Air-breathing Pulse Detonation Engine Research Articles

Multicycle Detonation Investigation by Emission–Absorption-Based Temperature Diagnostics

In order to analyze and improve the performance of pulse detonation engines (PDEs), detailed detonation processes deserve much more attention. However, the measurements of characteristic parameters are difficult because the flow field in detonation is unsteady, with high pressure and high temperature. A new device based on the emission–absorption principle is developed specially for measuring pulsed temperature in a PDE plume. Experimental results show that the measured pulsed temperature can diagnose the PDE operation, such as multicycle detonation wave formation, operation frequency, and overfilling process. Effects of PDE configuration, operation frequency, and fuel on PDE plume temperature were investigated experimentally. The plume temperature increases with operation frequency. The PDRE average peak plume temperature is much higher than direct-connected PDEs and air-breathing PDEs. The newly developed plume temperature measurement method is simple, cheap, and easy to operate, which provides a useful tool to diagnose PDE multicycle operation and interaction of external flow field and PDE operation.

Internal Flow Dynamics in a Valveless Airbreathing Pulse Detonation Engine

The internal flow dynamics in a valveless airbreathing pulse detonation engine operating on ethylene fuel is studied numerically. The system involves no mechanical valves in the air flowpath, and the isolation between the inlet and combustor is achieved through gas-dynamic means. The valve operation timing for the fuel injection and initiator is determined based on the local flow conditions. The analysis accommodates the full conservation equations in axisymmetric coordinates and takes into account simplified finite-rate chemistry and variable properties for an ethylene/air/oxygen system. The detailed flow evolution and detonation dynamics during the limit-cycle operation is explored systematically. The calculated pressure history and propulsive performance agree well with experimental data. A sensitivity study of operation timing is also conducted to further elucidate the system dynamics and to provide guidelines for engine design optimization.

Performance of propellant decomposition products as fuel in an airbreathing PDE

Decomposition products of a solid propellant are considered as a possible fuel in an airbreathing pulse detonation engine (PDE). However, these decomposition products contain not only gaseous species but also a significant amount of solid carbon particles. Whether performance can be improved by burning these particles is investigated numerically. Thermodynamic calculations allow predicting the quantity of additional air required for optimum performance. Gasdynamic numerical simulations indicate that particle burning has an effect on the pressure impulse on the thrust wall. The particle size determines the detonation structure, according to the model of hybrid detonations, thus governing the delay and rate of heat release from particle combustion behind the detonation front. In the situation investigated here, the particles are incompletely burnt inside a 0.6-m-long tube. As a result, smaller particles ( ≤ 5μm) contribute to an increase in the impulse, by up to 6%. However, larger particles either have a negligible effect on the pressure impulse, if around 10 μm, or result in a decrease, if around 20 μm. Overall, the calculations show that the best efficiency is obtained for this fuel by diluting the gaseous decomposition products with an additional quantity of air, allowing for incomplete particle combustion rather than letting them behave as if inert, absorbing part of the energy released by gaseous combustion.

Model for the Performance of Airbreathing Pulse-Detonation Engines

A simplified flowpath analysis of a single-tube airbreathing pulse detonation engine is described. The configuration consists of a steady supersonic inlet, a large plenum, a valve, and a straight detonation tube (no exit nozzle). The interaction of the filling process with the detonation is studied, and it is shown how the flow in the plenum is coupled with the flow in the detonation tube. This coupling results in total pressure losses and pressure oscillations in the plenum caused by the unsteadiness of the flow. Moreover, the filling process generates a moving flow into which the detonation has to initiate and propagate. An analytical model is developed for predicting the flow and estimating performance based on an open-system control volume analysis and gasdynamics. The existing single-cycle impulse model is extended to include the effect of filling velocity on detonation tube impulse. Based on this, the engine thrust is found to be the sum of the contributions of detonation tube impulse, momentum, and pressure terms. Performance calculations for pulse detonation engines operating with stoichiometric hydrogen–air and JP10–air are presented and compared to the performance of the ideal ramjet over a range of Mach numbers.

Optimization study of spray detonation initiation by electric discharges

Development of air-breathing pulse detonation engines is faced with a challenging problem of detonation initiation in fuel sprays at distances feasible for propulsion applications. Extensive experimental study on initiation of a confined n-hexane spray detonation in air by electric dis- charges is reported. It is found that for direct initiation of spray detonation with minimal energy requirements (1) it is worth to use one discharger located near the closed end of a detonation tube and at least one additional discharger down- stream from it to be triggered in-phase with primary shock wave arrival; (2) the discharge area should be properly insu- lated to avoid electric loss to metal tube walls; (3) discharge duration should be minimized to at least 50 µs; (4) discharge channel should preferably occupy a large portion of a tube cross-section; (5) test tube should be preferably of a diame- ter close to the limiting tube diameter; (6) gradual transition between the volume with electric discharger and the tube should be used; and (7) a powerful electric discharger uti- lized for generating a primary shock wave can be replaced by a primary shock wave generator comprising a relatively low-energy electric discharger, Shchelkin spiral, and tube coil. With all these principles implemented, the rated elec- tric energy of about 100 J was required to initiate n-hexane spray-air detonation in a 28-mm tube at a distance of about 1 m from the atomizer.

Thrust Chamber Dynamics and Propulsive Performance of Single-Tube Pulse Detonation Engines

This pape r deals with the modeling and simulation of the thrust chamber dynamics in an airbreathing pulse detonation engine (PDE). The system under consideration includes a supersonic inlet, an air manifold, a rotary valve, a single -tube combustor , and a convergent -divergent nozzle. The analysis accommodates the full conservation equations in two - dimensional coordinates, along with a calibrated one - progress -variable chemical reaction scheme for a stoichiometric hydrogen/air mixture. The combustion and flow dynamics involved in typical PDE operations are carefully examined. In addition, a flow -path based performance prediction model is established to estimate the theoretical limit of the engine propulsive performance. Various performance loss mechanisms, including refilling process, mismatch of nozzle exit flow conditions with the ambient state, nozzle flow divergence, and internal flow dynamics, are identified and quantified. The internal flow loss, which mainly arises from the shock waves within the chamber, play s a dominant role in degrading the PDE performance. The effects of engine operating parameters and nozzle configurations on the system dynamics are also studied in depth. Results indicate the existence of an optimum operating frequency for achieving a be st performance margin. For a given cycle period and purge time, the performance increases with decreasing valve close -up time in most cases. On the other hand, a larger purge time decreases the specific thrust but increases the specific impulse for a giv en cycle period and valve close -up time. The nozzle throat area affects both the flow expansion process and chamber dynamics, thereby exerting a much more significant influence than the other nozzle geometrical parameters.

空気吸い込み式パルスデトネーションエンジンの高充填圧化による推力増大効果

空気吸い込み式パルスデトネーションエンジンの高充填圧化による推力増大効果

System Performance and Thermodynamic Cycle Analysis of Airbreathing Pulse Detonation Engines

A modular approach to the study of system performance and thermodynamic cycle efficiency of airbreathing pulse detonation engines (PDEs) is described. Each module represents a specific component of the engine, and its dynamic behavior is formulated using conservation laws in either one or two spatial dimensions. A framework is established for assessing quantitatively the influence of all known processes on engine dynamics. Various loss mechanisms limiting the PDE performance are identified. As a specific example, a supersonic PDE for high-altitude applications is studied comprehensively. The effects of chamber configuration and operating sequence on the engine propulsive efficiency are examined. The results demonstrate the existence of an optimum cycle frequency and valve close-up time for achieving maximum performance in terms of thrust and specific impulse. Furthermore, a choked convergent-divergent nozzle is required to render the PDE competitive with other airbreathing propulsion systems, such as gas-turbine and ramjet engines.