Pulse Detonation Engine Research Articles

Analytical Assessment of Blended Fuels for Pulse Detonation Engine Performance

A pulse detonation engine (PDE) is possible to be a next-generation high-performance propulsion system in aerospace-related applications. To generate power or thrust, PDE uses repeated detonations. The current study evaluates the PDE performance with alternative and blended fuels in the Zeldovich–von Neumann–Doring (ZND) model. Parameters such as temperature ratio, pressure ratio, detonation velocity, and specific impulse were determined analytically for the fuels. The computed detonation parameters and specific impulse were compared with those available in NASA’s open-source program, Chemical Equilibrium with Applications (CEA), to ensure the results' sufficient validity. It was found that the highest specific impulse was achieved with hydrogen at an equivalence ratio of 1. Analytical values of all the parameters were in an acceptable range as defined by NASA CEA. As compared to pure butane and propane, their blends yielded higher values (1 to 10 percent) of specific impulse. Propane and butane are safe, non-toxic, clean-burning fuels, great energy sources, and can be used as alternative fuels in PDE.

Numerical investigation of the effect of jet intensity from internal jet tube on detonation initiation characteristics

Detonation initiation is one of the key problems in the application of pulse detonation engine (PDE). In recent years, the experimental research and numerical simulation results of multi-point jet initiation show that multi-point jet initiation can expand ignition energy and accelerate Deflagration-to-Detonation Transition (DDT) process. However, it will bring some difficulties to the actual implementation process due to the increase in the number of jet tubes. In order to reduce the number of ignition sources and keep multiple jets, this paper proposed a new structure of jet tube, in which the jet tube was inserted into the detonation tube, and multiple jets were generated by opening holes at the jet tube wall. The effect of the jet intensity propagated from the jet tube through the jet hole on the detonation initiation characteristics was studied by changing the initial pressure of the ignition zone. Stoichiometric hydrogen-air mixture was used. The simulation results indicated that the jet intensity had a great influence on the characteristics of detonation wave. When the initial pressure was 0 or 0.2 MPa, the stable detonation wave could not be initiated due to the jet intensity was weak. When the initial pressure of ignition zone reached 0.4 MPa, the intensity of the jet propagating from the jet tube was obviously strengthened. Then, a local detonation point was generated near the center axis of the jet tube at about x = 20 mm and developed into detonation wave. The detonation wave attenuated into quasi-Chapman-Jouguet (C-J) detonation wave, and the coupling of pressure and temperature gradually declined through the transversal jet hole. Finally, high pressure points were formed near the wall of the detonation tube, interacted at the center of the detonation tube, and a plane detonation wave was generated through reflection from the wall of the detonation tube. As the initial pressure of ignition zone continued to increase to 0.6 MPa, the development process of detonation wave was similar to that of 0.4 MPa, but the jet intensity was further improved, which made the distance and time of DDT significantly shortened. In addition, multi-stage jets could obviously reduce DDT distance and time compared with the transverse jet.

Thrust Chamber Dynamic and Propulsive Performance of Biofuels Under Detonation Combustion

Detonation is a shock wave obtained from the energy that releases after the combustion. Chapman-Jouguet(CJ) theory can be used to identify the behaviour of the detonation in gasses. Pulse Detonation Engines (PDEs) is one of the engines that implement the detonation in its combustion system. The Humphrey cycle is the thermodynamic cycle which is similar to the Pulse Detonation Engines (PDEs). It is the modification of the Brayton cycle where the constant-pressure heat addition process of the Brayton cycle is replaced by a constant-volume heat addition process. The Humphrey cycle can provide the pressure rise combustion by utilizing the shock inside the combustion chamber. Compared to the Brayton cycle, the Humphrey cycle has higher thermodynamic efficiency. However, the detonation process has unsteady combustion which makes it more difficult to handle. The purpose of the study is to calculate the performance of the aircraft by using alternative fuel in the ZND model. An analytical model is started by having the molecular structure of each biofuel and it has been used to determine detonation velocity, Mach number at C-J point, temperature ratio, pressure ratio, density ratio, Brayton and Humphrey efficiency, specific impulse, and specific thrust. In addition, the physical properties of the flow are investigated by changing the initial temperature, initial pressure, and mass flux. The pressure ratio, temperature ratio, and density ratio will all decrease as the initial pressure varies. The variation of mass flux and initial temperature, on the other hand, generates the opposite outcome as the change of pressure. The feasibility of the fuels in the detonation combustion can be known as they show high propulsive performance after the initial condition is changing.

Temperature Distribution Analysis of Pulse Detonation Engines

In pulse detonation engines (PDE), combustion temperatures can rise as high as 3000 K across the detonation wave. The continuous exposure to such elevated temperature may risk the integrity of the structural components of the engines. In order to be able to estimate the heat load accurately. Hence, numerical and experimental studies of the temperature distribution on a pulse detonation engine model was conducted to quantify the heat load. Navier-Stokes conservation equations with viscosity and chemical reaction for deflagration-to-detonation transition (DDT) in detonation engines were solved through computational fluid dynamics. Reactive flow field of premixed mixtures (propane-oxygen) was modeled for detonation process. In the simulation, short-term detonation combustion (ms) and long-term wall heating process(s) are carried out together. Both single detonation and multiple continuous detonations were simulated and tested, and the simulation results are consistent with the experimental results. The results show that there is a correlation between heat flux and detonation wave structure and the instantaneous maximum heat flux appears in the detonation wave region of the detonation tube wall. The distribution of transient heat flux in time and space is very uneven, and the difference between transient heat flux and average heat flux is large. The position of detonation wave formation is the turning point of PDE wall temperature, and the temperature at the front end of the turning point is lower than that at the back end. The results show that the fresh mixtures have cooling effect on the detonation tube wall, which leads to the increase of the inner wall temperature with oscillation and the continuous increase of the outside wall temperature. The maximum wall temperature and the speed of temperature rise are positively correlated with detonation frequency. The results also show that the heat transfer coefficient of detonation tube has an effect on the initiation of detonation wave. When the heat transfer coefficient is large, detonation wave can not initiate in the studied engine. The focus of thermal protection is different between single detonation and multiple continuous detonations. Heat management of the detonation engines highlights an important part on the engine construction.

Development of an S-Shaped Pulse Detonation Engine for a Sounding Rocket

This paper presents the results of an S-shaped pulse detonation engine (PDE) ground firing test in the form of a detonation engine system. The world’s first technology demonstration of PDE in space using a sounding rocket is planned, and the aim is to control the rocket spin rate in the axial direction using pulsed detonation. The PDE operation at full sequence was successful. The despin rate change of the rocket between continuous oxygen supply and successful PDE operation is expected to be per run. This change in despin rate can be measured by an onboard gyro sensor, making the system flyable. The test results were compared with data from thrust measurement tests conducted in a laboratory, the results of which confirmed the thrust generation under an ambient pressure of . The average thrust values in the thrust measurement experiments showed good agreement of with a quasi-steady-state model introduced to predict the PDE thrust. These results demonstrate the feasibility of the newly developed PDE and its system as the world’s first technology demonstration of detonation propulsion in space.

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.

Analysis on impulse characteristics of pulse detonation engine with nozzles

Abstract In order to study the influence of different nozzle configurations on the gas–liquid two-phase pulse detonation engine (PDE) propulsion performance, the measurement system based on the tunable diode laser absorption spectroscopy (TDLAS) technology is built to measure the velocity and the temperature, while the high frequency dynamic pressure sensor is used to measure the nozzle gas pressure. Based on the momentum principle, the contribution mechanism of unsteady gas jet on thrust is obtained indirectly by TDLAS data. The results show that the impulses of PDE with non-nozzle, convergent nozzle, divergent nozzle and convergent–divergent nozzle are 1.95, 2.08, 1.85 and 2.16 N∙s within 20 ms of the exhaust period, respectively. The analysis reveals that the impulses of PDE with convergent and convergent–divergent nozzles are larger than that with non-nozzle, while the impulse of PDE with divergent nozzle is smaller than that with non-nozzle. The research results in this paper can provide reference for the design of nozzles for PDE.

Analysis on impulse characteristics of pulse detonation engine with nozzles

Abstract In order to study the influence of different nozzle configurations on the gas–liquid two-phase pulse detonation engine (PDE) propulsion performance, the measurement system based on the tunable diode laser absorption spectroscopy (TDLAS) technology is built to measure the velocity and the temperature, while the high frequency dynamic pressure sensor is used to measure the nozzle gas pressure. Based on the momentum principle, the contribution mechanism of unsteady gas jet on thrust is obtained indirectly by TDLAS data. The results show that the impulses of PDE with non-nozzle, convergent nozzle, divergent nozzle and convergent–divergent nozzle are 1.95, 2.08, 1.85 and 2.16 N∙s within 20 ms of the exhaust period, respectively. The analysis reveals that the impulses of PDE with convergent and convergent–divergent nozzles are larger than that with non-nozzle, while the impulse of PDE with divergent nozzle is smaller than that with non-nozzle. The research results in this paper can provide reference for the design of nozzles for PDE.

Research on Optical Diagnostic Method of PDE Working Status Based on Visible and Near-Infrared Radiation Characteristics

Fill fraction not only has a profound impact on the process of deflagration to detonation in pulsed detonation engine, but also affects the propulsion performance in both flight and ground tests. In this paper, a novel optical diagnostic method based on detonation exhaust radiation in visible and near-infrared region within 300–2600 nm is developed to determine the current working state in the gas–liquid two-phase pulsed detonation cycle. The results show that the radiation characteristic in each stage of detonation cycle is unique and can be a good indicator to infer the fill fraction. This is verified experimentally by comparison with the laser absorption spectroscopy method, which utilizes a DFB laser driven by ramp injection current to scan H2O transition of 1391.67 nm at a frequency of 20 kHz. Due to concentrated radiation intensity, time duration reaching accumulated radiant energy ratio of 50% in detonation status would be smaller than 1.2 ms, and detonation status would be easily distinguished from deflagration with this critical condition. In addition, the variation of important intermediates OH, CH, and C2 radicals during detonation combustion are obtained according to the analysis of detonation spectrum, which can also be proposed as a helpful optical diagnostics method for the combustion condition based on C radical concentration. The study demonstrates the feasibility of optical diagnostics based on radiation in visible and near-infrared regions, which could provide an alternative means to diagnose and improve pulsed detonation engine performance.

Ежекторний детонаційний двигун на екологічно чистих компонентах палива

The subject of research in the article is engines operating on the detonation principle of converting the energy of the working fluid. In recent years, there has been an exponential growth in the number of scientific papers devoted to detonation engines, and the most promising direction is the study of detonation engines with an ejector nozzle (EN). The work aims to obtain the results of studies of the defining characteristics of a detonation engine with an ejector nozzle. The main tasks are the scientific analysis of the working process of the pulse detonation engine with EN; modeling of working processes occurring in the flow path of the engine; numerical implementation of a mathematical model and a computational experiment. Methods, for the numerical implementation of the model of a detonation engine with an ejector, a finite-difference TVD scheme of the second order of accuracy was used. According to the results of the work performed, we observe two regions on the pressure curves, within which the pressure remains unchanged for a certain time interval (pressure plateau). An increase in the length of the ejector leads to an increase in the duration of the stage of the outflow of detonation products from the flow path of the engine, an increase in the added mass of atmospheric air, and contributes to a significant increase in the specific impulse of thrust. The value of the thrust impulse was obtained by integrating the excess pressure on the traction wall over time. Conclusions. The scientific novelty is as follows. The change in pressure overtime on the traction wall of the detonation chamber when using cylindrical EHs of different lengths was investigated by the method of numerical simulation. The value of the thrust coefficient of the ejector nozzle for the starting conditions is obtained. The studies carried out in this work are aimed at analyzing the operating mode of a promising propulsion system and are aimed at modeling the gas-dynamic processes of a pulsed detonation engine with an ejector to obtain the data necessary for preliminary design, consideration of alternative design options, and an operational assessment of the possible characteristics of an engine with an ejector. The main advantages of the engine are the ultra-high-speed of energy release in the detonation process, which leads to an increase in the efficiency of the thermodynamic cycle, simplification and cost reduction of the design, and a significant gain in in-flight performance.

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.

Internal flow dynamics and performance of pulse detonation engine with alternative fuels

In this study, analytical and computational analysis is performed to determine the effect of thermodynamic detonation parameters on the performance of the pulse detonation engine. For analytical study along with pure fuels blend of hydrogen (50 %) + kerosene (50 %), hydrogen (50 %) + methane (50 %) and methane (50 %) + kerosene (50 %) are considered. The ANSYS FLUENT program is utilized two-dimensional computational fluid dynamics (CFD) simulation using a stoichiometric mixture of three pure fuels: hydrogen-air, methane-air, and kerosene-air. Time-dependent numerical simulations are used to explore the flow condition inside the detonation tube. Excellent performance is observed for hydrogen-air fuel. Hydrogen shows the highest velocity of 2524.36 m/s and a specific impulse of 6842.16 s. The lowest velocity and specific impulse are produced by kerosene of 1520 m/s and 1473.6 s, respectively. It is shown that measured parameters could vary significantly depending on the choice of fuels used. The results infer that hydrogen blends of methane and kerosene fuels are also suitable for pulse detonation engine (PDE) application. Finally, these analytical and simulated results are validated with the previously published literature and NASA CEA (national aeronautics and space administration -chemical equilibrium with applications).

Experimental and low-dimensional numerical study on the application of conventional NOx reduction methods in pulse detonation combustion

Although research interest in pressure gain combustion (PGC) remains high, information on pollutant emissions from detonation-based devices such as pulse detonation engines is sparse, especially lacking extensive experimental parameter studies. Nevertheless, available results indicate potentially very high exhaust levels of nitrogen oxides (NOx) due to the significantly increased combustion temperatures and pressures induced by the detonation wave. To counter this issue, this study applies conventional NOx reducing measures in the form of fuel-lean mixtures and nitrogen dilution (emulating exhaust gas recirculation) to a pulse detonation combustor in multi-cycle operation. Their impact on the exhaust gas composition is measured and compared to numerical predictions by two available simplified models. To allow for a broader range of comparison and better assess the capabilities of these numerical models, emissions from fuel-rich and oxygen-enriched mixtures are measured as well. Experimental results confirm high levels of NOx up to several thousand ppm for near-stoichiometric, undiluted mixtures. When conventional NOx reduction measures are applied, significant NOx abatement can be achieved, with further reduction potential primarily limited by unsuccessful deflagration to detonation transition (DDT). Comparison with numerical results shows that simplified models allow for good qualitative agreement and can also deliver good quantitative predictions over a wide range of conditions if a suitable heat-loss model is chosen.

Effect of fill flow rate on flame acceleration in a detonation channel

In a pulse detonation engine, filling fresh reactive mixtures into the detonation chamber is an indispensable process. The fill flow rate would significantly influence the subsequent flame acceleration and detonation initiation processes. Nevertheless, the existing works regarding the flame acceleration and detonation initiation are mostly performed on the quiescent mixtures. This work, therefore, investigates the effect of fill flow rate on the flame acceleration process in a square cross-section, obstructed detonation channel. Ethylene was utilized as the fuel, and oxygen-enriched air with an oxygen volume fraction of 40% as the oxidizer. The flame acceleration processes of quiescent and moving mixtures were observed by high-speed Schlieren and chemiluminescence techniques. It was found in this work that the fill flow rate dominates the flame propagation in the early stage of the flame acceleration (i.e., to the sound velocity of reactants). The initial flame structures vary from smooth (quiescent) to wrinkled (50 g/min) and cellular (100 g/min and 150 g/min), and to turbulent (200 g/min) with the increase of the fill flow rate. The Schlieren measurements of the filling processes show that the flow instabilities and the shear layer shedding from the obstacle surfaces into the mainstream are responsible for the promoted flame acceleration in high fill flow rate cases.

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.

Effect of equivalence ratio on the detonation noise characteristics of pulse detonation engine

Abstract The experimental system of pulse detonation engine (PDE) is set up to investigate the influence of equivalence ratios on detonation noise characteristics. The research results show that as the equivalence ratio increasing, the amplitudes of detonation noise in all angles and locations increase, and the tB also increases simultaneously, while the tA increases first and then decreases. The equivalence ratio also has a great influence on the intensity of the detonation noise signal in the frequency band of 10–100 Hz, which increases firstly and then decreases with the increase of the equivalence ratio, and the maximum value is obtained at equivalence ratio of 1.1. The results are of great significance to study the mechanism of detonation noise and promote the process of the engineering application.

Effect of equivalence ratio on the detonation noise characteristics of pulse detonation engine

Abstract The experimental system of pulse detonation engine (PDE) is set up to investigate the influence of equivalence ratios on detonation noise characteristics. The research results show that as the equivalence ratio increasing, the amplitudes of detonation noise in all angles and locations increase, and the tB also increases simultaneously, while the tA increases first and then decreases. The equivalence ratio also has a great influence on the intensity of the detonation noise signal in the frequency band of 10–100 Hz, which increases firstly and then decreases with the increase of the equivalence ratio, and the maximum value is obtained at equivalence ratio of 1.1. The results are of great significance to study the mechanism of detonation noise and promote the process of the engineering application.

Role of overdriven state of ignition wave in pre-detonators on detonation transition modes in a flat chamber

Using the small-diameter pre-detonator is an important method to provide reliable and fast detonation to the denotation engines (i.e., pulse detonation engines or rotating detonation engines). This work examines the role of the overdriven state of ignition waves generated in pre-detonators on detonation transition modes in a flat chamber. For this purpose, a series of experiments are performed using different lengths of pre-detonators (Lp) with different mixtures to initiate the detonation in the main chamber. Results show that maintaining an overdriven state at the pre-detonator exit can significantly enhance the probability of fast detonation initiation (i.e., supercritical/critical mode) in the main chamber. Especially for the high nitrogen diluting ratio (β) mixtures, forming the overdriven detonation at the pre-detonator exit becomes a necessary condition for the fast initiation. As a result, the fast detonation initiation mode distributes in an upper-right shrinking ‘canyon’ in the Lp-β map. It is illustrated that the increased overdriven degree required for transitioning detonation wave under the higher β cases is responsible for this observation.

Adjoint-based optimisation of detonation initiation by a focusing shock wave

An optimisation study of a shock-wave-focusing geometry is presented in this work. The configuration serves as a reliable and deterministic detonation initiator in a pulsed detonation engine. The combustion chamber consists of a circular pipe with one convergent–divergent axisymmetric nozzle, acting as a focusing device for an incoming shock wave. Geometrical changes are proposed to reduce the minimum shock wave strength necessary for a successful detonation initiation. For that purpose, the adjoint approach is applied. The sensitivity of the initiation to flow variations delivered by this method is used to reshape the obstacle’s form. The thermodynamics is described by a higher-order temperature-dependent polynomial, avoiding the large errors of the constant adiabatic exponent assumption. The chemical reaction of stoichiometric premixed hydrogen-air is modelled by means of a one-step kinetics with a variable pre-exponential factor. This factor is adapted to reproduce the induction time of a complex kinetics model. The optimisation results in a 5% decrease of the incident shock wave threshold for the successful detonation initiation.

Oxygen concentration distribution in a pulse detonation engine with nozzle–ejector combinational structures

Pulse detonation engines (PDEs) with three different types of nozzle–straight ejector combinational structures at three different ejector positions were simulated by the unsteady 2-D axisymmetric method to understand the influence of nozzle–ejector combinational structures on the performance of PDEs. Three types of nozzles included the straight nozzle, convergent nozzle, and convergent–divergent (CD) nozzle. Three ejector positions were considered according to the ratio of the distance between the nozzle outlet and the ejector inlet to the diameter of PDEs (Δx/d). Propane was used as the fuel and air as the oxidizer. The simulation results indicated that for the PDE with the straight nozzle, it took the shortest time for high-temperature burnt gas to exhaust from the detonation tube. For the PDE with the CD nozzle, the time at which the ejector was filled with external air was the fastest. Within the time range of t = 0–10 ms, the ejected air was less than the original air in the ejector among all the nine combinational structures. The maximum ejected air was obtained with the convergent nozzle, followed by the CD nozzle, and the minimum with the straight nozzle. For certain nozzles, the maximum air was ejected at the ejector position of Δx/d = +1, followed by the ejector position of Δx/d = 0, and the minimum at the ejector position of Δx/d = −1. For the convergent nozzle–ejector combinational structure, the air ejection speed was the fastest. Oxygen concentration distribution in the PDE with the CD nozzle was more uniform along the axial direction than the other nozzles.