Numerical study on the influence of blockage ratio on hydrogen turbulent premixed flames in a small scale obstructed chamber

© 2020 ASME Although hydrogen is a clean and renewable fuel, there is still a need to understand and evaluate the potential risks posed in the event of an accidental explosion. This paper presents large eddy simulation (LES) numerical analysis for lean hydrogen premixed flames propagating inside a small laboratory combustion chamber with built in solid obstructions. The small-scale chamber is 0.625 litres in volume with three removable turbulence generating baffles and a square solid obstacle. A lean equivalence ratio of 0.7 is selected in this study. The LES model is utilised to investigate the influence of obstruction configuration and area blockage ratio on the flame characteristics and the generated combustion overpressure. The LES turbulence technique is used with an in-house computational fluid dynamics (CFD) model for compressible flows. The numerical simulations are carried out with various arrangements of the baffle plates and a solid obstacle to examine the effects of the area blockage ratio and generated turbulence on the flame structure and generated over-pressure. Two different area blockage ratios of 0.24 and 0.5 are studied. Four configurations with different baffle arrangements are studied to examine the resulting turbulence effects on the generated overpressure, flame position-time traces and flame transient speed following ignition. Direct comparisons are made between the different baffle/flow configurations to identify the various effects of an increased area blockage ratio. Numerical results showing the flame structure at various time windows after ignition are presented and compared with published experimental images. High speed laser induced fluorescence (LIF-OH) images of the reaction zones obtained from the experiments at a rate of 5 kHz provide the flame position data and convey the impact of the turbulence generated by the baffles and solid obstacle on the propagating flame structure [1]. The pressure is recorded at a rate of 25 kHz using a piezo-electric pressure transducer in the base plate of the chamber [2]. The rise in over-pressure as a result of increased turbulence due to additional baffles and an increased area blockage ratio is found to be consistent with experimental data. This is also found to be consistent for the flame position-time and speed-time traces across all configurations. Main points of interest such as the peak over-pressure, maximum rate of pressure rise and the flame propagation trends are also observed along with variations in flame speed as the flame interacts with the baffles and obstacles. Validation of the numerical results against available published experimental data conveys good agreement confirming the ability of the numerical model to predict numerical results for an increased area blockage ratio. Further numerical simulations are also carried out for flame/flow parameters where experimental data is unavailable due to physical limitations. Satisfactory agreement between numerical results and experimental data endorses further predictions for computational models in studying vented hydrogen explosions where there is an increased risk or limited experimental data

Histological joint destruction in paw sections.

<p>Synovial inflammation is suppressed in CIA in DBA1J TLR4 negative mice (A, C) compared to wt mice (B, D). Representative front paw sections showing wrist and carpal joints and stained in H&E, original magnification ×10 are shown in (A) and (B) and interphalangeal joints with extensive pannus formation and bone destruction stained with Nuclear Fast Rubine-Aniline Blue-Orange G in (C) and (D), original magnification ×100. Histological joint scores reflecting significantly suppressed inflammation and cartilage and bone destruction in TLR4 defective mice are shown in (E).</p

B and T cell responses.

<p>No significant difference in peripheral blood anti-collagen type II antibody concentrations of the IgG2a subclass at days 34 and 89 in TLR4 negative versus positive groups of mice (A). Anti-cyclic citrullinted peptide (CCP) antibody concentrations (anti-LXP) are significantly higher in TLR4 positive groups of mice at day 34 after immunization, while anti-non-citrullinated controle peptide antibody concentrations are comparable (B). T cell recall responses in TLR4 negative mice were significantly stronger than in wt mice at the lower tested antigen concentration (C). No influence on foxp3 positive Treg numbers was seen (D).</p

Incidence and severity of arthritis.

<p>Suppressed incidence (A) and severity (B) of collagen induced arthritis (incomplete Freund's adjuvant) in TLR4 defective DBA/1J (n = 17) compared to TLR4 pos/pos (n = 17) DBA1/J mice.</p

Additional file 11: Figure S2. of Improved detection of gene-microbe interactions in the mouse skin microbiota using high-resolution QTL mapping of 16S rRNA transcripts

Manhattan plot of Neisseria_OTU1320 QTL mapping. Significant thresholds (p ≤ 0.05) are shown in a continuous line; suggestive thresholds (p ≤ 0.10) are shown in a discontinuous line. Chr: chromosome. (TIF 219 kb

Additional file 4: Table S3. of Improved detection of gene-microbe interactions in the mouse skin microbiota using high-resolution QTL mapping of 16S rRNA transcripts

Summary statistics of CMM OTUs and alpha diversity indices as profiled based on DNA. Means, standard deviations (STD), minimum (Min), maximum (Max), and coefficient of variation (CV) values of relative abundances in population G15 (n = 270). Un: unclassified. (XLSX 12 kb

Additional file 14: Table S11. of Improved detection of gene-microbe interactions in the mouse skin microbiota using high-resolution QTL mapping of 16S rRNA transcripts

Full details of pathway and biological process enrichment analyses for candidate regions. (XLSX 71 kb

Relative expression of cytokines mRNA in CNS homogenates.

<p>Fourteen days after EAE induction, brains and spinal cords were collected and levels of mRNAs were assessed by real time quantitative PCR as described in <i>Materials and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022841#s4" target="_blank">Methods</a></i>. Data represent mean ± SEM of 7–12 mice per strain. *, <i>P</i><0.05; **, <i>P</i><0.01; ***, <i>P</i><0.001.</p