scholarly journals Investigating Instabilities in a Rotating Detonation Combustor Operating With Natural Gas–Hydrogen Fuel Blend—Effect of Air Preheat and Annulus Width

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Arnab Roy ◽  
Clinton R. Bedick ◽  
Donald H. Ferguson ◽  
Todd Sidwell ◽  
Peter A. Strakey
Keyword(s):  
Natural Gas ◽  
Detonation Wave ◽  
Air Temperature ◽  
Detonation Waves ◽  
Operating Pressure ◽  
Hydrogen Fuel ◽  
Fuel Blend ◽  
Operational Envelope ◽  
Rotating Detonation ◽  
Gap Width

Abstract Propagation characteristics of a detonation wave in an air-breathing rotating detonation combustor (RDC) using natural gas (NG)–hydrogen fuel blends is presented in this paper. Short-duration (∼up to 6 s) experiments were performed on a 152.4 mm OD uncooled RDC with two different annulus gap widths (5.08 mm and 7.62 mm) over a range of equivalence ratios (0.6–1.0) at varying inlet air temperatures (∼65–204 °C) and NG content (up to 15%) with precombustion operating pressure slightly above ambient. It was observed that the RDC, with an annulus gap width of 5.08 mm, was inherently unstable when NG was added to the hydrogen fuel while operating at precombustion pressures near ambient and at an inlet air temperature of 65 °C. Increasing the annulus gap width to 7.62 mm improved the stability of the detonation wave at similar temperatures and pressure permitting operation with as much as 5% NG by volume. While observed speeds of the detonation waves were still below theoretical values, an increase in inlet air temperature reduced the variability in wave speed. The frequency analysis thus explored in this study is an effort to quantify detonation instability in an RDC under varying operational envelope. The data presented are relevant toward developing strategies to sustain a stable detonation wave in an RDC using NG for land-based power generation.

scholarly journals Investigating Instabilities in a Rotating Detonation Combustor Operating With Natural Gas-Hydrogen Fuel Blend: Effect of Air Preheat and Annulus Width

2019 ◽  
Author(s):  
Arnab Roy ◽  
Clinton Bedick ◽  
Donald Ferguson ◽  
Todd Sidwell ◽  
Peter Strakey
Keyword(s):  
Natural Gas ◽  
Detonation Wave ◽  
Air Temperature ◽  
Gas Content ◽  
Detonation Waves ◽  
Operating Pressure ◽  
Hydrogen Fuel ◽  
Fuel Blend ◽  
Rotating Detonation ◽  
Gap Width

Abstract Propagation characteristics of a detonation wave in an air-breathing Rotating Detonation Combustor (RDC) using natural gas-hydrogen fuel blends is presented in this paper. Short duration (∼up to 6s) experiments were performed on a 152.4mm OD uncooled RDC with two different annulus gap widths (5.08mm and 7.62mm) over a range of equivalence ratios (0.6–1.0) at varying inlet air temperatures (∼65°C-204°C) and natural gas content (up to 15%) with pre-combustion operating pressure slightly above ambient. It was observed that the RDC, with an annulus gap width of 5.08mm, was inherently unstable when natural gas (NG) was added to the hydrogen fuel while operating at pre-combustion pressures near ambient and at an inlet air temperature of 65°C. Increasing the annulus gap width to 7.62mm improved the stability of the detonation wave at similar temperatures and pressure permitting operation with as much as 5% NG by volume. While observed speeds of the detonation waves were still below theoretical values, an increase in inlet air temperature reduced the variability in wave speed. The frequency analysis thus explored in this study is an effort to quantify detonation instability in an RDC under varying operational envelope. The data presented is relevant towards developing strategies to sustain a stable detonation wave in an RDC using natural gas for land based power generation.

scholarly journals Numerical Analysis of Detonability Assessment in a Natural Gas-Air Fueled Rotating Detonation Engine

2019 ◽  
Author(s):  
Pankaj Saha ◽  
Peter Strakey ◽  
Donald Ferguson ◽  
Arnab Roy
Keyword(s):  
Natural Gas ◽  
Detonation Wave ◽  
Hydrogen Fuel ◽  
Air Breathing ◽  
Wave Characteristics ◽  
Fuel Blends ◽  
Rotating Detonation Engine ◽  
Continuous Detonation ◽  
Detonation Engine ◽  
Rotating Detonation

Abstract Rotating Detonation Engines (RDE) offer an alternative combustion strategy to replace conventional constant pressure combustion with a process that could produce a pressure gain without the use of a mechanical compressor. Recent numerical and experimental publications that consider air as the oxidizer have primarily focused on the ability of these annular combustors to sustain a stable continuous detonation wave when fueled by hydrogen. However, for this to be a viable consideration for the land-based power generation it is necessary to explore the ability to detonate natural gas and air within the confines of the annular geometry of an RDE. Previous studies on confined detonations have expressed the importance of permitting detonation cells to fully form within the combustor in order to achieve stability. This poses a challenge for natural gas–air fueled processes as their detonation cell size can be quite large even at moderate pressures. Despite the practical importance, only a few studies are available on natural gas detonations for air-breathing RDE applications. Moreover, the extreme thermodynamic condition (high temperature inside the combustor) allows limited accessibility inside the combustor for detailed experimental instrumentations, providing mostly single-point data. Recent experimental studies at the National Energy Technology Laboratory (NETL) have reported detonation failure at higher methane concentration in an air-breathing RDE fueled by natural gas-hydrogen fuel blends. This encourages to perform a detailed numerical investigation on the wave characteristics of detonation in a natural gas-air fueled RDE to understand the various aspects of instability associated with the natural gas-air detonation. This study is a numerical consideration of a methane-air fueled RDE with varying operating conditions to ascertain the ability to achieve a stable, continuous detonation wave. The simulations have been performed in a 2D unwrapped RDE geometry using the open-source CFD library “OpenFOAM” employing an unsteady pressure-based compressible reactive flow solver with a k–ε turbulence model in a structured rectangular grid system. Both reduced and detailed chemical kinetic models have been used to assess the effect of the chemistry on the detonation wave characteristics and the underlying flow features. A systematic grid sensitivity study has been conducted with various grid sizes to quantify the weakly stable overdriven detonation on a coarse mesh and oscillating features at fine mesh resolutions. The main focus of the current study is to investigate the effects of operating injection pressure on detonation wave characteristics of an air-breathing Rotating Detonation Engine (RDE) fueled with natural gas-hydrogen fuel blends. Wave speeds, peak pressures and temperatures, and dominant frequencies have been computed from the time histories. The flow structures were then visualized using 2D contours of temperature and species concentration.

scholarly journals Characteristics of a Non-Premixed Rotating Detonation Combustor Using Natural Gas-Hydrogen Blend at Elevated Air-Preheat Temperature and Backpressure

2018 ◽  
Author(s):  
Arnab Roy ◽  
Donald Ferguson ◽  
Todd Sidwell ◽  
Peter Strakey
Keyword(s):  
Experimental Study ◽  
Natural Gas ◽  
Detonation Wave ◽  
Inlet Temperature ◽  
Operational Mode ◽  
Atmospheric Conditions ◽  
Theoretical Understanding ◽  
Air Inlet ◽  
Continuous Detonation ◽  
Rotating Detonation

Operational characteristics of an air breathing Rotating Detonation Combustor (RDC) fueled by natural gas-hydrogen blends are discussed in this paper. Experiments were performed on a 152 mm diameter uncooled RDC with a combustor to inlet area ratio of 0.2 at elevated inlet temperature and combustor pressure while varying the fuel split between natural gas and hydrogen over a range of equivalence ratios. Experimental data from short-duration (∼6sec) tests are presented with an emphasis on identifying detonability limits and exploring detonation stability with the addition of natural gas. Although the nominal combustor used in this experiment was not specifically designed for natural gas-air mixtures, significant advances in understanding conditions necessary for sustaining a stable, continuous detonation wave in a natural gas-hydrogen blended fuel were achieved. Data from the experimental study suggests that at elevated combustor pressures (2–3bar), only a small amount of natural gas added to the hydrogen is needed to alter the detonation wave operational mode. Additional observations indicate that an increase in air inlet temperature (up to 204°C) at atmospheric conditions significantly affects RDC performance by increasing deflagration losses through an increase in the number of combustion (detonation/Deflagration) regions present in the combustor. At higher backpressure levels the RDC exhibited the ability to achieve stable detonation with increasing concentrations of natural gas (with natural gas / hydrogen-air blend). However, losses tend to increase at intermediate air preheat levels (∼120°C). It was observed that combustor pressure had a first order influence on RDC stability in the presence of natural gas. Combining the results from this limited experimental study with our theoretical understanding of detonation wave fundamentals provides a pathway for developing an advanced combustor capable of replacing conventional constant pressure combustors typical of most power generation processes with one that produces a pressure gain.

Application of a Convolutional Neural Network for Wave Mode Identification in a Rotating Detonation Combustor Using High-Speed Imaging

2020 ◽  
Author(s):  
Kristyn B. Johnson ◽  
Donald H. Ferguson ◽  
Robert S. Tempke ◽  
Andrew C. Nix
Keyword(s):  
Neural Network ◽  
Detonation Wave ◽  
High Speed ◽  
Wave Mode ◽  
Classification Performance ◽  
Detonation Waves ◽  
Single Image ◽  
High Speed Imaging ◽  
Mode Identification ◽  
Rotating Detonation

Abstract Utilizing a neural network, individual down-axis images of combustion waves in a Rotating Detonation Engine (RDE) can be classified according to the number of detonation waves present and their directional behavior. While the ability to identify the number of waves present within individual images might be intuitive, the further classification of wave rotational direction is a result of the detonation wave’s profile, which suggests its angular direction of movement. The application of deep learning is highly adaptive and therefore can be trained for a variety of image collection methods across RDE study platforms. In this study, a supervised approach is employed where a series of manually classified images is provided to a neural network for the purpose of optimizing the classification performance of the network. These images, referred to as the training set, are individually labeled as one of ten modes present in an experimental RDE. Possible classifications include deflagration, clockwise and counterclockwise variants of co-rotational detonation waves with quantities ranging from one to three waves, as well as single, double and triple counter-rotating detonation waves. After training the network, a second set of manually classified images, referred to as the validation set, is used to evaluate the performance of the model. The ability to predict the detonation wave mode in a single image using a trained neural network substantially reduces computational complexity by circumnavigating the need to evaluate the temporal behavior of individual pixels throughout time. Results suggest that while image quality is critical, it is possible to accurately identify the modal behavior of the detonation wave based on only a single image rather than a sequence of images or signal processing. Successful identification of wave behavior using image classification serves as a stepping stone for further machine learning integration in RDE research and comprehensive real-time diagnostics.

scholarly journals Combustion Characteristics in Rotating Detonation Engines

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Yuhui Wang ◽  
Wenyou Qiao ◽  
JialingLe
Keyword(s):  
Detonation Wave ◽  
Flow Rate ◽  
Detonation Waves ◽  
Outer Diameter ◽  
Combustion Mode ◽  
Hydrogen Flow ◽  
Pulsed Detonation ◽  
Rotating Detonation Engine ◽  
Rotating Detonation Engines ◽  
Rotating Detonation

A lot of studies on rotating detonation engines have been carried out due to the higher thermal efficiency. However, the number, rotating directions, and intensities of rotating detonation waves are changeful when the flow rate, equivalence ratio, inflow conditions, and engine schemes vary. The present experimental results showed that the combustion mode of a rotating detonation engine was influenced by the combustor scheme. The annular detonation channel had an outer diameter of 100 mm and an inner diameter of 80 mm. Air and hydrogen were injected into the combustor from 60 cylindrical orifices in a diameter of 2 mm and a circular channel with a width of 2 mm, respectively. When the air mass flow rate was increased by keeping hydrogen flow rate constant, the combustion mode varied. Deflagration and diffusive combustion, multiple counterrotating detonation waves, longitudinal pulsed detonation, and a single rotating detonation wave occurred. Both longitudinal pulsed detonation and a single rotating detonation wave occurred at different times in the same operation. They could change between each other, and the evolution direction depended on the air flow rate. The operations with a single rotating detonation wave occurred at equivalence ratios lower than 0.60, which was helpful for the engine cooling and infrared stealth. The generation mechanism of longitudinal pulsed detonation is developed.

Application of a Convolutional Neural Network for Wave Mode Identification in a Rotating Detonation Combustor Using High-Speed Imaging

2021 ◽  
pp. 1-22
Author(s):  
Kristyn B. Johnson ◽  
Donald H. Ferguson ◽  
Robert S. Tempke ◽  
Andrew C. Nix
Keyword(s):  
Neural Network ◽  
Detonation Wave ◽  
High Speed ◽  
Wave Mode ◽  
Classification Performance ◽  
Detonation Waves ◽  
Single Image ◽  
High Speed Imaging ◽  
Mode Identification ◽  
Rotating Detonation

Abstract Utilizing a neural network, individual down-axis images of combustion waves in a Rotating Detonation Engine (RDE) can be classified according to the number of detonation waves present and their directional behavior. While the ability to identify the number of waves present within individual images might be intuitive, the further classification of wave rotational direction is a result of the detonation wave's profile, which suggests its angular direction of movement. The application of deep learning is highly adaptive and therefore can be trained for a variety of image collection methods across RDE study platforms. In this study, a supervised approach is employed where a series of manually classified images is provided to a neural network for the purpose of optimizing the classification performance of the network. These images, referred to as the training set, are individually labeled as one of ten modes present in an experimental RDE. Possible classifications include deflagration, clockwise and counterclockwise variants of corotational detonation waves with quantities ranging from one to three waves, as well as single, double and triple counter-rotating detonation waves. The ability to predict the detonation wave mode in a single image using a trained neural network substantially reduces computational complexity by circumnavigating the need to evaluate the temporal behavior of individual pixels throughout time. Results suggest that while image quality is critical, it is possible to accurately identify the modal behavior of the detonation wave based on only a single image rather than a sequence of images or signal processing.

scholarly journals Experimental Investigation of a Piloted, Natural Gas-Air Rotating Detonation Wave Combustor

2018 ◽  
Author(s):  
Ian V. Walters ◽  
Chris Journell ◽  
Aaron Lemcherfi ◽  
Rohan Gejji ◽  
Stephen D. Heister ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Natural Gas ◽  
Detonation Wave ◽  
Rotating Detonation

scholarly journals Descending Modal Transition Dynamics in a Large Eddy Simulation of a Rotating Detonation Rocket Engine

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3387
Author(s):  
Armani Batista ◽  
Mathias C. Ross ◽  
Christopher Lietz ◽  
William A. Hargus
Keyword(s):  
Detonation Wave ◽  
Failure Time ◽  
Rocket Engine ◽  
Detonation Waves ◽  
Rocket Engines ◽  
Operation Performance ◽  
Eddy Simulation ◽  
Upstream Pressure ◽  
Detonation Failure ◽  
Rotating Detonation

Rotating detonation rocket engines (RDREs) exhibit various unsteady phenomena, including modal transitions, that significantly affect their operation, performance and stability. The dynamics of the detonation waves are studied during a descending modal transition (DMT) where four co-rotating detonations waves decrease to three in a gaseous methane-oxygen RDRE. Detonation wave tracking is applied to capture, visualize and analyze unsteady, 3D detonation wave dynamics data within the combustion chamber of the RDRE. The mechanism of a descending modal transition is the failure of a detonation wave in the RDRE, and in this study, the failing wave is identified along with its failure time. The regions upstream of each relative detonation show the mixture and flow-field parameters that drive detonation failure. Additionally, it is shown that descending modal transitions encompass multiple phases of detonation decay and recovery with respect to RDREs. The results show high upstream pressure, heat release and temperature, coupled with insufficient propellants, lead to detonation wave failure and non-recovery of the trailing detonation wave during a descending modal transition. Finally, the Wolanski wave stability criterion regarding detonation critical reactant mixing height provides insight into detonation failure or sustainment.

scholarly journals Numerical Investigations of Instabilities in a Natural Gas-Air Fueled Rotating Detonation Engine

2019 ◽  
Author(s):  
Pankaj Saha ◽  
Pete Strakey ◽  
Donald Ferguson
Keyword(s):  
Natural Gas ◽  
Detonation Wave ◽  
High Frequency ◽  
Methane Content ◽  
Gas Content ◽  
Wave Characteristics ◽  
Fuel Blends ◽  
Gas Fuel ◽  
The Stability ◽  
Rotating Detonation

Abstract Recent numerical and experimental studies of Rotating Detonation Engines (RDEs) using air as the oxidizer have primarily focused on the ability to sustain a stable continuous detonation wave when fueled with hydrogen. For RDEs to be a viable technology for land-based power generation it is necessary to explore the ability to detonate natural gas and/or coal-syngas with air in the confines of the annular geometry of an RDE. There are major challenges in obtaining a stable detonation wave for a natural gas–air fueled RDE and to a lesser extent for coal-syngas and air. Recently published computational studies have, however, successfully simulated the underlying flow physics of detonative combustion for two-dimensional (2D) unrolled RDE geometries. In the present work, detonation wave characteristics of a hydrogen-natural gas fueled RDE have been numerically investigated and analyzed to understand the stability of natural gas detonations and detonability limits of fuel blends at relatively low operating combustor pressure. A series of detonation sensitivity studies have been conducted by varying the natural gas content in a hydrogen-natural gas fuel mixture, to assess the stability limit of natural gas detonations in an air breathing RDE. The current study explores the maximum percentage of natural gas content in a hydrogen-natural gas fuel blend that produces self-sustained, stable detonation waves. The simulations have been performed in a 2D unwrapped RDE geometry using the open-source CFD library OpenFOAM employing an unsteady pressure-based compressible reactive flow solver with a k–ε turbulence model in a structured rectangular grid system. Both reduced and detailed chemical kinetic models have been used to assess the effect of the chemistry on the detonation wave characteristics and underlying flow features. A systematic grid sensitivity study has been conducted with various grid sizes to quantify the weakly stable overdriven detonation on a coarse mesh and oscillating features at fine mesh resolutions. The low and high frequency instabilities have been analyzed from the time dependent pressure and temperature collected at various fixed spatial locations within the detonation height region. The results show that the peak pressure oscillates at low frequencies while for the high frequency instabilities, the peak pressure oscillates irregularly. Furthermore, at higher methane content, the high frequency instability leads to detonation extinction due to decoupling of the flame-front from the shock front. Wave speeds, peak pressures and temperatures, and dominant frequencies have been computed from the time histories. 2D contour maps of temperature and species concentrations have been used to visualize the flow structures, and calculate detonation height. Global wave speed and detonation height variations for varying methane content indicate the pathway to detonation failure at higher methane content for the current low pressure RDE. Experimental data from an air-breathing RDE fueled by natural gas-hydrogen fuel blends conducted in a detonation research laboratory at NETL, has been incorporated to verify the numerical findings.

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