Pulse Detonation Combustor Research Articles

Lean Operation of a Pulse Detonation Combustor by Fuel Stratification

Abstract Pressure gain combustion is a promising concept to substantially increase the thermal efficiency of gas turbines. One possible implementation that has been frequently investigated is pulse detonation combustors (PDCs), as they permit stable and reliable operation. At the same time, the need for part-load operation and low NOx emissions requires combustion concepts in the lean regime. However, realizing lean combustion is still very challenging in PDCs since the deflagration to detonation transition (DDT) is very sensitive to the reactant composition. This work investigates an approach to realize lean combustion in PDC by applying fuel stratification experimentally. The scope is to find the necessary increase of fuel concentration inside the predetonation chamber to provide reliable DDT with respect to the overall equivalence ratio. Emission measurements in the exhaust of the PDC allow for a quantification of the NOx emissions as a function of the injected fuel profile. A valveless PDC test rig is used, which contains a shock focusing geometry for detonation initiation and is ignited by a spark plug close to the upstream end wall. The subsequent expansion of the burned gas and interaction of the flame front with turbulence leads to the formation of a leading shock inside the predetonation chamber, which is then focused inside a converging-diverging geometry. The successful initiation of a detonation wave by shock focusing is very sensitive to the pressure ratio across the leading shock, which can be influenced by initial pressure, reactant composition and flow velocity. Results reveal that fuel stratification allows for reliable detonation initiation at a global equivalence ratio of φglob=0.65, whereas repeatable successful operation with nonstratified fuel injection is limited to φglob≥0.85.

Unsteady Effects on NOx Measurements in Pulse Detonation Combustion

Emission measurements from unsteady combustion systems such as Pulse Detonation Combustion (PDC) are challenging due to the inherently large variations in pressure, temperature, composition, and flow velocity of the exhaust gas. Comparison of experimental data is additionally complicated by differences in operating conditions and gas sampling setup between different facilities. Qualitative considerations with regard to the sampling process from PDC, based on one-dimensional simulations, indicate a systematic influence of the sampling setup and extraction process on the resulting concentration measurements. Therefore, operating frequency, sample time, fill time, as well as PDC outlet and probe geometry were varied experimentally in order to assess the degree to which each of these parameters impact the resulting measured {rm NO}_{rm x} in order to better inform researchers of these effects when making measurements. It was shown that measured {rm NO}_{rm x} emissions can vary significantly depending on the choice of these parameters and therefore care must be exercised in order to reduce the influence of the sampling technique when aiming for comparable results.

Effect of operating parameters on application based performance analysis of PDC: A recent review

Pulse detonation engines (PDEs) are advanced propulsion device for next generation of propulsion systems. The PDE combustion processes are filling of fuel-oxidizer, combustion reaction, blow down and purging. In conventional engine deflagration combustion takes places, which propagation speed is less (Ma < 1) rather than detonation combustion process. But detonation combustion process in pulse detonation engine takes place and its flame propagation speed is much higher than sonic (Ma = 1) velocity. So researchers are focusing on PDE combustion process and different propulsion performances enhancement process. Deflagration to detonation transition process takes placed inside the combustor due to effect of different operation conditions and combustor geometry. Further NOx emission mitigation techniques from Pulse detonation combustor (PDC) are big drawback to reduce the pollution. In these regards review studies on recent advances techniques on flame acceleration, NOx formation and propulsion performance have been indicated to increase the performance of the system. Further state of arts of application indicates that pulse detonation engine can be used for green manufacturing process, surface coating and pharmaceutical product manufacturing.

A theoretical and 1-D numerical investigation on a valve/valveless air-breathing pulse detonation engine

The important operating characteristics of pulsed Pressure Gain Combustion (PGC) propulsion are the pressure gain of the combustor component and the propulsive performance gain of the engine. A ramjet-type valve/valveless air-breathing pulsed detonation engine with a supersonic internal compression inlet is investigated. Based on an ideal thermal cycle, the ideal equivalent pressure ratios (πcb) of the Pulsed Detonation Combustor (PDC) are obtained theoretically which are directly related with the propulsive performance of the engine. By introducing an orifice loss model into the cycles, the critical pressure drop ratios through the orifice for the PDC achieving pressure gain and the engine achieving thrust gain are studied. More influencing factors are investigated by the use of a one-dimensional (1-D) numerical simulation model. The operating characteristics of the pulse detonation engine are investigated with changes of the valve type, the inlet/outlet area ratio of the PDC, the nozzle area ratio, and flight conditions. All these factors can affect πcb of the PDC, and πcb can be optimized by changing the geometry of the engine. The most important influence parameter is the valve type. When using an orifice-type aerodynamic valve, simulation results show that the PDC cannot achieve the pressure gain characteristics. When a supersonic internal compression inlet is introduced to the engine, whether the Pulse Detonation Engine (PDE) can achieve thrust gain comparable with that of an ideal Brayton cycle engine not only is related to the pressure gain of the combustor, but also needs to optimize the engine structure to reduce the total pressure loss.

Numerical investigation of detonation initiation by a focusing shock\xa0wave

This work presents a numerical study of detonation initiation by means of a focusing shock wave. The investigated geometry is a part of a pulsed detonation combustion chamber, consisting of a circular pipe in which the flow is obstructed by a single convergent–divergent axisymmetric nozzle. This obstacle acts as a focusing device for an incoming shock wave, serving as a low-energy detonation initiator. The chamber is filled with stoichiometric premixed hydrogen-enriched air. The simulation uses a one-step chemical model with variable parameters optimized by the adjoint approach in terms of the induction time tau _{text {c}}. The model reproduces tau _{text {c}} of a complex kinetics model in the range of pressures and temperatures appearing at the focusing point. The results give a comprehensive description of the shock-induced detonation initiation, which is the mechanism for the deflagration-to-detonation transition in this type of configurations. Potential geometry design improvements for technical applications are discussed. The first attempt to parameterize the transition process is also undertaken.

High-Speed Schlieren and Particle Image Velocimetry of the Exhaust Flow of a Pulse Detonation Combustor

The exhaust flow of a pulse detonation combustor (PDC) is investigated for different operating conditions. The PDC consists of two units: the deflagration to detonation transition section, and the exhaust tube with a straight nozzle. High-speed high-resolution schlieren images visualize the shock dynamics downstream of the nozzle. The flow dynamics during one full PDC cycle is examined via high-speed particle image velocimetry. A well-suited solid tracer particle for supersonic reactive flow is determined in a preliminary study to minimize the PIV measurement error. The investigated operating conditions of the PDC differ in fill fraction, which is the percentage of the tube filled with a reactive mixture. With increasing fill fraction, the flow features grow in size and strength as the propagation velocity of the leading shock increases. The blowdown process of the PDC is characterized by several exhaust and suction phases. An increase in the fill fraction results in a stronger first exhaust phase, whereas the subsequent suction and exhaust phases remain almost unaffected.

Numerical analysis of detonation combustion wave in pulse detonation combustor with modified ejector with gaseous and liquid fuel mixture

The detonation combustion phenomenon is supersonic combustion process and follows on thermal explosion in combustor. Deflagration to detonation transition occurs in detonation tube due to pressure oscillation in PDE combustor, which is driven by acoustic combustion phenomena in detonation tube. As this combustion process has great significance role for future propulsion system, the present objective is to investigate the effect of modify ejector having half angles of α = (− 4°, 0°, + 4°) on detonation combustion wave propagation regime. Further the propulsion thrust of liquid kerosene and gaseous hydrogen–air mixture are also analyzed. This numerical simulation has been analyzed by LES turbulence model for DDT and shock wave pressure oscillation in pulse detonation combustor at Fluent based CFD plat form. The one-step irreversible chemical kinetics model analyzes the details exothermic chemical reaction mechanism inside the combustor. However, the shrouded ejector with taper angle of α = +4° performed the strong starting vortex generation and shortest possible time of 0.032 s for fully developed detonation wave. The simulation results also shows that thrust force augmentation of hydrogen–air mixture is greater compared to combustion process of liquid kerosene–air mixture with significant magnitude of 38 N. Although kerosene–air mixture produces less pollutant number but the propagation flame velocity is 2550 m s−1 for hydrogen/air mixture, which is near about C–J velocity and comparatively higher than kerosene/air combustion process.

Structural response and wall thickness design of pulse detonation combustor

This paper deals with the structural response and wall thickness design of pulse detonation combustor. The pulse detonation combustor is a chamber with cylindrical shell structure, which is loaded with internal moving detonation pressure and thermal load. Much higher strain and stress can be excited under moving pressure load than static load. How to choose the attenuation coefficient during detonation pressure were discussed. The results of structural response simulation based on finite element method were compared with analytical result in the literature. The multi-cycle detonation pressure load and thermal load were measured on a pulse detonation engine principle prototype initialed through deflagration-to-detonation transition for the first time. The structural response characteristics of the detonation chamber were studied based on the measured load under different working frequencies. A series of comparison between numerical simulation and experimental measurement were carried out. The wall thickness of the chamber was designed based on the fatigue load spectrum under real detonation load and the chamber’s target fatigue life. Special attention was paid to the mutual influence between the dynamic amplification factor and the wall thickness.

Detonation initiation by shock focusing at elevated pressure conditions in a pulse detonation combustor

This work contains experimental investigations on the correlation of the detonation initiation process via a shock-focusing device with various initial pressures and mass flow rates. A pulse detonation combustor is operated with stoichiometric hydrogen--air--oxygen mixtures in single cycle operation. A rotationally symmetric shock-focusing geometry evokes the onset of a detonation by the focusing of the reflected leading shock wave, while a blockage plate at the rear end of the test rig is applied to induce an elevated initial pressure. The results show that the reactivity has a major influence on the success rate of detonation initiation. However, measurements with different blockage plates suggest that the mass flow rate has to be considered as well when predicting the success rate. Three main statements can be drawn from the results. (1) An increase in the mean flow velocity induces higher velocity fluctuations which result in a stronger leading shock ahead of the accelerating deflagration front. (2) An increase in the initial static pressure reduces the critical shock strength that must be exceeded to ensure successful detonation initiation by shock focusing. (3) Since the initial pressure is directly linked to the mass flow rate, these contrary trends can cancel each other out, which could be observed for 40% vol. of oxygen in the oxidizer. High-speed images were taken, which confirm that the detonation is initiated in the center of the converging--diverging nozzle due to focusing of the leading shock.

Efficient Implementation of a Binary Iterative Learning Control

Iterative learning control (ILC) is an adequate control approach to handle various types of cyclic control tasks. However, when in each iteration the calculation of the control trajectory requires the solution of a high dimensional constrained quadratic program, the algorithm is bound to be infeasible for real-time applications with very small cycle lengths in the order of milliseconds due to the prohibitively large computational cost. In this contribution, an approach is presented to reduce the computational burden to solve an optimization-based iterative learning control that is restricted to a binary domain by orders of magnitude. The method is suitable for control trajectories that contain only few 1’s, but a large number of 0’s in each iteration for a specific class of problems, e.g., for cyclic firing synchronization of combustion tubes.The presented setup is tested experimentally at an acoustic mock-up of an annular pulse detonation combustor to determine an appropriate fire synchronization. More specifically, it is used to adjust the firing pattern of multiple simulated combustion tubes in order to reduce pressure fluctuations measured downstream in an annular plenum, which is a prerequisite to apply such a new thermodynamically efficient combustion process in a real gas turbine.

Technological advancements in Pulse Detonation Engine Technology in the recent past: A Characterized Report

Pulse Detonation Engine (PDE), is an emerging and promising propulsive technology all over the world in the past few decades. A pulse detonation engine (PDE) is a type of propulsion system that uses detonation waves to combust the fuel and oxidizer mixture. Theoretically, a PDE can be operate from subsonic to hypersonic flight speeds. Pulsed detonation engines offer many advantages over conventional air-breathing engines and are regarded as potential replacements for air-breathing and rocket propulsion systems, for platforms ranging from subsonic unmanned vehicles, long-range transportation, high-speed vehicles, space launchers to space vehicles. This article highlights the operating cycle of PDE, starting with the fuel-oxidizer mixture, combustion and Deflagration to detonation transition (DDT) followed by purging. PDE combustion process, a unique process, leads to consistent and repeatable detonation waves. This pulsed detonation combustion process causes rapid burning of the fuel-oxidizer mixture, which cannot be seen in any other combustion process as it is a thousand times faster than any other mode of combustion. PDE not only holds the capability of running effectively up to Mach 5 but it also changes the technicalities in space propulsion. The present paper is the extension of the previous study which is also a well characterized status report of PDE in different areas. The present study deals with the categorization of the design approach, computations &amp; simulations, flow visualization, DDT &amp; Thrust enhancement, PDRE’s, experimental detonation engines with some of the experience and research undertaken in Punjab Engineering College under the complete supervision and guidance of Prof. Tejinder Kumar Jindal followed by applications of PDE technology.

Investigation of pulse detonation combustors — Axial turbine system

A circular array of six pulse detonation combustors is integrated to an axial turbine, to extract power from the detonative combustion process that is ignited cyclically in the array of tubes. The effect of pulsing frequency, fill fraction and rotor revolution frequency on the extracted power is ascertained. A method is presented to estimate the component thermal efficiency using experimentally acquired variables. The resulting thermal efficiency values suggest that for a regime of operating conditions, the detonation cycle is more efficient than the Brayton cycle utilizing deflagration. This range of operating conditions appears to depend on the interaction of the different sectors — that are in different operational phases due to cyclic ignition — with the turbine.

A review of pollutants emissions in various pressure gain combustors

Recent years have witnessed a significant growth in the advancement and study of various unsteady combustors because of the prospective stagnation pressure gain offered by them. The pressure gain combustion produced by this class of combustors is poised to produce a step-change increase in the thermodynamic efficiency of gas-turbine engines. The current manuscript is oriented toward presenting a review on the pollutant emission characteristics of these devices; specifically, studies done so far on wave rotor combustors, pulsejet combustors, pulse detonation combustors, and rotating detonation combustors are evaluated. Because of the inherent fluid dynamic unsteadiness peculiar to pressure gain combustion devices, their emissions behavior is not well understood, and is notably different from the more conventional, steady combustors. The global view provided herein is expected to further the understanding of pressure gain combustion systems and ascertain the practicality of implementing them in real-world applications.

Optical Measurement of Fluid Motion in Semi-Valveless Pulse Detonation Combustor with High-Frequency Operation

ABSTRACTThe purge layer of a semi-valveless pulse detonation cycle (PDC) needs to be minimized for operating at a gas-dynamic upper frequency limit. Therefore, it is essential to better understand the process of burned gas backflow for minimizing the purge layer thickness. The flow field of the semi-valveless PDC was visualized to illustrate the movement of burned gas. A combustor of length of 95 mm with a 10-mm-square cross section was used. Supercritical ethylene and oxygen gas were used as fuel and oxidizer, respectively, and the operation frequency was 604 Hz. The unsteady refilling process of the detonable mixture was modeled by an isentropic flow. In addition, the detailed burned gas blowdown process with deflagration-to-detonation transition (DDT) and the backflow were captured. It was shown that the retonation wave generated by the DDT process was the primary trigger of the burned gas backflow. When the duration required for the DDT process was sufficiently shorter than that of the burned gas blowdown process, it was found the latter could be reproduced with approximately 90% accuracy by one-dimensional numerical analysis without the DDT process.

Numerical Study on NOx Reduction in Pulse Detonation Combustion by Using Steam Injection Decoupled From Detonation Development

Recently, the focus has been laid on the characteristics of pollutant emissions from pulse detonation combustion (PDC). Initial studies indicate possibly high nitrogen oxides (NOx) emissions, so the assessment of potential primary reduction methods is advisable. The present work considers the following reduction methods: lean combustion, nitrogen and steam dilution, as well as flue gas recirculation. Since such changes in the combustion mixture reduce its reactivity and thus detonability, they can impair a reliable operation in technical systems. In order to explore the potential and limitations of each of these reduction methods, they are compared for mixtures featuring an identical characteristic detonation cell size at given initial conditions. Furthermore, building upon the use of steam dilution, a modified method to add steam to the combustible mixture is investigated. In order to avoid the strong reduction of mixture detonability by steam addition and ensure a robust detonation formation, steam is injected into the already developed detonation front. It was found that, for sufficiently even steam distribution, NOx reduction comparable to a premixed dilution could be achieved. This approach enables the realization of NOx reduction in PDC also for such conditions, for which premix dilution is not feasible. Therefore, combining the premix dilution with postshock injection offers a promising strategy to substantially reduce NOx emissions from PDC, while at the same time ensuring its reliable operation.

How to utilize the kinetic energy of pulsed detonation products?

The possibility of utilizing the kinetic energy of detonation products by a pulse turbine of the simplest water-wheel-like design during the implementation of the Zel'dovich thermodynamic cycle with pulse detonation combustion of fuel is investigated computationally and experimentally. The coefficients of utilization of the momentum and kinetic energy of detonation products in the pulse turbine with unoptimized mass and dimensions are found to be as low as 8%–16%. To improve the efficiency of the pulse turbine, it is necessary to take measures for eliminating unnecessary reflections of shock waves, to select the optimal mass and dimensions of the turbine rotor and the number of blades, to profile the blades and to select the optimal angle of attack, to optimize the size of the lateral gap between the rotor and the housing, and to select the optimum location of the exhaust duct. It is expected that the efficiency of a combined cycle including the optimized pulse turbine and conventional gas and/or steam turbines attached to the exhaust duct could be higher than the efficiency of a conventional hybrid cycle by at most 9%.

Detonation initiation in pipes with a single obstacle for mixtures of hydrogen and oxygen-enriched air

This work presents an experimental and numerical study of a pulsed detonation combustion chamber. It consists of a pipe obstructed by one convergent–divergent nozzle, filled with a stoichiometric mixture of hydrogen and oxygen-enriched air. The proposed geometry is analysed with regard to its influence on the outset of detonation and its suitability for pulse detonation engines (PDEs). The study reveals the essential aspects for detonation initiation. The results of one of the configurations indicate a deterministic and reliable deflagration-to-detonation transition (DDT) with a short run-up distance, crucial for technical applications. The simulation reproduces the measurements in great detail and the origin of detonation is unequivocally identified.

Assessment of CO2 and NOx Emissions in Intercooled Pulsed Detonation Turbofan Engines

In the present paper, the synergistic combination of intercooling with pulsed detonation combustion is analyzed concerning its contribution to NOx and CO2 emissions. CO2 is directly proportional to fuel burn and can, therefore, be reduced by improving specific fuel consumption (SFC) and reducing engine weight and nacelle drag. A model predicting NOx generation per unit of fuel for pulsed detonation combustors (PDCs), operating with jet-A fuel, is developed and integrated within Chalmers University's gas turbine simulation tool GESTPAN. The model is constructed using computational fluid dynamics (CFD) data obtained for different combustor inlet pressure, temperature, and equivalence ratio levels. The NOx model supports the quantification of the trade-off between CO2 and NOx emissions in a 2050 geared turbofan architecture incorporating intercooling and pulsed detonation combustion and operating at pressures and temperatures of interest in gas turbine technology for aero-engine civil applications.

The efficiency of a pulsed detonation combustor–axial turbine integration

The paper presents a detailed numerical investigation of a pulsed detonation combustor (PDC) coupled with a transonic axial turbine stage. The time-resolved numerical analysis includes detailed chemistry to replicate detonation combustion in a stoichiometric hydrogen–air mixture, and it is fully coupled with the turbine stage flow simulation. The PDC–turbine performance and flow variations are analyzed for different power input conditions, by varying the system purge fraction. Such analysis allows for the establishment of cycle averaged performance data and also to identify key unsteady gas dynamic interactions occurring in the system. The results obtained allow for a better insight on the source and effect of different loss mechanisms occurring in the coupled PDC–turbine system. One key aspect arises from the interaction between the non-stationary PDC outflow and the constant rotor blade speed. Such interaction results in pronounced variations of rotor incidence angle, penalizing the turbine efficiency and capability of generating a quasi-steady shaft torque.

Acoustic Characterization of Pulse Detonation Combustors

The Paper deals with the investigation of the effect of multiple facets of pulse detonation combustors on its acoustic signature. First, the acoustic signature is characterized in both the near- and far-field regimes in an anechoic test facility. The shock strength and speed are mapped as functions of radial distance and direction (60–180 deg) from the combustor exhaust plane. The generated pressure field is then compared to a theoretical point-source explosion model. Second, the far-field sound pressure level is obtained, at different directivity angles, generated by a combustor tube at varied conditions of operating frequency, equivalence ratio, fill fraction, nitrogen dilution for a mixture of ethylene–oxygen–nitrogen and exit nozzle geometries. Shadowgraphy is performed to qualitatively account for the impact of these nozzle geometries on the shock wave and supersonic jet that characterize the combustor exhaust flow. Finally, the far-field acoustic signature of a system composed of two pulse detonation combustors is investigated. The firing time delay between the detonation tubes is varied to determine if any leading shock interactions affect the far-field noise. Further investigation is made into the cross-talk and separation distance between the detonation tubes.