Ignitability and mixing of underexpanded hydrogen jets

Ruggles, Adam James; Ekoto, Isaac

doi:10.1016/j.ijhydene.2012.03.063

Cited by 79 publications

(53 citation statements)

References 28 publications

(57 reference statements)

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“…Mach disk dimensions (its height and width), as well as the reflected shock angle, were predicted by LES very close to values that could be extracted from the Schlieren images of [40]. The present LES investigation predicted higher values for the Mach disk height and width by 1.3% and 3.0%, respectively (3.09 mm and 1.34 mm) compared to those stated in [40] (3.05 mm and 1.30 mm, respectively). In further agreement with [40], the present LES study predicted the reflected shock (at the triple point) to be inclined ~28° against the nozzle centreline axis.…”

Section: Model Validationsupporting

confidence: 75%

“…The present LES investigation predicted higher values for the Mach disk height and width by 1.3% and 3.0%, respectively (3.09 mm and 1.34 mm) compared to those stated in [40] (3.05 mm and 1.30 mm, respectively). In further agreement with [40], the present LES study predicted the reflected shock (at the triple point) to be inclined ~28° against the nozzle centreline axis. The reflected shock angle for the methane test case (NPR=8.5) was measured to be ~28.5°, which in addition to the Mach disk height (H disk ≈1.9D) were in agreement with the recent work of Vuorinen et al [13,37] on a nozzle of 1.4 mm dimeter, NPR=8.5 and under-expanded nitrogen and methane jets.…”

Section: Model Validationcontrasting

confidence: 56%

“…As discussed comprehensively in [14,42] in order to validate the current computational framework first a simulation of hydrogen injection with NPR=10 (P ∞ ≈1 bar) was setup based on the experimental work of [40]. Mach disk dimensions (its height and width), as well as the reflected shock angle, were predicted by LES very close to values that could be extracted from the Schlieren images of [40].…”

Section: Model Validationmentioning

confidence: 91%

“…Recently large eddy simulation (LES) was employed to investigate under-expanded methane and nitrogen jets [13,35]. However, very limited experimental and computational studies are available in the literature on under-expanded hydrogen and methane jets and specifically with respect to applications in DI gaseous engines [36][37][38][39][40][41]. Recently, the authors of the present paper used LES to investigate the near-nozzle shock structure and mixing characteristics of highly under-expanded hydrogen and methane jets with NPR=8.5-70 issuing from a circular nozzle into a low ambient pressure (P ∞ ≈1 bar) [14,42].…”

Section: Present Contributionmentioning

confidence: 99%

“…This consisted of a high pressure tank that was linked to a low pressure air-containing chamber by a converging nozzle with exit diameter D=1.5 mm. The geometry and dimensions of the converging nozzle were obtained from an experimental test case available in the literature [40] to enable validation work. The current work examined under-expanded hydrogen (NPR=8.5, 10) and methane (NPR=8.5) jets issued into quiescent air ambient with various pressures.…”

Section: Simulation Setup and Validationmentioning

confidence: 99%

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Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

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The current study used large eddy simulations to investigate the sonic and mixing characteristics of turbulent under-expanded hydrogen and methane jets with various nozzle pressure ratios issued into various ambient pressures including elevated conditions relevant to applications in direct injection gaseous-fuelled internal combustion engines. Due to the relatively low density of most gaseous fuels such as hydrogen and methane, DI requires high injection pressures to achieve suitable mass flow rates for fast in-cylinder fuel delivery and rapid fuel-air mixing. Such pressures typically form an under-expanded fuel jet past the nozzle exit. Test cases of hydrogen injection with nozzle pressure ratio (NPR) of 10 issued into quiescent air with pressure P ∞ ≈1, 5 and 10 bar were simulated. Direct comparison between hydrogen and methane jets with NPR=8.5 and P ∞ ≈1 was also made. The effect of ambient pressure on features of transient development of the nearnozzle shock structure and tip vortices (vortex ring) was investigated. It was observed that at constant NPR, higher ambient pressure resulted in slightly faster formation of the Mach reflection and shorter Mach disk settlement time. Different mechanisms were observed between hydrogen and methane with regards to transient formation of their initial tip vortex rings. It was found that the initial transient tip vortices of hydrogen jets may also contribute to the flow instabilities at the boundary of the intercepting shock and, unlike for methane, promote fuel-air mixing before the Mach reflection. It was also shown that the nearnozzle shock structure was only affected by NPR regardless of the ambient pressure. Furthermore, no flow recirculation zone was found just downstream of the Mach disk, a finding comparable to all previous experimental investigations. Also, it was observed that a locally richer mixture was created for jets with higher NPR or with higher ambient pressure at constant NPR. Based on the results of the current study, correlations were proposed for the shock cell spacing and jet tip penetration of highly under-expanded jets issued from millimetre-size circular nozzles.

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Section: Model Validationsupporting

confidence: 75%

Section: Model Validationcontrasting

confidence: 56%

Section: Model Validationmentioning

confidence: 91%

Section: Present Contributionmentioning

confidence: 99%

Section: Simulation Setup and Validationmentioning

confidence: 99%

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Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Hamzehloo

Aleiferis

2016

International Journal of Hydrogen Energy

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Statistically advanced, self-similar, radial probability density functions of atmospheric and under-expanded hydrogen jets

Ruggles

2015

Exp Fluids

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used to separate the turbulent and pure air data, and thusly estimate intermittency. Beta-distributions (four parameters) are used to accurately represent the turbulent distribution moments. This combination of measured intermittency and four-parameter beta-distributions constitutes a new, simple approach to model scalar mixing. Comparisons between global moments from the data and moments calculated using the proposed model show excellent agreement. This was attributed to the high quality of the measurements which reduced the width of the correctly identified, noiseaffected pure air distribution, with respect to the turbulent mixing distribution. The ignitability of the atmospheric jet is determined using the flammability factor calculated from both kernel density estimated (KDE) PDFs and PDFs generated using the newly proposed model. Agreement between contours from both approaches is excellent. Ignitability of the under-expanded jet is also calculated using KDE PDFs. Contours are compared with those calculated by applying the atmospheric model to the under-expanded jet. Once again, agreement is excellent. This work demonstrates that self-similar scalar mixing statistics and ignitability of atmospheric jets can be accurately described by the proposed model. This description can be applied with confidence to under-expanded jets, which are more realistic of leak and fuel injection scenarios.Abstract This paper presents improved statistical insight regarding the self-similar scalar mixing process of atmospheric hydrogen jets and the downstream region of underexpanded hydrogen jets. Quantitative planar laser Rayleigh scattering imaging is used to probe both jets. The self-similarity of statistical moments up to the sixth order (beyond the literature established second order) is documented in both cases. This is achieved using a novel self-similar normalization method that facilitated a degree of statistical convergence that is typically limited to continuous, pointbased measurements. This demonstrates that image-based measurements of a limited number of samples can be used for self-similar scalar mixing studies. Both jets exhibit the same radial trends of these moments demonstrating that advanced atmospheric self-similarity can be applied in the analysis of under-expanded jets. Self-similar histograms away from the centerline are shown to be the combination of two distributions. The first is attributed to turbulent mixing. The second, a symmetric Poisson-type distribution centered on zero mass fraction, progressively becomes the dominant and eventually sole distribution at the edge of the jet. This distribution is attributed to shot noise-affected pure air measurements, rather than a diffusive superlayer at the jet boundary. This conclusion is reached after a rigorous measurement uncertainty analysis and inspection of pure air data collected with each hydrogen data set. A threshold based upon the measurement noise analysis is

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A Novel Real-Time, Lightweight Chaotic-Encryption Scheme for Next-Generation Audio-Visual Hearing Aids

et al. 2019

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Next-generation audiovisual (AV) hearing-aids stand as a major enabler to realise more intelligible audio. However, high data rate, low latency, low computational complexity, and privacy are some of the major bottlenecks to the successful deployment of such advanced hearing-aids. To address these challenges, we propose a novel framework based on an integration of 5G Cloud-Radio Access Network (C-RAN), Internet of Things (IoT), and strong privacy algorithms to fully benefit from the possibilities these technologies have to offer. Background: Existing audio-only hearing-aids are known to perform poorly in noisy situations where overwhelming noise is present. Current devices make the signal more audible but remains deficient to restore intelligibility. Thus, we need hearing aids that can selectively amplify the attended talker or filter out acoustic clutter.

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Ignitability and mixing of underexpanded hydrogen jets

Cited by 79 publications

References 28 publications

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures

Statistically advanced, self-similar, radial probability density functions of atmospheric and under-expanded hydrogen jets

A Novel Real-Time, Lightweight Chaotic-Encryption Scheme for Next-Generation Audio-Visual Hearing Aids

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