超声速气流中的爆震推进理论与研究进展

爆震燃烧近似为等容燃烧,理论上其热循环效率高于基于等压燃烧的爆燃燃烧,在超声速推进系统中具有潜在的应用价值.通过总结超声速气流中的爆震推进理论与研究进展,分析其需要解决的关键科学与技术问题,指导未来高超声速发动机的基础研究.文章重点总结了适用于高超声速飞行的斜爆震发动机、超声速脉冲爆震冲压发动机的基础研究进展.其中对斜爆震发动机的应用模式、相关实验研究思路及方法、数值仿真现状进行了总结分析.对超声速脉冲爆震冲压发动机的基础理论研究现状和目前研究的难点进行了梳理.基于爆震燃烧的超燃冲压发动机具有推进系统自增压、燃烧效率高、推力性能好、推进效率高、燃烧室长度短、结构重量轻等优势,文章总结了该发动机当前的发展进程和最新的研究进展,并对其未来的发展方向以及存在的技术问题进行了分析.      

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.     

旋转爆震燃烧室与涡轮导向器组合实验研究

旋转爆震涡轮发动机正获得广泛的关注,但旋转爆震燃烧室出口存在着高频的压力波动,压力波动会降低涡轮的工作效率并减小涡轮的工作寿命.基于旋转爆震波的传播特点,开展了旋转爆震燃烧室与涡轮导向器组合结构的实验研究.燃料为H₂,由位于燃烧室前端的120个小孔喷入燃烧室;氧化剂为空气,由径向环缝喷入燃烧室.在燃烧室内起爆旋转爆震波后,爆震产物直接流入导向器内.研究结果表明,随当量比的增加,燃烧室内爆震波的传播速度呈先增大后减小的趋势.在导向器出口仍存在与燃烧室内旋转爆震波同主频的振荡压力,但相对于导向器前的振荡压力,出口压力振幅减小了约64%.旋转爆震波传播速度的相对偏差先减小后增大,并且爆震波传播越稳定,其速度损失越小.      

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.     

煤油氧气脉冲爆震火箭发动机爆震特性

脉冲爆震火箭发动机(PDRE)是一种利用脉冲式爆震波产生高温、高压燃气发出的冲量来产生推力的推进系统.与常规液体火箭发动机相比,脉冲爆震火箭发动机具有更高的性能,并且结构更简单.本文以航空煤油为燃料、氧气为氧化剂、压缩氮气为隔离气体,并利用电磁阀控制燃料、氧化剂和隔离气体的间歇式供给.利用低的点火能量(50mJ),在内径50mm,长度1.1m的爆震管内进行了大量的多循环爆震试验,研究煤油氧气电磁阀脉冲爆震火箭发动机的爆震波特性.研究结果为进一步研究气液两相多次爆震燃烧机理提供了依据,为研制工程应用的PDRE提供理论和实践基础.     

气-液组合横向射流中气体种类的影响

吸气式旋转爆震发动机中燃料的良好雾化对爆震燃烧的组织极其重要,气-液组合横向射流是其中一种重要的燃料喷注技术。为获取气体种类在超声速来流中对其的影响,通过数值方法对液体射流穿透深度和辅助射流气体分布进行研究。采用Euler-Lagrange方法研究不同气体射流对液体射流的作用规律,结果表明：气体射流通过激波结构降低局部来流动量通量提升液体射流穿透深度,相同的来流条件下气体射流动量通量越大,液体射流穿透深度越高,且主要影响扩张段之前的流场区域,气体种类的变化对于后场液体射流穿透深度和雾化特性几乎无影响。     

冷等离子体放电区长度对爆震特性影响的实验研究

快速高效的起爆对脉冲爆震发动机工作特性的作用十分关键.文章以乙炔为燃料、空气为氧化剂,使用双爆震管研究冷等离子体和火花塞两种点火方式对起爆特性的影响规律.冷等离子体发生器采用自主设计产品,研究中通过改变冷等离子体放电区长度,测试爆震波的传播过程,给出了放电区体积大小对爆震特性的影响.实验结果表明:冷等离子体点火起爆特性明显优于火花塞;在基本保证放电功率不变时,放电区长度的变化对火焰传播时间、火焰传播速度、爆震波峰值压力影响不大.因此,在工程实践中,采用小区域放电能够减少冷等离子的体积且不影响起爆性能.      

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.      

火花点火发动机的末端气体自燃及爆震的研究

本文介绍了火花点火发动机的末端气体自燃和爆震研究的结果。作者采用高速摄影方法，通过经改装的二冲程发动机气缸盖上的观察窗，拍摄了燃烧室内末端气体自燃和火焰传播，同时测取了气缸内三个不同位置处的压力曲线。实验结果表明，火花点火发动机的爆震是由末端气体自燃引起的。自燃一般是多点同时发生的，并在极短时间内使末燃混合气体全部燃烧。自燃通常会，但并不总是引起爆震。爆震是以缸内压力振荡的出现、碳烟的形成和爆震发生后产生气体的高速运动为特征的。     

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。     

Oblique detonation waves stabilized in rectangular-cross-section bent tubes

Oblique detonation waves, which are generated by a fundamental detonation phenomenon occurring in bent tubes, may be applied to fuel combustion in high-efficiency engines such as a pulse detonation engine (PDE) and a rotating detonation engine (RDE). The present study has experimentally demonstrated that steady-state oblique detonation waves propagated stably through rectangular-cross-section bent tubes by visualizing these waves using a high-speed camera and the shadowgraph method. The oblique detonation waves were stabilized under the conditions of high initial pressure and a large curvature radius of the inside wall of the rectangular-cross-section bent tube. The geometrical shapes of the stabilized oblique detonation waves were calculated, and the results of the calculation were in good agreement with those of our experiment. Moreover, it was experimentally shown that the critical condition under which steady-state oblique detonation waves can stably propagate through the rectangular-cross-section bent tubes was the curvature radius of the inside wall of the rectangular-cross-section bent tube equivalent to 14–40 times the cell width.     

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.     

Investigation of the structure of detonation waves in a non-premixed hydrogen–air rotating detonation engine using mid-infrared imaging

The structure of detonation waves propagating through the annular channel of an optically accessible non-premixed rotating detonation engine (RDE) are investigated using mid-infrared imaging. The RDE is operated on hydrogen–air mixtures for a range of air mass flow rates and equivalence ratios. Instantaneous images of the radiation intensity from water vapor are acquired using a mid-infrared camera and a band-pass filter (2.890?±?0.033?µm). The instantaneous mid-infrared images reveal the stochastic nature of the detonation wave structure, position and angle of oblique and reflected shock waves, presence of shear layer separating products from the previous and current cycles, and extent of mixing between the reactants and products in the reactant fill zone in front of the detonation wave. The images show negligible signal directly in front of the detonation waves suggesting that there is minimal mixing between the reactants and products from the previous cycle ahead of the detonation wave for most operating conditions. The mid-infrared images provide insights useful for improving fundamental understanding of the detonation structure in RDEs and benchmark data for evaluating modeling and simulation results of RDEs.     

Critical condition of inner cylinder radius for sustaining rotating detonation waves in rotating detonation engine thruster

We describe the critical condition necessary for the inner cylinder radius of a rotating detonation engine (RDE) used for in-space rocket propulsion to sustain adequate thruster performance. Using gaseous C₂H₄ and O₂ as the propellant, we measured thrust and impulse of the RDE experimentally, varying in the inner cylinder radius r_i from 31 mm (typical annular configuration) to 0 (no-inner-cylinder configuration), while keeping the outer cylinder radius (r_o = 39 mm) and propellant injector position (r_inj = 35 mm) constant. In the experiments, we also performed high-speed imaging of self-luminescence in the combustion chamber and engine plume. In the case of relatively large inner cylinder radii (r_i = 23 and 31 mm), rotating detonation waves in the combustion chamber attached to the inner cylinder surface, whereas for relatively small inner cylinder radii (r_i = 0, 9, and 15 mm), rotating detonation waves were observed to detach from the inner cylinder surface. In these small inner radii cases, strong chemical luminescence was observed in the plume, probably due to the existence of soot. On the other hand, for cases where r_i = 15, 23, and 31 mm, the specific impulses were greater than 80% of the ideal value at correct expansion. Meanwhile, for cases r_i = 0 and 9 mm, the specific impulses were below 80% of the ideal expansion value. This was considered to be due to the imperfect detonation combustion (deflagration combustion) observed in small inner cylinder radius cases. Our results suggest that in our experimental conditions, r_i = 15 mm was close to the critical condition for sustaining rotating detonation in a suitable state for efficient thrust generation. This condition in the inner cylinder radius corresponds to a condition in the reduced unburned layer height of 4.5–6.5.     

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.     

Characterizing continuously rotating detonation via nonlinear time series analysis

The sampled pressure signals in continuously rotating detonation combustors have the inherence of nonlinear dynamics. To dig out more information on combustion modes, the nonlinear time series analysis method is thus applied to the pressure-time series obtained at a hydrogen/air rotating detonation combustor by using the phase space reconstruction and wavelet entropy algorithm. The variation of wavelet entropy is approved to be associated with the periodicity variation of pressure signals. Different structures of attractor as well as wavelet entropy distribution in the phase diagram can distinguish the deflagration mode from the unstable and stable detonation modes under the conditions of different air flow rates. The limit-cycle oscillation is exhibited in the phase space diagram with a very low flow rate, here 25 g/s. The mean wavelet entropy of pressure-time series can be a quantitative index of different combustion modes occurring in the combustor. The present study is expected to enhance the understanding of the physical mechanism of continuously rotating detonation and contribute on the development of detonation propulsion technology.     

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.     

180°圆弧形钝感炸药的爆轰波传播

 采用贴体坐标下与Level Set方法相结合的爆轰冲击波动力学（DSD）计算方法,研究了180°圆弧形钝感炸药中非理想爆轰波的传播过程。通过数值模拟计算和实验测量的对比分析,得到了180°圆弧形炸药中爆轰波传播的一些规律：圆弧形钝感炸药可以实现定常爆轰,即在极坐标中整个爆轰波以固定角速度转动。这种定常阵面的形状和角速度与圆弧的外半径无关,定常体系依赖于圆弧形炸药的内半径和覆盖圆弧的外壳物质。对描述圆弧形炸药中爆轰波传播规律的经验公式进行了研究,结果表明这些经验公式能够准确描述爆轰波速度的变化,在实验测量和预估方面具有一定的参考价值。