Improved Injection Scheme Yielding Robust Operation of a Radial Rotating Detonation Engine with an Aerospike

2025-01-03

A new injection and mixing scheme was developed and tested a Radial Rotating Detonation Engine (RRDE). This 3rd generation RRDE is supplied with reactants at the outer periphery where detonation takes place. The product gases flow towards the center of the device where an integrated aerospike turns and expands the flow in the axial direction, producing usable thrust. Experiments were conducted with methane-oxygen reactant mixtures including some tests with air dilution to attain varying levels of oxygen concentration. Operation of the engine is analyzed using a) capillary tube attenuated pressure (CTAP) ports in the combustor channel, at the geometric exhaust throat, and on the aerospike surface, b) high-speed fluctuating wall static pressure measurements by PCB piezo-electric probes, and c) thrust data acquired by a six-axes load cell. The parameter space consisted of varying reactant flow rates, oxygen concentrations, and equivalence ratios. The new injection scheme produced steady RRDE operation and varying wave modes across a wide range of parameters.

Spatially and Temporally Synchronous OH* and CH* Chemiluminescence Imaging in the Exhaust of a Rotating Detonation Engine

2025-01-03 · 1 citations

This study utilizes a novel optical technique for spatially and temporally synchronous imaging of chemiluminescence (CL) from hydroxyl (OH*) and methylidyne (CH*) radicals in a rotating detonation engine (RDE) exhaust plume. The optical apparatus employes a single high-speed camera system to image both species and eliminates measurement uncertainties otherwise imposed by parallax and optical pathlength differences in current systems. RDE performance is characterized for methane and enriched oxygen reactants across equivalence ratios of 0.6 to 1.4. By tracking CH* as an indicator of fuel decomposition regions and OH* as a marker of oxidation zones, this work provides insight into the spatial relationship between reaction zones. The diagnostic's fidelity was validated through frequency analysis, showing excellent correlation with pressure measurements while providing high temporal resolution to identify cycle-to-cycle variations. Over the various equivalence ratios, the present technique successfully captured spatial distinctions between the two radials enabling a detailed characterization of wave stability, combustion completeness, and parasitic deflagration behavior.

Performance Characterization of a Radial Rotating Detonation Combustor With Axial Exhaust

Journal of Engineering for Gas Turbines and Power · 2024-08-06 · 7 citations

Abstract This experimental study characterizes the performance of a radial rotating detonation combustor (RDC). An aerospike nozzle for rocket propulsion has been integrated into the center of the combustor, although the same combustor could also be coupled with turbomachinery. The radial RDC (RRDC) utilized a rapid to gradual (RTG) area change in the flow direction to effectively confine the detonation region close to the inlet plane and to improve the uniformity of the flow exiting the RDC. Three test cases were analyzed, (a) a baseline case at a total reactant mass flowrate, m˙ = 0.136 kg/s and equivalence ratio, ϕ = 0.6, (b) a higher reactant flowrate, m˙ = 0.318 kg/s and ϕ = 0.6, and (c) a higher ϕ = 0.8 at m˙ = 0.318 kg/s. All tests were conducted using methane and a 67% oxygen and 33% nitrogen (by mole) oxidizer mixture. Measurements were acquired using CTAP probes inside the combustion channel and along the aerospike to characterize the performance, PCB and ion probes near the detonation region to identify wave modes and their variations during the test, and thrust measurements using a six-axis force sensor. Results show highly complex wave modes with multiple corotating and/or counter-rotating waves depending upon the reactant flowrate. The pressure and thrust measurements are consistent with the wave mode analysis. In general, a positive (combustor only) pressure gain was inferred when losses associated with the injection system were excluded. The study highlights the challenges associated with fuel–air mixing and integrating the RDC with downstream hardware.

Performance Characterization of a Radial Rotating Detonation Combustor With Axial Exhaust

2024-06-24

Abstract This experimental study characterizes the performance of a radial rotating detonation combustor (RDC). An aerospike nozzle for rocket propulsion has been integrated into the center of the combustor, although the same combustor could also be coupled with turbomachinery. The radial RDC utilized a rapid to gradual (RTG) area change in the flow direction to effectively confine the detonation region close to the inlet plane and to improve the uniformity of the flow exiting the RDC. Three test cases were analyzed, (a) a baseline case at a total reactant mass flow rate, ṁ = 0.136 kg/s and equivalence ratio, ϕ = 0.6, (b) a higher reactant flow rate, ṁ = 0.318 kg/s and ϕ = 0.6, and (c) a higher ϕ = 0.8 at ṁ = 0.318 kg/s. All tests were conducted using methane and a 67% oxygen and 33% nitrogen (by mole) oxidizer mixture. Measurements were acquired using CTAP probes inside the combustion channel and along the aerospike to characterize the performance, PCB and ion probes near the detonation region to identify wave modes and their variations during the test, and thrust measurements using a six-axis force sensor. Results show highly complex wave modes with multiple co-rotating and/or counter-rotating waves depending upon the reactant flow rate. The pressure and thrust measurements are consistent with the wave mode analysis. In general, a positive (combustor only) pressure gain was inferred when losses associated with the injection system were excluded. The study highlights the challenges associated with fuel-air mixing and integrating the RDC with downstream hardware.

Effect of Insert Porosity on Combustion Instability in a Lean Premixed Combustor Analyzed by a POD-Based Phase Reconstruction Technique

2023-06-26

Abstract Lean premixed (LPM) combustion is very effective at mitigating emissions but is vulnerable to strong thermoacoustic instabilities. A porous insert in the shape of an annular ring placed at the dump plane of the combustor has been proven to be an effective passive technique for mitigating these instabilities across a wide range of operating conditions. However, it is unclear if the change results from the insert geometry or porosity of the insert. In this study, swirl-stabilized LPM combustion is investigated for three configurations — without any insert, with a porous insert, and with a geometrically similar solid insert. Acoustics, flow, and heat release rate behavior of the three test geometries are investigated using diagnostics including dynamic pressure and acoustic probes, particle image velocimetry (PIV), and OH* chemiluminescence (OH*CL) imaging. Synchronized measurements at a fixed equivalence ratio were acquired at 40 kHz using sound probes and at 3.5 kHz using PIV and OH*CL. Results include time-series and spectral measurements of pressure, velocity, and OH*CL, and mode analysis by proper orthogonal decomposition (POD). In addition, the dynamics of the instability are investigated by high-resolution phase reconstructions of velocity and OH*CL data using a novel implementation of POD introduced in this work. Results show two different instability modes: a longitudinal instability for the solid insert case and a helical, precessing vortex driven instability for the no insert case. In both cases, the flow field and heat release rate oscillations are coupled to produce the instability. No such coupling or oscillations are observed for the porous insert case. These results ascertain the unique capabilities of the porous insert in protecting against instability from different, simultaneous driving mechanisms and demonstrate that the insert porosity and flow dynamics associated with it are the primary mitigating factors.

Effect of Insert Porosity on Combustion Instability in a Lean Premixed Combustor Analyzed by a Proper Orthogonal Decomposition-Based Phase Reconstruction Technique

Journal of Engineering for Gas Turbines and Power · 2023 · 4 citations

• Materials science
• Mechanics
• Acoustics

Abstract Lean premixed (LPM) combustion is very effective at mitigating emissions but is vulnerable to strong thermoacoustic instabilities. A porous insert in the shape of an annular ring placed at the dump plane of the combustor has been proven to be an effective passive technique for mitigating these instabilities across a wide range of operating conditions. However, it is unclear if the change results from the insert geometry or porosity of the insert. In this study, swirl-stabilized LPM combustion is investigated for three configurations—without any insert, with a porous insert, and with a geometrically similar solid insert. Acoustics, flow, and heat release rate behavior of the three test geometries are investigated using diagnostics including dynamic pressure and acoustic probes, particle image velocimetry (PIV), and OH* chemiluminescence (OH*CL) imaging. Synchronized measurements at a fixed equivalence ratio were acquired at 40 kHz using sound probes and at 3.5 kHz using PIV and OH*CL. Results include time-series and spectral measurements of pressure, velocity, and OH*CL, and mode analysis by proper orthogonal decomposition (POD). In addition, the dynamics of the instability are investigated by high-resolution phase reconstructions of velocity and OH*CL data using a novel implementation of POD introduced in this work. Results show two different instability modes: a longitudinal instability for the solid insert case and a helical, precessing vortex driven instability for the no insert case. In both cases, the flow field and heat release rate oscillations are coupled to produce the instability. No such coupling or oscillations is observed for the porous insert case. These results ascertain the unique capabilities of the porous insert in protecting against instability from different, simultaneous driving mechanisms and demonstrate that the insert porosity and flow dynamics associated with it are the primary mitigating factors.

Effects of Porous versus Solid Inserts Pertaining to Instability Mitigation in Lean Direct Injection Combustion

AIAA SCITECH 2022 Forum · 2022-01-03

View Video Presentation: https://doi.org/10.2514/6.2022-2349.vid Lean direct injection (LDI) is an emerging combustion strategy to meet the increasingly stringent emissions requirements for carbon monoxide, nitric oxide, soot, and unburned hydrocarbons for aviation gas turbines. The LDI process is designed such that the fuel-air mixing occurs vigorously at the combustor inlet, to produce a globally lean combustion process. Studies have shown that LDI combustion systems are vulnerable to thermoacoustic instabilities. Previously, we have shown that a porous annular disc placed at the dump plane of the combustor can be effective at reducing the strength of thermoacoustic instabilities in LDI systems. Conversely, a solid insert of the same bulk geometry has been shown to be detrimental to combustion stability under some flow conditions. This paper includes a parametric study of acoustic behavior over a range of equivalence ratios to identify conditions when fundamental mechanisms of flame stability may change. Using the results of this parametric study, simultaneous OH* chemiluminescence and particle image velocimetry will be applied at a test condition with marked change in the acoustic behavior, allowing a spectral analysis of both heat release and velocity fluctuations. Additionally, proper orthogonal decomposition and phase-averaging techniques are used to clearly identify structures that drive flame dynamics, with the purpose of evaluating how insert porosity alters the flow-flame interactions.

Biaxially Formed Flexible Organic Electronics for 3D LC Optics and Displays

Proceedings of the International Display Workshops · 2022 · 2 citations

• Computer Science
• Materials science
• Optoelectronics

The genetic architecture of sexual dimorphism in the moss<i>Ceratodon purpureus</i>

Proceedings of the Royal Society B Biological Sciences · 2021 · 16 citations

• Biology
• Evolutionary biology
• Genetics

contained both symmetric and asymmetric elements, indicating that the response to sexually antagonistic or sexually concordant selection, and the constraint to sexual dimorphism, are highly dependent on the traits experiencing selection. The patterns of genetic variances and covariances among these fitness components is consistent with partly sex-specific genetic architectures having evolved in order to partially resolve multivariate genetic constraints (i.e. sexual conflict), enabling the sexes to evolve towards their sex-specific multivariate trait optima.

Retrato de una epidemia: Intoxicación aguda por opioides en adultos

Nursing (Ed española) · 2019-05-01