镁颗粒-空气混合物一维非稳态爆震波特性数值模拟研究

镁颗粒因其能量密度高、点火特性和燃烧效率好的优势,作为燃料或添加剂应用于爆震燃烧动力系统具有广阔的应用前景.本文建立了镁颗粒-空气混合物的一维非稳态爆震波模型,数值模拟爆震波传播过程及其内部流场分布.研究结果表明,爆震波传播过程中爆震波压力峰值和空间分布均存在小幅度波动.考虑燃烧产物氧化镁在颗粒表面的沉积过程,镁颗粒的反应速率和爆震波的稳定传播速度增大.在考虑爆震管壁面损失的前提下,随管径减小,爆震波稳定速度和厚度均减小,同时爆震波内未能反应的镁颗粒比例增大.考虑壁面损失条件下,爆震波稳定传播速度以及厚度均随颗粒初始粒径的增大而减小,且镁颗粒初始为双粒径分布时对应的爆震波速度和厚度明显低于镁颗粒初始为统一单粒径的工况;稳定传播速度随颗粒初始当量比的增大而先增后减,厚度随初始当量比的增加单调递减. MgO熔化发生在CJ平面附近时, MgO熔化过程对爆震波传播稳定性无明显影响,而爆震波厚度显著增大.选取适当的点火区参数,能够使爆震波达到稳定传播状态所经历的距离明显缩短.     

涡轮导向器对旋转爆轰波传播特性影响的实验研究

为了研究涡轮导向器对旋转爆轰波传播特性的影响,以氢气为燃料,空气为氧化剂,在不同当量比下开展了实验研究.基于高频压力传感器及静态压力传感器的信号,详细分析了带涡轮导向器的旋转爆轰燃烧室的工作模式以及涡轮导向器对非均匀不稳定爆轰产物的影响.实验结果表明:在当量比较低时,爆轰燃烧室以快速爆燃模式工作;逐渐增大当量比,爆轰燃烧室开始以不稳定旋转爆轰模式工作;继续增大当量比,爆轰燃烧室以稳定旋转爆轰模式工作,且旋转爆轰波的传播速度和稳定性均随当量比的增大逐渐提高.爆轰波下游的斜激波与涡轮导向器相互作用,涡轮导向器对压力振荡的幅值具有明显的抑制作用,但对压力振荡频率的影响较小.随着当量比的增大,涡轮导向器上下游的静压均同时增大,经过涡轮导向器的作用,涡轮下游静压明显降低.     

当量比对圆盘结构下旋转爆震波传播的影响

为研究反应物当量比对旋转爆震波传播过程的影响，在圆盘形旋转爆震发动机上进行H₂/air的旋转爆震实验研究，并统计分析了当量比对爆震波传播模态及参数的影响规律.实验结果表明，固定质量流率，同一种传播模态下，随着当量比的增大，爆震波的压力峰值及传播速度增大，且旋转爆震波的传播过程更加稳定.不同质量流率条件下，当量比对传播模态的影响规律不同.空气质量流率小于100 g/s时，旋转爆震波皆以单波模态传播.空气质量流率大于150 g/s时，随着当量比的增大，旋转爆震波的传播模态由单波模态向双波模态转变，再转变为不对称双波模态，最后又回到单波模态.并且在不对称双波模态中发现了低频振荡现象，振荡频率约为300 Hz.质量流率继续增大，燃烧室中发现了同向三波传播模态.随着质量流率的增加，双波模态的当量比下限降低，不对称双波模态的当量比上限增大，而双波与不对称双波模态的分界线受质量流率的影响较小.      

燃烧过程测量、模拟及爆震燃烧技术应用专题序言

爆震燃烧是基本的燃烧模态之一具有极高的强度和极快的燃烧速率以其构建热力循环并将其应用于先进动力装置具有区别于爆燃燃烧过程的显著优势是人们始终追求的梦幻动力.然而也恰恰由于爆震燃烧过程剧烈因此在受限空间内形成稳定、可控、高频率的爆震波成为挑战.在工程上发展稳定的爆震燃烧动力装置需要解决可靠点火起爆、燃料/氧化剂快速掺混、爆震波稳定传播等关键技术难题.近些年连续旋转爆震取得了长足的进展.连续旋转爆震仅需单次成功点火在环形或者圆柱形燃烧室内形成周向传播的爆震波从而使得不断充入燃烧室的未燃混合气快速起爆.基于连续旋转爆震的火箭发动机、冲压发动机甚至连续旋转爆震涡轮发动机都取得了创造性的成绩.尽管在工程化应用的征途上仍然需要解决诸多爆震物理基础问题和关键技术但人们孜孜以求的决心和动力从未泯灭也必将带来颠覆性技术的诞生.     

初始点火条件引起的三维旋转爆震波单/双波传播模式

在不同工况下,旋转爆震波能够以单波、双波、多波模式进行传播.但在同一工况下,是否存在不同模式的稳定传播爆震波还有待进一步研究.基于Euler方程,耦合氢气/空气的有限化学反应速率模型,并采用高分辨率的5阶有限差分格式WENO-PPM5离散对流项,对三维旋转爆震波进行了数值模拟.计算结果表明,在同一特定工况下,旋转爆震波能够以两种不同的传播模式稳定传播,即单波模式和双波模式.详细地对比了两种传播模式下的流场特征、爆震波传播特性、推力性能等.在同一工况下,两种传播模式的爆震波周向传播速度相差不多,但双波模式的频率约为单波模式的2倍;双波模式下质量流量、比冲、推力的平均值均略高于单波模式;且双波模式的可燃混气层高度约为单波模式的1/2,这有助于缩小旋转爆震发动机的长度,使之更加紧凑.      

质量流率对旋转爆震波传播速度影响实验研究

实验研究了质量流率对旋转爆震波传播速度的影响,结果表明:对于给定几何结构的发动机,存在一个临界质量流率,当质量流率小于该值时,旋转爆震波的速度较低且存在较大随机性;当质量流率大于临界值时,旋转爆震波的速度变化趋势与CJ爆震理论一致。针对低质量流率工况下出现的较大速度亏损现象,提出了两种导致该现象的可能机制,即燃烧室发生声学耦合燃烧和燃烧产物在爆震波到达之前与反应物充分混合,进一步分析对比了这两种机制,分析结果表明,两种假设都能够较好解释低质量流率下爆震波的较大速度亏损现象,但燃烧室发生声学耦合燃烧的假设更符合实验结果。     

H_2/Air旋转爆震发动机起爆实验研究

为揭示旋转爆震发动机的点火特性,采用普通火花塞和高能火花塞作为发动机点火装置,对以氢气/空气为反应物的旋转爆震发动机进行了实验研究,结合高频压力测量与高速摄影结果分析了旋转爆震波的建立过程,并通过一系列点火实验得到了发动机的稳定工作范围。研究结果表明,两种点火方式均能成功起爆发动机,点火产生的燃烧波通过火焰加速与DDT过程形成旋转爆震波,增大点火能量能够大幅缩短旋转爆震波建立时间。发动机共有三种工作模式,稳定工作范围随燃料质量流量的增加而扩大,且不同工作模式会随反应物当量比的变化而相互转换。     

镁颗粒-空气混合物一维稳态爆震波特性数值模拟

镁颗粒因其能量密度高、点火特性和燃烧效率好的优势,作为燃料或添加剂应用于爆震燃烧动力系统具有广阔的应用前景.本文建立了镁颗粒-空气混合物的一维稳态爆震波模型,数值模拟爆震波稳态传播过程及其内部流场分布.结果表明,镁颗粒-空气混合物爆震波仅能以特征值速度稳定自维持传播,特征值爆震速度的高低并不仅仅取决于反应放热多少,两相间的相互作用也会影响热能向气相动能的转化效率.当爆震波末端氧化镁处于熔化过程时,满足一定的来流速度和镁颗粒密度条件,爆震波仍能够稳定自维持传播.气相吸收反应放热膨胀加速至声速的过程主要发生在镁颗粒纯蒸发反应阶段,但在氧化镁熔化阶段由于熔化过程吸热量大,使气相吸热膨胀过程近乎停止.颗粒粒径变化主要影响爆震波尺寸,而对特征值爆震速度以及波后声速面参数影响甚微.在常温常压的初始条件下,爆震波稳定自维持传播过程中波内不涉及氧化镁的汽化离解过程.     

基于连续旋转爆震的推进技术研究进展

基于爆震燃烧的推进技术是未来空间技术的重要发展趋势，特别是可实现结构简单化设计和高热力学效率.针对火箭式连续旋转爆震发动机、吸气式爆震发动机的实验测试和数值仿真，文章综述了其国内外研究进展，分别总结了不同燃料、燃烧室结构、喷注方式以及工作方式等对连续旋转爆震波的传播规律和发动机的特性影响规律.虽然上述探索性研究得到了诸多有益的结论，但是由于连续旋转爆震燃烧技术涉及的流动、物理化学过程十分复杂，对旋转爆震燃烧的机理研究仍然有待进一步深入开展.      

煤油／空气脉冲爆震发动机激波反射起爆研究

为了研究煤油/空气脉冲爆震发动机爆震室内激波遇到障碍物发生反射促使PDE通常完成爆燃向爆震转变的起爆技术,设计加工了环型孔板和双半V型楔面体,并安装在内径100 mm的爆震管内,进行了多循环爆震试验,成功实现了煤油/空气脉冲爆震发动机工作频率30 Hz稳定工作,获得稳定传播的爆震波.研究结果表明:在爆震室内安装合理结构的障碍物能够有效提高激波反射,缩短爆燃向爆震转变的距离(时间),成功获得稳定传播的爆震波.研究结果为优化设计煤油/空气脉冲爆震发动机原理样机提供了初步理论基础.     

Experimental study of internal flow structures in cylindrical rotating detonation engines

The internal flow structures of detonation wave were experimentally analyzed in an optically accessible hollow rotating detonation combustor with multiple chamber lengths. The cylindrical RDC has a glass chamber wall, 20 mm in diameter, which allowed us to capture the combustion self-luminescence. A chamber 70 mm in length was first tested using C₂H₄O₂ and H₂–O₂ as propellants. Images with a strong self-luminescence region near the bottom were obtained, confirming the small extent of the region where most of the heat release occurs as found in our previous research. Based on the visualization experiments, we tested RDCs with shorter chamber walls of 40 and 20 mm. The detonation wave was also observed in the shorter chambers, and its velocity was not affected by the difference in chamber length. Thrust performance was also maintained compared to the longer chamber, and the short cylindrical RDC had the same specific impulse tendency as the cylindrical (hollow) or annular 70-mm chamber RDC. Finally, we calculated the pressure distributions of various chamber lengths, and found they were also consistent with the measured pressure at the bottom and exit. We concluded that the short-chamber cylindrical RDC with equal length and diameter maintained thrust performance similar to the longer annular RDC, further expanding the potential of compact RDCs.     

Enhancement of continuously rotating detonation in hydrogen and oxygen-enriched air

The enhancement of continuously rotating detonation in oxygen-enriched air was demonstrated in an annular rotating detonation combustor (RDC) under a diffusive supply of hydrogen and an oxidizer. Experimental tests were performed to reveal the effects of oxygen volume fraction, mass flow rate, and equivalent ratio on the propagation of continuously rotating detonation wave (CRDW). It is observed that an increase in the air mass flow rate from 25 g/s to 225 g/s causes an increase in the propagation velocity of the stable CRDW in the RDC. For an oxygen volume fraction up to 35%, the difference between the propagation velocity of detonation and the theoretical Chapman–Jouguet value is less than 5%. Under the chemical stoichiometric ratio condition for air, the CRDW is stabilized when the air mass flow rate reaches 185 g/s. However, stabilized CRDW is observed even when the air flow rate is only 45 g/s under the presence of 30% or 35% oxygen. Increase in the oxygen volume fraction leads to an extension of the rich/lean limit for generating a stable CRDW. This study aims to provide guidance for the modulation of continuously rotating detonation.     

基于乙烯或氢气的吸气式旋转爆轰发动机实验

基于氢气的旋转爆轰发动机研究较多,而碳氢燃料与空气混合较为困难,导致基于乙烯的旋转爆轰发动机燃烧技术难度很高.使用宽视野范围的可视化燃烧室观察旋转爆轰波的研究在国内尚未开展.在同一燃烧室内进一步开展了乙烯或氢气的吸气式旋转爆轰实验,来流总温为283~284 K,燃烧室壁面有140°石英玻璃观察窗,便于观察旋转爆轰波运动过程.空筒燃烧室爆轰环腔外径为100 mm,轴向长度为151 mm.燃料通过150个直径0.8 mm圆柱孔进入燃烧室,空气通过喉部1 mm宽的收敛扩张环缝流入环腔.高速摄影和低高频压力传感器均验证了旋转爆轰波的存在和速度值.以氢气为燃料的旋转爆轰波速度最高可达理论值的101%,爆轰波增压效应可达40%左右,乙烯旋转爆轰波速度可达理论值的89%.旋转爆轰波结构容易发生变化,不规则.氢气旋转爆轰的维持对燃烧室的结构要求比碳氢燃料要低,比乙烯旋转爆轰波更加稳定.      

Three-dimensional numerical simulation of the operation of the rotating-detonation chamber

The aim of this work is to apply three-dimensional numerical simulation to determining the conditions of the stable operation of the rotating-detonation chamber (RDC), the thermal state of the chamber walls, as well as the most important parameters of the flow at the inlet and outlet, keeping in mind the possibility of placing the RDC between a compressor and a turbine in a prospective gas turbine installation. The model is based on a system of three-dimensional unsteady Reynolds-averaged Navier-Stokes, energy, and species conservation equations for a multicomponent reacting gas mixture supplemented by a turbulence model. The system is solved using a combined algorithm based on the finite-volume and particle methods. The capabilities of the computer program are demonstrated by the example of a circular RDC with inner and outer walls 260 and 306 mm in diameter and with axial introduction of a hydrogen-air mixture through an annular gap at the bottom of the chamber (with a relative area of 0.6). The detonation wave spun over the bottom at a frequency of ??126000 rpm. Calculations have shown that such an RDC can operate in a steady mode with one detonation wave.     

Effect of injection dynamics on detonation wave propagation in a linear detonation combustor

The effect of reactant injection and mixing on detonation wave propagation is studied in a self-excited, optically-accessible linear detonation combustor operated with natural gas and oxygen. Fuel injection and mixing processes are captured with 100 kHz planar laser induced fluorescence (PLIF) measurements of acetone tracer injected into the fuel stream. Measurements are acquired at multiple orthogonal planes downstream of the reactant injection site to investigate the three-dimensional mixing field in the chamber. The fuel distribution field is correlated with simultaneously acquired OH${}^{*}$ chemiluminescence measurements that provide a qualitative indication of heat release in the combustor. These measurements are used to provide quantitative information of the fuel injector recovery process and its impact on detonation wave structure across a range of equivalence ratios. While significant differences in the detonation wavefront are observed with change in equivalence ratio, the characterization of the fuel refill process into the chamber after the passage of the detonation wave highlights some key generalizable features. The time available for fuel recovery is consistently between 12 – 19% of the detonation wave period across an equivalence ratio range of 0.83 – 1.48. A linear correlation between injector recovery times and the ratio of the average detonation wave pressure amplitude relative to the pressure drop across the fuel injector is observed. Instantaneous and phase-averaged measurements of acetone-PLIF with the time-coincident OH${}^{*}$ chemiluminescence images provide qualitative information of wave structure and injection dynamics along with quantification of fuel injector recovery, a key metric that drives combustor operation and performance. These measurements significantly enhance the ability to obtain detailed information on the intra- and inter-cycle spatiotemporal evolution of the reactant refill process and its coupled effects on the detonation wave structure and propagation.     

Investigation of combustion modes and pressure of reflective shuttling detonation combustor

Detonation combustors are considered promising alternatives to conventional combustors because they offer high thermal efficiency and fast combustion. However, especially for the rotating detonation combustor, the theoretical propulsive performance has not been confirmed in experimental studies because the highly unsteady flow field hinders the measurements process. To understand the involved phenomena in more detail, a reflective shuttling detonation combustor (RSDC) with a rectangular combustion chamber was developed. The interior of the chamber can easily be visualized owing to its two-dimensional quality. Utilizing the RSDC, several combustion tests with gaseous ethylene and oxygen were conducted for different values of mass flow rates and equivalence ratios. Combustion modes from the tests were classified into four types based on the fast Fourier transform (FFT) analysis of the luminous intensity of the CH* self-luminescence images captured by a high-speed camera and a band pass filter. Simultaneously, the theoretical total pressure of a conventional isobaric combustor was compared to the static pressure measured at the bottom of the RSDC chamber. For the detonation modes, the ratio between experimentally measured static pressure and the theoretical pressure varied depending on the location in the chamber owing to the distribution of the time-averaged static pressure. Furthermore, the pressure ratio of the detonation modes was up to 18% lower than that of the deflagration mode potentially owing to the flow velocity induced by the detonation waves.     

Experimental characterization of RDE combustor flowfield using linear channel

An experimental study was conducted to characterize fundamental behavior of detonation waves propagating across an array of reactant jets inside a narrow channel, which simulated an unwrapped rotating detonation engine (RDE) configuration. Several key flow features in an ethylene-oxygen combustor were explored by sending detonation waves across reactant jets entering into cold bounding gas as well as hot combustion products. In this setup, ethylene and oxygen were injected separately into each recessed injector tube, while a total of 15 injectors were used to establish a partially premixed reactant jet array. The results revealed various details of transient flowfield, including a complex detonation wave front leading a curved oblique shock wave, the unsteady production of transverse waves at the edge of the reactant jets, and the onset of suppressed reactant jets re-entering the combustor following a detonation wave passage. The visualization images showed a complex, multidimensional, and highly irregular detonation wave front. It appeared non-uniform mixing of reactant jets lead to dynamic transverse wave structure. The refreshed reactant jets evolving in the wake of the detonation wave were severely distorted, indicating the effect of dynamic flowfield and rapid pressure change. The results suggest that the mixing between the fuel and oxidizer, as well as the mixing between the fresh reactants and the background products, should affect the stability of the RDE combustor processes.     

Stabilization mechanisms of longitudinal pulsations in rotating detonation combustors

This work investigates the stabilization mechanisms of two types of longitudinal pulsations in rotating detonation combustors. The first type is linked to operating modes with two counter-rotating waves in combustors with open outlets and appears as a minor peak in the pressure spectrum. The second type is observed as pulsed operation of the combustor when the outlet is restricted. Different combustor lengths are studied and the susceptibility to these longitudinal pulsations is investigated. Pressure measurements along the length of the combustor and around the perimeter are used to identify the operating mode and to describe the propagation and stabilization mechanisms of the two longitudinal modes. The results show that both modes are linked to the longitudinal acoustic resonance of the combustor. The length-to-perimeter ratio and the mass flux are identified as the driving parameters for the existence of these longitudinal modes. The first mode is shown to be an acoustic resonance supported by the intersections of counter-rotating waves. The second mode is controlled by the reflection of an explosion induced shock wave propagating through a high velocity bulk flow.