提高脉冲爆震发动机工作频率的实验研究

实验采用汽油为燃料,压缩空气为氧化剂,通过改善气源、点火结构以及燃油雾化效果的方法,对如何提高脉冲爆震发动机工作频率进行了实验研究．脉冲爆震发动机的最高工作频率可达35Hz,此时得到的平均推力为142．8N．测试了不同爆震频率下的爆震波压力、推力及爆震波速,所测得的爆震波压力、波速和结构接近充分发展的理想爆震波,说明已产生了稳定的、充分发展的爆震．脉冲爆震发动机的平均推力随着工作频率的提高接近线性增大．     

脉冲爆震火箭发动机间接起爆实验研究

采用航空煤油为燃料、氧气为氧化剂、压缩氮气为隔离气体，进行了大量的两相脉冲爆震火箭发动机原理性实验。利用8个压力传感器测量了爆震室轴向沿程的压力，所测得爆震波压力接近充分发展的C—J爆震波。两个实验模型分别使用了0．45和0．9m的Shchelkin螺旋作为DDT（deflagration to detonation transition）间接起爆的增强装置。实验模型Ⅰ的DDT距离约为0．65m，爆震波速约为1873m／s；实验模型Ⅱ的DDT距离约为0．55m，爆震波速约为1838m／s。两种实验模型DDT距离的差异主要是由爆震室内Shchelkin螺旋长度不同引起的。虽然Shchelkin螺旋在缩短DDT距离上起到积极作用，但在形成充分发展爆震波后会降低爆震波的强度。     

喷雾爆震起爆过程实验观察

实验测量了爆震室内不同轴向位置的压力和离子信号的演变过程,并利用高速阴影系统直接观察了透明方形管道内汽油/空气两相混合物动态填充过程中,弱火花点火后火焰加速传播、火焰与障碍物的相互作用、激波的出现、热点形成、爆燃向爆震转变、爆震波在障碍物管道中和光滑管道中的传播过程,分析影响爆震波传播速度的关键因素,用烟膜板记录了起爆区的胞格结构.     

火焰射流点火起爆的实验探索

为了实现快速短距起爆,火焰射流点火系统被尝试应用在脉冲爆震火箭发动机上.采用航空煤油为燃料、氧气为氧化剂、压缩氮气为隔离气体,在两相脉冲爆震火箭发动机上成功进行了火焰射流点火起爆实验.利用安装在点火位置后方的多孔孔板来形成火焰射流.实验研究表明,采用火焰射流点火方法,能够在较短距离形成充分发展的两相爆震,在本实验条件下爆燃向爆震转变距离约为管径的4倍.较之爆震管内安装螺旋来促进爆燃向爆震转变的方法,在同一模型机上采用火焰射流点火起爆能够使爆燃向爆震转变的距离缩短60%.     

填充系数对脉冲爆震发动机压力波影响的实验研究

以汽油为燃料，空气为氧化剂，在内径为56mm的脉冲爆震发动机模型内成功地产生了充分发展的爆震。测试了在同一余气系数α、不同填充系数β下的爆震波压力，并对其变化进行了分析。分析实验结果发现，在同一余气系数下，爆震室长度一度时，随着填充系数的减小，爆震波压力降低，使脉冲爆震发动机模型性能下降。当填充系数小于临界填充系数βci时，爆震室内的燃烧方式为爆燃，而不能形成爆震。     

关于爆震波除灰器系统设计的理论研究

通过对锅炉爆震波除灰器系统设计和应用实践的理论研究,认为:其指导理论的基础应当是爆震燃烧理论;认清爆震燃烧中C-J爆震波理论模型、ZND爆震波结构模型和缓燃向爆震转变的DDT过程,了解爆震波的形成和传播的机理,对于成功设计锅炉爆震波除灰器系统具有决定性的作用;为了使设计对工程具有较强的针对性,提出系统设计的主要环节应当注意的有关要求.     

分开喷注方式下旋转爆震发动机三维数值模拟

对环缝-小孔喷注方式下旋转爆震发动机内流场进行三维数值模拟,氧化剂(空气)由环缝喷入环形燃烧室,燃料H2由周向均匀分布的90个小孔喷入环形燃烧室.分析了燃料与氧化剂的混合效果以及三维旋转爆震波的发展过程.研究结果表明:环缝的喷注压力对混合效果的影响较大,过大的环缝喷注压力不利于燃料与氧化剂的混合;对于环缝-小孔喷注方式存在最短混合距离,爆震波在该距离内传播极不稳定,通常会经历爆震波的形成-消失-再形成等过程.要获得稳定传播的旋转爆震波,爆震波高度需大于该最小混合距离.     

脉冲爆震发动机起爆点火系统方案研究

在分析爆震波的基本理论、脉冲爆震发动机(PDE)的工作原理及对现有航空发动机和汽车点火系统进行研究的基础上,根据PDE对起爆系统点火能量和火花频率可调的要求,提出了以晶闸管为开关控制元件和电容储能的半导体高能点火系统方案．设计的倍压整流、半波整流和直流供电的脉冲爆震发动机起爆点火系统实现了点火能量和火花放电频率的控制．电路模拟仿真表明,设计的起爆点火系统可满足脉冲爆震发动机的要求．     

脉冲爆震发动机性能计算与分析

本文在ZND爆震波理论基础上,结合脉冲爆震发动机工作原理,介绍了单次爆震火箭式脉冲爆震发动机推力,比冲性能参数的计算方法,以性能分析模型为基础分析了物理参数、化学参数、结构参数等因素对发动机性能的影响,为火箭式脉冲爆震发动机优化设计提供参考。     

不同化学反应机理对爆震波模拟的影响

采用三阶TVD迎风格式和Strang-splitting算子分裂法以及H-O单步总反应和4种简化反应对爆震燃烧波进行了一维数值模拟,计算结果表明,这5种反应机理都成功起爆并且形成了爆震波.采用单步总反应方程得不到Von-Neumann压力平台区,虽然其Von-Neumann压力峰值与C-J理论最为接近,但是其峰值温度以及爆震波速度过高.采用多步反应机理能很好地捕捉到ZND结构,其爆震波速度与峰值温度能很好地与C-J值一致,采用48反应得到的诱导区长度最小.用CHEMKIN软件计算各化学反应机理得到OH质量分数,采用34反应与CHEMKIN的结果误差最小.采用多步基元反应得到的结果比采用单步总反应所得的爆震波参数更为理想,OH原子团的质量分数可以作为评价化学反应机理是否准确的一个标准.     

Investigations on multicycle spray detonations

Experimental investigations were carried out on a 50-I.D. multicycle pulse detonation engine (PDE) model, and liquid fuel (gasoline) was used. The average of pressure peak, as measured by piezoelectricity pressure transducer, increased versus distance to thrust wall before fully-developed detonation came into being. According to the pressure history, the pressure in detonation tube would not rise abruptly until the flame front advanced a certain distance downstream the spark. Just at that moment, two compression waves spreading to opposite direction were formed. One was enforced by combustion and became detonation rapidly. The other was weakened because of obstacles and insufficiency of fuel. Two methods were used to determine the induction length of two-phase detonation wave through the pressure history. Ignition delay time was found to be longer than deflagration-to-detonation transition (DDT) time, and the sum of the two would change little as cycle frequency increased. So they could be the most important factors controlling two-phase PDE frequency. Filling process and blowdown process were also analyzed. Translated from Journal of Combustion Science and Technology, 2006, 12(1): 90–95 [译自: 燃烧科学与技术]     

Experimental investigation on two-phase pulse detonation engine

This paper presents some results of experimental investigation on a two-phase pulse detonation engine (PDE) model. Proof-of-principle experiments of this model with liquid C₈H₁₆/air mixture were successfully conducted. Efforts were focused on initiation and propagation of detonation waves by means of one-step detonation initiation method, low-energy ignition system (total stored energy of 50 mJ), and effective Schelkin spiral. Three PDE models with different sizes were tested: 30 mm-I.D. by 2 m-length; 56 mm-I.D. by 2 m-length and 50 mm by 1 m, which were operated over a repetition frequency range from 1 Hz to 36 Hz. One-way valves were used to adaptively control intermittent supplies of air and fuel flows. The results of detonation velocity, over-pressure and impulse measurements were presented. The measured pressure ratio of detonation wave was close to that of C-J detonation. The effects of equivalence ratio, PDE diameter, length, and detonation frequency on its performance were experimentally investigated. The obtained results have demonstrated that the averaged thrust of PDE is approximately proportional to the volume of detonation chamber and detonation frequency. For liquid C₈H₁₆/air mixture, the PDE operation with as short a length as 1000 mm and detonation frequency up to 36 Hz was successfully realized, which made an important step to practical PDE.     

Experimental study of a hydrogen-air rotating detonation combustor

The rotating detonation engine can generate continuous thrust via one or more detonation waves. In this study, rotating detonation experiments were performed on a combined structure which included a rotating detonation combustor (RDC) and a centrifugal compressor. Air, which functioned as an oxidiser, was obtained from the environment by the compressor, and hydrogen, which was used as fuel, was provided by the supply system. The propagation velocity of the rotating detonation wave (RDW) reached 81% of the Chapman–Jouguet value in experiments. With the increase of the air-injection area, the detonation-wave pressure increased, but the stability decreased. An air-injection area of 495 mm² was selected for long-duration experiments, and the frequency of the RDW ranged from 3 to 3.5 kHz. Through the self-adjustment of the combined structure, the air pressure ultimately reached a stable state after a certain period of time, and a stable detonation wave was formed in the RDC.     

Experimental investigation on propagation characteristics of liquid-fuel/preheated-air rotating detonation wave

The rotating detonation combustor can be applied to the turbine engine to develop into a new power device, and the liquid-fuel/air rotating denotation has important research significance for engine applications. In this research, the propagation characteristics of liquid-fuel/air rotating detonation wave were experimentally investigated. A hydrocarbon mixture—liquid gasoline was employed for the fuel, the oxidizer was high-temperature air preheated by a hydrogen-oxygen heater, and the rotating detonation wave was initiated via a hydrogen-oxygen pre-detonator. The effects of the equivalence ratio, ignition pressure, and air total temperature on the propagation characteristics of the liquid-fuel rotating detonation wave were analyzed. The liquid-fuel/air continuous rotating detonation wave can be successfully obtained with a single-wave mode, and the velocity and peak pressure of the rotating detonation waves increase as the equivalence ratio increases. As the detonation-wave pressures at the outlet of the pre-detonator increase, the establishment time of the rotating detonation wave gradually decreases, and the average establishment time is 4.01 ms. Stable rotating detonation waves are obtained with the air total temperature of 600–800 K, but the intensity of the detonation wave has a large deficit due to some instabilities.     

Numerical study on the characteristics of rotating detonation wave with multicomponent mixtures

In order to investigate the effects of gas mixture components on the combustion characteristics of rotating detonation wave, two-dimensional simulation is presented to simulate the propagation process of rotating detonation wave with different methane conversions. The results indicate that there are five propagation modes of rotating detonation wave with different components: single-wave mode, single wave with counter-rotating components mode, double-waves mode, triple-waves mode and quadruple-waves mode. The detonation wave propagates along the forward direction in all five modes. With the increase of methane conversion, multi-wave mode appears in the combustion chamber. The fuel component has a great influence on the heat release ratio of detonation combustion. The velocity of detonation wave decreases with the increase of methane conversion. With the increase of methane conversion, the chemical reaction rate gradually increases, which leads to the intensification of chemical reaction on the deflagration surface. The reaction on the deflagration surface develops to the unburned fuel zone, which eventually leads to the formation of compression waves and shock waves in the fuel refill zone. When the shock wave sweeps through the fresh premixed gas, the reactant is compressed to form a detonation point and then ignite the fuel. A new detonation wave is finally formed. The total pressure ratio decreases with the increasing methane conversion, and the uniformity of the total pressure of outlet decreases with increasing methane conversion.     

多循环PDE模型机爆震室壁温分布数值模拟

分析了两相多循环脉冲爆震发动机工作过程中爆震室内、外壁换热特性,建立了爆震室壁温分布计算模型。采用ANSYS的瞬态热分析模块,对一脉冲爆震发动机模型机在不同工作频率下,内、外壁若干位置处温度随时间的变化规律进行数值模拟。研究发现,脉冲爆震发动机(PDE)外壁面温度随工作时间的增加连续升高,内壁面温度振荡上升,但两者的变化规律基本相同;内、外壁温度分布存在一个热平衡时间,该时间随爆震频率的升高而减小;热平衡时刻,外壁面温度分布呈现从前到后逐渐升高的趋势;同一轴向位置处,外壁面温度的平衡值随爆震频率的升高而升高,但升高幅度随爆震频率的增加而略有减小。     

二维守恒元和求解元方法在两相爆轰流场计算中的应用

应用二维守恒元和求解元方法数值模拟脉冲爆轰发动机内汽油/空气两相燃烧转爆轰的过程.分析了爆轰波从开始产生到形成稳定的全过程.研究了点火能量对燃烧转爆轰过程的影响:点火能量越小,DDT时间越长;若点火能量过小就不能形成DDT.同时研究了液滴半径对爆轰参数的影响:液滴半径增大,爆轰波压力和速度随之减小,DDT时间增加;液滴半径过大,则爆轰波不能形成.爆轰波压力计算值与实验值两者趋势符合得较好.     

Investigation of rotating detonation wave fueled by “ethylene-acetylene-hydrogen” mixture

In this study, the stable operating range and basic characteristics including the pressure and speed of a rotating detonation are researched. The fuel is an “ethylene–acetylene–hydrogen” mixture, examined at three mixing ratios of 2:1:4, 2.2:1:4, and 1.8:1:4 (ethylene:acetylene:hydrogen). The pressure of the rotating detonation wave (RDW) increases when the equivalence ratio (ER) is near the stoichiometric ratio, but it is little affected by the flow rate. The detonation wave speed maintains at 1200–1400 m/s, approximately 70% of the Chapman-Jouguet (C-J) speed, which is hardly impacted by the ER and flow rate. The speed of the RDW in the long-duration tests is higher than in the short-duration tests, and the time taken for the formation of a stable RDW is longer. The stable operating range is broadened and speed is increased with the increase in the acetylene and hydrogen in the mixture. The instabilities in the RDW are found to be correlated with the planar acoustic waves, whereas the mechanisms of the decoupling and re-ignition of the RDW are explained from the perspective of thermoacoustic coupling.