Increase In P0 Research Articles

Deflagration characteristics of N2 diluted propanal/air mixtures at elevated pressures

Hydrocarbon fuels, in addition to being direct sources of energy, also serve as crucial raw materials for numerous industrial processes. In this study, the oxidation of propanal to propionic acid under elevated pressures has garnered our attention due to the substantial heat release during the mixing of propanal and oxidants, posing considerable hazards to production. Fortunately, the introduction of N2 effectively mitigates these risks by reducing the laminar burning speed (SL) and peak deflagration pressure (Pm), and even preventing the ignition of mixtures. On this basis, the deflagration characteristics of propanal/N2/air mixtures were investigated in a 20 L spherical vessel at 348 K under various equivalent ratios (φ, 0.5 - 2.0), dilution rates (D, 0 - 0.5) and initial pressures (P0, 0.1 - 1.0 MPa). The combustion characteristics of propanal/N2/air were also analyzed through the 1-D laminar flame speed model, and the sensitivity analysis was performed to elucidate the effect of φ, D and P0 on the combustion of propanal. Results reveal that the addition of N2 stabilizes the flame propagation, and the Pm of propanal/N2/air mixtures decreases with the increasing D, with a sudden drop observed at a certain D level. However, the reduction of SL does not undergo an abrupt decrease across the entire dilution rate range. Furthermore, Pm exhibits a linear relationship with P0 at lower D, but this linear trend disappears once D approaches the critical suppression concentration. Interestingly, the critical suppression concentration of N2 increases with P0 at fuel-rich conditions, yet remains unaffected by P0 at fuel-lean conditions. Near the critical suppression concentration, a limiting burning speed (Slim) emerges, below which the flame is incapable of spontaneous propagation. Notably, Slim is not a fixed value, but varies according to the composition and initial state of the mixture. For a given gas component, an increase in P0 leads to a decline in Slim, while for gases with varying components, Slim is observed to be lower under fuel-rich conditions compared to fuel-lean scenarios. Also, both the addition of N2 and the augmentation of P0 significantly reduce the SL. When SL is comparable to the gas rise speed due to natural convection, the flame propagation becomes vulnerable to buoyancy instability. Meanwhile, the flame propagation may also be influenced by thermal diffusion instability and hydrodynamic instability. Under the combined effect of these instabilities, the flame is prone to be unstable. More importantly, when the flame contacting the upper wall of the is in a critical state where it can or cannot propagate downward, the irregularity of the disturbed flame may introduces uncertainty into the subsequent propagation, resulting in markedly different Pm even among mixtures with identical compositions.

Investigation of the impact of probes and internals on power and flow in stirred tank reactors

This study characterises the power requirements and flow patterns in several commercial stirred tank bioreactors with working volumes ranging from 60 mL to 1 L, and investigates the isolated impact of internals, i.e. baffles and probes, on the power number, P0. Results show that the presence of probes leads to a rise of the turbulent power number, P0, equivalent to the presence of baffles, and as the number of internals increases the variation of P0 gets smaller until it plateaus for large probe quantity and high-volume blockage. Internals have a greater impact on flow with radial flow impellers, causing a significant increase in P0 in comparison to axial flow impellers. An experimental and computational flow dynamics study is also conducted to investigate the interaction between the probe wake and the impeller trailing vortices, and an estimate is provided of the form drag from the pressure distribution acting on the probe, with a good agreement to the corresponding power number increase. A comparison between P0 data obtained from conventional-cylindrical and novel-streamlined probe configurations shows that optimising probe geometry and location with respect to the incoming flow can be an effective approach for reducing power requirements, local values energy dissipation rate and stress levelsinside the tank. This study provides valuable insights into the impact of internal components and flow type on power input per unit volume, P/V, in small-scale bioreactors and supports the development of more robust scaling procedures for the biopharma industry.

The friction-weakening cause by localized wear-induced damage and its effect on liquefaction resistance of sandy soil using DEM

Localized wear-induced damage caused by stress concentration at the contact point can lead to the decrease of the frictional coefficient (μ) of sandy soil, further affecting the liquefaction resistance. In this study, a bi-linear the friction-weakening model is proposed to describe the decreasing trend of μ with the increase of normal contact force (fn). Through a series of undrained cyclic triaxial tests, the influence of localized wear-induced damage on the characteristics of cyclic liquefaction is investigated from both macroscopic and microscopic perspectives. The macroscopic results indicate that samples have weaker liquefaction resistance due to the friction-weakening. Under low confining pressure (P0), the influence of the friction-weakening on the liquefaction resistance is relatively limited. With the increase of P0, the decrease of liquefaction resistance gradually becomes significant. However, the effect of friction-weakening on the liquefaction resistance does not remain constant, but shows a decreasing trend with the accumulation of excess pore water pressure ratio (EPWPR). From the microscopic perspective, the reduction of liquefaction resistance can be explained by the coordination number (Z) and the contact sliding ratio. Although higher Z caused by the friction-weakening may lead to greater liquefaction resistance, higher sliding contact ratio have been found to weaken the liquefaction resistance, and its influence exceeds Z.

Confined deflagration of propanal/air in the presence of intrinsic instability at elevated pressures

The partial oxidation process is a chemical technique with a high risk of deflagration, which involves directly mixing of fuels with oxidizers at elevated conditions. Under non-standard conditions, the deflagration behaviors of fuels are often unavailable to the general public, which hampers progress in further basic research. In this study, the deflagration behaviors of propanal-air mixtures at 75 °C and 0.1–1.0 MPa were investigated, and the effect of initial pressure (P0) and equivalence ratio (φ) on the deflagration characteristics of propanal was discussed. To explain the similarities and differences in the deflagration characteristics under various conditions, the buoyancy instability, hydrodynamic instability and thermal-diffusion instability suffered by the flames were also analyzed. Results show that the pressure generated by the burned mixture is a cubic function of time, and the state of flame propagation can be determined by the monotonicity of the second-order derivative of pressure. Moreover, the peak deflagration pressure (Pm) is more sensitive to changes in φ on the fuel-lean side, but Pm/P0 at the fuel-rich condition is markedly higher than Pm/P0 at the fuel-lean condition. At all φ, an increase in P0 effectively shortens the ignition time and reduces the minimum ignition energy. Nevertheless, there are discernible differences in the variation patterns of the deflagration time (θm) with P0 at various φ. Specifically, θm gradually prolongs with increasing P0 at fuel-lean conditions, whereas it tends to be the same at different P0 and φ = 1. Furthermore, under fuel-rich conditions, θm progressively shortens as P0 increases. The decrease in θm is attributed to the increasing flame speeds in the presence of intrinsic instability, and the self-accelerating flame yields pressure waves, which travel faster than the flame. Then a series of reflected pressure waves are formed after the pressure waves strike the vessel wall, interacting with the flame front and resulting in the pressure oscillation. Moreover, increasing P0 advances the pressure oscillation and augments the intensity of pressure oscillation.

Research on the Elastoplastic Theory and Evolution Law of Plastic Zone Contours of Horizontal Frozen Walls under Nonuniform Loads

The study of the changes in stress and deformation of frozen walls during excavation has always been a hot topic in underground freezing engineering, and the size of the plastic zone is an important basis for evaluating the stability of frozen walls. In response to the shortcomings in the current design of horizontal frozen walls, based on the internal excavation unloading conditions of the frozen wall in artificial ground freezing, an elastoplastic mechanical model for the interaction between a circular horizontal freezing wall and unfrozen soil mass is established under nonuniform loads to obtain the corresponding solutions for stress and displacement in the system. In this study, considering the shear stress of the plastic zone, the method for solving the traditional plastic zone contour equation is modified; consequently, the modified solution of the contour equation of the plastic zone for the frozen wall is obtained. Using this theoretical solution, the influence of the external load p0 and the lateral pressure coefficient λ on the contour line of plastic zone and tensile stress zone are analyzed by combining the project case, the calculation results show that: the λ=0.485 is the critical point where the inner edge of the frozen wall just happens to have tensile stress. When λ<0.485, the tensile stress zone is inevitable in the inner edge of the frozen wall vertical direction, and its range is only related to λ and increases with the decrease of λ. The p0 only affects the magnitude of tensile stress in the region, but does not affect its range. At this time, the frozen wall compression plastic zone contour evolves from crescent shaped to ear shaped with the increase of p0. When 0.485<λ<0.61, there will be no tensile stress zone, the frozen wall compression plastic zone contour also evolves from crescent shaped to ear shaped with the increase of p0. When λ>0.61, there will be also no tensile stress zone, with the increase of p0, the compression plastic zone contour evolves from the crescent shaped in the horizontal direction to the elliptical shaped, and there is no ear-shaped plastic zone in the whole evolution process. Based on our results, we show that our method can be used to provide a theoretical basis for the stability evaluation and parameter (thickness) design calculation of horizontal frozen walls under nonuniform loads.

Effect of initial pressure on the critical characteristics and overpressure of hydrogen-air premixed gas combustion and explosion

In order to ensure the safe utilization of hydrogen, the flame characteristics and explosion overpressure at lean-burn, stoichiometric and rich-burn conditions are investigated systematically by varying initial pressures. Experiments were conducted in a constant-volume combustion chamber using the Schlieren system to investigate the critical characteristics of hydrogen-air premixed flames at different equivalence ratios (from 0.2 to 6.5) and initial pressures (from 50 kPa to 150 kPa). The cellular instabilities of hydrogen-air premixed flames were interpreted and evaluated from the viewpoint of thermal-diffusive and hydrodynamic instabilities. The influence of initial pressure on the cellular instability and combustion and explosion characteristics were analyzed. The results show that the variation of thermal-diffusive instability dominantly governs the cellular instability at lean-burn conditions (φ = 0.3–1.0). In contrast, the cellular instability at rich-burn conditions (φ > 1.5) is governed by the variation of hydrodynamic instability. The increase of initial pressure promotes the cellular instabilities noticeably caused by the rise of the hydrodynamic instability. With the increase of P0, the Lewis number Le and thermal expansion ratio σ almost remain the same while flame thickness δ noticeably decreases. Increasing initial pressure at lean-burn and stoichiometric conditions (φ < 2.0) facilitates cellular instability, making the explosion more intense and resulting in higher explosion overpressure. In contrast, the variation of initial pressure suppresses the laminar combustion at rich-burn conditions (φ > 3.0).

Exploring the effect of surface wettability on heterogeneous condensation of carbon Dioxide: A molecular dynamics study

The condensation characteristics of carbon dioxide (CO2) are critical for several engineering applications, including pressurized liquefied natural gas technology and carbon capture, utilization, and storage (CCUS). This study applies molecular dynamics simulations to investigate CO2 condensation on different solid surfaces by modulating the solid–liquid interaction coefficient, α, to alter wettability. The CO2 condensation process is categorized into three phases: nucleation, coalescence, and growth. Our findings suggest that increasing the α value not only enhances surface wettability but also alters the condensation of CO2 from a droplet to a film form. Higher α values are linked with increased condensation rate and liquefaction degree, thus leading to improved heat transfer performance. The effects of different initial system pressure (p0) and cooling temperatures (Tcold) on CO2 condensation are also examined. A reduction in Tcold and an increase in p0 both contribute to an enhanced liquefaction rate and degree of CO2 and improve heat transfer. For instance, when α = 0.10, decreasing Tcold from 200 K to 180 K increases the CO2 liquefaction rate from 46.68% to 72.95%, and when α = 0.24, the rate grows from 80.81% to 91.99%. This study provides pioneering insights into the heterogeneous condensation and heat transfer processes of CO2 at the microscopic level, potentially offering valuable knowledge for optimizing CO2 capture or removal in engineering applications.

Explosion behaviors of hydrogen-nitrous oxide mixtures with propane addition

In the present work, the explosion of hydrogen-propane-nitrous oxide mixtures with various equivalence ratios (ϕ=0.2-2.4), propane fractions (ωC=0-1.0) and initial pressures (P0=50-100 kPa) at ambient temperature (288 K, room temperature) was experimentally performed in a standard 3.375-L cubic vessel. The maximum explosion pressure (Pmax), maximum pressure rise rate ((dp/dt)max) and explosion time (te) were obtained in light of pressure–time curves, and the normalized maximum explosion pressure (Pmax/P0) and normalized explosion time (td/te) were analyzed as well. Moreover, the adiabatic pressure (Pad) and laminar burning velocity (SL) were also calculated for argumentation. The results indicate that with the increase of ωC, Pmax and (dp/dt)max both present three characteristic variation trends for different ϕ, while the inflections of Pmax-ϕ and (dp/dt)max-ϕ transient gradually from lean to rich mixtures. Besides, te and td/te are monotonously rising with ωC, illustrating that propane addition can remarkably decelerate the explosion process. In addition, with the increase of P0, Pmax/P0 raises monotonously and is asymptotic to Pad/P0 at ωC⩽0.2, demonstrating that heat loss decreases under higher P0. Linear dependence is also found between (dp/dt)max and P0 for any composition. Furthermore, te monotonically decreases with P0, due to the flame acceleration occurring in the combustion period. In general, the presence of nitrous oxide (N2O) with a large content makes the explosion extremely unstable, and a spot of propane can dramatically alter the explosion characteristics of H2-N2O mixtures. These results will be meaningful for the development of explosion-mitigation devices and technology in case of underlying explosion and fire hazards.

Rail rolling contact fatigue response diagram construction and shakedown map optimization

The shakedown map is one of the key prediction models used in railway engineering to evaluate rolling contact fatigue (RCF) damages of wheels and rails. The objective of this work is to construct the response diagram of RCF and optimize the classical shakedown map based on the rolling-sliding tests. A method based on rolling-sliding tests for constructing the response diagram was presented. Firstly, the traction coefficient (μ) and load factor (P0/ke) were taken as the X-axis coordinate and Y-axis coordinate of the coordinate system of the classical shakedown map, respectively. Then, test parameters (P0 and μ) were designed and obtained using the various X and Y coordinate in four different regions of shakedown map (i.e., different plots of μ versus P0/ke). After that, for various test parameters, the rolling-sliding tests were carried out using a twin-disc testing apparatus under dry condition to investigate the RCF damages of U75V rail steel. The results showed that three types of damage states could be observed after rolling-sliding tests under different test parameters: (I) neither plastic flow of materials nor fatigue cracks, (II) plastic flow, and (III) fatigue cracks with plastic flow. Thus, the response diagram consists of the above three damage regions. Furthermore, with the increase of P0 and μ, all the depth of plastic flow, the length of fatigue cracks and the wear rates were increased. Moreover, materials were work hardened in the damage states of plastic flow and fatigue cracks. The hardness increment was increased with P0 and μ. In addition, the boundary of ratchetting region (i.e., shakedown limit) in the classical shakedown map for partial slip was optimized based on the RCF damages and the new response diagram. The shape of optimized shakedown limit curve was same as that of the classical one, whereas the position of the optimized curve was decreased.

Effects of acute intermittent hypoxia on P0.1 in humans with spinal cord injury

Spinal cord injury (SCI) disrupts neural pathways to respiratory motor neurons, diminishing respiratory drive and breathing function. Breathing impairment remains a leading cause of illness and death after SCI. Therapeutic acute intermittent hypoxia (tAIH; 15, 1-minute episodes of 9% inspired O 2 , 1.5 min normoxic intervals), a promising strategy to restore breathing function after SCI, promotes spinal neuroplasticity in rodent models. However, in humans, respiratory drive is unchanged after a single tAIH session; thus we tested the hypothesis that tAIH on five successive days increases neuromechanical respiratory drive in humans living with chronic SCI. Sixteen participants with chronic SCI (1 female; 33.5 + 15.3 years of age; 1-28 years post-SCI; 11 cervical, 5 thoracic; C1-T6 AIS A-D) were studied; their respiratory function was 52% ± 19% of age predicted expiratory pressure generation, and 123% ± 32% for inspiratory pressure. Five days of tAIH or Sham treatment were delivered in a randomized, cross-over design (minimum 3 weeks apart). Airway occlusion pressure in the first 0.1s of inspiration (P0.1), a surrogate for neuromechanical respiratory drive prior to within-breath sensory feedback, was collected at baseline and at 1, 3, and 7-days post-treatment. Repeated measures ANOVA revealed no significant effect of time (F(3)=.49; P=.69) or group (F(3)=1.33; P=.27). Despite the lack of significant differences in this preliminary analysis, P0.1 increased by 25% on day 3 versus 0.8% after Sham. Because of this change, pairwise comparisons were conducted, revealing a near significant increase in P0.1, 3 days post tAIH (MD=-.17; P =.06). Thus, although P0.1, a surrogate for neuromechanical respiratory drive, did not significantly increase after 5 days of AIH in people with SCI, the marginally significant change at day 3 suggests further investigation is warranted. Next steps include assessment in a larger sample, investigation of biomarkers for treatment effects, and examination of combinatorial interventions including task specific training and/or mild CO 2 elevations to enhance AIH-induced neuroplasticity in the drive to breathe. DoD SCIRP Clinical Trial Award W81XWH-17-SCIRP-CTA; The Craig H. Neilsen Foundation (JW); NIH T32 HL134621 (MM); and the UF McKnight Brain Institute. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The inspiratory activity of respiratory center and respiratory muscles strength after COVID-19

The respiratory pump that provides pulmonary ventilation includes the respiratory center, peripheral nervous system, chest and respiratory muscles.The aim of this study was to evaluate the activity of the respiratory center and the respiratory muscles strength after COVID-19 (COronaVIrus Disease 2019).Methods. The observational retrospective cross-sectional study included 74 post-COVID-19 patients (56 (76%) men, median age – 48 years). Spirometry, body plethysmography, measurement of lung diffusing capacity (DLCO), maximal inspiratory and expiratory pressures (MIP and MEP), and airway occlusion pressure after 0.1 sec (P0.1) were performed. In addition, dyspnea was assessed in 31 patients using the mMRC scale and muscle strength was assessed in 27 of those patients using MRC Weakness scale.Results. The median time from the COVID-19 onset to pulmonary function tests (PFTs) was 120 days. The total sample was divided into 2 subgroups: 1 – P0.1 ≤ 0.15 kPa (norm), 2 – &gt; 0.15 kPa. The lung volumes, airway resistance, MIP, and MEP were within normal values in most patients, whereas DLCO was reduced in 59% of cases in both the total sample and the subgroups. Mild dyspnea and a slight decrease in muscle strength were also detected. Statistically significant differences between the subgroups were found in the lung volumes (lower) and airway resistance (higher) in subgroup 2. Correlation analysis revealed moderate negative correlations between P0.1 and ventilation parameters.Conclusion. Measurement of P0.1 is a simple and non-invasive method for assessing pulmonary function. In our study, an increase in P0.1 was detected in 45% of post-COVID-19 cases, possibly due to impaired pulmonary mechanics despite the preserved pulmonary ventilation as well as normal MIP and MEP values.

Experimental Study of the Dynamic Shear Modulus of Saturated Coral Sand under Complex Consolidation Conditions

The shear modulus is an essential parameter that reflects the mechanical properties of the soil. However, little is known about the shear modulus of coral sand, especially under complex consolidation conditions. In this paper, we present the results of a multi-stage strain-controlled undrained cyclic shear test on saturated coral sand. The influences of several consolidation state parameters: effective mean principal stress (p0′), consolidation ratio (kc), consolidation direction angle (α0), and coefficient of intermediate principal stress (b) on the maximum shear modulus (G0), the reference shear strain (γr) and the reduction of shear modulus (G) have been investigated. For a specified shear strain level, G will increase with increasing p0′ and kc, but decrease with increasing α0 and b. However, the difference between G for various α0 and b can be reduced by the increase of shear strain amplitude (γa). G0 shows an increasing trend with the increase of p0′ and kc; on the contrary, with the increase of α0 and b, G0 shows a decreasing trend. To quantify the effect of consolidation state parameters on G0, a new index (μG0) with four parameters (λ1, λ2, λ3, λ4) which is related to p0′, kc, α0, b is proposed to modify the prediction model of G0 in literature. Similarly, the values of γr under different consolidation conditions are also evaluated comprehensively by the four parameters, and the related index (μγr) is used to predict γr for various consolidation state parameters. A new finding is that there is an identical relationship between normalized shear modulus G/G0 and normalized shear strain γa/γr for various consolidation state parameters and the Davidenkov model can describe the G/G0–γa/γr curves. By using the prediction model proposed in this paper, an excellent prediction of G can be obtained and the deviation between measured and predicted G is all within ±10%.

Assessment of respiratory muscle strength and inspiratory drive in patients with pulmonary tuberculosis

Respiratory muscles (RM) are a part of the respiratory system that enables ventilation. RM dysfunction exacer-bates breathing insufficiency. The aim: to study the RM strength and inspiratory drive in pulmonary tuberculo-sis (PT). Materials and methods. In 247 patients with verified PT we measured the maximal occlusion inspira-tory (PImax), expiratory (PEmax) pressures and shut off airways during the first 100 ms of inspiration (P0.1). Cli-nical manifestations of tuberculosis, computed tomog-raphy and perfusion scintigraphy data were evaluated. Results. The decrease of PImax was in 49.6%, PEmax — in 17.8%, both — in 32.6%. PEmax had weak negative dependence on the disease duration, contralateral lung blood flow, and a weak direct dependence with BMI. Statistically significant dependence was not found be-tween PImax and the clinical and instrumental charac-teristics of PT. A moderate dependence of P0.1 was with the PT clinical form, its duration, total volume of foci, blood flow disorders in the lung, the weak dependence of P0.1 was with BMI and the contralateral lung blood flow. The frequency of RM dysfunction in different PT forms did not differ. An increase of P0.1 in patients with fibrosis and cavities was 3–3.5 times more frequent than in the others patients. There were no statistically signifi-cant differences in PImax, PEmax, P0.1 in the group of fi-brosis and cavities and group of infiltrative foci with the same total lesion volume. Conclusion. The RM strength and inspiratory drive were significantly dependent on the duration of the disease, the extent of the lesion and the state of the pulmonary blood flow

Effectiveness and safety of hypotensive therapy of primary glaucoma with a Russian generic fixed combination of dorzolamide and timolol

Purpose: a comparative study of the efficacy and safety of the generic drug Dorzial Plus, an analogue of the original reference drug Cosopt®, in patients with primary open-angle glaucoma (POAG).Material and methods. The study involved 80 patients of both sexes aged 55–75 with newly diagnosed POAG of the initial and advanced stages with uncompensated intraocular pressure (IOP), of which 40 patients (study group) received Dorzial Plus and 40 patients (comparison group) received the reference drug (Cosopt®). Hypotensive efficacy of the drugs in both groups was assessed using a portable ophthalmic tonometer Icare PRO (Finland) by reducing IOP from the initial level after 1 week, 1 month and 3 months of treatment.Results. In both groups, the screening showed comparable average IOP values: 26.7 ± 3.2 mm Hg in the reference drug group and 27.4 ± 2.8 mm Hg in the Dorzial Plus group. After 1 week of therapy with Cosopt, IOP showed a significant decrease of 33% (reduction to 17.9 ± 3.2 mm Hg), while the group receiving Dorzial Plus demonstrated a 31% decrease (reduction to 18.9 ± 1.7 mm Hg). After 1 month of the instillation regimen, a slight increase in P0 (of about 3%) was recorded in both groups (increase to 18.7 ± 2.3 and 19.7 ± 2.0 mm Hg, respectively). By the end of the 3 months’ follow-up period, IOP decrease level with respect to the baseline remained practically the same, amounting to 30 and 29% (up to 18.6 ± 1.8 and 19.5 ± 2.3 mm Hg), respectively. The state of the ocular surface showed a slightly negative dynamics of tear film rupture time and OSDI index in the reference drug group, which could be observed throughout 3 months of therapy. In the study group, therapy with preservative-free drug containing a moisturizing agent (sodium hyaluronate) revealed a significantly changed OSDI index, manifesting itself in restructured severity of the evaluated features.Conclusion. Dorzial Plus reduces IOP in POAG patients by an average of 30% of the baseline, so that its hypotensive efficacy is comparable to the original fixed combination Cosopt. The tolerability analysis of the study drug demonstrates a significant positive dynamic of the state of the ocular surface as soon as 3 months after therapy start.

Deflagration-to-detonation transition and detonation propagation characteristics in a millimetre-scale spiral channel

The flame propagation processes involving deflagration-to-detonation transition (DDT) and detonation propagation in a novel millimetre-scale spiral channel (MSDC) are studied experimentally. The channel is of 3.0 mm in width and 5.2 m in length, embedded in a stainless-steel plate. In particular, a tiny gap of 0.02-mm width is reserved between the upper cover plate and the channel. Stoichiometric propane/hydrogen/air mixtures were adopted as the reactant. The combustion modes are investigated with various initial pressure (P0) and hydrogen blend ratio (XH), ranging from 100 to 500 kPa and 0.6 to 1.0, respectively. For lower P0 and XH, the flame gradually develops into an isobaric flame owing to significant thermal losses in narrow channels. With the increase of P0 and XH, the excess-enthalpy effect plays an important role, and a quantity of high-temperature burned gas in the inner turn enter the outer turn through the gap resulting in a spontaneous flame ahead of the wave front. It promotes the flame acceleration and the onset of local explosion. In subsequent detonation propagation process after DDT, multiple flame combination between the detonation wave and the secondary flame arise and the displacement speed of leading front dramatically increases, even more than 3 DCJ. Furthermore, benefited from excess enthalpy effect and the compact structure of MSDC, the displacement between the DDT location and the ignition spark is of the order of as small as 10 mm. It is of a great potential in application to miniature detonation engines, in which rapid DDT in narrow channels is of strong demand.

The effect of loading frequency on the long-term cyclic behavior of dense calcareous sand

Transportation infrastructure foundations filled with calcareous sand are exposed to long-term cyclic loading under various frequencies. This study presents experimental results about the drained cyclic triaxial tests conducted on dense calcareous sand under different mean effective stresses ([Formula: see text]), cyclic stress ratios (ζ), and loading frequencies (f) to examine the effect of f on the long-term cyclic behavior. Results show that the increase in f causes the significant increase in the accumulated axial strain ([Formula: see text]). As ζ increases, [Formula: see text] becomes more sensitive to f, while the increase of p0 could limit the aggravating effect of f on [Formula: see text]. At a higher ζ, increasing f can even lead to a failure and larger dilated volumetric strain of dense calcareous sand specimens. The increase in f has a considerable impairing effect on the shakedown behavior, which can cause the stable shakedown behavior to transform into transitional or unstable shakedown behaviors. More accurate shakedown discriminant boundaries suitable for calcareous sand under different f were therefore proposed.

Experimental Investigations on Polarization Switching and Bistability in a 1550 nm VCSEL Subject to Orthogonal Optical Injection With Time-Varying Injection Power

Polarization switching (PS) and polarization bistability (PB) characteristics of a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection (OOI) with time-varying injection power are experimentally investigated for the first time. To implement the optical injection, a Mach-Zehnder modulator (MZM) modulated by a triangular radio wave is adopted, and the influences of some typical parameters on the performances of PS and PB are analyzed. Under suitable operation conditions, PB in the VCSEL subject to OOI with time-varying injection power can be observed only for the input power P0 of MZM locating within a determined range, and the width of hysteresis loop gradually decreases with the increase of P0 from the minimum P0, min to the maximum P0, max. Under different frequency detuning Δ ν between the injection light and the X polarization mode of the VCSEL, the determined ranges of P0 required for PB are different. With the variation of Δ ν from a negative value to a positive value, both P0, min and P0, max present a trend of decrease first and then increase. Additionally, with the increase of the modulation frequency, the hysteresis loop width firstly increases rapidly and then gradually tends saturation.

Response of lean premixed swirl tubular flame to acoustic perturbations

This study experimentally examined the response of a lean premixed methane/air swirl tubular flame to the longitudinal acoustic perturbations. Experiments were conducted by varying the acoustic frequency (f0), acoustic power (P0) and inlet air flow rate (QA) to systematically study the acoustic-excited flame dynamics, including the flame stability, flame structure, heat release rate and acoustic pressure fluctuations. The results demonstrated that the lean tubular flame was much sensitive to longitudinal perturbations below 210 Hz. Even at low power of P0, the flame was forced to oscillate intensively when the perturbation was operated in two discontinuous frequency ranges of f0 = 150–200 and f0 = 50–100 Hz, while a weakened oscillation regime was observed in the middle range of f0 = 100–150 Hz; a lower frequency (less than 50 Hz) would extinguish the flame. An increase in P0 intensified the flame oscillation under the perturbations of 50–100 Hz, and even resulted in flame lift-off and blow off with f0 between 150 and 200 Hz. In comparison to f0 and P0, the effects of air flow rate (QA) seemed to be weaker. The proper orthogonal decomposition (POD) analysis was performed to interpret the contributions from the mean mode and fluctuating axial and circumferential modes that led to combustion instability. It was found that as the energy fraction of the axial mode exceeded 5.0%, the flame lift-off appeared in the lean swirl tubular configuration.

Experimental and Estimation Studies of Resilient Modulus of Marine Coral Sand under Cyclic Loading

Coral sand is an important filler resource that can solve the shortage of terrestrial fillers in coastal areas. Recently, the foundations of many infrastructures in the South China Sea have been built with coral sand as fillers, which have been subjected to wave and traffic cyclic loads. Resilient modulus (Mr) is an important design parameter in marine engineering, but there are few studies on the resilient modulus response of coral sand under cyclic loading. A series of drained cyclic triaxial tests were carried out to investigate the effects of the initial mean effective stress (p0) and cyclic stress ratio (ζ) on the resilient modulus response of the coral sand from the South China Sea. The change of fractal dimension (αc) can reflect the rule of particle breakage evolution. The αc of coral sand shows a tendency of almost maintaining stable and then increasing rapidly with the increase of mean effective stress p0 under each cyclic stress ratio ζ. There is a threshold of p0, when the p0 exceeds this threshold, αc will increase significantly with the increase of p0. The increase of p0 has a beneficial effect on the improvement of the Mr, while the increase of ζ has both beneficial and detrimental effects on the improvement of the Mr. A new prediction model of the Mr considering particle breakage was established, which can better predict the Mr of coral sand in the whole stress interval. The research results can provide guidance for the design of marine transportation infrastructures, which can promote the development of marine transportation industry and energy utilization.

Effect of hydrogen addition on the detonation performances of methane/oxygen at different equivalence ratios

Detonation performances of methane/hydrogen/oxygen (CH4/H2/O2) mixtures were investigated experimentally in a 3000 mm long tube with an inner diameter of 30 mm at different initial pressures p0 (ranging from 10 kPa to 50.5 kPa). Mixtures with different proportions of H2 in the total fuel α (0%, 14.29% and 25%) and different equivalence ratios Φ (0.8, 1.0 and 1.2) were tested. Signals of flame front and pressure were obtained by ion probes and high frequency pressure transducers, respectively. Results showed that with the increase of p0, αand Φ, the average velocity of steady detonation Vave increased. For mixtures with the given α, when Φ increased by 0.2, Vave increased by 100 m/s. In the present study, velocity deficits were found to be within 5%, and when p0 was higher than 20 kPa, the velocity deficits were within 2%. The average peak pressure of steady detonation pave was close to the von Neumann pressure pvN. Both the increase of p0 and Φ led to the increase of the pave. But the addition of H2 led to the decrease of pave, and pave decreased with the increased of α.