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Strakey, Peter

Publications and source records attributed to Strakey, Peter.

Experimental Study of Instabilities in Hydrogen-Air Fueled Rotating Detonation Combustion Presentation

Conventional gas turbine engines rely on an idealized constant pressure combustion process that in reality produces a pressure decrease as a result of viscous and other non-reversible losses. An alternative approach is rotating detonation combustion (RDC) which is a form of pressure gain combustion in which one or more detonation waves propagate an annular channel resulting in an increase in pressure across, subsequently providing greater work availability compared to deflagration ultimately leading to opportunities for greater thermodynamic efficiency when used in gas turbine engines that conventionally relies on constant. Modern gas turbine engines often rely on pre-mixed reactants to limit NOx emissions, although this may result in greater susceptibility to instabilities such as flashback and thermoacoustic oscillation, particularly for applications that utilize hydrogen as the fuel. Research in RDC has focused on non-premixed reactants thus limiting the occurrence of flashback, and high frequency detonation wave propagation (kHz) may interfere with the occurrence of thermoacoustic oscillations. Thermal NOx emissions are controlled through rapid combustion and sudden expansion of the working fluid. Although RDC may not be susceptible to instabilities encountered in conventional state of the art gas turbine engine combustion, there may be other mechanisms occurring that support instabilities that could be detrimental to performance.

Weber, Justin↗

Flashback Measurements in Hydrogen Enriched Low Swirl Flames Using High Speed OH-PLIF

The fundamentals of stabilized flame dynamics and flashback events in a premixed low swirl burner (LSB) configuration are visualized experimentally using nanosecond (ns)-based high-speed hydroxyl radical planar laser-induced fluorescence (OH-PLIF). Swirlers with two different turning angles, 〖26〗^o and 〖33〗^o and three different center-body hole diameters, 1.08, 1.12 and 1.16 mm with measured swirl numbers varying from 0.43 to 0.49 are tested in this study at atmospheric temperature and pressure inlet conditions. An increase in flashback propensity is observed with increasing ϕ, X_(H_2 ) and decreasing V via detailed investigation of flame lift-off length (L) above the burner rim. Flashback ϕ (ϕ_FB) investigations show an expected linearly increasing trend with decreasing X_(H_2 ) and increasing V for each swirler studied and the results agree well with detailed L investigations in a stable flame configuration. ϕ_FB studies for different swirlers show an increase in flashback resistance with the increase in center-body hole diameter and swirl angle. Spatiotemporally resolved kHz-rate OH-PLIF is a promising technique to observe rapidly occurring flashback events and it can be applied for turbulence-chemistry interaction model validation.

Parajuli, Pradeep↗

Development of 250 kW Ammonia and Hydrogen Industrial Burner Test Facility at the National Energy Technology Laboratory

In an effort to investigate the viability of ammonia and hydrogen as fuels in the industrial heating sector, the Department of Energy’s National Energy Technology Laboratory is developing a 250 kW burner test facility. The pursuit of a decarbonized industrial heating sector requires innovative approaches to convert existing assets to alternative fuels while maintaining adequate radiative heat transfer and limiting NOx. This new capability will leverage NETL’s experience and prior investments in ammonia and hydrogen combustion, to advance atmospheric pressure industrial combustion systems for industries such as cement kilns and glass factories. The intention in coming years is to collaborate with burner manufacturers and heavy industry partners to study, develop, and validate strategies for converting existing hardware from carbon-based fuels to next-generation clean ammonia and hydrogen technologies.

May, Kristyn Johnson↗

High-Speed OH-PLIF Diagnostics of Flame Flashback in Low Swirl Hydrogen-Enriched Flames

Hydrogen-enrichment is a potential strategy to reduce carbon emissions for the development of next-generation lean premixed combustors. However, the higher flashback propensity with hydrogen enrichment owing to the faster chemical kinetics is one of the key challenges in existing natural gas turbine combustors. The fundamentals of stabilized flame dynamics and flashback events in a premixed low swirl burner (LSB) configuration are visualized experimentally using nanosecond (ns)-based high-speed hydroxyl radical planar laser-induced fluorescence (OH-PLIF). Swirlers with two different turning angles, 26 and 33 and three different center-body hole diameters, 1.08, 1.12 and 1.16 mm with measured swirl numbers varying from 0.43 to 0.49 are tested in this study at atmospheric temperature and pressure inlet conditions. The inlet conditions are varied systematically with respect to pre-mixer velocities (V), flame equivalence ratio (ϕ) and hydrogen content (X_(H_2 )) for 50%-90% (H2, by mole) H2/ CH4 reactant mixtures and OH-PLIF characterization is performed in a stable flame at 20 kHz repetition rate. An increase in flashback propensity is observed with increasing ϕ, X_(H_2 ) and decreasing V via detailed investigation of flame lift-off length (L) above the burner rim.

Parajuli, Pradeep↗

High-Speed OH-PLIF Diagnostics of Flame Flashback in Low Swirl Hydrogen-Enriched Flames

This paper reports flashback events observed in hydrogen-enriched flames stabilized in a low swirl burner (LSB) at atmospheric pressure and temperature conditions. The fundamentals of hydrogen-rich stable flames and spatiotemporal investigation of flashback phenomena were observed experimentally using a high-repetition-rate nanosecond (ns)-duration hydroxyl radical planar laser-induced fluorescence (OH-PLIF) diagnostic. Testing was conducted in an optically accessible pre-mixing section of a LSB with inlet pre-mixing velocities ranging from 5 to 10 m/s for methane and hydrogen (50 – 90% by mole) blends. Swirlers with two different turning angles, 26o and 33o, and three different perforated plate hole diameters, 1.08, 1.12 and 1.16 mm, with measured swirl numbers varying from 0.43 to 0.49 were used in this study at atmospheric temperature and pressure inlet conditions. The flashback propensity showed a dependence on the proximity of the lifted flame to the burner exit (termed as lift-off length, L) which was dependent on the pre-mixer velocity (V), hydrogen content (XH2) and equivalence ratio (ϕ) at constant temperature and pressure conditions. High-speed OH-PLIF images revealed lifted flames were first observed at low ϕ/ XH2 condition which then changed to a M-shaped flame attached to burner rim with the increase in ϕ/ XH2. Further increases in ϕ/XH2, depending upon other inlet parameters, triggered flame flashback into the pre-mixing section. Flashback occurred when burning began in the outer shear layer and the leading flame brush propagated into the nozzle. Such spatiotemporally resolved high-speed OH-PLIF imaging provides insights on different stages of flashback in a LSB – flashback initiation, transition of flame propagation from burner exit to the swirler and flashback to flame holding transition. Flame ϕ at flashback showed an expected linearly increasing trend with increasing V and decreasing XH2 and the conclusions drawn aligned well with detailed investigations. For identical inlet conditions, flashback propensity decreased with increasing perforated-plate hole diameter and increasing swirler vane angle.

Parajuli, Pradeep↗

Flame Flashback Investigations in Hydrogen-Enriched Low Swirl Flames using High-Speed Hydroxyl (OH) Planar Laser-Induced Fluorescence

This study reports flashback mechanism observed in hydrogen-enriched flames stabilized in a low swirl burner (LSB) at atmospheric pressure and temperature conditions. The fundamentals of hydrogen-rich stable flames and spatiotemporal investigation of flashback phenomena were observed experimentally using a high-repetition-rate nanosecond (ns)-duration hydroxyl radical planar laser-induced fluorescence (OH-PLIF) diagnostic. Testing was conducted in an optically accessible pre-mixing section of LSB with inlet pre-mixing velocities from 5 to 10 m/s for methane and hydrogen (50 – 90% by mole) blends. Swirlers with two different turning angles, 26 and 33 degrees and three different perforated plate hole diameters, 1.08, 1.12 and 1.16 mm with measured swirl numbers varying from 0.43 to 0.49 were used. The flashback propensity showed dependence on the proximity of the lifted flame to the burner exit which was dependent on pre-mixer velocity, hydrogen content and equivalence ratio (ER). High-speed OH-PLIF images revealed lifted flames were first observed at low ER condition which is changed to M-shaped flame attached to burner rim with the increase in ER. Then, further increase in ER triggers flame flashback into the nozzle. Flashback occurred when burning occurs in the outer shear layer and the leading flame brush ingresses into the nozzle.

Parajuli, Pradeep↗

Flame Flashback Investigations in Hydrogen-Enriched Low Swirl Burner using High-Speed Hydroxyl Planar Laser-Induced Fluorescence

Hydrogen/ Hydrogen-rich flame is a potential strategy to reduce carbon emissions for the development of next-generation lean premixed combustors. However, the higher flashback propensity with hydrogen-enrichment owing to faster chemical kinetics is one of the key challenges in existing natural gas turbine combustors. In this study, the fundamentals of stabilized flame dynamics and flashback events in a premixed low swirl burner (LSB) configuration are visualized experimentally using nanosecond (ns)-based high-speed hydroxyl radical planar laser-induced fluorescence (OH-PLIF). The LSB has an optically accessible pre-mixing tube allowing laser diagnostic investigation of flashback events. The inlet conditions are varied systematically with respect to pre-mixer velocities, flame equivalence ratio (ϕ), and hydrogen content and OH-PLIF characterization is performed in stable flame at 20 kHz repetition rate. An increase in flashback propensity is observed with increasing ϕ, hydrogen content, and decreasing V via detailed investigation of flame lift-off length (L) above the burner rim. Flashback ϕ investigations show an expected linearly increasing trend with decreasing hydrogen content and increasing V for each swirler studied and the results agree well with detailed L investigations in stable flame configuration. The propagating flame anchored likely on the back side of the perforated plate within 30-40 ms of the entrance forming the distorted conical flame front.

Parajuli, Pradeep↗

Flashback Studies of High-Hydrogen Flames using High-Speed OH Planar Laser-Induced Fluorescence

Flame flashback is a crucial challenge during the application of high-hydrogen fuels for the development of next-generation lean premixed combustors. The fundamentals of stable flame configuration, flashback phenomena, and spatiotemporal information of flame dynamics in a premixed, swirl-stabilized burner are investigated experimentally at atmospheric pressure conditions using high-repetition-rate nanosecond (ns)-duration hydroxyl radical planar laser-induced fluorescence (OH-PLIF) measurements. The inlet conditions are varied systematically with respect to equivalence ratio (ϕ), hydrogen percentage in a hydrogen-methane mixture (50%–90%) and pre-mixer velocities and the experiments are performed on the burner modified to provide optical access to the premixing section. Signal interferences such as saturation effects, background chemiluminescence, and laser non-uniformity issues were minimized or corrected during data acquisition and subsequent data processing steps. A stable flame characterization was performed at 20 kHz-repetition-rate for varied pre-mixer velocities, hydrogen content and ϕ in the reactant mixture and lift-off length (L) investigation showed dependence on each of these parameters. Flame dynamics such as flame flashback events, local ignition, local extinction, flame curvature as well as the main reaction zone of the combustion mechanism are well characterized. Flashback ϕ showed an expected linearly increasing trend with increasing pre-mixer velocity and decreasing hydrogen content and the conclusions drawn aligned well with detailed L investigation. Such spatially and temporally resolved kHz-rate OH-PLIF is a promising technique to observe rapidly occurring flashback dynamics and can further validate turbulence-chemistry interaction models of swirling flames.

Parajuli, Pradeep↗

Transition to High-Hydrogen Fueled Advanced Gas Turbine Engines for Land-Based Power Generation and Industrial Applications

Invited lecture presented as part of the 2023 University of Central Florida - Mechanical and Aerospace Engineering Seminar Series. These slides discuss the role of multi-sourced hydrogen for electrical power generation. Particular focus is given to the combustion of hydrogen for the purpose of chemical to thermal energy. Pressure gain combustion is given as an example technology that could leverage hydrogen as a fuel source ultimately leading to higher rates of energy conversion (chemical to electrical) resulting in greater energy security and reduced cost of electricity.

advanced gas turbines↗

Flashback of Hydrogen-Methane Mixtures in a Fixed-Vane, Low-Swirl Burner at Atmospheric Pressure

Equivalence ratio at flashback, 𝜙FB, of low swirl injectors for 60% – 95% (H2, by mole) hydrogen-methane mixtures was determined experimentally in a < 100 kW atmospheric pressure burner. Pre-mixer velocities equaled 5, 7.5, and 10 m/s, with the reactants entering the burner at 294 K. The swirler design was selected following a literature review, and the test articles were additively manufactured. The test articles had two turning angles, 26° and 33°, with center-body hole diameters equaling 1.08 and 1.16 mm. A test article was built with each parameter combination, which yielded four test articles with measured swirl numbers varying from 0.43 to 0.49. The results showed agreement with prior work. 𝜙FB increased with increasing pre-mixer velocity and decreasing percent hydrogen. 𝜙FB was also observed to increase with swirl angle and decrease with increasing center-body hole diameter. The data was correlated using a semi-empirical quenching approach, with 𝐶quench=0.01, where the chemical time scale was calculated using a perfectly stirred reactor (PSR) model. Two different chemical kinetics mechanisms independently yielded the same results. The correlation makes the present small-scale laboratory results relevant to large, high-pressure gas turbines. The flashback data set is available for computational fluid dynamics (CFD) validation.

Searle, Matthew↗