B_(12)H_(12)的点火与燃烧特性,采用激光点火实验测定了当量直径为1.11mm试样的点火与燃烧参数,同时采用热重-质谱联用技术测定了材料在氮气和空气气氛中的热解行为,探究了其燃烧过程机制。结果表明,十二氢十二硼酸双四乙基铵具有较高的热稳定性,在氮气及空气中加热至300℃以上发生裂解,在裂解过程中材料会同步氧化,加热至约650℃时材料强烈氧化增重;该材料的点火燃烧性能较好,激光点火能量密度为4.72×10~6W/m~2时其点火延迟时间为45.8ms,总燃烧时长为2.467s,燃烧过程中样品表面温度在1600～1800℃;结合热解行为推断其在燃烧过程中不仅释放出H_2,同时发生骨架裂解释放出碳氢燃气,碳氢燃气燃烧可导致燃烧过程中出现明显的烟气痕迹。     

MgH2对含能材料点火燃烧性能影响的实验研究

为了研究MgH_2对典型含能材料点火燃烧性能的影响规律,采用激光点火和高速摄影可视化技术对MgH_2与RDX等5种含能材料的混合物进行了点火延迟时间和火焰传播速度的测试与计算。结果表明,MgH_2的质量分数为50%和11.1%时对于提高RDX点火燃烧性能的效果最佳;质量分数11.1%的MgH_2最有利于HMX点火燃烧性能的改善;对于CL-20,添加质量分数20%～33.3%的MgH_2可显著提升其火焰传播速度,但是当MgH_2的质量分数为50%和11.1%时混合物的点火延迟时间更短;FOX-7和ADN与MgH_2混合物的点火延迟时间均小于含能组分和MgH_2各自的点火延迟时间,即此类含能材料与MgH_2的点火过程具有相互促进的作用;综合考虑FOX-7点火性能和火焰燃烧性能的提升,添加质量分数11.1%的MgH_2最为有利;MgH_2对ADN点火燃烧性能的提升与MgH_2的添加量成正比。MgH_2促进含能材料点火燃烧性能提升的原因在于MgH_2的分解产物促进了含能材料相态转变,最终促进了点火燃烧性能的提升。     

RDX聚光点火和反应过程的光学诊断

为拓展含能材料在聚光加热下点火和燃烧特性的实验方法,探究了燃烧反应过程中的物种变化及化学反应,基于聚光点火平台,采用高速摄影、化学发光、激光诱导荧光的方法,研究了聚光点火前后RDX反应的自发光过程、NO化学发光信号变化和RDX火焰内部OH自由基的二维浓度分布。结果表明,RDX聚光点火和反应过程分为4个阶段,分别为吸热、蒸发热解、点火和反应结束;整个反应过程的点火延迟时间为16.735s,燃烧持续时间为355ms,而高延迟的原因是由于聚光点火能量较低所致;NO化学发光显示,NO的产生存在明显的两阶段生成过程,且NO的生成受RDX蒸气和HCN、NO_2多种分解产物影响;OH的高浓度区主要分布于火焰的中部两翼,可由NO反应而产生。     

全氟十四酸包覆纳米铝粉的制备及点火燃烧性能

在氮气气氛下,采用全氟十四酸(FS)对纳米铝粉(nmAl)进行了表面包覆,采用扫描电镜(SEM)、X射线衍射(XRD)和傅里叶变换红外(FT-IR)光谱对其形貌和结构进行了表征.用激光点火装置和低压火药燃烧测试装置对表面处理前后纳米铝粉的点火燃烧性能进行了研究.结果表明,全氟十四酸包覆的纳米铝粉(nmAl/FS),其分散性提高,颗粒分布更均匀;全氟十四酸羧基中的两个氧原子与纳米铝粉表面的A1原子以桥接的方式相结合;与未处理的纳米铝粉相比,在激光热流密度较低时,nmAl/FS的点火延迟时间短;在激光点火燃烧过程中,nmAl/FS的燃烧反应较剧烈,火焰亮度高,在低压火药燃烧测试装置中燃烧时,其燃烧火焰更集中,火焰亮度更高,燃烧更充分.     

不同气氛对铝粉点火燃烧特性的影响分析

为了研究流化气体对粉末推进剂点火燃烧性能的提高作用,采用CO_2激光点火器和光纤光谱仪相结合的实验方法,研究了不同气氛条件下Al粉的点火燃烧特性。采用光谱信号拟合测温法计算了Al粉在不同气氛环境中的点火温度。结果表明,常压环境下,粒径1μm的Al粉在N_2O和空气氛围下的点火延迟时间分别为10ms和359ms,从点火成功过渡到全面燃烧的时间分别为829ms和1 579ms,说明Al粉在N2O环境中点火阶段的表面异相反应速率与燃烧阶段的反应速率均快于在空气中;粉径1μm的Al粉在N2O和空气环境下的点火温度分别为1 550~1 650K和1 450~1 500K,两者相近,但都明显低于毫米级Al粉的点火温度(2 300K),说明Al粉的点火温度受粒径影响较大。     

氨硼烷分解制氢及其再生的研究进展

氨硼烷具有储氢密度高（152.9g/L）、放氢条件温和、无毒以及常温下为稳定的固体而易于储运等特点而成为最有前景的储氢材料之一。本文综述了近年来氨硼烷在不同催化剂作用下,通过热解、醇解和水解这3种方式制氢以及分解后的副产物循环再生氨硼烷的研究进展。分析讨论了氨硼烷的热解制氢研究主要集中在降低温度和抑制气态副产物的生成这两方面,而水解或醇解制氢的研究热点是二元或三元非贵金属纳米核壳或负载型催化剂。与氨硼烷的热解相比,水解或醇解由于条件温和、制氢速度快而更具实用性。指出氨硼烷作为储氢材料最大的挑战是其再生问题,氨硼烷分解脱氢后的副产物不能直接氢化而再生氨硼烷,需要通过一系列反应来进行间接的离线再生,因此氨硼烷的再生将是今后的重点研究方向。     

四种混合不同碳材料的FOX-7粉末激光点火：点火延迟实验与简化计算（英文）

针对1,1-二胺-2,2-二硝基乙烯(FOX-7)因点火相对困难而限制其广泛应用的问题，利用CO₂激光器在一定的功率密度范围对4种混合不同碳材料的FOX-7粉末开展了点火实验，研究点火延迟时间的变化趋势。采用两种简化模型对点火延迟时间进行计算与分析，以探究点火机理和指导FOX-7的点火性能提升。结果表明，几种碳材料的添加会导致FOX-7粉末点火延迟时间发生不同程度的缩短。石墨烯和氧化石墨烯在缩短点火延迟方面表现出相对较强的促进作用，石墨的效果较为轻微。计算结果显示，模型1比模型2更适合预测FOX-7粉末的点火延迟时间。机理分析表明，石墨烯的添加能够有效提升FOX-7粉末对辐照能量的吸收且减小能量损失。研究表明FOX-7粉末样品的主要点火诱导过程受到激光辐照下传热性质的强烈影响。     

铝粉-空气混合物的燃烧转爆轰过程

利用自行设计的长29.6 m、内径199 mm配有40套喷粉扬尘装置的大型水平爆轰管,研究了细片状铝粉-空气混合物在40 J弱点火条件下火焰从发生到加速、最后实现爆轰转捩的全过程,探讨了铝粉浓度和点火延迟时间对爆轰参数的影响.结果表明,铝粉-空气混合物燃烧转爆轰(DDT)过程可分为慢速反应压缩阶段和快速反应冲击阶段.当点火延迟时间为370 ms,铝粉质量浓度为300 g/m~3时,在管道中距离点火位置83倍长径比处峰值超压为9.8 MPa,爆速为1 670 m/s,发生了DDT过程.在铝粉-空气混合物自持爆轰波的传播过程中,由于呈现螺旋爆轰波结构,爆速和峰值超压随着传播距离振荡.     

金属/AP颗粒混合物燃烧特性的光谱分析

为了使Al/AP双组元粉末火箭发动机密度比冲最大化,将燃烧室特征长度由2.31 m增至 12.62 m进行了Al/AP粉末火箭发动机点火测试.采用光谱仪、CCD 相机、CO2 激光点火器等对 Al/AP 混合物在 1.0132 5 × 105 Pa的氮气环境中的点火延迟、燃烧时间、燃烧平稳性等燃烧性能进行了研究.测量了Al颗粒的表观堆积密度.作为一种替代燃料,对镁颗粒也进行了研究.结果表明,增加燃烧室特征长度至 12.62 m 时,可以得到最大燃烧室压强振荡幅度±2 .43%的平稳燃烧性能.含粒径 1μm 铝粉的 Al/AP 混合物其燃烧过程的光强远大于含粒径10μm铝粉的样品,并且其在波长 568 nm 发射光谱的光子数强度超过了光谱仪检测上限(65 000 数).而含粒径10μm铝粉样品燃烧过程的568 nm发射光谱信号出现间断且其全程强度低于 19 036 数.粒径 10μm 铝粉点火延迟时间为粒径1μm铝粉点火延迟时间的3.65 倍,燃烧时间为3.03 倍以上,最大RAlO却比 1μm铝粉少 14.3%,密度低21 .3%,说明粒度小的铝粉具有更好的燃烧性能,但是其堆积密度也更低.虽然Mg/AP的理论比冲为Al/AP的95.6%,但是其堆积密度比粒径1μm铝粉高8%,其点火延迟时间比粒径10μm铝粉短 90.3%.火焰照片也表明镁粉可在很大程度上减少凝相沉积.     

金属/AP颗粒混合物燃烧特性的光谱分析（英文）

为了使Al/AP双组元粉末火箭发动机密度比冲最大化,将燃烧室特征长度由2.31m增至12.62m进行了Al/AP粉末火箭发动机点火测试。采用光谱仪、CCD相机、CO2激光点火器等对Al/AP混合物在1.0132 5×105Pa的氮气环境中的点火延迟、燃烧时间、燃烧平稳性等燃烧性能进行了研究。测量了Al颗粒的表观堆积密度。作为一种替代燃料,对镁颗粒也进行了研究。结果表明,增加燃烧室特征长度至12.62m时,可以得到最大燃烧室压强振荡幅度±2.43%的平稳燃烧性能。含粒径1μm铝粉的Al/AP混合物其燃烧过程的光强远大于含粒径10μm铝粉的样品,并且其在波长568nm发射光谱的光子数强度超过了光谱仪检测上限(65 000数)。而含粒径10μm铝粉样品燃烧过程的568nm发射光谱信号出现间断且其全程强度低于19 036数。粒径10μm铝粉点火延迟时间为粒径1μm铝粉点火延迟时间的3.65倍,燃烧时间为3.03倍以上,最大RAlO却比1μm铝粉少14.3%,密度低21.3%,说明粒度小的铝粉具有更好的燃烧性能,但是其堆积密度也更低。虽然Mg/AP的理论比冲为Al/AP的95.6%,但是其堆积密度比粒径1μm铝粉高8%,其点火延迟时间比粒径10μm铝粉短90.3%。火焰照片也表明镁粉可在很大程度上减少凝相沉积。     

垃圾衍生燃料燃烧历程的试验研究*

采用热重、质谱和红外测试等热分析技术,对垃圾衍生燃料(RDF)在不同气氛、不同升温速率、不同氧化钙和无烟煤掺量条件下燃烧过程的失重特性进行了研究。结果表明:(1)垃圾衍生燃料的燃烧过程包含四个阶段,第一阶段为自由水的蒸发过程;第二和第三失重段在空气气氛下表现为纤维类和橡胶等物质的裂解与燃烧,在氮气条件下体现为裂解;第四阶段为固定碳的燃烧及燃烧中间产物的分解过程。(2)空气气氛下的失重速率高于氮气气氛。(3)氧化钙和无烟煤的掺入可以提高RDF的着火温度、延缓燃尽时间。     

Thermal properties of polyethylene flame retarded with expandable graphite and intumescent fire retardant additives

Low‐density polyethylene was flame retarded by combinations of expandable graphite with either ethylenediamine phosphate or 3,5‐diaminobenzoic acid phosphate. Cone calorimeter, laser pyrolysis, and open flame exposure tests (supported by video and infrared camera data capture and analysis) were conducted to assess ignition and burn behavior. Cone calorimeter results indicated substantial reductions in the peak heat release rates for all flame‐retarded samples but with reduced ignition times and increased flame out times. Smoke generation was suppressed in the presence of expandable graphite. Infrared and video data from open flame fire tests indicated cohesive bonding of expanded strings and thermal shielding properties in all binary systems. All binary systems delivered fire retardation exceeding any of the single fire retardant compounds. They were also able to withstand higher temperatures before ignition, burn through, or sag occurred. All ethylenediamine phosphate‐containing binary systems prevented sample burn through, maintaining structural integrity of samples until eventual melting of the polymer media occurred. Thermogravimetric analysis laser pyrolysis results confirmed the good thermal shielding imparted by the intumescent additives. Copyright © 2016 John Wiley & Sons, Ltd.     

Numerical modeling of straw combustion in a fixed bed

Straw is being used as main renewable energy source in grate boilers in Denmark. For optimizing operating conditions and design parameters, a one-dimensional unsteady heterogeneous mathematical model has been developed and experiments have been carried out for straw combustion in a fixed bed. The straw combustion processes include moisture evaporation, straw pyrolysis, gas combustion, and char combustion. The model provides detailed information of the structure of the ignition flame front. Simulated gas species concentrations at the bed surface, ignition flame front rate, and bed temperature are in good agreement with measurements at different operating conditions such as primary air-flow rate, pre-heating of the primary air, oxygen concentration, moisture content in straw, and bulk density of the straw in the fixed bed. A parametric study indicates that the effective heat conductivity, straw packing condition, and heat capacity of the straw have considerable effects on the model predictions of straw combustion in the fixed bed.     

铝–油酸/正庚烷基纳米浆体燃料液滴着火燃烧特性

采用液滴悬挂法研究了正庚烷液滴、油酸/正庚烷混合燃料液滴、含20wt%纳米铝粉的铝–油酸/正庚烷基纳米浆体燃料液滴在不同温度下(600~800℃)的着火燃烧特性。用高速摄像机观测液滴进入管式电阻炉后的着火燃烧过程，使用热电偶记录液滴周围的气相温度变化，同时通过对应的温度曲线计算液滴的着火延迟时间。结果表明，纳米铝粉和油酸的添加均能降低正庚烷液滴的着火延迟时间。随温度升高，正庚烷、油酸/正庚烷混合燃料、铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间显著降低，但变化趋势逐渐趋于平缓。铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间与环境温度满足阿累尼乌斯方程。与纯正庚烷、油酸/正庚烷混合液滴的燃烧过程相比，铝–油酸/正庚烷基浆体燃料液滴的燃烧过程有显著差异，其燃烧经历3个阶段：正庚烷稳定燃烧阶段、正庚烷微爆炸阶段和表面活性剂微爆炸阶段。铝–油酸/正庚烷基浆体燃料液滴燃烧时间延长，火焰熄灭后又复燃，且燃烧过程中发生剧烈的火焰形变和铝颗粒溅射现象，大部分铝以团聚体形式在第三阶段完成氧化还原反应。     

油炸干燥污泥的热解与燃烧特性研究

在氮气和空气气氛下,利用热重分析方法研究了40%含油率的油炸污泥的热解和燃烧特性。结果表明,油炸污泥的热解反应主要在189至550℃,在700℃时基本完成,实验条件下,油炸污泥样品着火点为290℃,燃尽温度为660℃。     

The relationship of knock during controlled autoignition to temperature inhomogeneities and fuel reactivity

Experiments have been performed in a rapid compression machine (RCM), to investigate the conditions for and the origins of ‘knock’ in controlled autoignition (CAI), or homogeneous charge compression ignition (HCCI). Ignition in an RCM is the closest approach to that in a CAI engine without engendering the full complexity of reciprocating motion and fuel+air charge induction. As a representative fuel of intermediate reactivity, the combustion of n-pentane in air was studied at the compositions φ=1.0, 0.75 and 0.6 at end-of-compression pressures of 0.80-0.86 MPa (7.9-8.4 bar) and 1.4-1.5 MPa (13.8-14.8 bar), respectively, over the compressed gas temperature range 690-820 K. Autoignition is characterised by a two-stage development in these ranges of conditions, a ‘cool flame’ being followed by hot stage combustion.Filtered Rayleigh scattering from a planar laser sheet was used to characterise the temperature field that developed in the combustion chamber following rapid compression. High resolution pressure records, combined with image intensified, natural light output originating from chemiluminescence, were used to characterise the transition from non-knocking to knocking reaction and the evolution of the spatial development of chemical activity in this temperature field. It appears that knock originates from a localised development of the incandescent hot stage of ignition. Even though non-homogeneities prevail in the non-knocking reaction, it is associated with a relatively benign development, in which the cool flame is followed by a second stage, blue flame rather than the normal incandescent hot flame. The kinetics that may contribute to this distinction are discussed.     

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。     

Formation and reduction of nitric oxide in fixed-bed combustion of straw

Mechanisms of nitric oxide (NO) formation and reduction in fixed-bed combustion of straw have been modeled mathematically and verified experimentally. The model for the straw combustion and nitrogen chemistry consists of sub-models for evaporation, pyrolysis, tar and char combustion, nitrogen conversion, and energy and mass conservation. Twenty chemical reactions are included, of which 12 belong to the fuel nitrogen reaction network. Volatile nitrogen is assumed to be NO, NH₃, HCN and HNCO, and char nitrogen is converted to NO during char oxidation. The model predictions are in qualitative agreement with the measurements during the ignition phase, i.e. when the combustion front passes through the un-burnt fuel. The yield of NO can be reduced considerably by using a low primary air flow due to the longer gas residence in the fixed-bed, while the NO exhaust concentration is insensitive to the bed temperature. The NO exhaust concentration initially reaches a maximum and then decreases towards a stable value after the straw bed is ignited. Variations of NO, NH₃, HCN, and HNCO concentrations in the ignition flame front indicate that a large quantity of NO can be reduced in the thin flame front zone. The developed model is further validated by separate experiments in which NO or NH₃ was added at the middle through tubes or at the bottom of the bed with the primary air flow. Both the simulations and measurements showed that the variation of the NO exhaust concentration is small as compared with the injected NO or NH₃ concentration. According to the simulations and experiments, it is proposed that flue gas recirculation may be a very effective method of reducing NO emissions from flue gas in the fixed-bed combustion of straw. Calculations indicated that about 20% of the flue gas may be recirculated without significantly affecting the combustion behavior.     

Decomposition and Ignition of the High‐Nitrogen Compound Triaminoguanidinium Azotetrazolate (TAGzT)

The high‐nitrogen compound triaminoguanidinium azotetrazolate (TAGzT) belongs to a class of C, H and N compounds that are free of both oxygen and metal, but retain energetic material properties as a result of their high heat of formation. Its decomposition thus lacks secondary oxidation reactions of carbon and hydrogen. The fact that TAGzT is over 80% nitrogen makes it potentially useful as a gas generant and energetic material with a low flame temperature to increase the impulse in gun or rocket propellants. The burning rate, laser ignition and flash pyrolysis (T‐jump/FTIR spectroscopy) characteristics were determined. It was found that TAGzT exhibits one of the fastest low‐pressure burning rates yet measured for an organic compound. Both the decomposition and ignition behavior of TAGzT are dominated by condensed phase reactions. T‐Jump/FTIR spectroscopy indicates that condensed phase reactions release about 65% of the energy, which helps to explain the high burning rate at low pressure.