Pulse Detonation Engine Research Articles

Experimental Study on the Ignition Characteristics of Scramjet Combustor with Tandem Cavities Using Micro-Pulse Detonation Engine

This experimental investigation focused on the ignition and combustion characteristics of a tandem cavity-based scramjet combustor with side-by-side identical cavities. This study utilized the Pusan National University-direct connect scramjet combustor (PNU-DCSC), which was capable of simulating flight conditions at Mach number 4.0–5.0 and altitudes of 20–25 km using the vitiated air heater (VAH). The combustion tests were conducted under off-design point conditions corresponding to low inlet enthalpy. It is a condition in which self-ignition does not occur, and a micro pulse detonation engine (μPDE) ignitor is used. The results revealed that as the injection pressure of the gaseous hydrogen fuel (GH2) and the corresponding equivalence ratio increased, the combustion mode transitioned from the cavity-shear layer flame to the jet-wake flame. Furthermore, the measured wall static pressure profiles along the isolator and scramjet combustor indicated that the region of elevated pressure distribution caused by the shock train expanded upstream with higher equivalence ratios. When ignited from the secondary cavity, the combustion area did not extend to the primary cavity at lower equivalence ratios, while it expanded upstream faster with higher equivalence ratios. Therefore, the combustion characteristics of the tandem cavity were found to vary based on the overall equivalence ratio of the main fuel (GH2) and ignition position.

Experimental study of DDT run-up distance and detonation wave velocity deficit for stoichiometric hydrogen-oxygen mixture in micro spiral channels

The determination of the deflagration-to-detonation transition (DDT) run-up distance LDDT is crucial in both the design of pulse detonation engines (PDEs) and safety protection. In this paper, the LDDT of stoichiometric hydrogen–oxygen premixed mixtures in millimeter-scale spiral channels were studied experimentally and high-speed photography was employed to capture the flame propagation process. The mixtures in three different rectangular cross-sectional channel widths and various initial pressures were tested. The present results show that the LDDT decreases with increasing the initial pressure, and with increasing the channel width, the larger LDDT is observed. When fitted with the LDDT ∝ P0−m relationship, the values of m obtained in this study ranged from 0.997 to 4.222. The critical value of 0.1 for the equivalent area divergence induced by the boundary layer ξ is proposed to distinguish the behaviors between micro and macro channels, regardless of the type of mixture and channel configuration. Additionally, an empirical formula considering the influence of the boundary layer is obtained, which allows for the quantitative prediction of LDDT. Because of the influence of curvature effect, the smaller the channel width, the greater the prediction deviation. Due to the boundary layer effect, the momentum and heat dissipation are more pronounced in smaller tubes, resulting in a loss of velocity for the detonation wave. It is suggested that the detonation wave velocity increases as the channel width and initial pressure increase. Fay's model was employed to estimate the theoretical velocity deficit, and the experimental results were in good agreement with the theoretical predictions. The current findings are valuable for the field of micro PDE and may help the assessment of the potential risk of hydrogen detonation in micro systems.

Experimental and Numerical Study of Pulse Detonation Engine with Ethylene as a Fuel

This paper presents an insight on the study of transient, compressible, intermittent pulsed detonation engine with one-step overall reaction model to reduce the computational complexity in detonation simulations. Investigations are done on flow field conditions developing inside the tube with the usage of irreversible one-step chemical reactions for detonations. In the present simulations one and two-dimensional axisymmetric tubes are considered for the investigation. Studies are also performed with different grid sizes which influence the prediction of Von-Neumann spike, CJ Pressure and detonation velocity. Numerical studies are conducted using 66mm diameter tube and compared with the literature values. The simulation result from the single-step reaction model agrees well with the previous published literature of multi-step reaction models. The present studies shows that one-step overall reaction model is sufficient to predict the flow properties with reasonable accuracy. Experiments are conducted in a 25mm dia. tube with Ethylene/Air mixtures. The reactants are premixed and injected into the detonation tube using solenoid valves. The equivalence ratio of the fuel/oxidizer mixture and the length of the detonation tube are varied to understand their effects on detonation parameters. Finally the results from the present numerical study are compared and validated using NASA CEA and experiments.

ON THE DETERMINATION OF THE SPECIFIC HEAT FLUX VALUE IN A PULSE DETONATION ENGINE’S CHAMBER

Abstract. The development of detonation engines (DE) is one of the most promising areas of rocket and space engine manufacturing. They are more efficient as compared to the liquid rocket engines and are structurally simpler. At the same time, the detonation engine chamber’s structure is subjected to much higher thermal loads. Therefore, at the development stage of the DEs, to create an efficient cooling system for the engine’s chamber, it is necessary to be able to determine the value of thermal energy, which is absorbed by the walls of the DE’s chamber. The goal of this research is to determine the specific heat flux from the detonation products towards the walls of the pulse detonation engine’s (PDE) chamber. The task of the work is to establish the methodology for calculating the values of the specific heat flux transmitted to the walls of the PDE’s chamber. The main tools for solving this problem are the method of mathematical simulation using computational fluid dynamics (CFD), and the method of regression analysis. The main results of this study: the possibility to utilize the well-known Ievlev methodology to determine the convective specific heat flux for the PDE’s chamber was analyzed; it was shown that for the conditions of the PDE’s chamber, the Ievlev methodology calculation results differ significantly from the experimental data, which can be explained by the presence of a clearly pronounced non-stationary nature of the detonation process; it was proven the utilization of the Viegas formula to obtain the values of the convective specific heat flux for the PDE’s chamber gives better results as compared to the known experimental data and the results of the mathematical simulations; it was also demonstrated that the average integral value of the specific heat flux, determined by the described methodology, can be used to calculate the thermal state of the PDE's chamber. Conclusion: a methodology for calculation of the specific heat flux value for the pulse detonation engine's chamber was proposed. The obtained calculation results are in good agreement with the results of mathematical simulations and known experimental data. The described methodology can be used in the design of cooling systems for the pulse detonation engine’s chambers.

Deflagration to Detonation Transition in Heterogeneous Mixtures Containing Ethanol/Acetone and Oxygen

Liquid fuel is the choice for volume-limited propulsion systems, including detonation-based propulsion. A liquid fuel with high vapor pressure has the advantage of more fuel vapor in the mixture, which supports the transition from deflagration to detonation. This paper reports on an experimental study of deflagration-to-detonation transition (DDT) in a pulse detonation engine with heterogenous mixtures of oxygen and ethanol or acetone. Single-cycle tests were taken for different fuels, equivalence ratios, and DDT enhancement methods. The size distribution of fuel droplets was characterized at the atomizer and engine exit. The effect of the fuel evaporation was dominant for the acetone spray only. Comparing the measured detonation velocities of the two mixtures, a lower velocity deficit relative to the theoretical Chapman–Jouguet detonation velocity was measured for the acetone–oxygen mixtures, and this behavior is related to the higher amount of fuel vapor that existed in the mixtures. Moreover, a shorter transition to detonation was observed in the acetone–oxygen mixture. The addition of a Shchelkin spiral reduced the DDT distance; however, the Chapman–Jouguet condition could be reached only downstream of the obstacle. The measured detonation cell size of the heterogeneous acetone–oxygen mixture was smaller than that of the ethanol–oxygen mixture, indicating that it is more detonable.

Impact of nozzles on the wall-temperature in a valveless pulse detonation engine

As the increase of wall-temperature during the long-duration operation, pre-ignition of the fresh mixture in the filling process often occur in the detonation tube, resulting in the failure of operation. An experimental work has been conducted to investigate the impact of nozzle on the wall-temperature of the detonation tube. In the present study, kerosene and oxygen enriched air were employed in the experiments, and an internally grooved semi-circle spiral, instead of traditional Shchelkin spiral was utilized to facilitate the deflagration to detonation transition (DDT) process. The theoretical results showed that the temperature of fresh mixture increase along the detonation tube during the filling process, and it is likely to be ignited near the open end. It was observed from the experimental results that the convergent section and the divergent section of the exit nozzle has different influence on the wall-temperature. The convergent nozzle will not prevent the wrapping flame near the open end of the detonation tube, and lead to the increase of equilibrium wall-temperature. The nozzle with a diverging section will eliminate the occurrence of wrapping flame during the operation, and the wall temperature near the open end are dramatically decreased. In addition, smaller expansion ratio of the nozzle will lead to lower equilibrium wall-temperature.

Effects of detonation instability and boundary layer on flame propagation behavior in millimeter-scale smooth tubes

Small pre-detonators have potential applications in practical pulse detonation engines or rotating detonation engines. The effects of detonation stability parameter and area divergence on flame propagation in capillary tubes are experimentally analyzed using high-speed cinematography. The four mixtures (namely, stoichiometric methane/oxygen, ethylene/oxygen, propane/oxygen and stoichiometric acetylene/oxygen/50% Ar mixtures) used have different values of stability parameter. The inner diameters of the tubes (namely, 0.5, 1.0, 2.0, and 4.0 mm) investigated provide a variation in area divergence at initial pressures p0 ranging from 5 to 100 kPa. The results show that stability parameter and area divergence play positive and inhibitory roles, respectively, in the process of flame propagation. Five propagation modes are observed (namely, steady detonation, stuttering detonation, galloping detonation, deflagration, and no flame), among which the stuttering detonations have three different forms, depending on the product of stability parameter and area divergence. For the most-unstable mixture (stoichiometric methane/oxygen, with the largest values of stability parameter), the range of the product of stability parameter and area divergence in which steady detonation can occur is the narrowest. The results also indicate that the stoichiometric ethylene/oxygen and stoichiometric propane/oxygen, with similar values of the product of stability parameter and area divergence, have the same propagation modes. Further analysis suggests that the Chapman–Jouguet deflagration-to-detonation transition (DDT) distance L decreases with increasing of stability parameter and area divergence for all four mixtures. Compared with the other three mixtures, stoichiometric methane/oxygen, which has the smallest values of L because it is the most unstable mixture with the greatest propensity for hotspot formation, is most likely to undergo DDT under the same initial and boundary conditions. These conclusions agree well with the various characteristics of L obtained for larger tubes.

Методика проведення чисельного дослідження камери імпульсного детонаційного двигуна

The subject of research in this article is the process of detonation propagation in the chamber of a pulse detonation engine. Experimental research on detonation engines is a complex and expensive process that requires high-speed, high-precision equipment to obtain high-quality reliable results. Therefore, to conduct preliminary research, numerical experiment methods using mathematical simulation tools should be used. This work analyzes the possibility of applying known calculation models to study the detonation propagation process in the chamber of a pulse detonation engine. The task: to study the influence of the application of existing calculation models on the accuracy of numerical simulation of the detonation process; analyze the use of existing calculation models for the study of the detonation propagation process. The main method used in this work is the method of mathematical simulation using CFD technologies. The following results were obtained. The work considered the application of various turbulence models, chemical transition models, solvers and mesh sizes in modeling processes in the chamber of a pulse detonation engine. The application k-ε and k-ω turbulence models and their modifications are considered. The closest to the real result is obtained when applying k-ω model turbulence with SST modification. Generalized modification of this model averages the parameters on the front of the detonation wave, which leads to the destruction of the structure of the front. Taking into account the peculiarities of the processes occurring at the front of the detonation wave, the eddy-dissipation concept method will be better for modeling chemical transition, compared to the finite-rate method. Using the finite-rate method shows instantaneous combustion at the front of the detonation wave. This leads to a sharp increase in the parameters at the detonation front with its further separation from the main flow. To obtain a qualitatively reliable result of the parameters at the front of the detonation wave, cell dimensions of no more than 1/16 mm should be used. The application of the eddy-dissipation concept method with k-ω SST turbulence model allows obtaining the closest results to the experimental data. The deviation of pressure and velocity values obtained during modeling does not exceed 5% from their actual values. The temperature deviation does not exceed 10%. This is determined by the selected kinetic scheme of chemical transitions. All considered models and methods affect only the structure and development of the detonation wave front. There are no significant differences in the values of the parameters along the front (in the Taylor zone). Conclusion. The obtained results are of practical importance for the design and research of detonation engines. The use of the proposed calculation models will allow conducting numerical experiments for the pulse detonation engine chamber with sufficient accuracy, in comparison with experimental data.

Vojna zelena tehnologija - sadašnjost i budućnost

Introduction/purpose: This paper aims to present military green technology through present concepts, solutions and challenges, as well as through future trends, particularly in wireless communication. Methods: Analyses and syntheses were used to consider various aspects, challenges and developments of military green technology. Results: Important aspects of organization, challenges and strategies in military green technologies are presented. Next, the role of a green energy action plan is emphasized. Furthermore, green defence solutions and security challenges are considered. Besides presenting green technologies of today, primarily focused on wireless networks, especially 5G, the paper also considers the impact of biofuels, methanol-based fuel cells, hydrogen fuel cells, hybrid electrical vehicles and photovoltaic energy. Finally, green technologies for the future are presented through some of the most important technologies: next generation wireless networks, pulse detonation engines, piezoelectricity, and biodegradable platforms. Conclusion: Military green technology is now necessary for approaching wireless networking in order to meet challenges of high demands of wireless traffic and energy consumption. Also, military green technology will require further constant considerations in the field of efficiency and sustainability of application as well as research to provide different acceptable solutions, not only in technical, but also in the organizational domain, in order to be applied in military environment.

Ion Sensors for Pulsed and Continuous Detonation Combustors

Presented in the article are the design and operation principles of ion sensors intended for detecting the propagating reaction fronts, the deflagration/detonation mode, apparent subsonic/supersonic propagation velocity of the reaction front, and duration of heat release by measuring the ion current in the reactive medium. The electrical circuits for ion sensors without and with intermediate amplifiers, with short response time and high sensitivity, as well as with the very wide dynamic range of operation in the reactive media with highly variable temperature and pressure, are provided and discussed. The main advantages of ion sensors are their very short response time of about 1 ms, versatility of design, and capability of detecting and monitoring reaction fronts of different intensities directly in combustion chambers. Several examples of ion sensor applications in sensing deflagration-to-detonation transition in pulsed detonation engines and developed detonations in rotating detonation engines operating on different fuel–air and fuel–oxygen mixtures are presented and discussed.

Initiation of an upstream propagating detonation wave near the open end of the detonation tube operating in the valveless and purgeless scheme

Controllable and sustainable operations are the basic need for the practical pulse detonation engines (PDEs). Previous works have demonstrated that the valveless and purgeless scheme is beneficial to achieve high frequency detonations. However, steady deflagration often arises in the implementation of a long duration operation, especially when the more reactive fresh mixture is employed. To this end, three types of detonation tubes, named as type-A, type-B, and type-C, in which an upstream propagating detonation wave will be produced are experimentally investigated. In this study, the detonation wave is initiated near the open end of the detonation tube through the deflagration to detonation transition (DDT) process, and thus, the fresh reactive mixture was consumed by the upstream propagating detonation wave. Experimental results indicate that the detonation cycles can be maintained by utilizing the upstream detonation waves, and the sustainability has been dramatically improved. Especially, the available oxygen volume fraction of the oxidizer is improved to about 80% for the type-C detonation tube. In addition, the propulsive performance has been improved by 9.5% utilizing the upstream propagating detonation wave in the type-C detonation tube, and meanwhile the fluctuation of the thrust during the detonation cycle can be decreased.

Flame behaviors and explosion characteristics of two‐phase propylene oxide/air mixture under different ambient pressures

AbstractPropylene oxide (PO) is widely used in fuel‐air explosives and pulse detonation engines. Based on computational fluid dynamics, the effects of ignition position, initial pressure, and mass concentration on the explosion characteristics of the PO/air mixture were studied by using a 20 L spherical container. The results showed that the ignition position had a significant effect on the flame structure. When the fuel cloud was ignited at the center, the flame structure experienced spherical, elliptical, and tulip shapes. The explosion time first decreased and then increased with the increase of ignition position, while the maximum explosion pressure decreased correspondingly. The maximum explosion pressure and the temperature had an inverted “U” correlation with concentration at normal pressure. However, the overpressure was insensitive to concentration in the negative pressure condition. The maximum flame temperature showed different flame behaviors under different initial negative pressures and cloud concentrations. This study provides a theoretical basis for understanding the explosion behaviors of PO/air mixture with different ignition positions and initial vacuum pressures, which is of great significance in preventing explosion accidents.

Explosion behaviors of vapor–liquid propylene oxide/air mixture under high-temperature source ignition

Propylene oxide (PO) is widely used in fuel–air explosive (FAE) and pulse detonation engines (PDE). The explosion process of PO/air mixture in a 20 L spherical container under high-temperature source ignition was studied through experiment and numerical simulation. A good agreement was observed between the experimental and simulation results. The ignition temperature (1100–2500 K) and initial droplet size (10–200 μm) had no obvious effect on the maximum explosion pressure (Pmax) at a nominal concentration of 130 g/m3. Explosion time (te) and reaction time (tr) of PO aerosol explosion increased with the increase in initial droplet size. The flame propagation process in the direction of 90° was not the same as that of 45°. Explosion flame propagated from the center to the surrounding area, then sagged along wall facing the center and presented a U-shape. Explosion time at ignition temperature of 1600 K was 29.63 ms, which was the shortest compared with the temperature of 2000 K, 2500 K, and 1100 K. The influence of ignition temperature on te was more obvious than that of initial droplet size. The flame propagation mechanism of droplet sizes of 10 μm and 50 μm was different from that of 100 μm and 200 μm. The time to reach the maximum flame temperature(tf) increased with the increase in droplet size; the flame propagation speed decreased with the increasing droplet size, and the maximum flame velocity can reach 6.07 m/s.

Effects of wedge-angle change on the evolution of oblique detonation wave structure

Compared to pulse detonation engine and rotating detonation engine, oblique detonation engine has the advantage of higher flight Mach number. However, it is still challenging to achieve stabilized oblique detonation wave for a broad range of flight conditions. To control oblique detonation wave, this study focuses on the oblique detonation wave structure evolution induced by changing the wedge angle. Transient two-dimensional simulations are conducted for wedge-stabilized oblique detonation wave in a stoichiometric hydrogen/air mixture. The detailed chemistry of hydrogen combustion is considered, and the thermal states of the reactants are determined by the specified flight altitude and the Mach number. The angle change between inflow and wedge can be achieved in two ways: inflow-angle change with fixed wedge angle and wedge-angle change with fixed inflow direction. Results indicate that no new autoignition zone exists in the transient wave evolution caused by wedge-angle change, which is different from that of inflow-angle change observed in previous studies. For the wedge-angle change process, the effects of wedge-angle change rate on transient oblique detonation wave structure evolution are further assessed. It is found that the transient oblique detonation wave structure is more sensitive to the wedge-rotation angular velocity for increasing wedge angle (controlled by the thermodynamic properties of the mixture) than that for decreasing wedge angle (controlled by the shock wave dynamic). For the quasi-steady triple-wave structure during wedge-angle decreasing process, a normal detonation wave occurs and becomes dominant in the wave structure evolution, whose formation mechanism is analyzed by the polar curve theory.

Flight Demonstration of Pulse Detonation Engine Using Sounding Rocket S-520-31 in Space

A detonation engine system is successfully demonstrated for the first time in space using sounding rocket S-520-31 of the Japan Aerospace Exploration Agency/Institute of Space Astronautical Science. Detailed flight results of an S-shaped pulse detonation engine (PDE) installed in the rocket are presented herein. The flight is conducted to confirm that the PDE and its system operate at scheduled sequences in space, confirm the reproducibility of the PDE cycle, and despin the rocket around its axis. It is confirmed that the PDE operated successfully for 14 cycles in space. The experimental plateau pressure of is of the calculated plateau pressure, which suggests that detonation occurred in 14 cycles. The pressure profiles of the cycles are similar, and the pressure integrals are , confirming the excellent reproducibility of the PDE cycle. A probability statistical approach assuming a Gaussian distribution is applied to determine the average angular acceleration difference between processes of the PDE operation, mixture supply, and oxygen supply. The results suggested that the PDE despun the rocket via the thrust produced via detonation combustion, which is consistent with a quasi-steady-state model with an accuracy of .

Experimental study of the influence of annular nozzle on acoustic characteristics of detonation sound wave generated by pulse detonation engine

Acoustic characteristics of the detonation sound wave generated by a pulse detonation engine with an annular nozzle, including peak sound pressure, directivity, and A duration, are experimentally investigated while utilizing gasoline as fuel and oxygen-enriched air as oxidizer. Three annular nozzle geometries are evaluated by varying the ratio of inner cone diameter to detonation tube exit diameter from 0.36 to 0.68. The experimental results show that the annular nozzles have a significant effect on the acoustic characteristics of the detonation sound wave. The annular nozzles can amplify the peak sound pressure of the detonation sound wave at 90° while reducing it at 0° and 30°. The directivity angle of the detonation sound wave is changed by annular nozzles from 30° to 90°. The A duration of the detonation sound wave at 90° is also increased by the annular nozzles. These changes indicate that the annular nozzles have an important influence on the acoustic energy distribution of the detonation sound wave, which amplify the acoustic energy in a direction perpendicular to the tube axis and weaken it along the direction of the tube axis.

Performance analysis of a hybrid pulse detonation engine using liquid hydrogen as fuel

Aimed at enhancing the comprehensive performance of the air turbo rocket engine (ATR), two schemes of hybrid pulse detonation engine (PDE) configurations based on the ATR were proposed. The engines are fueled by liquid hydrogen, and the oxidant is the incoming air or self-carried liquid oxygen. The ideal thermodynamic cycle processes of the engines were analyzed, and the relevant mathematical models were established. The fuel pump pressure ratio of the ATREX and the oxidant-fuel ratio of the ATR-GG are respectively used as iterative variables. The performances of the two engine schemes at the design point were obtained and compared with that of the traditional ATR. The results show that, under ideal conditions, the specific thrust and specific impulse of the hybrid PDE based on the ATREX are about 20% higher than those of the traditional ATREX. Moreover, the mass of the oxidant required by the hybrid PDE based on the ATR-GG is about 49.5% lower than that of the traditional ATR-GG, while the specific thrust and specific impulse are not reduced as compared with those of the traditional ATR-GG.

Experimental study of pulse detonation engine with liquid ethanol and oxygen mixtures

Experimental study of pulse detonation engine with liquid ethanol and oxygen mixtures

Experimental research on operation performance and acoustic behavior of two-phase dual-tube pulse detonation engine

In order to research the operation synchronous of dual-tube pulse detonation engine, the operation performance and acoustic behavior of dual-tube pulse detonation engine under different fill fractions are studied experimentally. The results show that the instability of deflagration to detonation transition is the main reason for the non-synchronous work of the two tubes. With the increase of fill fraction, the detonation sound pressure increases gradually. In the region near the tube exit, the pressure and velocity of the shock wave attenuate rapidly, and the attenuation speed gradually slows down while the propagation distance increases. The time interval of detonation waves arriving at the tube exit of the two tubes can significantly affect the peak sound pressure and the duration of the sound wave outside the tube. With the increase of time interval, the peak sound pressure decreases and the total duration as well as the duration of the positive pressure increase. The synchronization of the working process of the dual-tube pulse detonation engine can be diagnosed by analyzing the pressure and duration of the sound wave outside the tube. The research results in this paper have certain reference significance for improving the synchronous of multi-tube pulse detonation engine and will be useful for the application of multi-tube pulse detonation engine in aircraft power system.

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.