Deflagration-to-detonation Transition Distance Research Articles

Effects of mixture initial conditions on deflagration to detonation transition enhanced by transverse jets

To explore the effects of mixture initial conditions on the deflagration to detonation transition (DDT) enhanced by transverse jets, numerical studies were conducted on the flame acceleration of H2/Air mixture under different initial conditions, including initial pressure, temperature, and equivalence ratio. The results indicate significant differences in flame acceleration processes under different initial pressures (0.05, 0.1, 0.15, and 0.2 MPa). Changes in jet intensity and combustion rate induced by variations in mixture initial pressure collectively influence the flame acceleration process, but the impact of jet intensity is more significant. However, effective coupling between transverse wave propagation and flame acceleration is also crucial for the DDT process. Changes in mixture initial temperature (300, 350, 400, and 450 K) and equivalence ratio (0.8, 1.0, 1.2, and 1.4) have negligible impact on jet intensity. The variation trend of flame velocity under different initial temperatures or equivalence ratios is consistent, but the detonation initiation performance is slightly different. As the initial temperature increases, the DDT distance and DDT time are shortened. With an increasing equivalence ratio, the DDT distance and DDT time initially decrease and then increase, reaching the shortest at slightly rich fuel conditions.

Effects of Copper Foam Wall/Obstacles on the Deflagration-to-Detonation Transition

To investigate the process of deflagration-to-detonation transition (DDT) of the copper foam wall in the pulse detonation engine, detonation combustion experiments were carried out using ethylene and oxygen-enriched air (oxygen concentration: 40%) as fuel and oxidant. The effects of copper foam pore size, thickness, installation length, and structure on the flame acceleration were studied experimentally, as were the effects of blockage ratio and mixture equivalence ratio. The results show that among the four pore sizes selected, the 10 PPI case produces the fastest flame development on the porous flat wall. For conditions with successful detonation, the 10 PPI case reduces the DDT distance and time by 34.97 and 42.57%, respectively, compared with the 40 PPI case. Regarding the installation length of copper foam, it is found that copper foam with a large pore size (10 PPI) and a short installation length achieves stable detonation. The general structure of copper foam was also analyzed, including the porous flat wall, porous obstacle, and solid obstacle with the same installation length. These three structures effectively accelerate the initiation of detonation. Particularly, porous obstacles show more pronounced effects on flame acceleration than the commonly used solid obstacles. These results are instructive for optimizing the short-distance ignition ability of pulsed detonation engines.

A study of the occurrence of DDT in an array of obstacles: Combined effects of longitudinal and transverse obstacle spacings

Combustion wave propagation in a channel containing a stoichiometric hydrogen-air mixture and an array of obstacles was investigated, aiming to explore the effects of longitudinal (ls) and transverse (ts) spacings of the obstacles on the occurrence of deflagration-to-detonation transition (DDT). A high-order numerical algorithm and adaptive mesh refinement were adopted to solve reactive Navier-Stokes equations. The spacings, ls and ts, are varied from 1.2 to 6 times the obstacle diameter (do = 12.7 mm). The results show that the occurrence of DDT is largely dependent on ts. The DDT is likely to occur when the ratio of transverse obstacle gap to detonation cell size d/λ ≥ 0.64. The DDT run-up distance and time are closely related to ls and ts. For large ts, the DDT occurrence time increases with ls. However, the DDT distance may decrease significantly as ls increases when ls is relatively small, due to frequent local explosions in the isolated pockets of unreacted material. A requirement for the generation of these isolated explosions can be quantified as (ls/ts)2(12–4br) < 1, where br is the blockage ratio of the channel. For small ts, the increase of DDT distance with ls/ts slows down notably when ls/ts exceeds a threshold, because there is a mechanism characterized by large fluctuations in flame surface area that promotes the occurrence of DDT in the case with a large enough ls/ts.

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.

Influence of longitudinal obstacle spacing on the deflagration-to-detonation transition through a bank of obstacles in a hydrogen-air mixture

Flame acceleration and deflagration-to-detonation transition (DDT) in a channel containing an array of staggered cylindrical obstacles and a stoichiometric hydrogen-air mixture were studied by solving the fully-compressible reactive Navier-Stokes equations using a high-order numerical algorithm and adaptive mesh refinement. Four different longitudinal spacings (ls) of the neighboring obstacle rows (i.e., ls = 15.28, 19.1, 25.4, and 38.2 mm, corresponding to 1.2, 1.5, 2 and 3 times of obstacle diameter, respectively) were used to examine the effect of obstacle spacing on flame acceleration and DDT. The results show that the main mechanisms of flame acceleration and transition to detonation in all the cases studied are consistent. While the flame acceleration is caused by the growth of flame surface area in the initial stage, it is governed by shock-flame interactions in the later stage when shock waves are generated. The focusing of strong shocks at flame front is responsible for the initiation of detonation. It was found that the flame propagation speed and the DDT run-up distance and time are highly dependent on ls. Specifically, the flame acceleration declines as ls increases, since a larger ls leads to less disturbance of flow by obstacles per unit channel length. For detonation initiation, both the run-up distance and time increase with the increase of ls. It is interesting to note that the DDT distance and time increase significantly as ls increases from 19.1 mm to 25.4 mm. This is related to the slowdown of the increase rate of energy release over a period before DDT occurs under large ls condition, because every time the flame passes over an obstacle row the shock-flame interaction is delayed and numerous isolated pockets of unburned gas material are formed.

Experimental Investigations on Detonation Initiation Characteristics of a Liquid-Fueled Pulse Detonation Combustor at Different Inlet Air Temperatures

The detonation initiation characteristics of a single tube liquid-fueled pulse detonation combustor (PDC) is investigated at different inlet air temperatures in this paper. The inner diameter of the PDC is 62 mm. Gasoline and air are used as fuel and oxidant, respectively. The inlet air temperature is 288–523 K and the operating frequency of the PDC is 10~30 Hz. The experimental results show that the deflagration to detonation transition (DDT) distance, detonation initiation time, DDT time and jet ignition time decrease with the increasing operating frequency at the same inlet temperature. When the inlet temperature is 288 K, the DDT distance is shortened from 860.5 mm to 787.7 mm as the operating frequency increases from 10 Hz to 30 Hz. The detonation initiation time, the jet ignition time and the DDT time are reduced from 10.01 ms, 7.66 ms and 2.35 ms to 6.55 ms, 4.99 ms and 1.56 ms, respectively. When the inlet air temperature increases, the atomization and evaporation of the gasoline is improved, which also leads to the decrease in the DDT distance, the detonation initiation time, the jet ignition time and the DDT time. For example, when the inlet air temperature increases from 288 K to 523 K at the frequency of 10 Hz, the DDT distance is shortened from 860.5 mm to 747.2 mm and the detonation initiation time, the jet ignition time and the DDT time is reduced to 5.867 ms, 2.51 ms and 1.11 ms, respectively. Additionally, the self-ignition caused by high inner wall temperature occurs when PDC is operating at high frequency under high inlet air temperature.

Deflagration-to-Detonation Transition in Stochiometric Propane–Hydrogen–Air Mixtures

Hydrocarbon–hydrogen blends are often considered as perspective environmentally friendly fuels for power plants, piston engines, heating appliances, home stoves, etc. However, the addition of hydrogen to a hydrocarbon fuel poses a potential risk of accidental explosion due to the high reactivity of hydrogen. In this manuscript, the detonability of stoichiometric C3H8–H2–air mixtures is studied experimentally in terms of the run-up time and distance of deflagration to detonation transition (DDT). The hydrogen volume fraction in the mixtures varied from 0 to 1. Three different configurations of detonation tubes were used to ensure the DDT in the mixtures of the various compositions. The measured dependences of the DDT run-up time and distance on the hydrogen volume fraction were found to be nonlinear and, in some cases, nonmonotonic with local maxima. Blended fuel detonability is shown to increase sharply only at a relatively large hydrogen volume fraction (above 70%), i.e., the addition of hydrogen to propane in amounts less than 70% vol. does not affect the detonability of the blended fuel significantly. The observed nonlinear/nonmonotonic dependences are shown to be the manifestation of the physicochemical properties of hydrogen-containing mixtures. An increase in the hydrogen volume fraction is accompanied by effects leading to both an increase and a decrease in mixture sensitivity to the DDT. Thus, on the one hand, the increase in the hydrogen volume fraction increases the mixture sensitivity to DDT due to an increase in the laminar flame velocity and a decrease in the self-ignition delay at isotherms above 1000 K and pressures relevant to DDT. On the other hand, the mixture sensitivity to DDT decreases due to the increase in the speed of sound in the hydrogen-containing mixture, thus leading to a decrease in the Mach number of the lead shock wave propagating ahead of the flame, and to a corresponding increase in the self-ignition delay. Moreover, for C3H8–H2–air mixtures at isotherms below 1000 K and pressures relevant to DDT, the self-ignition delay increases with hydrogen volume fraction.

Flame Acceleration and DDT in a Channel with Continuous Triangular Obstacles: Effect of Blockage Ratio

ABSTRACT Experiments were conducted in a stoichiometric hydrogen-oxygen mixture at initial pressure of 1 atm to study the flame acceleration and deflagration-to-detonation transition (DDT) in a 20 mm high channel equipped with continuous triangular obstacles. Effect of blockage ratio (br) was explored by considering different obstacle heights of 0, 1 mm, 3 mm, 5 mm, and 7 mm, corresponding to br = 0, 0.1, 0.3, 0.5, and 0.7, respectively. High-speed schlieren photography and OH* chemiluminescence recording were used to visualize the processes. Results show that blockage ratio has a significant effect on the scales and velocities of the vortices generated in the gaps between neighboring obstacles and consequently on the subsequent flame-vortex interactions. Higher br leads to faster flame acceleration via stronger flame-vortex interactions. The intricate shock-flame interactions cause successive local explosions in the br = 0.3, 0.5, and 0.7 cases, creating conditions for DDT. An eventual choking regime occurs in the br = 0.7 case due to energy losses by continuous diffractions at the obstacle vertices. It was found that the onset of DDT is triggered when the critical height of the unobstructed passage is approximately greater than three detonation cell sizes. The mechanism of DDT changes as the br decreases. One important feature observed is that the br = 0.1 case has the shortest DDT distance. In addition, the final flame speed (~740 m/s, 1.4 times unburned sound speed) before DDT for br = 0.1 is significantly smaller than those (~1300 m/s, 2.4 times unburned sound speed) for br ≥ 0.3. The reason is that the low obstacles retain the characteristics of the obstacle, while mimicking the wall roughness, resulting in both shock compression of unburned gas and viscous heating in the boundary layer ahead of the flame front. The combined effects promote the occurrence of DDT for the case with br = 0.1.

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.

Effects of obstacle layout and blockage ratio on flame acceleration and DDT in hydrogen-air mixture in a channel with an array of obstacles

Numerical simulations were performed to study flame acceleration and deflagration-to-detonation transition (DDT) in hydrogen-air mixture in a channel with a two-dimensional array of cylindrical obstacles. A high-order numerical algorithm with adaptive mesh refinement was applied to solve reactive Navier-Stokes equations. The effect of obstacle layout was examined by considering three layouts at a fixed blockage ratio of 0.5: staggered, inline-concentrated, and inline-scattered. Three blockage ratios, 0.33, 0.5, and 0.67, were used for the case of staggered obstacles to explore the influence of blockage ratio. The results show that both obstacle layout and blockage ratio have significant effects on flame acceleration and DDT occurrence, although the basic mechanism of detonation initiation is consistent for all the cases involving shock focusing. In the staggered case, the head-on collisions of flame and pressure waves with obstacles greatly promote the growth of flame surface area and thus lead to the fastest flame acceleration and shortest detonation onset time. In the inline-concentrated case, flame propagates slower than that in the staggered case due to smaller flame surface area. However, compared to the zigzag path in the staggered case, the straight passages parallel to flame propagation direction in the inline-concentrated case are more conducive to producing strong shock focusing and thus result in the shortest DDT distance. In the inline-scattered case, the straight passage along the centerline of channel facilitates the early acceleration of flame, but it has the slowest flame propagation in lateral directions and thereby the longest DDT time and distance. For the staggered obstacles at different blockage ratios, flame acceleration rate increases with increasing blockage ratio. The occurrence of DDT is hindered by the most congested obstacles, because the shock focusing is insufficiently strong to initiate detonation after passing through the excessively narrow gaps.

Numerical investigation of detonation initiation for low-volatility liquid fuel/air mixtures

Numerical simulation has been performed to characterize the detonation initiation and propagation for low-volatility liquid fuel /air mixtures in an obstructed tube. The effects of the shock waves formation and the vaporization of the droplets on the flame acceleration were researched based on comparison with the corresponding gaseous detonation behavior. The computational results indicate that the time delay of liquid-fueled detonation initiation mainly derives from the slow deflagration stage where the atomization and evaporation of liquid fuel introduced by the hot products dominates the time scale. Longer run-up distance in two phase system is mainly attributed to the incomplete combustion. Besides, the hotspots are generated at different position and controlled by different regimes in gaseous and liquid fuel cases. Then, the detonation initiation characteristics under different small droplet sizes (10 μm, 20 μm, 30 μm) were discussed in detail. As the droplet diameter increases from 10 μm into 30 μm, the deflagration to detonation transition (DDT) time increases by 126%, while the DDT distance increases by 33.8%, which indicates that the run-up time is more sensitive to the changes of droplet size. Furthermore, the factors such as weakening effects of droplets on leading shock, fuel vapor content and incomplete combustion are found to have great impact on the velocity deficit in liquid-fueled case. The achievements in current work aid understanding of natural detonation behavior and serve as a possible design suggestion of future PDE based on liquid fuel.

Effects of Transverse Jet Parameters on Flame Propagation and Detonation Transition in Hydrogen–Oxygen–Argon Mixture

ABSTRACT Two-dimensional numerical simulation is performed with the open-source program AMROC to study the effects of transverse jets (act as fluidic obstacles within a detonation tube) on the flame acceleration and deflagration to detonation transition (DDT). The slot transverse jets have been studied and compared with conventional solid obstacles in tubes. The jet initial parameters, such as mixture composition, stagnation temperature, pressure, and mass flow rate, are investigated. The results demonstrate that a hydrogen-oxygen-argon reactive fluidic obstacle leads to the shortest DDT distance and time compared with solid obstacles and fluidic obstacles composed of pure oxygen or argon. The fluidic obstacles can induce more vorticities to accelerate flame propagation. The DDT distance and time decrease with the jet initial temperature, pressure, and mass flow rate rise, while a high jet initial stagnation temperature is counterproductive to shorting DDT distance and time. The local static pressure rise plays an important role in flame acceleration when increasing the initial pressure of the fluidic obstacle. Higher jet pressure and a wider jet induce more compression waves, which can make the initial flame front more unstable and accelerate the flame as well.

Numerical Simulation of Hot Jet Detonation with Different Ignition Positions

Ignition position is an important factor affecting flame propagation and deflagration-to-detonation transition (DDT). In this study, 2D reactive Navier–Stokes numerical studies have been performed to investigate the effects of ignition position on hot jet detonation initiation. Through the stages of hot jet formation, vortex-flame interaction and detonation wave formation, the mechanism of the hot jet detonation initiation is analyzed in detail. The results indicate that the vortexes formed by hot jet entrain flame to increase the flame area rapidly, thus accelerating energy release and the formation of the detonation wave. With changing the ignition position from top to wall inside the hot jet tube, the faster velocity of hot jet will promote the vortex to entrain jet flame earlier, and the DDT time and distance will decrease. In addition, the effect of different wall ignition positions (from 0 mm to 150 mm away from top of hot jet tube) on DDT is also studied. When the ignition source is 30 mm away from the top of hot jet tube, the distance to initiate detonation wave is the shortest due to the highest jet intensity, the DDT time and distance are about 41.45% and 30.77% less than the top ignition.

Effects of jet in crossflow on flame acceleration and deflagration to detonation transition in methane–oxygen mixture

The fluidic jet turbulator has been a novel perturbation generator in the pulse-detonation engines research field for the past few years. In this paper, an experiment is performed to study the deflagration to detonation transition (DDT) process in a detonation chamber with a reactive transverse methane–oxygen mixture jet in crossflow (JICF). The jet injection arrangement is fundamentally investigated, including single jet and various double jets patterns. Corresponding two-dimensional direct numerical simulations with a multistep chemical kinetics mechanism are employed for analyzing details in the flow field, and the interaction between the vortex and flame temporal evolution is characterized. Both the experiments and simulations demonstrate that the JICF can distinctly accelerate flame propagation and shorten the DDT time and distance. The vortex stream induced by the jet distorts and wrinkles the flame front resulting in local flame acceleration. Moreover, the double jet patterns enhance flame acceleration more than the single jet injection because of the intrinsic counter-rotating vortex pairs and enhanced turbulence intensity.

Experimental investigations on effects of wall-temperature on performance of a pulse detonation rocket engine

To study the effects of wall-temperature on performance of a pulse detonation rocket engine (PDRE), long-duration experiments were conducted. An internally grooved semi-circle spiral, instead of traditional Shchelkin spiral, was utilized to facilitate the deflagration to detonation transition (DDT) process and prolong run time in the present study. Four pressure transducers and a type K thermocouple were employed to collect data during the experiments. Experiments were carried out at three different operating frequencies, such as 10Hz, 20Hz and 30Hz, until unstable operation happened. The results showed that wall-temperature increased faster at higher operating frequency. It was observed that DDT time and DDT distance both decreased with the increase of wall-temperature, and detonation pressure increased sharply with wall-temperature first and then decreased slowly when wall-temperature exceeded a certain value. Both of them were believed to be due to the impact of hot-wall on fuel vaporization and reactant temperature. Unreasonably high wall-temperature was found to cause pre-ignition of fuel–oxidizer mixture, and this was why unstable operation of the PDRE happened after long-duration runs. In addition, effects of wall-temperature on specific impulse was also discussed.

Combined effects of vortex flow and the Shchelkin spiral dimensions on characteristics of deflagration-to-detonation transition

The objective of this investigation was to achieve the shortest possible distance for the deflagration-to-detonation transition (DDT) for a pulse detonation engine without losing the engine’s simplicity. The effects of rapid flame propagation, rotating velocity, and Shchelkin spiral dimensions in the vortex flow (VF) on DDT characteristics were examined. A VF field was established in the ignition and transition domains of a detonation tube using a VF-type injector. The flame propagation in the ignition domain was observed by a high-speed video camera and the detonation propagation process was observed by measuring the pressure and ionization current in the detonation tube. The DDT distance in the VF could be shortened by 50–57 % of that in the counterflow by optimizing the VF and the Shchelkin spiral dimensions. The shortening effect became remarkable as the rotating velocity increased. The governing factors for this effect are considered to be the formation of an area of higher energy density in the ignition domain of the tube, as well as flame acceleration due to rapid flame propagation in the VF and turbulence promotion near the tube wall by the rotating velocity and the Shchelkin spiral in the transition domain of the tube. However, the combined effects of VF and the Shchelkin spiral on the shortening of the DDT distance were deteriorated in very strong turbulence. It is necessary to optimize the rotating velocity and dimensions of the Shchelkin spiral to achieve the shortest possible distance of DDT in the VF.

Studies of DDT enhancement approaches for kerosene-fueled small-scale pulse detonation engines applications

Two-phase small-scale pulse detonation engine (SPDE) offers a competitive alternative for small-scale propulsion systems from a high cycle efficiency and structural simplicity standpoint. SPDE models are designed with the aero-valve, and three different cases of obstacle combinations are used as deflagration-to-detonation transition (DDT) devices. The inner diameters of detonation tubes are 29 mm, and the lengths of three SPDEs are 995, 1,100, and 1,175 mm. Using kerosene-air as the fuel-oxidizer, a series of high-frequency detonation tests is conducted to seek efficient DDT enhancement approaches that reduce DDT distance and time and increase the frequency of kerosene-fueled SPDE. The results show that the fully developed detonation wave can be achieved at a distance of 3.4 times the minimum characteristic distance for gaseous detonation formation from the igniter and that the SPDE can steadily operate at a maximal frequency of 62.5 Hz. By adopting these DDT enhancement approaches, the detonability of kerosene is significantly improved. In addition, experiments are performed to study the effects of firing frequencies on detonation transitions. The results clearly indicate that the values of detonation wave pressures and velocities, the degree of overdriven wave, the ignition delay times, and detonation initiation times vary with frequencies. In terms of the performance, the optimal frequencies of three SPDE models are 20, 42.5, and 50 Hz, respectively.

Experimental Research on Induction Systems of an Air-breathing Valveless Pulse Detonation Engine

An air-breathing valveless PDE model was designed and manufactured, which was made up of subsonic inlet, mixing chamber, ignition chamber, detonation chamber. The total pressure recovery coefficient, flux coefficient and intake resistance with six different induction systems were measured by a semi free subsonic flow field. The proof-of-principle experiments of PDE model with different induction systems were all successfully carried out, by using liquid gasoline-air mixture with low-energy system (total stored energy less than 50 mJ). The measured detonation wave pressure ratio was very close to that of C-J detonation. The air-breathing PDE model was easy to initiate and worked in good condition. The deflagration to detonation transition (DDT) and operation frequency effect on pressure traces were also investigated by experiments. The results indicated the oscillation of pressure peak at P6 enhanced with the operation frequency increased. DDT accomplished before P6 and the DDT distance was about 0.9 m (from the ignitor).

Experimental Investigation of a Multi-Cycle Single-Tube Pulse Detonation Rocket Engine with a Coaxial Rotary Valve

We developed a novel coaxial rotary valve for a multi-tube PDE. Since this single valve can supply three different gases (fuel, oxidizer and purge gas) into a combustor, the unification of the valve systems for three different gases is possible by using our newly designed valve. A PDRE system can be simple and lightweight by using this valve, and thus its thrust-weight ratio can be increased. We proposed the design of a multi-tube rotary-valved PDRE system by this rotary valve. Moreover, in preparation for a multi-tube rotary-valved PDRE, we carried out the multi-cycle operation experiment by the single-tube rotary-valved PDRE system. The combustion wave velocity was measured to confirm the operation of the PDRE system. Deflagration-to-detonation transition (DDT) was confirmed and DDT distance decreased under the condition of high operation frequency. In addition, a maximum operation frequency was 159 Hz.

Optical and thrust measurement of a pulse detonation combustor with a coaxial rotary valve

We developed a rotary valve for a pulse detonation engine (PDE), and confirmed its basic characteristics and performance. In a square cross-section combustor, we visualized a multi-shot of a pulse detonation rocket engine (PDRE) cycle at an operation frequency of 160 Hz by using a high-speed camera (time resolution: 3.33 μs, space resolution: 0.4 mm) and a Schlieren method. The propellant filling process and the purge process were confirmed, and each process was modeled. Moreover, we confirmed the processes of detonation wave generation and burned gas blowdown. In addition, we investigated the impact of shortening the passage width of a combustor and negative-time ignition (ignition time is earlier than the end-time of the propellant filling process) on the deflagration-to-detonation transition (DDT) distance and time. The DDT distance did not depend on the passage width of a combustor and decreased under the negative-time ignition condition. With a passage width of 20 mm, the DDT distance decreased by 22% under the negative-time ignition condition to a minimum value (76 ± 8 mm). The DDT time from spark time reached a minimum value (69 ± 14 μs) under the condition of a passage width of 10 mm and negative-time ignition. The detonation initiation time and the DDT distance were represented by the time until the flame expanded toward the tube-axis one-dimensionally from ignition (characteristic time). We also carried out thrust measurement using a PDRE system composed of a circular cross-section combustor and the newly developed valve. We obtained a stable time-averaged thrust in a wide range of operation frequency (40–160 Hz) and confirmed the increase of specific impulse due to a partial-fill effect. At a maximum operation frequency of 159 Hz, we achieved a maximum propellant-based specific impulse of 232 s and a maximum time-averaged thrust of 71 N.