立式激波管内云雾爆轰胞格尺寸的测定与分析

采用烟迹技术在立式激波管中测定了环氧丙烷、90#汽油、硝酸异丙酯、庚烷、癸烷、戊二烯等几种燃料气液两相云雾爆轰的胞格尺寸。结果表明,云雾爆轰的胞格尺寸随当量比的变化呈U形曲线关系,且最小胞格尺寸并不是对应于等化学当量比而是偏向于富燃料一侧,这与气相爆轰的结论是一致的。胞格尺寸随起爆能的增加而减小。当起爆能达到一定值后,胞格尺寸变化不明显,若起爆能继续增加,在通常的胞格内出现精细结构。云雾爆轰波胞格长度与宽度的比值比气相爆轰小。另外,根据烟迹记录分析了云雾爆轰作用机制,认为液滴的碎解、汽化过程以及燃烧区前导是控制气液两相云雾爆轰的主要因素。     

液体碳氢燃料云雾爆轰特性的实验研究

采用升降法和烟迹技术在立式激波管中分别实测了液态燃料（环氧丙烷、硝酸异丙酯、己烷、C5~C6、庚烷、癸烷）与空气混合物直接起爆的临界起爆能和胞格尺寸。数据表明,气液两相云雾爆轰的临界起爆能与当量比呈U形曲线关系,这与气相爆轰得到的结论是一致的;临界起爆能的最小值并不是对应于等化学当量的混合物而是偏向于富燃料;根据三波点运动的烟迹记录,分析了云雾爆轰作用机制,认为液滴的碎解、汽化过程以及燃烧区前导是控制气液两相云雾爆轰的主要步骤。此外,还测定了无限空间下可燃气云的临界起爆能,并将激波管内得到的临界起爆能数据外推到无约束气云的临界起爆能,理论推算结果与实验值吻合较好。     

燃料-空气云雾爆轰的直接引爆实验研

在直径240mm的立式激波管中环氧丙烷(PO)、正己烷、癸烷分别与空气混合进行了直接起爆,测定了不同燃料、不同当量比的云雾直接引爆的临界起爆能。实验发现,当PO 空气混合物、正己烷 空气混合物及癸烷 空气混合物的当量比分别为1.05、1.12及1.15时,其临界起爆能均最小;三种混合物的可爆下限当量比分别为0.47(质量浓度4.23%)、0.75(质量浓度5.29%)及0.89(质量浓度5.8%)。实验表明,在本实验条件下,三种燃料与空气混合物的云雾都容易在较大当量比范围内引发爆轰并实现爆轰波稳定传播。     

环氧丙烷-空气混合物爆轰波胞格结构的研究

对碳氢燃料云雾爆轰波胞格结构的影响因素进行了分析:比较了初始温度在25℃和100℃条件下碳氢燃料胞格尺寸,发现胞格尺寸相差不大;胞格尺寸随初始压力的降低而增大,在相对压力为负压条件下得到清晰的爆轰波胞格结构;起爆能的增大可以导致更加复杂的爆轰波次胞格结构出现。     

可燃液体爆燃特性及其抑制实验

设计了一套可燃液体爆炸特性实验装置,利用该装置和立式爆轰管对RP-5油料、RP-3油料及工业酒精的爆炸特性、1301惰性气体对这3种燃料的抑制进行了研究。结果表明:RP-5油料、RP-3油料及工业酒精爆炸的体积分数范围分别为1.53%～7.73%、0.82%～7.17%及 3.38%～18.25%;酒精云雾爆轰的临界起爆能为2.11 MJ/m2、爆速和爆压分别为1 609 m/s 、1 480 kPa,爆轰波传播的胞格宽度为14.5 mm,长度为16.2 mm。1301惰性气体对RP-5油料、RP-3油料及工业酒精的最小惰化体积分数分别为6.75%、6.8%及 5.56%;二氧化碳和氮气对RP-3油料的最小惰化体积分数分别为45%和49%;1301惰性气体对油料爆炸抑制效果明显好于二氧化碳与氮气。     

C2H4-O2混合气体直接起爆的临界能量

主要基于化学动力学和Ng模型,对C2H4-O2混合气体的爆轰胞格尺寸进行预测;结合Lee表面积能量模型,预测物质在不同初始压力和化学当量比的条件下,直接起爆引起球面爆轰的临界起爆能量。直接起爆实验主要采用高压电点火提供起爆能量,起爆能量通过放电过程中电流的输出信号确定。结果表明,理论预测与实验值较吻合。首先,通过化学动力学计算得出ZND模型的爆轰参数,利用Ng模型得出爆轰胞格尺寸与ZND诱导区长度之间的比例因数A在不同初始压力与当量比的条件下分别为:A=43.815(1+p1/p0)-0.123 71和A=8.531exp(φ/3.135)+28.644,在此基础上对爆轰胞格尺寸进行定量预测。胞格尺寸的理论预测与实验结果吻合。其次,把爆轰胞格尺寸作为中间特征参数并结合Lee的表面积能量模型,提出可以预测临界起爆能量的定量模型,并得出C2H4-O2混合气体直接起爆的临界起爆能量与初始压力和化学当量比的参量拟合关系分别为Ec=0.332(p1/p0)-2.017和Ec=exp[3.951(φ-1.401)2-1.9]。     

直管内胞格爆轰的基元反应数值研究

基于基元反应和二维欧拉方程，对直管内胞格爆轰进行了数值模拟。采用5阶WENO(weighted essentially nonoscillatory scheme)求解对流项，采用2阶附加半隐的龙格-库塔法处理化学反应源相引起的刚性。获得了密度、压力、温度和典型组元质量分数流场及数值胞格结构等。结果表明:网格精度的差异明显影响胞格的规则性和爆轰的平衡模数，随着网格尺度的减小，胞格由不规则变为规则。预混气组成、初压、初温及管道宽度给定，三波点数收敛为确定值。足够强度的初始扰动可再现胞格爆轰，最终形成的自持胞格爆轰模数与初始扰动的形状、大小、位置均无关。沿胞格中心线，爆轰波速度变化范围为0.88DCJ~1.5DCJ，爆轰波平均速度与CJ爆轰速度仅偏差0.88％。峰值压力与初压之比为14~50。计算爆轰波平均速度、胞格宽长比与实验值基本一致，但计算胞格宽度比实验值略小。数值模拟加深了对横波的产生和发展、未反应气囊、爆轰胞格的二次起爆等胞格爆轰特性的认识。     

液态燃料对连续旋转爆轰发动机爆轰特性的影响

为了研究液态燃料对连续旋转爆轰发动机爆轰特性的影响,采用CE/SE方法对以汽油/富氧空气为燃料的CRDE进行数值模拟,分析了不同液滴半径、当量比对爆轰性能参数的影响。计算结果表明:随着液滴半径增大,爆轰压力峰值、温度峰值以及爆轰波速度均降低,且压力峰值与温度峰值在爆轰波传播过程中出现不稳定现象;当增大到70 μm时,爆轰波将无法成功起爆。随着当量比的增大,CRDE爆轰波速度及平均推力增大,爆轰压力、温度以及气相周向速度的峰值均先增大后减小。在当量比1.1附近,爆轰压力与温度的峰值出现极大值;而气相周向速度峰值的极大值出现在当量比0.9附近。基于燃料的比冲随着当量比增大而减小。     

FAE爆炸场超压与威力的实验研究

利用现场测试系统动态灵敏度标定技术,分别等精度测试了FAE和TNT爆炸场峰值超压。在此基础上获得了各自的爆炸波峰值超压随传播距离的拟合曲线和TNT当量比。结果表明:FAE爆炸场超压分布规律与TNT有显著区别,前者属于大体积云雾爆炸,爆炸场可划分为云雾爆轰区、云雾边缘区和冲击波作用区;在云雾爆轰区,超压平均值在2.6MPa左右,在小于2/3云雾半径的范围内比同质量的TNT低,在大于2/3的云雾半径范围则显著大于TNT;在冲击波作用区,环氧丙烷燃料的FAE爆炸超压约是TNT爆炸效果的5倍,超压均呈衰减趋势,但FAE衰减比TNT缓慢许多。     

含RDX四组元HTPB固体推进剂的冲击起爆特性研究

为了研究含RDX四组元HTPB固体推进剂的冲击起爆行为和在低温条件下的适应性,在常温和低温条件下,对该固体推进剂进行了冲击加载拉氏分析实验。采用锰铜压力计测量了推进剂中不同位置处的压力变化历程,采用电离探针测量了固体推进剂的爆速。分析了固体推进剂的爆轰成长规律,获得了推进剂的临界起爆压力、爆速、爆压和爆轰成长距离等爆轰特征参量。通过对比不同条件下的特征参量发现,低温对固体推进剂的冲击起爆特性影响较小。此外,还对固体推进剂的冲击起爆过程进行了数值模拟,标定了固体推进剂点火增长模型的反应速率方程参数和推进剂的未反应JWL状态方程参数。     

Experimental study on detonation parameters and cellular structures of fuel cloud

In this paper,detonation parameters of fuel cloud,such as propylene oxide(PO),isopropyl nitrate(IPN),hexane,90 # oil and decane were measured in a self-designed and constructed vertical shock tube.Results show that the detonation pressure and velocity of PO increase to a peak value and then decrease smoothly with increasing equivalence ratio.Several nitrate sensitizers were added into PO to make fuel mixtures,and test results indicated that the additives can efficiently enhance detonation velocity and pressure of fuel cloud and one type of additive n-propyl nitrate(NPN) played the best in the improvement.The critical initiation energy that directly initiated detonation of all the test liquid fuel clouds showed a U-shape curve relationship with equivalence ratios.The optimum concentration lies on the rich-fuel side(φ > 1).The critical initiation energy is closely related to molecular structure and volatility of fuels.IPN and PO have similar critical values while that of alkanes are larger.Detonation cell sizes of PO were respectively investigated at 25 C,35 C and 50 C with smoked foil technique.The cell width shows a U-shape curve relationship with equivalence ratios at all temperatures.The minimal cell width also lies on the rich-fuel side(φ > 1).The cell width of PO vapor is slightly larger than that of PO cloud.Therefore,the detonation reaction of PO at normal temperature is controlled by gas phase reaction.     

An experimental study on DDT distance of JP-8 mixtures

Previous research into detonation physics has mostly utilized gaseous fuels such as hydrogen, acetylene, ethylene, and propane. If these fuels were to be used for a pulse detonation engine, they have to be stored under high pressure in steel containers which increase weight safety risks. In order to increase energy density of fuel, liquid fuel was chosen. Tests were conducted on detonation initiation of JP-8/oxygen mixtures at different initial temperatures and equivalence ratios. These tests found a reduction in the rich limit with increasing initial temperature, and the minimum deflagration-to-detonation run-up distance was approximately 200 mm, which was similar to propane/oxygen mixture results. A rapid increase in deflagration-to-detonation run-up distance was observed at equivalence ratios close to the lean and rich limits. Experiments of JP-8/oxygen and propane/oxygen mixtures with nitrogen dilution were also conducted. As the nitrogen/oxygen ratio increased, the lean and rich limits decreased while the detonation wave could not be successfully initiated as the nitrogen-to-oxygen ratio was greater than 0.4.     

氢气/丙烷/空气预混气体爆轰性能的实验研究

通过采用压力传感器和烟灰板两种测试设备,开展了常温常压下氢气/丙烷和空气混合气体爆轰性能的实验研究。实验过程中观察到自持爆轰波,爆轰速度比值在0.99~1之间,爆轰压力比值在0.8~1.2之间。爆轰胞格尺寸在10~50 mm范围内,建立了爆轰胞格尺寸和化学诱导长度的关系式。随着丙烷不断添加,爆轰速度减小,而爆轰压力和胞格尺寸增加。这种变化趋势起初较快,而后变缓。因为起初氢气摩尔分数较大,混合气体趋向于氢气/空气的爆轰性能;而后因丙烷摩尔质量较大,丙烷逐渐起主要作用,混合气体表现出丙烷/空气的爆轰性能。     

基于液体碳氢燃料的旋转爆轰燃烧特性研究

为了探索液体碳氢燃料参与旋转爆轰所产生的不完全燃烧现象,采用守恒元与求解元方法,开展柱坐标系下的汽油/空气两相旋转爆轰燃烧室三维数值模拟研究,针对燃料喷注压力和反应物当量比对旋转爆轰流场结构及燃烧室性能的影响进行分析。分析结果表明:保持总当量比为1.00,随着燃料喷注压力的上升,燃烧室内燃料不均匀分布增强,产生局部富燃区,燃料在燃烧室未能完全反应,导致燃烧室燃料比冲下降;保持喷注压力不变,减小当量比,在贫燃工况下依然存在局部富燃区,导致燃烧室内出现不完全燃烧现象,降低燃烧室比冲性能。由此可知,反应物喷注方案对气液两相旋转爆轰的不完全燃烧有显著影响。     

Detonability of fuel-oxygen and fuel-air mixtures

An analysis of theoretical models and experimental investigations of the detonability of unconfined detonation in uniform gaseous mixtures shows a disparity in results. The present study is limited to propane, acetylene and methane diluted with oxygen or air in variable proportions and initial pressures at ambient temperature conditions. Because of the disparity in results, a simple and general formulation of critical initiation energy for gaseous detonations has been investigated. The problem has been formulated using the conservation equation of total energy enclosed by the shock. From this, a simple form for the critical energy has been deduced. This approach leads to a good simulation in uniform mixtures, regardless of initiation conditions. Some applications are presented in this paper. A new experimental study on the detonability of methane/oxygen mixtures diluted with propane and/or nitrogen is reported. The gaseous mixtures are confined in a cylindrical vessel. The initial conditions are various equivalence ratio and pressure under room temperature. In the case of methane/oxygen mixtures, the predetonation radius varies directly with the cell width. The constant ratio is in the order of 18, slightly different from the classical relation R _c= 20λ. For propane the slope variation of the critical energy versus initial pressure depends on the dilution. We have compared the critical energy obtained by several authors with the theoretical values. Fuel ratio and initial pressure are the chosen parameters. These comparisons show that the formulation allows for the prediction of the critical energy of detonation of uniform mixtures with a good estimation range. The correlation between the different geometries has been deduced and a test has been conducted as well in the case of stoichiometric methane/oxygen and acetylene/oxygen mixtures versus initial pressure for a cylindrical detonation. Received 9 January 1996 / Accepted 24 January 1997