Air-breathing Pulse Detonation Engine Research Articles

Influence of Aerodynamic Valve Structural Parameters on Detonation initiation and Back Pressure Characteristics of Air-Breathing Pulse Detonation Engine

In order to enhance the stability of detonation initiation in air-breathing pulse detonation engines (APDE), while simultaneously mitigating the non-stationary back pressure disturbance due to the huge pressure gain in the APDE, a central blunt body aerodynamic valve (aero-valve) was developed and tested with a single-tube pulse detonation combustor (PDC). The detonation initiation and back pressure characteristics of PDC were then discussed. In order to reveal the influence of the aero-valve's structural parameters on the cold-state filling, detonation initiation, and back pressure characteristics of PDC, numerical simulations were carried out based on the experimental setup. The numerical results indicated that the cold-state flow characteristics within the aero-valve was predominantly influenced by the inner diameter of the aero-valve shell (Das), while the cold-state flow inside the combustor was primarily dominated by the axial distance from the thrust wall to the aero-valve shell (Lx) and the inner diameter of the aero-valve outlet (dout). And dout has a larger impact on the cold-state flow inside the combustor. During the hot state, reducing Lx or dout is beneficial for both the generation of detonation and the suppression of back pressure, with the most significant gain effect coming from decreasing dout. The optimal combination scheme for the aero-valve is identified as Das/R = 4.5, Lx/R = 0.25 and dout/R = 0.7, where R is the detonation combustor radius. The PDC equipped with this optimized aero-valve not only has better detonation initiation characteristics, but also a smaller pressure oscillation ratio.

Numerical study of back-propagation suppression and intake loss in an air-breathing pulse detonation engine

In order to reduce the back-propagation pressure and the back-propagation distance of burnt gas in the air-breathing pulse detonation engine effectively, two back-propagation suppression structures were proposed in this paper. The influences of channel width (D) and unit length (L) in the corresponding back-propagation suppression structure on the intake loss and the back-propagation characteristics were studied by the 2-D numerical simulation which was based on stoichiometric propane/air mixture to obtain the optimal structure. The grid independence and the reliability of numerical simulation were verified. The simulation results indicated that the back-propagation suppression structure with a flow channel formed by the annular cavities and the convergent sections was the structure with the optimal back-propagation suppression performance. And the following two methods were proved to be effective in this paper. By the means of propagating the pressure wave along the arc-shaped channel, the propagation distance of the pressure wave increased, which resulted in an attenuation of the back-propagation pressure. And the back-propagation pressure was reduced by the way of making the pressure wave propagate toward the downstream of the engine after colliding with the wall of the annular cavity and offsetting with the expansion wave.

Effect of inlet-valve structures on thrust of air-breathing pulse detonation engines

Experimental studies were conducted in order to improve the understanding of the thrust generation and the pressure/flame reverse propagation of the air-breathing pulse detonation engines (APDEs) with self-designed inlets and valves structures. The present experimental research utilized a gasoline/air APDE (with 68 mm inner-diameter, 2050 mm length and maximum operating frequency not less than 40 Hz which was as a benchmark structure) at different operating frequencies, with freestream air inflow of 1.1 atm and 0 °C. The theoretical equivalence ratio of gasoline/air was 1. Two kinds of inlets with centerbody or without were considered and combined with two kinds of self-designed valves (the elastic-valve and the convergent aero-valve) specially designed for comparative experiments. During the test, the inflow parameters, the pressure along the longitudinal direction inside the engine and the thrust force were measured for the APDE operating characteristic analysis, including the detonation combustion, the aerodynamic drag, the pressure/flame reverse propagation and the thrust generation. The research results indicate that: The inlet centerbody does not increase drag but plays a positive effect on airflow stability and operation matching. The elastic-valve and the convergent aero-valve, though increase the inlet aerodynamic drag, have obvious effects on suppressing the detonation wave and pressure forward propagation, resulting in effective thrust increase. Effects of the convergent aero-valve are the best when the flow choked, while the effects of elastic-valve are better and continuously stable in a wider range of frequency. The wmaximum nondimensional thrust increases with the elastic-valve is reached about 1.12 at the frequency of 8–9 Hz, and about 0.97 with the convergent aero-valve at the frequency of 7 Hz. The maximum fuel specific impulse is 2514.6 s when using the convergent aero-valve. And this study provides technical reserve for the APDE optimization design.

Back-propagation suppression study based on intake configuration optimization for an air-breathing pulse detonation engine

In order to reduce the back-propagation of an air-breathing pulse detonation engine efficiently, a suppression method based on the optimization of the intake configuration with wedge-shaped angle and blockage ratio was proposed and studied in this paper. The 2-D numerical simulation based on propane/air combustible mixture was carried out to study the configuration, wedge-shaped angle and the blockage ratio effects of the air intake segment on the back-propagation in the air-breathing pulse detonation engine. The reliability of the numerical simulation was verified with the experimental results. The simulation results indicated that the wedge-shaped configuration was the most efficient geometry for back-propagation suppression in this paper. The back-propagation suppression performance in the case of wedge-shaped angle of 30° was better than that of wedge-shaped angle of 45° and 60°. In addition, based on the wedge-shaped air intake segment with a wedge-shaped angle of 30°, the back-propagation intensity and the arrival range of the burnt gas both decreased accordingly at the increased blockage ratio. When the blockage ratio was 0.8, the burnt gas could not flow into the inlet. In order to achieve the optimal performance of back-propagation suppression, the configuration and the blockage ratio of the air intake segment should both be optimized further according to the characteristics of the back-propagation pressure.

Experimental study on the temperature and structure of the exhaust plume in valveless pulse detonation engines

The experiments of multi-cycle detonation were carried out based on a direct-connected pulse detonation engine (PDE) and an air-breathing PDE. The ignition energy was less than 50 mJ generated by a spark plug. The gasoline and air were used as the fuel and oxidizer. The pressure variation along the length of the direct-connected PDE and air-breathing PDE at several different operating frequencies was measured by the piezoelectric pressure sensors. The temperature of the exhaust plume from the PDEs was measured by the temperature and water vapor concentration instrument based on infrared spectrum measurement principle. Meanwhile, the average thrust of the air-breathing PDE with three different nozzles, including convergent nozzle, divergent nozzle, and convergent-divergent nozzle was measured by the force sensor. The experimental results indicated that there was a reflected shock wave propagating upstream when the detonation wave reached the convergent nozzle, while there was no reflected shock wave for the divergent nozzle. The exhaust plume temperature increased slightly with the increasing operating frequency. The exhaust plume temperature of the PDE with the convergent nozzle was lower than that of the divergent nozzle and convergent-divergent nozzle, while the PDE with divergent nozzle obtained the highest exhaust plume temperature. Analogously, the average thrust of PDE with the convergent nozzle was the largest while the PDE with the divergent nozzle obtained the minimum average thrust. The spontaneous flow field of the exhaust plume under the condition of multi-cycle was observed by a high speed camera. Several Mach disks looked like diamonds were generated at the center of exhaust plume and the flow was supersonic for a while. The flow field was similar to that of the supersonic unexpanded free jet.

A theoretical and 1-D numerical investigation on a valve/valveless air-breathing pulse detonation engine

The important operating characteristics of pulsed Pressure Gain Combustion (PGC) propulsion are the pressure gain of the combustor component and the propulsive performance gain of the engine. A ramjet-type valve/valveless air-breathing pulsed detonation engine with a supersonic internal compression inlet is investigated. Based on an ideal thermal cycle, the ideal equivalent pressure ratios (πcb) of the Pulsed Detonation Combustor (PDC) are obtained theoretically which are directly related with the propulsive performance of the engine. By introducing an orifice loss model into the cycles, the critical pressure drop ratios through the orifice for the PDC achieving pressure gain and the engine achieving thrust gain are studied. More influencing factors are investigated by the use of a one-dimensional (1-D) numerical simulation model. The operating characteristics of the pulse detonation engine are investigated with changes of the valve type, the inlet/outlet area ratio of the PDC, the nozzle area ratio, and flight conditions. All these factors can affect πcb of the PDC, and πcb can be optimized by changing the geometry of the engine. The most important influence parameter is the valve type. When using an orifice-type aerodynamic valve, simulation results show that the PDC cannot achieve the pressure gain characteristics. When a supersonic internal compression inlet is introduced to the engine, whether the Pulse Detonation Engine (PDE) can achieve thrust gain comparable with that of an ideal Brayton cycle engine not only is related to the pressure gain of the combustor, but also needs to optimize the engine structure to reduce the total pressure loss.

Utilization of Nonthermal Plasma in Pulse Detonation Engine Ignition

Nonthermal plasma ignition using alternating-current-driven dielectric barrier discharge is applied to a pulse detonation engine. Five different geometrical in-house design plasma generators are tested to obtain more effective discharge performance. The selected plasma igniter, with 4.0 mm discharge gap between two electrodes with a dielectric barrier, can be powered by an alternating-current supply with output voltage and sinusoidal wave frequency. The required discharging waveforms, and hence ignition energy, can be obtained by the automatic frequency-control system, via which the operating frequency can be adjusted up to 500.0 Hz holding with almost unchanged breakdown voltages and currents in practical application. The respective mixture of hydrogen, acetylene, and ethylene was allocated with an excess air coefficient ranged from 0.6 to 1.4. The initial pressure of the mixture changed from 0.04 to 0.1 MPa and was tested in the single-trial experiments. The shortened deflagration-to-detonation transition and detonation waves show the effectiveness of nonthermal plasma-assisted ignition for wider excess air coefficients. The multicycle mode is also conducted to show the performance of 15.0 Hz collaborative operation using the plasma igniter in an airbreathing pulse detonation engine. The feasibility of the present alternating-current-driven dielectric barrier discharge technology to generate nonthermal plasma is thus verified for single-trial detonation tube and multicycle pulse detonation engine ignition in laboratory.

Ignition Study on a Rotary-valved Air-breathing Pulse Detonation Engine

AbstractIn the present study, the ignition effect on detonation initiation was investigated in the air-breathing pulse detonation engine. Two kinds of fuel injection and ignition methods were applied. For one method, fuel and air was pre-mixed outside the PDE and then injected into the detonation tube. The droplet sizes of mixtures were measured. An annular cavity was used as the ignition section. For the other method, fuel-air mixtures were mixed inside the PDE, and a pre-combustor was utilized as the ignition source. At firing frequency of 20 Hz, transition to detonation was obtained. Experimental results indicated that the ignition position and initial flame acceleration had important effects on the deflagration-to-detonation transition.

Experimental study of pressure back-propagation in a valveless air-breathing pulse detonation engine

Experimental studies were performed to improve the understanding of pressure back-propagation in a valveless air-breathing pulse detonation engine (APDE). Liquid gasoline was used as the fuel and air as the oxidizer in the two-phase APDE. The evolution of pressure field along the length of APDE was analyzed, and it was found that the pressure plateau was first maintained by the thrust wall and then widened by the arrival of the retonation wave when the pressure declined to a certain value. The disturbance in the air inlet was primarily caused by the backward deflagration wave induced by the spark ignition. The retonation wave had little influence on the upstream air in the inlet, but the geometry of the air inlet could lead to wave interaction, which reinforced the pressure at the present operating conditions. The effects of ignition energy and fill-fraction on the pressure of backflow were investigated as well. The results indicated that the peak pressure in the air inlet increased at the increased ignition energy and this trend was more obvious at the lower operating frequencies. The intensity of the disturbance in the air inlet was nonlinear but fluctuated with the fill-fraction. This was caused by the different filling conditions and the complicated flow field in the engine.

Thrust characteristics of an airbreathing pulse detonation engine in flight at mach numbers of 0.4 to 5.0

Multidimensional calculations are performed to demonstrate that, by its characteristics, the pulse detonation engine (PDE) is a unique type of ramjet propulsion system, which can be used in both subsonic and supersonic aircraft. By a number of examples, it is shown that, in various thrust characteristics, such as the specific impulse, specific fuel consumption, and specific thrust, the PDE substantially exceeds ramjet engines.

Shock-Initiated Combustion in an Airbreathing, Pulse Detonation Engine-Crossover System

An airbreathing pulse detonation engine-crossover system is developed to characterize the feasibility of shock-initiated combustion within an airbreathing pulse detonation engine. A shock wave is transferred through a crossover tube that connects a spark-ignited driver pulse detonation engine to the airbreathing, driven pulse detonation engine. Detonations in the driven pulse detonation engine develop from shock-initiated combustion caused by shock wave reflection. The pulse detonation engine-crossover system increases system efficiency through decreased deflagration-to-detonation transition distance while employing a single spark source to initiate a system consisting of multiple detonation tubes. The initiation effectiveness of shock-initiated combustion is compared to spark discharge initiation and detonation injection through a predetonator. Increasing the Reynolds number enhances combustion wave acceleration. However, for all initiation methods, the system requires a device to transition the combustion wave to a detonation. Shock-initiated combustion and predetonator initiation produce comparable detonation transition runup lengths. With an incident shock wave Mach number of , the runup length is decreased by up to 61% compared to the spark discharge method. Similar combustion evolution is observed for an incident shock wave of strength .

Ignition method effect on detonation initiation characteristics in a pulse detonation engine

The detonation initiation performance of a kerosene fueled air-breathing pulse detonation engine was investigated. Three ignition methods were investigated experimentally, including spark ignition, hot jet, and pre-detonator. The deflagration-to-detonation transition distance measured using the hot jet initiation method was 1130 mm, a reduction of approximately 150 mm compared to the baseline spark ignition method. As the length of jet pipe decreased to 100 mm, the detonation frequency increased to 35 Hz. The PDE operating frequency had little impact on detonation initiation time when pre-detonator ignition method was used, and there was a slight deviation error of detonation initiation time at each of the operating frequencies. However, when spark and hot jet ignition methods were used, detonation initiation time decreased at the increased operating frequency and the deviation error of detonation initiation time was much higher. The shortest detonation initiation time of 2–3 ms and deflagration-to-detonation transition distance of 700 mm were obtained using the pre-detonator ignition method.

Experimental research on a rotary-valved air-breathing pulse detonation engine

An experimental research on flame acceleration and deflagration-to-detonation transition (DDT) in an air-breathing pulse detonation engine was performed. The inner diameter of the detonation tube and pulse detonation engine overall length were 8.6 cm and 155 cm, respectively. A rotary-valve configuration was developed to control air-filling process. The stability and effectiveness of the rotary valve was investigated. Also, a control system was employed to support valve rotating, fuel supply and ignition timing accurately. Utilizing air as oxidizer as well as purge gas and kerosene as fuel, multi-cycle detonations in pulse detonation engine were conducted. Three DDT enhancement devices were used to examine their impacts on transition to detonation. Pressure transducers and ionization probes were used to measure pressures and flame velocities, respectively. This rotary-valved pulse detonation engine was capable of detonating fuel-air mixtures that successive detonations at 15 and 20 Hz were observed. By utilizing three DDT enhancement devices, the detonability of kerosene-air mixtures is remarkably promoted. The effectiveness of geometry shape of DDT enhancement approaches is investigated. The results represent that when DDT enhancement devices geometry shape as well as ignition frequency vary, the pressure and flame velocity, overpressure value and flame regime are different.

3D versus 2D calculation of thrust characteristics of the air-breathing pulse detonation engine under supersonic flight conditions

3D calculations are used to confirm the conclusion that the specific thrust of the air-breathing pulse detonation engine is 20–30% higher than that of the ideal ramjet in which normal combustion takes place.

Experimental investigation on the operating characteristics in a multi-tube two-phase valveless air-breathing pulse detonation engine

A four-tube two-phase gasoline/air valveless air-breathing pulse detonation engine (PDE) was designed and tested to investigate the operating characteristics of multi-tube air-breathing PDE. The PDE was operated at a maximum frequency of 30 Hz per tube with a total maximum frequency of 120 Hz. Four different firing patterns were successfully carried out: single tube firing, dual tubes firing simultaneously, three tubes firing simultaneously, and four tubes firing simultaneously. The synchronicity of the detonation waves and back-propagation pressure waves under multi-tube firing patterns were quantified and compared. The averaged peak pressure of back-propagation pressure waves in the air plenum chamber was discussed. The experimental results indicated that the four-tube PDE could be operated successfully under the four firing patterns and transformed from one firing pattern to another. The time of arrival differences of detonation waves showed up in all multi-tubes firing patterns, which led to greater arrival differences of back-propagation pressure waves. The averaged peak pressure of back-propagation pressure waves in the air plenum chamber had the same change trend under multi-tube firing patterns. Single tube firing pattern resulted in the smallest pressure peak in the air plenum chamber and the pressure peak increased at the increased fired tubes.

Thrust characteristics of an airbreathing pulse detonation engine in supersonic flight at various altitudes

The main thrust characteristics, such as thrust force, specific impulse, specific fuel consumption, and specific thrust, of a pulse detonation engine (PDE) with an air intake and nozzle in conditions of flight at a Mach number of 3 and various altitudes (from 8 to 28 km above sea level) are for the first time calculated with consideration given to the physicochemical characteristics of the oxidation and combustion of hydro-carbon fuel (propane), finite time of turbulent flame acceleration, and deflagration-to-detonation transition (DDT). In addition, a parametric analysis of the influence of the operation mode and design parameters of the PDE on its thrust characteristics in flight at a Mach number of 3 and an altitude of 16 km is performed, and the characteristics of engines with direct initiation of detonation and fast deflagration are compared. It is shown that a PDE of this design greatly exceeds an ideal ramjet engine in specific thrust, whereas regarding the specific impulse and specific fuel consumption, it is not inferior to the ideal ramjet.

Experimental investigation on valveless air-breathing dual-tube pulse detonation engines

Two-phase dual-tube air-breathing pulse detonation engine (APDE) experiments were performed to improve the understanding of the characteristics of valveless multi-tube APDE. Two different operation patterns were studied: simultaneously and single-tube firing. The synchronicity of detonation waves was quantified. The time interval was less than 1 ms and decreased with the increasing frequency. It was found which detonation wave arrived firstly had a degree of randomness. The situation that the detonation wave in a certain tube always kept ahead never happened in the experiments. The back-propagation pressure wave in the upstream inlet was also not synchronous. Its synchronicity was a little inferior than the detonation wave's and also improved with the increasing frequency. The pressure-rise occurred twice successively in the common air inlet and prolonged the period of pressure oscillations therein. The results of single-tube firing showed that the flow field in the non-detonate chamber was not only influenced by the diffracted wave downstream from the neighboring tube but also by the upstream-propagating pressure wave. Compared with the dual-tube firing, the operation pattern of single-tube firing is beneficial to reduce the pressure disturbance in the common air inlet.

Experimental Investigation of Nozzle Effects on Thrust and Inlet Pressure of an Air-breathing Pulse Detonation Engine

Nozzle effects on thrust and inlet pressure of a multi-cycle air-breathing pulse detonation engine (APDE) are investigated experimentally. An APDE with 68 mm in diameter and 2 050 mm in length is operated using gasoline/air mixture. Straight nozzle, converging nozzle, converging-diverging nozzle and diverging nozzle are tested. The results show that thrust augmentation of converging-diverging nozzle, diverging nozzle or straight nozzle is better than that of converging nozzle on the whole. Thrust augmentation of straight nozzle is worse than those of converging-diverging nozzle and diverging nozzle. Thrust augmentations of diverging nozzle with larger expansion ratio and converging-diverging nozzle with larger throat area range from 20% to 40% on tested frequencies and are better than those of congeneric other nozzles respectively. Nozzle effects on inlet pressure are also researched. At each frequency it is indicated that filling pressures and average peak pressures of inlet with diverging nozzle and converging-diverging nozzle with large throat cross section area are higher than those with straight nozzle and converging nozzle. Pressures near thrust wall increase in an increase order from without nozzle, with diverging nozzle, straight nozzle and converging-diverging nozzle to converging nozzle.

Numerical simulation of the operation process and thrust performance of an air-breathing pulse detonation engine in supersonic flight conditions

Multidimensional simulations of the unsteady gasdynamic flow in the duct of an air-breathing pulse detonation engine (ABPDE) operating on propane gas and the flow around it in supersonic flight at Mach numbers M of 3.0 and an altitude of 9.3 and 16 km are performed. It is shown that, at a length and diameter of the duct of 2.12 m and 83 mm, respectively, an ABPDE with an air intake and a nozzle can operate in a cyclic mode at a repetition frequency of 48 Hz, with a rapid deflagration-to-detonation transition (DDT) occurring at a distance of 5–6 combustion chamber diameters. To determine the thrust performance of the ABPDE in flight conditions, a series of working cycles were simulated with consideration given to the external flow around the engine. Calculations showed that the specific impulse of the ABPDE is approximately 1700 s. This value is much higher than the specific impulse typical of ramjet engines operating on conventional combustion (1200–1500 s) and substantially lower than the specific impulse obtained for the atmospheric conditions at sea level at zero flight velocity (∼2500 s).

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.