Propulsive performance of a liquid kerosene/oxygen pulse detonation rocket engine

Thrust and specific impulse are two critical parameters to estimate the performance of rocket engine. Utilizing liquid kerosene as the fuel, oxygen as oxidizer and nitrogen as purge gas, a series of multi-cycle detonation experiments were conducted to systemically investigate the relationships among the operating frequency, fill fraction and performance parameters of the pulse detonation rocket engine (PDRE). The operating frequency of PDRE was up to 49 Hz. The mass flow of liquid kerosene was measured by orifice meter and the mass flow of oxygen was measured based on the method of gas collection. The detonation chamber pressure traces were recorded by dynamic piezoelectric pressure transducers. A dynamic piezoelectric thrust transducer was used to record the instantaneous thrust produced by PDRE. Average thrust and detonative mixture-based specific impulse of PDRE with different operation frequency were obtained by experiments. The experimental results indicate that in the practical operation, the operating frequency caused the change of fill fraction, which resulted in a thrust enhancement. Due to the effect of fill fraction, average thrust did not linearly increase as the frequency rises. Fill fraction has a significant influence on the specific impulse of PDRE. The detonative mixture-based specific impulse presented a second order exponential decay with fill fraction, and was correspondingly increased with the raise of the operating frequency. With the strategy of partial filling in detonation tube, the specific impulse can be remarkably enhanced.     

Thermal degradation of two liquid fuels and detonation tests for pulse detonation engine studies

The use of liquid fuels such as kerosene is of interest for the pulse detonation engine (PDE). Within this context, the aim of this work, which is a preliminary study, was to show the feasibility to initiate a detonation in air with liquid-fuel pyrolysis products, using energies and dimensions of test facility similars to those of PDEs. Therefore, two liquids fuels have been compared, JP10, which is a synthesis fuel generally used in the field of missile applications, and decane, which is one of the major components of standard kerosenes (F-34, Jet A1, ...). The thermal degradation of these fuels was studied with two pyrolysis processes, a batch reactor and a flow reactor. The temperatures varied from 600°C to 1,000°C and residence times for the batch reactor and the flow reactor were, respectively, between 10–30 s and 0.1–2 s. Subsequently, the detonability of synthetic gaseous mixtures, which was a schematisation of the decomposition state after the pyrolysis process, has been studied. The detonability study, regarding nitrogen dilution and equivalence ratio, was investigated in a 50 mm-diameter, 2.5 m-long detonation tube. These dimensions are compatible with applications in the aircraft industry and, more particularly, in PDEs. Therefore, JP10 and decane were compared to choose the best candidate for liquid-fuel PDE studies. This paper was based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive Systems, Montreal, Canada, July 31 – August 5, 2005.     

Time-of-flight diode-laser velocimeter using a locally seeded atomic absorber: Application in a pulse detonation engine

A diode-laser velocimeter based on atomic absorption spectroscopy has been developed and applied to a pulse detonation engine (PDE). The velocimeter uses a salt-coated sting to seed an atomic absorber at any desired location and a single, fixed-wavelength diode laser to monitor the absorber's presence downstream of the sting. Salt particles stripped from the sting tend to form distinct "clouds" of the atomic absorber rather than a uniform absorber stream. Gas velocity is inferred by measuring the time of flight of these clouds over a known distance. The properties of the salt coating can, in principle, be adjusted to tailor the velocimeter to a variety of flows and optimize its time response. In a PDE operating on C₂H₄ / O₂, CsCl salt was seeded from a 150 m diameter sting, and the D₂ transition of atomic Cs near 852 nm was probed. Gas velocity histories, spanning 0-1000 m/s over a duration of 6 ms, were recorded in the PDE and used to validate detonation models. Images obtained using an array of stings in a PDE are presented to demonstrate the potential for multidimensional velocimetry and to provide insight into the physics of the salt seeding.Received: 24 June 2002, Accepted: 23 January 2003, Published online: 25 March 2003PACS: 07.60.-j, 47.40.-x, 82.33.VxS.T. Sanders: Present address: 109 Engineering Research Bldg., 1500 Engineering Dr., Madison, WI 53706, USAAn abridged version of this paper was presented at the 23rd Int. Symposium on Shock Waves at Fort Worth, Texas, from July 22 to 27, 2001     

Experimental study of an air-breathing pulse detonation engine ejector

Experimental studies were performed in order to improve the understanding of the performance of ejector driven by an air-breathing pulse detonation engine (PDE) with a convergent nozzle. This research utilized a gasoline-air PDE at four different operating frequencies of 8 Hz, 10 Hz, 12 Hz and 15 Hz. The performance of PDE-ejector was quantified by thrust measurements. The effects of single ejector length and axial location on thrust augmentation were investigated. It was found that the single ejector with L/D of 2 showed the best performance and the maximum thrust augmentation occurred at a downstream placement of +1 tube diameter. The performances of two-stage and three-stage ejectors were also investigated. The results indicated that both the overlap ratio and the flow area between two stages should not be too large. The performance of the two-stage ejector was not as sensitive as single-stage ejector to axial position in current conditions. The three-stage ejector behaved better than the two-stage ejector but worse than the single-stage ejector in this work. A maximum thrust augmentation of 1.8 was obtained with an L/D of 2 at a downstream placement of +1 position and 15 Hz operating frequency.     

A numerical study of two- and three-dimensional detonation dynamics of pulse detonation engine by the CE／SE method

In this paper, the CE/SE method is developed to simulate the two- and three-dimensional flow-field of Pulse Detonation Engine (PDE). The conservation equations with stiff source terms for chemical reaction are solved in two steps. The detailed analysis of computational results of a PDE with a single detonation tube and a PDE with five detonation tubes are given in this paper. Complex wave systems are observed inside and outside a PDE. For a PDE with 5 detonation tubes, there is a big bow shock produced from a number of little shocks near the open ends of tubes. A lot of vortexes interact with shocks and a large expansion wave propagates forward and backward with respect to the PDE in a semi-oval shape.The project supported by the National Natural Science Foundation of China (59906005), the Teaching and Research Award Program for Outstanding Young Teachers in High Education Institutions of MOE, China     

单次脉冲爆轰发动机工作过程的数值模拟

通过求解14组分和19个基元反应的CH4-O2-N2详细化学反应动力学机理的二维轴对称Navier-Stokes方程,对爆轰管内半球形高温火团引发的爆轰过程和爆轰波进入外流场后的全流场分布进行数值模拟。模拟结果显示了爆轰波在管内的成长、稳定传播、进入尾喷管后衰减为激波和进入外流场的全过程,以及爆轰管出口端附近区域的复杂涡与激波的相互作用。对轴线上的压力分布和封闭端的压力等进行了讨论,为脉冲爆轰发动机的开发研制提供参考信息。     

Optimization study of spray detonation initiation by electric discharges

Development of air-breathing pulse detonation engines is faced with a challenging problem of detonation initiation in fuel sprays at distances feasible for propulsion applications. Extensive experimental study on initiation of a confined n-hexane spray detonation in air by electric discharges is reported. It is found that for direct initiation of spray detonation with minimal energy requirements (1) it is worth to use one discharger located near the closed end of a detonation tube and at least one additional discharger downstream from it to be triggered in-phase with primary shock wave arrival; (2) the discharge area should be properly insulated to avoid electric loss to metal tube walls; (3) discharge duration should be minimized to at least 50 μs; (4) discharge channel should preferably occupy a large portion of a tube cross-section; (5) test tube should be preferably of a diameter close to the limiting tube diameter; (6) gradual transition between the volume with electric discharger and the tube should be used; and (7) a powerful electric discharger utilized for generating a primary shock wave can be replaced by a primary shock wave generator comprising a relatively low-energy electric discharger, Shchelkin spiral, and tube coil. With all these principles implemented, the rated electric energy of about 100 J was required to initiate n-hexane spray–air detonation in a 28-mm tube at a distance of about 1 m from the atomizer. PACS 02.60.Cb; 05.10.Ln; 47.11.+j; 47.15.Cb; 47.40.Nm This paper was based on work that was presented at the 19th Inter-national Colloquium on the Dynamics of Explosions and Reactive Systems, Hakone, Japan, July 27 - August 1, 2003     

多循环脉冲爆震发动机流场数值研究

针对二维带有收敛扩张喷管的脉冲爆震发动机模型，采用带基元化学反应的Euler方程组和H2、空气的9组分20基元反应，对发动机在前六个工作循环的流场进行了数值模拟。通过对前几个循环流场进行比较，发现脉冲爆震发动机在第五个循环后流场就基本稳定，单循环得到的流场和多循环稳定后的流场有很大的差别，同时喷管对发动机内流场影响特别大。     

Performance of propellant decomposition products as fuel in an airbreathing PDE

Decomposition products of a solid propellant are considered as a possible fuel in an airbreathing pulse detonation engine (PDE). However, these decomposition products contain not only gaseous species but also a significant amount of solid carbon particles. Whether performance can be improved by burning these particles is investigated numerically. Thermodynamic calculations allow predicting the quantity of additional air required for optimum performance. Gasdynamic numerical simulations indicate that particle burning has an effect on the pressure impulse on the thrust wall. The particle size determines the detonation structure, according to the model of hybrid detonations, thus governing the delay and rate of heat release from particle combustion behind the detonation front. In the situation investigated here, the particles are incompletely burnt inside a 0.6-m-long tube. As a result, smaller particles ( ≤ 5μm) contribute to an increase in the impulse, by up to 6%. However, larger particles either have a negligible effect on the pressure impulse, if around 10 μm, or result in a decrease, if around 20 μm. Overall, the calculations show that the best efficiency is obtained for this fuel by diluting the gaseous decomposition products with an additional quantity of air, allowing for incomplete particle combustion rather than letting them behave as if inert, absorbing part of the energy released by gaseous combustion.This paper was based on a work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive Systems, Montreal, Canada, July 31–August 5, 2005.     

环缝宽度对旋转爆震发动机工作特性的影响

为研究环缝宽度对旋转爆震发动机(rotating detonation engine, RDE)工作特性的影响,在非预混RDE中进行实验,同时采用高频压力传感器、离子探针和高速摄影等测量设备,在同一入口质量流率的条件下,改变空气进气环缝宽度和燃烧室环缝宽度。获得了单波、双波、四波对撞及混合传播模态;当燃烧室环缝宽6 mm时,增加空气进气环缝宽度,爆震波由四波对撞转变为同向双波,最终以单波形式传播;而燃烧室环缝宽10或15 mm时,空气进气环缝宽度对爆震波传播模态的影响较小;此外,四波对撞模态下,爆震波压力峰值和离子信号峰值低于单波和双波模态时的值。     

脉冲爆震发动机进气道气动性能的数值研究

采用有限体积法计算了脉冲爆震发动机某轴对称超音速进气道在3种 不同出口条件(单个正弦扰动压力、某脉冲爆震发动机爆震室头部表压和进气道出口堵塞) 下的进气道内结尾正激波的运动情况，得出了进气道内结尾正激波运动特性和不同出口条件 的关系. 在计算中，采用了多块结构化网格，控制体积的界面无黏通量采用三阶迎风格 式插值获得，同时采用了minmod通量限制器以确保在激波处的解的物理特性；扩散通量采 用二阶中心差分格式插值获得. 定常计算采用当地时间步法，非定常计算采用双时间步法. 离散的代数方程采用交替方向迭代法求解。     

氢燃料缓燃向爆震转捩过程中波与火焰的匹配特性

为了解氢燃料爆震过程中压力波与火焰之间相互匹配的特性,在60mm60mm2000mm 方 爆震管内,用氢气和空气混合物进行了单爆震性能研究。在爆震转捩区内布置压力传感器与离子探针,用来 监控压力波和火焰的信号,同时利用高速摄影仪集中拍摄转捩区域。根据压力波和火焰面在爆震管不同时刻 的强度特性、速度特性及位置特性来分析爆震过程中波与火焰匹配的规律。结果表明:压力波和火焰的强度 呈现为相互正反馈匹配性质;缓燃向爆震转捩(DDT)过程中,压力波和火焰的速度表现为相互交替的变化过 程,且缓燃阶段中火焰速度的增幅大于压力波速度的增幅;当火焰面追赶上激波时,产生过爆,火焰面会临时 位于激波前面;在过爆衰减为正常爆震波的过程中,激波在火焰前面。     

爆轰波透射孔栅形成的高速爆燃波的结构和行为

以实验为主,研究光滑直管中乙炔氧气爆轰波透射孔栅形成的高速爆燃波结构和行为。实验以基于纹影平台的高速转鼓摄影记录孔栅下游近场内初始爆燃波的结构和发展,并以压力传感器跟踪其后继走向。研究发现,高速爆燃波是前驱激波和火焰的组合结构,随着初始压力的提升,它分别表现为紧随于前驱激波的层流和湍流燃烧火焰。入射爆轰胞格尺度小于或与孔栅扰动尺度相当时,湍流燃烧在下游近场迅速形成;层流结构的爆燃波通常无法抵制背景稀疏波而走向衰弱,而湍流燃烧结构可发生加速和向爆轰的转捩;他们之间存在一个不稳定的临界状态,高速爆燃波得以以0.5~0.6倍CJ爆轰速度传播较长距离,这一状态对应于双间断Rankine-Hugoniot关系的等容燃烧解。     

爆轰产物组成和爆轰参数计算方法的理论研究

为实现爆轰产物组成和爆轰参数的计算,采用拉格朗日乘数法和牛顿迭代的方法预测爆轰产物组成,利用BKW状态方程预测爆轰参数,在0~600 GPa和300~15 000 K压力温度范围内选取金刚石作为碳的生成相;对爆轰产物系统采用最小自由能原理,结合牛顿迭代法求解爆轰产物的化学平衡方程组;对BKW状态方程参数提出修订,取α=0.5,β=0.298,θ=6 620,κ=9.50;采用自编程序实现计算过程。使用此方法和Hugoniot关系计算密度为1.77 g/cm3的PETN爆轰CJ点爆轰参数验证计算精度,结果显示计算与实验结果的误差均小于1%。利用此方法结合Hugoniot关系预测出爆轰CJ点的产物密度为2.43 g/cm3。     

Experimental and numerical investigations on PDE performance augmentation by means of an ejector

To improve the performance of pulse detonation engines, a 48 cm long cylindrical combustion chamber of 5cm internal diameter (i.d.) is fitted with an ejector of constant section. The role of the ejector is (i) to provide partial confinement of the detonation products escaping from the chamber and (ii) to suck in fresh air and then to increase the mass ejected compared to the ejection of burned gases alone.The combustion chamber is fully filled with a stoichiometric ethylene/oxygen mixture at ambient conditions. Three parameters of the ejector are varied: the i.d. D, the length L, and the position d relative to the thrust wall of the combustion chamber. For various configurations, the specific impulse (I _sp) is determined in single shot experiments. The maximum operating frequency (f _max) and the maximum thrust are then deduced. I _sp is measured by means of the ballistic pendulum method, and f _max is derived from the pressure signal recorded on the combustion chamber thrust wall.The addition of an ejector increases the specific impulse up to 60% in the best configuration tested, from 164s without ejector to 260s with ejector. The specific impulse can be represented by a single curve using suitable dimensionless parameters. The thrust results for the main ejector studied (D = 80mm) indicate an optimal (L, d) configuration that provides a 28% thrust gain. For the same ejector, f _max remains constant and equal to the frequency obtained without ejector in a large range of (L, d) values, before decreasing.Two-dimensional unsteady numerical computations agree reasonably with the experiments, slightly overestimating the experimental values. The results indicate that 80% of the I _sp gain comes from the action of the expanding detonation products on the annular end surface of the combustion chamber, governed by the tube wall thickness.This paper was based on the work that was presented at the 19th International Colloquium on the Dynamics of Explosions and Reactive Systems, Hakone, Japan, July 27–August 1, 2003 PACS 47.40.Rs     

Optimization of the deflagration to detonation transition: reduction of length and time of transition

The aim of this experimental investigation is the study of Deflagration to Detonation Transition (DDT) in tubes in order to (i) reduce both run-up distance and time of transition (L _DDT and t _DDT) in connection with Pulsed Detonation Engine applications and to (ii) attempt to scale L _DDT with λ_CJ (the detonation cellular structure width). In DDT, the production of turbulence during the long flame run-up can lead to L _DDT values of several meters. To shorten L _DDT, an experimental set-up is designed to quickly induce highly turbulent initial flow. It consists of a double chamber terminated with a perforated plate of high Blockage Ratio (BR) positioned at the beginning of a 26 mm inner diameter tube containing a “Shchelkin spiral” of BR ≈ 0.5. The study involves stoichiometric reactive mixtures of H₂, CH₄, C₃H₈, and C₂H₄ with oxygen and diluted with N₂ in order to obtain the same cell width λ_CJ≈10 mm at standard conditions. The results show that a shock-flame system propagating with nearly the isobaric speed of sound of combustion products, called the choking regime, is rapidly obtained. This experimental set-up allows a L _DDT below 40 cm for the mixtures used and a ratio L _DDT/λ_CJ ranging from 23 to 37. The transition distance seems to depend on the reduced activation energy (E _a/RT _c) and on the normalized heat of reaction (Q/a ₀ ²). The higher these quantities are, the shorter the ratio L _DDT/λ_CJ is. PACS 47.40.Rs · 47.60.+i · 47.70.Pq · 47.80.CbThis paper was based on the work that was presented at the 19th International Colloquium on the Dynamics of Explosions and Reactive Systems, Hakone, Japan, July 27–August 1, 2003.