Initial Pressure Research Articles

Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action

Abstract In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.

Experimental study on the explosion characteristics of ammonia-hydrogen-air mixtures

Ammonia-hydrogen blended fuel has drawn substantial attention as an environmentally friendly, carbon-free fuel because it effectively overcomes the inherent disadvantages of pure ammonia in combustion performance, such as a high ignition energy, slow combustion rate, and low combustion efficiency. While recent research on the combustion performance of hydrogen-ammonia blends has advanced, there remains a scarcity of studies addressing the explosion characteristics of these fuels. In this paper, a series of experiments conducted within a standard 20-L spherical combustion chamber to investigate the explosion characteristics of ammonia-hydrogen-air premixed gases under diverse conditions, spanning from low to high pressures (0.02–0.3 MPa) and from fuel-lean to fuel-rich scenarios (0.7–1.5), are discussed. The results reveal that the explosion characteristics are pronouncedly enhanced by hydrogen addition. The maximum explosion pressure (Pmax) and maximum pressure rise rate ((dP/dt)max) increase, while the explosion time (texp) decreases with increasing hydrogen concentration. Pmax and (dP/dt)max exhibit linear increases as the initial pressure rises and reach their peaks at an equivalence ratio of 1.1; texp displays nonmonotonic variations with increasing initial pressure and equivalence ratio. Hydrogen addition remarkably increases the hydrodynamic instability and thermal-diffusion instability of the reactive mixture, enhances the thermal-mass diffusion on the flame front, and promotes flame deformation and cellular structure formation, resulting in an improvement of the flame propagation and compression effect on the unburnt reactant before the flame. Research into the explosion characteristics provides valuable insights for the safe storage and transportation of ammonia-hydrogen blended fuels. These results indicate avenues for further enhancing the detonation characteristics and explosion performance of ammonia-hydrogen blended fuels.

Investigating Pressure Patterns in Transformer Tanks after an Interturn Short Circuit: A Finite Element Approach

When an inter-turn short-circuit fault occurs during the operation of a transformer, the arc generates energy that causes the temperature in the tank to rise. This in turn increases the temperature of the insulating oil, vaporizing it, and the rising pressure in the tank acts on the tank such that it can easily explode. The arc energy is related to the initial pressure of the gas and its production in the tank. The pressure wave propagates in insulating oil, and the transient pressure at any point in the path of the pressure wave is the superposition of vectors of forward- and backward-traveling waves. The authors of this study applied a finite element simulation software to establish a model of the transformer tank and used it to analyze the changes in pressure in the tank and on the wall as well as the factors influencing this phenomenon. The results show that the wall pressure of the transformer increases with time after the failure of the interturn short circuit. The pressure wave travels from the initial position of the arc to the periphery and decreases with diffusion effects. The influence of pressure on the transformer tank can be reduced by selecting an appropriate location for the pressure-release valve and can in turn prevent the tank from rupturing due to the impact of rising pressure.

The effect of initial pressure on the thermal behavior of the silica aerogel/PCM/CuO nanostructure inside a cylindrical duct using molecular dynamics simulation

Amidst escalating fuel expenses and growing concerns over greenhouse gas pollution, the adoption of renewable alternative energy sources has become increasingly imperative. In response, scientists are fervently dedicated to identifying energy-saving solutions that are readily adaptable. Notably, silica aerogels have demonstrated remarkable efficacy in temperature management under both hot and cold conditions, while phase change materials are renowned for their capacity to store thermal energy. The study examines the effect of initial pressure on the thermal performance of silica aerogel/PCM/CuO nanostructure in a cylindrical duct. This was investigated using MD simulations and the LAMMPS software. The study will investigate several elements, such as density, velocity, temperature patterns, heat flux, thermal conductivity, and charge time or discharge time of the simulated structure. According to the results, with an increase in the initial pressure, the maximum density increases from 0.0838 atom/Å3 to 0.0852 atom/Å3, and the maximum velocity decreases from 0.0091 Å/fs to 0.0081 Å/fs. Also, the findings show that, by increasing the initial pressure, the temperature decreases from 931.42 K to 895.63 K, and thermal conductivity and heat flux decrease to 1.56 W/m.K and 56.66 W/m2 with increasing the initial pressure to 5 bar. Finally, the results show that charging time increases to 6.34 ns at 5 bar. The increase in charging time with increasing initial pressure may be attributed to the reduced mobility of particles within the structure as a result of the higher pressure. The findings of this study can help for a better understanding of energy-saving solutions, advanced thermal management systems, and the design of efficient energy storage technologies tailored to specific pressure-related operating conditions.

MRI-based clinical-radiomics nomogram to predict early neurological deterioration in isolated acute pontine infarction: a two-center study in Northeast China

ObjectiveTo predict the appearance of early neurological deterioration (END) among patients with isolated acute pontine infarction (API) based on magnetic resonance imaging (MRI)-derived radiomics of the infarct site.Methods544 patients with isolated API were recruited from two centers and divided into the training set (n = 344) and the verification set (n = 200). In total, 1702 radiomics characteristics were extracted from each patient. A support vector machine algorithm was used to construct a radiomics signature (rad-score). Subsequently, univariate and multivariate logistic regression (LR) analysis was adopted to filter clinical indicators and establish clinical models. Then, based on the LR algorithm, the rad-score and clinical indicators were integrated to construct the clinical-radiomics model, which was compared with other models.ResultsA clinical-radiomics model was established, including the 5 indicators rad-score, age, initial systolic blood pressure, initial National Institute of Health Stroke Scale, and triglyceride. A nomogram was then made based on the model. The nomogram had good predictive accuracy, with an area under the curve (AUC) of 0.966 (95% confidence interval [CI] 0.947–0.985) and 0.920 (95% [CI] 0.873–0.967) in the training and verification sets, respectively. According to the decision curve analysis, the clinical-radiomics model showed better clinical value than the other models. In addition, the calibration curves also showed that the model has excellent consistency.ConclusionThe clinical-radiomics model combined MRI-derived radiomics and clinical metrics and may serve as a scoring tool for early prediction of END among patients with isolated API.

Experimental Investigation of Fracture Propagation in Clayey Silt Hydrate-Bearing Sediments

More than 90% of the natural gas hydrate resources are reserved as marine clayey silt sediments. It is of great significance to efficiently develop a clayey silt hydrate. At present, there are problems of low single well production and small depressurization range in its production test, which is still a long way from commercial exploitation. The combination of hydraulic fracturing technology and other methods such as depressurization method is regarded as one of the potential technical means to achieve the commercial exploitation of the hydrate. However, compared with shale gas reservoirs and coalbed methane reservoirs, clayey silt hydrate reservoirs have special mechanical properties, resulting in unique hydraulic fracturing processes. Therefore, it is necessary to study the fracture initiation and propagation laws of clayey silt hydrate reservoirs. To this end, we carried out large-scale (30 × 30 × 30 cm) true triaxial hydraulic fracturing experiments using a simulated material with similar mechanics, porosity, and permeability to clayey silt hydrate-bearing sediments. The effects of completion method, fracturing method, and fracturing fluid displacement on hydraulic fracture propagation of clayey silt hydrate-bearing sediments were studied. The results showed that a perforated completion can significantly increase the fracture reconstruction area and decrease the fracture initiation pressure compared to an open hole completion. Due to the small horizontal stress difference, it is feasible to carry out temporary plugging fracturing in clayey silt hydrate reservoirs. Temporary plugging fracturing can form steering fractures and significantly improve fracture complexity and fracture area. Increasing the fracturing fluid displacement can significantly increase the fracture area as well. When conducting fracturing in clayey silt hydrate-bearing sediments, the fracturing fluid filtration area is obviously larger than the fracture propagation area. Therefore, it is recommended to use a high-viscosity fracturing fluid to reduce the filtration of the fracturing fluid and improve the fracturing fluid efficiency. This study preliminarily explores the feasibility of temporary plugging fracturing in clayey silt hydrate reservoirs and analyzes the effect of completion methods on the propagation of fracturing fractures, which can provide a reference for the research conducted on the fracturing stimulation of clayey silt hydrate reservoirs.

Evaluation of weak discontinuity in rotating medium with magnetic field, characteristic shock and weak discontinuity interaction

Abstract In this article we investigated the characteristic shock and weak discontinuity wave in a rotating medium of perfect gas in the case of one-dimensional (1-D) adiabatic motion under an axial magnetic field governed by the system of PDEs (partial differential equations). We have obtained some classes of analytical solutions of the system of PDEs that demonstrates the time-space dependency. With change in the values of rotational parameter, adiabatic index and the ratio of initial magnetic pressure to dynamic pressure, effect on the acceleration wave’s amplitude and jump in the flow variables across the characteristic shock is analyzed in detail. We have obtained an expression for the jump in shock acceleration, the amplitudes of transmitted and reflected waves caused by the incident wave on the characteristic shock after the interaction of a weak discontinuity. It is investigated that the jump function across the characteristic shock decay effect, and goes to 0 as time t → ∞, whereas a weak discontinuity wave may culminate into a shock wave, depending on the initial amplitude value. It is also found that the shock formation time reduces due to the consideration of magnetic field or rotating medium.

Multiphysics modeling of the influence of initial pressure on mechanical and electrochemical performance of all-solid-state batteries

All-solid-state batteries (ASSBs) are emerging as promising energy storage solutions owing to their enhanced safety and high energy density. However, the application of higher pressures is also required to improve electrochemical performance. This study employs a multiphysics approach by combining the discrete element method (DEM) and finite element method (FEM) to investigate the impact of the compression rate and initial pressure on electrochemical performance. To the best of the authors' knowledge, this is the first study to integrate the DEM and FEM methodologies for the prediction of electrochemical and mechanical responses, capitalizing on the advantages of both approaches. The DEM is used to investigate the compaction behaviors of solid electrolyte and electrode mixtures, yielding essential data on mechanical properties, which are subsequently incorporated into the FEM model. The FEM is utilized to systematically explore the electrochemical performance and mechanical responses. The findings highlight that elevated stress enhances geometric properties, including surface area and volume fraction, leading to improved electronic and ionic conductivity. Although higher compression ratios can enhance electrochemical performance, they also elevate stress levels, thereby increasing the potential for mechanical failure. Therefore, a well-balanced electrode design is crucial. This study provides valuable insights into the design of ASSBs.

Flame evolution and pressure dynamics of premixed stoichiometric ammonia/hydrogen/air in a closed duct

Ammonia is regarded as a promising energy carrier due to its zero-carbon emissions and its suitability for long-distance, large-scale storage, and transportation. Ammonia/hydrogen mixed combustion is an important way to solve the problem of high ignition temperature and low flame speed in the process of ammonia combustion. This study systematically investigates the evolution of flames and pressure dynamics in a closed duct for ammonia/hydrogen/air mixtures with varying hydrogen blending ratio (0–100 %). Simultaneously, the study assesses the impact of flame instability and heat release on the evolution of ammonia/hydrogen/air flames and pressure dynamics. The results show that the flame tip speed and overpressure increase with the increase of hydrogen blending ratio and initial pressure, and when the hydrogen blending ratio is more than 25 %, the growth range of flame tip speed peak and overpressure peak value increases significantly. At the same time, the flame thickness decreases after hydrogen blending, the hydrodynamic instability increases, and the degree of wrinkles on the flame surface increases, which promotes flame acceleration. The Froude number increases significantly, the influence of buoyancy instability gradually weakens, and the flame core does not undergo significant displacement. In the later stage of flame propagation, both the flame front propagation velocity and pressure show significant pulsation phenomena. The heat release calculation results show that hydrogen blending significantly increases the adiabatic flame temperature. Consistent with the evolution law of overpressure, when the hydrogen blending ratio is greater than 25 %, the net heat release increases significantly. The elementary reaction with the highest heat release rate changes from the chain termination reaction R41 to the chain termination reaction R3. The research results can provide theoretical basis and experimental data support for the formulation of safety standards during the regulation and utilization of the combustion structure of ammonia/hydrogen/air mixtures.

Laminar burning velocity of Ammonia/Air mixtures at high pressures

Ammonia (NH3) is one solution for decarbonizing the economy. This study used high-speed schlieren imaging to investigate the NH3/air flame morphology and propagation characteristics (laminar burning velocity (LBV) and flame thickness) inside a constant volume combustion chamber (CVCC), at conditions relevant to different types of combustors used in power generation. Experiments were carried out for equivalence ratios (ϕ) from 0.7 to 1.3, initial pressures from 1 atm to 10 atm, and an initial temperature of 298 K using a variable gap ignition system. A novel passivation method that minimized the effect of NH3 adsorption on stainless steel surfaces was used during the CVCC filling to reduce the uncertainty in the actual ϕ before ignition. Results showed that the low speed of NH3/air flames increased the effect of buoyancy on the flame shape, especially at high initial pressures or near the flammability limits when flames adopted a bean-shaped structure. A comparison of Rayleigh and Peclet numbers (indicators of buoyancy and diffusion phenomena in flames, respectively) supported these findings. Maximum LBV was measured at ϕ = 1.1 and decreased non-linearly with the initial pressure. Similarly, flame thickness decreased with pressure, and it was thinnest at ϕ = 1.1 for all the examined conditions. Numerical simulations using Cantera produced similar LBV values as the experiment. A sensitivity analysis indicated that reactions involving NH2 and NO have an important role on LBV. Reactions leading to H, O, and OH radicals generation had the strongest effects on LBV enhancement, while LBV-inhibiting reactions had more accentuated effects at high pressures at which LBV is lower.

Dynamic behavior of detonation waves in millimeter-scale tubes: unraveling the influence of tube diameter, initial pressure, and mixture

Dynamic behavior of detonation waves in millimeter-scale tubes: unraveling the influence of tube diameter, initial pressure, and mixture

Spray cooling technique in liquid piston gas compression and impact of air dissolution on efficiency evaluation at different pressure levels

For a compressed air-based energy storage, the integration of a spray cooling method with a liquid piston air compressor has a great potential to improve the system efficiency. To assess the actual applicability of the combination, air compressions with and without the spray were performed from different pressure levels of 1, 2, and 3 bars with the pressure ratio of 2. Under the testing conditions, compressions with the spray technique showed about 98–98.5 % isothermal efficiencies for all the three pressure levels, which are huge improvement from the efficiencies of 83–88 % without the spray. Droplet properties that are critical to determining the heat transfer were quantified to estimate how they were affected by a pressure level. Considering the spray work input, the overall efficiency drops at a higher pressure. In addition, the impact of air dissolution on the compression efficiency was estimated, and a suggestion for adjusting the conventional efficiency evaluation method is made. With the newly suggested approach, at a higher initial pressure, the actual efficiency is even lower than the conventionally calculated efficiency.

Explosion characteristics of hydrogen-nitrous oxide mixtures with carbon dioxide addition

In this work, the explosion of hydrogen/nitrous oxide/carbon dioxide mixtures with various equivalence ratios (0.6–1.0), initial pressures (40–100 kPa), and carbon dioxide fractions (20%–40 %) at ambient temperature (298 K) was conducted inside a normative 15.625-L cubic container. The maximum explosion pressure and pressure rise speed were obtained and analyzed. The results show that carbon dioxide plays a crucial role in weakening H2/N2O explosion intensity, flame instabilities, as well as the tendency of deflagration to detonation. In addition, the addition of carbon dioxide has affected the two competitive effects between adiabatic temperature and molecular number. The variations of maximum explosion pressure and pressure rise speed with equivalence ratios depend on the carbon dioxide fraction. Only a linear dependence was found between maximum pressure rise speed and original pressure. These results would be useful in developing explosion-proof devices in the event of potential fire and explosion hazards.

Improvement of MC method in SAE J2601 hydrogen refuelling protocol using dual-zone dual-temperature model

The MC method has been published in the SAE J2601 refuelling protocol to safely and quickly refuel hydrogen fuel cell vehicles. This article adopts a dual-zone dual-temperature model that distinguishes the hydrogen temperature from the tank wall temperature to replace the dual-zone single-temperature model of the original MC method. A model (0D1D) of lumped parameter gas (0D) and one-dimensional tank wall (1D) is established simultaneously to verify the modified MC method and generate simulation data. A modified formula to the original MC method for calculating final hydrogen temperature is derived, which contains a correction factor K. The formula and coefficients of the correction factor K are determined by fitting the simulated data from the 0D1D model. The correction factor K is expressed in a piecewise function. The formulas of K are relatively complicated, so another simpler correction factor k is derived, which is a linear function. Research shows that the modified MC method extends its applicability to situations of refuelling times <30 s, while the original MC method is unsuitable. In the conditions set in this article of ambient temperature 0 to 40 °C, precooling temperature −40 to −20 °C and initial pressure 2 to 60 MPa, the modified MC method reduces the errors of final hydrogen temperature between the 0D1D model by 2 to 7 °C compared to the original one, thus improving the calculation accuracy of the pressure target and reaching a more accurate state of charge. In a word, the modified MC method improves the accuracy of refuelling control and has positive significance for the operational safety of hydrogen refuelling stations and the driver's refuelling experience.

Study on the influence of perforation parameters on hydraulic fracture initiation and propagation based on CDEM

Perforation hydraulic fracturing plays a crucial role in the development of oil and gas reservoirs, and perforation layout can significantly affect the initiation and propagation of complex reservoir rock fractures. In this paper, we used a mixed finite-discrete element method with an explicit iterative scheme called the continuous–discontinuous element method (CDEM) to study the process of hydraulic fracture propagation through perforation. The coupling effects of fluid flow and reservoir mechanics are fully considered, and the accuracy of the model in simulating the directional propagation of perforation hydraulic fractures is validated by comparison with physical experimental results. We also discussed in detail the impact of perforation pattern, density, depth, and aperture on crack initiation, propagation, and complexity, and used the new index of fracture degree to quantitatively evaluate the fracturing effects under the influence of multiple perforation layout parameters. The results indicate that: (i) hydraulic fractures near the wellbore compete for initiation, and the length distribution of cracks is uneven and intricate; (ii) linear perforation patterns produce the maximum initiation pressure, which is negatively correlated with the perforation density and positively correlated with the perforation depth and aperture; (iii) the fracture degree is mainly affected by perforation density and depth, and is less affected by aperture. Perforation can effectively control the fracture morphology and initiation pressure, and has a substantial influence on the crack propagation layout near the wellbore. This study provides a basis for the rational selection and optimization of perforation parameters, which can effectively improve the fracturing effects of tight oil and gas reservoirs.

Experimental Observation of Flame Propagation Behavior of Hydrogen Enriched Flames Upstream of a Flame Arrester Housing with Parallel Plates as the Arrester Element

ABSTRACT The phenomenon of flame propagation in closed and semi-open ducts that have no obstacles is of interest due to the need to include alternative fuels into the energetic matrix. Tulip flames can develop under these configurations. Therefore, the behavior of flame propagation upstream of a flame arrester housing is relevant to assess the challenges of flame quenching under this configuration. The objective of this article is to investigate the effect of the effective Lewis (Leeff ) number, Zeldovich (Ze) number and initial pressure (p i ) on the flame propagation behavior upstream of a flame arrester housing with parallel plates as the flame arrester element. The Leeff and Ze numbers were varied between 0.60 and 1.36 and between 4.19 and 8.77 respectively. In addition, the initial pressure was varied from 40 kPa to 80 kPa. The mixtures considered involved natural gas, hydrogen, helium and air, which were stoichiometric in all cases. It was observed that the tulip flame developed in all cases, but with different positions of the tulip flame formation. This is important for the development and testing of flame arresters as the inlet velocity and pressure are influenced by this phenomenon. The maximum flame propagation velocities (V max ) and the maximum pressure ratios (p max /p i ) were also determined. It was found that V max decreased for higher values of the product Leeff ⨯Ze for all mixtures and initial pressures. Similarly, p max /p i decreased with increasing Le eff ⨯Ze for the initial pressures of 40 kPa and 60 kPa. A slightly different behavior was observed for pmax/pi at 80 kPa, which did not decrease significantly with higher Leeff ⨯Ze. Therefore, the flames were characterized by weak acceleration and moderate pressure ratios.

Intraorbital pressure-volume characteristics in a piglet model: In vivo pilot study.

Intracranial pressure measurement is frequently used for diagnosis in neurocritical care but cannot always accurately predict neurological deterioration. Intracranial compliance plays a significant role in maintaining cerebral blood flow, cerebral perfusion pressure, and intracranial pressure. This study's objective was to investigate the feasibility of transferring external pressure into the eye orbit in a large-animal model while maintaining a clinically acceptable pressure gradient between intraorbital and external pressures. The experimental system comprised a specifically designed pressure applicator that can be placed and tightly fastened onto the eye. A pressure chamber made from thin, elastic, non-allergenic film was attached to the lower part of the applicator and placed in contact with the eyelid and surrounding tissues of piglets' eyeballs. External pressure was increased from 0 to 20 mmHg with steps of 1 mmHg, from 20 to 30 mmHg with steps of 2 mmHg, and from 30 to 50 mmHg with steps of 5 mmHg. An invasive pressure sensor was used to measure intraorbital pressure directly. An equation was derived from measured intraorbital and external pressures (intraorbital pressure = 0.82 × external pressure + 3.12) and demonstrated that external pressure can be linearly transferred to orbit tissues with a bias (systematic error) of 3.12 mmHg. This is close to the initial intraorbital pressure within the range of pressures tested. We determined the relationship between intraorbital compliance and externally applied pressure. Our findings indicate that intraorbital compliance can be controlled across a wide range of 1.55 to 0.15 ml/mmHg. We observed that external pressure transfer into the orbit can be achieved while maintaining a clinically acceptable pressure gradient between intraorbital and external pressures.

Effect of vent area on vented ammonia-hydrogen-air deflagrations in a 1-m-long duct

Although ammonia-hydrogen blended fuel has become a research hotspot, it is essential to recognize that adding hydrogen to ammonia increases the potential explosion hazard before considering the development of ammonia-hydrogen fuel. In this study, the effect of vent area on vented deflagrations of ammonia-hydrogen-air mixtures is investigated in a 1-m-long horizontal rectangular duct with a right end opening at an initial temperature of 293 K and an initial pressure of 101 kPa. A dimensionless vent coefficient Kv is used to define the vent area in this work to clarify the evolution of flame structures and overpressure inside and outside the duct. For a specific Kv, the amplitude of the maximum internal explosion overpressure (Pmax) monitored at the left end of the duct (LE) has a greater difference compared with other pressure monitoring points. The maximum amplitude of Pmax is always reached at the LE for Kv ≤ 3.2, while the difference in the maximum amplitude of Pmax between different monitoring points decreased significantly for Kv > 3.2. With the increasing of Kv from 2.2 to 20.1, Pmax obtained at the right end of the duct (RE) and the center of the duct increases monotonously, but Pmax monitored at the LE shows a non-monotonic increasing trend. A spike structure of penetrating flame bubbles resulting from negative pressure balance is only observed inside the duct for Kv ≤ 5.6. Two types of oscillations (Helmholtz and Acoustic oscillations) can be distinguished in some tests, and only acoustic oscillations of overpressure can be clearly found in tests with Kv > 7.8. With the increasing of Kv from 2.2 to 20.1, the shape of the external fireball will change significantly. As Kv increases from 2.2 to 5.6, the external fireball shapes are always mushroom-shaped. However, the shapes of the fireball become elongated for Kv > 7.8, and even the external fireball presents a jet shape for Kv = 20.1. With the increasing of Kv from 2.2 to 20.1, The maximum external overpressure increases first, thereafter decreases, and finally increases.

Numerical investigation on turbulent flame jet characteristics of a pre-chamber fueled with CH4/O2 and CH4/NH3/O2 mixture under different initial pressures

Ammonia is a very potential carbon-free alternative fuel with extremely low reactivity. The application of ammonia in internal combustion engines faces the risks of ignition failure, low burning rate, and poor combustion stability. Pre-chamber turbulent jet ignition (TJI), which can provide much more ignition energy, is a promising method to ignite ammonia fuel. However, the transient propagation process of pre-chamber jet flame has not been fully investigated yet. In this paper, the propagation characteristic of methane jet flame was numerically studied based on a constant volume combustion system. The supersonic jet flame propagation and Mach disk phenomenon were further analyzed with numerical methods. And the propagation characteristic of methane/ammonia mixed jet flame was investigated. According to the results, the formation and propagation process of methane jet flame has different characteristics at different stages. In High-speed development stage (Stage II) and Low-speed oscillation development stage (Stage III), the penetration distance of flame jet tip is almost proportional to the penetration time. However, the penetration speed of the two stages is significantly different. The change trend of the jet velocity at the outlet of orifice hole can also be divided into four stages: slow increasing, rapid increasing, gradual decreasing, and periodic oscillation. The periodic oscillation of the jet tip velocity and the jet velocity at the outlet of orifice hole is caused by the effect of forward and reverse shock waves. The calculation results of CH4/NH3/O2 mixture jet flame show that the addition of ammonia has significant effects on the flame propagation process in PC, the thermodynamic state of PC, and the propagation characteristics of jet flame. With the increase of ammonia proportion, the maximum pressure of PC gradually decreases and the pressure rise rate slows down. Meanwhile, the two-stage (the high-speed development stage and the low-speed development stage) characteristic of jet propagation process gradually disappears. And the addition of ammonia is more likely to destroy the two-stage characteristic under low initial pressure.

A functional brace for treating Colles fractures; volunteer trial of a new design

BackgroundPresently used Colles' fracture treatments have similar outcomes with significant complications. Previous studies of a dynamic functional fracture brace, achieving similar or better results had no significant complications. A novel brace design is described to achieve optimal patient outcomes. MethodsPatient forearm measurements combined with data from a previously tested brace provided parameters for a brace formed using computer assisted design. Fracture swelling was simulated using a 40 ml (ml) plastic water filled bag placed over the dorsum of the lower radius. The interface pressure between the brace, skin and bag were measured on twelve human volunteers, four with forearm measurements to fit each of small, medium and large brace sizes. Measurements were taken at intervals reducing volume of fluid in the bag by 10 ml until empty, first wearing a brace, and then with a Colles plaster of Paris cast. FindingsThe brace produced interface pressures over the lower radius in the range of 62.5–90 (mm Hg) and when the bag was completely empty the pressure range was 43–83 mmHg. The initial interface pressures in the Colles casts were in the range of 15–18 mm of Mercury (mm Hg) and when 10 mls were removed from the plastic bag the interface pressure dropped immediately to almost zero. InterpretationThe brace measurements show pressures higher than a Colles cast which compensate for reduction of simulated swelling. It is safe and is potentially the optimal design to achieve significantly improved patient outcomes.