Pulse Detonation Engine Research Articles

Experimental investigations of momentum and heat transfer in pulse detonation engines

The pulse detonation engine (PDE) has recently become recognized as a possible new aerospace propulsionsystem. In the PDE system, self-sustained detonation waves propagate in tubes and burned gases are repeatedly exhausted backward from behind the detonation. The PDE system produces a momentum whose absolute value is equal to the exhausted gas momentum, but whose direction is opposite it. The PDE system has high thermal efficiency on account of its constant-volume combustion and has a simple structure composed of tubes. Although the high efficiency of the PDE system has been confirmed, few experimental reports have been based on a fundamental cyclic theory. In the present paper, we apply the Endo-Fujiwara simple cycle theory to the PDE in order to analyze the pressure history at an end wall (thrust wall) of the detonation tubes, the net momentum obtained on the PDE by direct-velocity measurement, and heat transfer from the burned gases to the tubes. Additionally, we estimated the PDE's specific impulse. Although the model overestimated the constant-pressure time duration by over 25% and simplified the exhaust phase as linear decay, the specific impulse obtained from the present experiments (187–361 s) is roughly identical to the theory (−23% to +49%). The pressure overestimation by the model was balanced by the experimentally obtained higher specific impulse due to the small filling rate of the PDE. The net specific impulse based on net impulse measurement (direct-velocity measurement) was 67–147 s, which was 28%–60% of the Endo-Fujiwara theory. The difference between the two specific impulses is due to the momentum transfer on the sidewall of the tubes that was neglected in the pressure measurement. Heat, 11–15 MJ/kg, was transferred from the burned gases to the tubes during one-cycle operation. This value was 8%–11% of the gross calorific value of 2H 2 +O 2 .

詳細化学反応を含む２次元数値流体力学によるＰＤＥ性能予測

One-dimensional numerical analyses of pulse detonation engine (PDE) have been performed by numerous workers. In one-dimensional codes, however, it is basically difficult to set adequate boundary conditions at exit plane, although PDE performance depends strongly on the boundary conditions. To evaluate the influence of boundary conditions, we performed a two-dimensional analysis for a straight single PDE, flying in an external environment under different fuel/oxidizer equivalence ratios. As a result, the physical processes in one PDE cycle and associated PDE performance are acquired.

Fundamentals of Idealized Airbreathing Pulse-Detonation Engines

The intent of the paper is to establish a relatively simple procedure for evaluating the idealized performance potential of a pulse-detonation engine (PDE) intended for the jet propulsion of air vehicles. The study focuses, exclusively, on PDEs using atmospheric air as the oxidant. The study is based on the proposition that, because of the very fast wave action, an idealized model of a PDE can be regarded as a tubular containment (detonation tube) that is, during combustion, effectively closed at both ends. Furthermore, the maximum possible energy available is that derivable from combustion, at constant volume, of the tube reactants regardless of details of the mode, or modes, of combustion in the detonation tube. This implies, therefore, that in order to establish the idealized performance of a PDE it is possible to avoid becoming engrossed in details relating to the detonation wave itself. Conclusions from the study are that major initial charge nonuniformities do not appear to have a significant impact on idealized PDE performances and that the idealized performances of PDEs improve with increasing flight Mach number.

The flowfield and performance of pulse detonation engines

Numerical simulations of an idealized pulse detonation engine consisting of a tube closed at one end and open at the other are presented in this paper. Uncertainties noted previously in the specification of open-boundary conditions in one-dimensional simulations are resolved by conducting multidimensional simulations and extracting the needed information. Further confidence in the simulations is gained by comparing some of the computed flow variables with recent experimental data. The results from the simulations are then used to elucidate the detailed features of the flowfield and the role of key parameters that determine the overall propulsive performance. Specific values for the performance measures of a pulse detonation engine operating on a stoichiometric ethylene/oxygen mixture are calculated from the simulations to be 2100 N s/m 3 for the impulse (independent of system size), 163–165 s for the mixture-based specific impulse and 725–740 s for the fuel-based specific impulse. The computed performance measures are found to be in good agreement with most experimental data and an explanation is provided where differences are observed. Results from various simulations are used to arrive at a general expression that can be used to estimate the impulse from various detonable mixtures.

Monitoring and control of a pulse detonation engine using a diode-laser fuel concentration and temperature sensor

Fuel measurements are needed to accurately tailor fued charges in pulse detonation engines (PDEs) to improve engine performance and to validate PDE models and computations. Here, we report simultaneous concentration and temperature measurements of C2H4 fuel in a PDE using a newly developed diode-laser absorption sensor. These measurements enable characterization of the fuel loading and ignition timing of the engine. Based on these characterizations, a real-time control system that optimizes fuel consumption and maximizes specific impulse in the engine has been realized. Similar measurements of C2H4 concentration and temperature were used to characterize pulse-to-pulse interference resulting from loading fresh fuel/oxygen reactants into hot combustion products. The sensor was used in a simple control scheme to minimize such interference, illustrating its potential role in control systems to maximize the engine's operation rate. During these studies, the sensor demonstrated two valuable improvements over traditional absorption spectroscopic techniques: (1) increased robustness and accuracy and (2) simultaneous measurements of concentration and temperature. These improvements are enbled by broad wavelength scanning of the Q-branch spectra of C2H4 near 1.62 μm. The success achieved in these small-scale tests provides strong support for expanded use of diode-laser sensors in propulsion applications.

Sensors for high-pressure, harsh combustion environments using wavelength-agile diode lasers

Practical combustors often produce a hostile environment for optical sensors, owing to elevated pressures, multiple phases, and unsteady behavior. Fortunately, new lasers and wavelength-tuning strategies have produced a class of wavelength-agile diode-laser sensors appropriate for such environments. Here, we demonstrate the extended capabilities of wavelength-agile sensors by applying a vertical cavity surface-emitting laser (VCSEL) to monitor gas temperature and pressure in a pulse detonation engine (PDE). Using aggressive injection current modulation, the VCSEL is scanned through a 10cm −1 spectral window at megahertz rates—roughly 10 times the scanning range and 1000 times the scanning rate of a conventional diode laser. The VCSEL probes absorption line shapes of the ∼852 nm D 2 transition of atomic Cs, seeded at ∼5 ppm into the feedstock gases of a PDE. Using these line shapes, detonated-gas temperature and pressure histories, spanning 2000–4000 K and 0.5–30 atm, respectively, are recorded with microsecond time response. To facilitate similar measurements using traditional spectroscopic targets such as H 2 O near 1.4 μm, where wavelength-agile lasers are not yet commercially available, we demonstrate a novel wavelength-tuning strategy. A standard distributed-feedback diode laser is thermally cycled from −10 to +50°C (scanning the output from 1399 to 1403 nm) at kilohertz rates by pulsed heating with an auxiliary 532 nm laser. Such 4 nm scans represent a 10-fold increase in the wavelength-scanning range offered by standard current-tuning techniques. Measurements of H 2 O in a static cell at 10 atm provide the groundwork for future measurements in aeropropulsion and piston engines.

A Simplified Analysis on a Pulse Detonation Engine Model.

The performance of pulse detonation engines was analytically estimated by using a simple model. A pulse detonation engine was modeled as a straight tube. One end of the tube was closed and the other was open, and a detonation wave was ignited at the closed end. One cycle of the pulse-detonation-engine operation was divided into three phases: combustion, exhaust, and filling phases. The combustion and exhaust phases were theoretically analyzed with some simplifications, using the Hugoniot relation for the Chapman-Jouguet detonation wave and flow relations for self-similar rarefaction waves. Based on the simplified theoretical analysis, useful formulas for impulse density per one-cycle operation and time-averaged thrust density were derived.

721 航空宇宙機用デトネーションエンジンの研究開発(OS7-6 航空宇宙推進(流体,燃焼))(OS7 北海道における航空宇宙工学研究の進展と未来)

In the present paper we studied detonation initiation processes in the pulse detonation engine system experimentally using piezo-pressure-gauge detonation-Mach-number measurements. Our pulse detonation engine system is a 3.728m-long 50mm-bore tube with a 0.8m^3 vacuum chamber. The igniter is a spark plug for automobile use. We did four kinds of experiments, closed-end initiation with and without Shchelkin spiral, and side-wall initiation with and without Shchelkin spiral. From the experimental results we ensured the Shchelkin spiral effects on the initiation processes, and possibility of open-end initiation which has advantage in gaseous mixing in the system.

Pulsed detonation engine. Numerical study

A renewal of interest to study the possibilities of using the gas detonation as a thrust - producing mechanism has been observed during the last ten years. This interest can be motivated by the wide simplicity of the design, the low cost of exploitation and the acceptable performance, so that the PDE can give to this propulsion concept a place as a serious competitor device. The aim of this paper consists on an analysis of the performance of a Hydrogen-Air mixture PDE, computed by the PLEXUS code, using an accurate CFD numerical scheme, for many geometric and operating configurations. The main characteristic of this approach is the possibility of using a geometry that could be structured or unstructured with the associated properties. In particular, the modeling of the detonation propagation can make into account the hydrodynamic effects and combustion one. The interaction of the gas jet, stemming from the combustion chamber, with the surrounded air is also examined and discussed. This may lead to study the PDE in flight configuration in particular with atmosphere configuration.

Review of Propulsion Applications of Detonation Waves

Applications of detonations to propulsion are reviewed. First, the advantages of the detonation cycle over the constant pressure combustion cycle, typical of conventional propulsion engines, are discussed. Then the early studies of standing normal detonations, intermittent (or pulsed) detonations, rotating detonations, and oblique shock-induced detonations are reviewed. This is followed by a brief discussion of detonation thrusters, lasersupported detonations and oblique detonation wave engines. Finally, a more detailed review of research during the past decade on ram accelerators and pulsed detonation engines is presented. The impact of the early work on these recent developments and some of the outstanding issues are also discussed.

Diode-laser sensor for monitoring multiple combustion parameters in pulse detonation engines

Diode-laser absorption spectroscopy techniques have been adapted and, applied for in situ measurements of pertinent combustion parameters in pulse detonation engines (PDEs). A sensor employing five multiplexed diode lasers operating in the 1300–1800 nm spectral region has been developed for monitoring gas temperature, H 2 O concentration, liquid fuel concentration, and soot volume fraction. Gas temperature is determined from the ratio of H 2 O absorbances at different wavelengths: water mole fraction and fuel and soot volume fractions are determined from the measured gas temperature and absorbances at selected wavelengths. The sensor's time response (0.5 μs) and non-intrusive, nature make it suitable for measurements in the hostile environment generated by PDEs. The sensor was used to monitor a 4 cm diameter PDE operating on a JP-10/oxygen aerosol. Measurements revealed charges of non-uniform equivalence ratio at ignition. Detonations processing such charges reached 95% of the Chapman-Jouget velocity and gas pressures predicted for a stoichiometric, uniform load. Gas temperature and H 2 O concentration, however, reached only ≈50% of the Chapman-Jouget predictions, as a result of the decreasing fuel concentration along the length of the engine. The sensor also revealed the presence of hot H 2 O for a long duration (>100 ms) relative to the duration of the pressure pulse (≈500 μs) in the blowdown following the detonation. The engine performance information recorded by the sensor is expected to enhance PDE modeling and optimization efforts, potentially enabling PDE combustion control.

Performance estimates of pulsed detonation engines

Pulsed detonation engines have recentlyreceived increasing attention. Various advantages claimed for the pulsed detonation engines depend on performance estimates. A review of previous computational studies of pulsed detonation engines shows a wide variation in the predicted performance of even an idealized system. In this paper, detailed, time-dependent numerical simulations are used to explore some plausible reasons for the observed differiences. The system simulated consists of a tube closed at one end and open at the other. The relaxation of the pressure at the exit of the tube to the ambient values is found to be a critical factor determining the specific impulse. Higher specific impulse can be attained with a gradual relaxato of the pressure at the exit of the tube. Numerically, different specifications of the outflow boundary conditions results in different relaxation rates and hence different values for the specific impulse. Experimentally, different effective rates of relaxation can be attained with different exhaust nozzle designs. The initial conditions used in simulations to initiate detonations are also found to contribute significantly to the overall performance. The results from these studies are used to reconcile previous performance estimates.

Detonation transmission and transition in channels of different sizes

Numerical simulations were conducted to investigate two types of detonation diffraction phenomena: (1) detonation transmission from a small two-dimensional channel to a large one, both filed with the same ethylene-based mixture; and (2) detonation transition from a small channel filled with a stoichiometic ethylene-oxygen mixture into a large channel filled with a stoichiometic, ethylene-air mixture. The transmission cases show that in the stoichiometic ethylene-oxyge mixture, the detonation originally generated in the small channel, containin eight pairs of triple points (8Λ), successfullytransmits into the large channel, and in the stoichiometric ethylene-air mixture, the detonation from the small channel, containing only four pairs of triple points (4Λ), fails after its transmission into the large channel. In the transition case, the detonation front from the small channel also containing eight pairs of triple points (8Λ), survives its transition into the stoichiometric ethylene-air mixture in the large channel. It is interesting to note that the mixture in the large channel is the same as the mixture used in the transmission case where the detonation fails to transmit into the large channel. After the transition, the triple-point spacing increases from that observed when the detonation was still in the small channel. In all cases, the expansion waves generated at the exit of the small channel weaken the detonation front from its edges. However, the expansion wave is onlyable to equench the detonation in the ethylene-air to ethylene-air case. Also, the reflected shocks from the channel walls can created local regions of high pressure and temperature and, therefore, re-ignite the mixture near the walls. However, the overall effect of the reflected shocks is quite limited in the casees studied here. The significance of these results to research on the pulse detonation engine is also discussed.

Strategies for Pulsed Detonation Engine Performance Optimization

The pulsed detonation engine (PDE) concept is systematically analyzed with respect to design variations, and the potential performance is measured from computational e uid dynamics simulations. Variations in cone guration geometry are examined e rst through single-pulse computations. These show that the presence of a nozzle can greatly affect the performance of the PDE by increasing thrust delivery during the ignition phase. It is further shown that it is not necessary to e ll the entire tube with a fuel ‐ air mixture and that signie cant gains in specie c impulse can be obtained by appropriate fueling strategies. Multicycle computations are performed next and the effect of cycling parameters is studied. It is shown that the cycling frequency can be signie cantly increased by selecting the pressure parameters and the extent of refueling. We also show that multicycle performance can be very different from the single-pulse estimates, and that it is not possible to optimize separately the ignition phase from the injection phase. Finally, the question of open-end initiation is examined and a comparison between quasi-one-dimensional and two-dimensional computations is performed.

Review of propulsion applications and numerical simulations of the pulsed detonation engine concept

Here we review experimental and computational studies of the pulsed detonation engine concept (PDEC) and present results of our recent numerical study of this concept. The PDEC was proposed in the early 1940s for small engine applications; however, its potential was never realized due to a complicated, unsteady operation regime. In this study, we demonstrate the use of current advances in numerical simulation for the analysis of the PDEC. The high-thrust/engine volume ratio obtained in our simulations demonstrates promising potential of the pulsed detonation engine concept.