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Coalbed methane represents an important kind of natural gas resource in many countries. However, the low-concentration property of coalbed methane limits its applications. To gain insight into the combustion kinetics of coalbed methane and facilitate its combustion utilization, this work reports an experimental and kinetic simulation study on the autoignition properties of methane at ultra-lean and lean conditions. A shock-tube (ST) facility is used for ignition delay time (IDT) measurements with equivalence ratios at 0.5, 0.1, and 0.05 with pressure at 2 and 10 bar under the temperature ranging from 1320 to 1850 K. The measured IDTs can be correlated into a general Arrhenius expression, and the equivalence ratio effect on IDTs is then analyzed. Seven detailed chemical kinetic mechanisms are employed to predict the IDTs and statistical error indicators are used to evaluate their performance. Detailed kinetic analysis via sensitivity and reaction path analysis is performed to uncover the kinetic differences among the seven mechanisms. It is shown that some of the reaction paths only exist in the NUIGMech1.3 mechanism, while the other detailed mechanisms do not consider them. Reaction path analysis indicates that the reactions related to O2, OH and O species become more important compared to the reactions involving CH3 and H radicals as the equivalence ratio decreases from lean to ultra-lean conditions. Detailed chemical kinetics analysis is also conducted to demonstrate the uncertainty of key reactions. The present work should be valuable to gain insight into the methane ignition characteristics and to facilitate kinetic mechanism optimization of methane combustion.

This research has investigated the effect of reinforcement corrosion on the flexural response of reinforced concrete beams subjected to blast loading. Five beams, with and without corrosion, were tested under blast loads using a shock‐tube. The corroded specimens were subjected to an accelerated corrosion regime prior to testing, with a mass loss of up to 22% in the longitudinal steel reinforcement over the mid‐span or full‐span regions. A companion set of two beams was tested under quasi‐static four‐point bending. The results from the static tests show that corrosion of the longitudinal reinforcement decreased the strength and ductility, and ultimately changed the failure mode from ductile to brittle. Under blast loading, the steel corrosion increased maximum displacements and support rotations, reduced blast capacity, increased damage and fragmentation, and led to more brittle failure as the % mass loss increased. The effects of corrosion on blast response were moderate when the steel was corroded over the full‐span region. Furthermore, the blast response of the beams was predicted using dynamic inelastic single‐degree‐of‐freedom (SDOF) analysis, with the resistance functions developed using 2D finite element modeling, while accounting for the reduction in steel stress–strain properties and corrosion‐induced cracking. The SDOF analysis showed acceptable results in terms of ability to predict maximum displacements of the flexural‐governed beams (corroded and un‐corroded). [ABSTRACT FROM AUTHOR]

Coalbed methane represents an important kind of natural gas resource in many countries. However, the low-concentration property of coalbed methane limits its applications. To gain insight into the combustion kinetics of coalbed methane and facilitate its combustion utilization, this work reports an experimental and kinetic simulation study on the autoignition properties of methane at ultra-lean and lean conditions. A shock-tube (ST) facility is used for ignition delay time (IDT) measurements with equivalence ratios at 0.5, 0.1, and 0.05 with pressure at 2 and 10 bar under the temperature ranging from 1320 to 1850 K. The measured IDTs can be correlated into a general Arrhenius expression, and the equivalence ratio effect on IDTs is then analyzed. Seven detailed chemical kinetic mechanisms are employed to predict the IDTs and statistical error indicators are used to evaluate their performance. Detailed kinetic analysis via sensitivity and reaction path analysis is performed to uncover the kinetic differences among the seven mechanisms. It is shown that some of the reaction paths only exist in the NUIGMech1.3 mechanism, while the other detailed mechanisms do not consider them. Reaction path analysis indicates that the reactions related to O 2 , OH and O species become more important compared to the reactions involving CH 3 and H radicals as the equivalence ratio decreases from lean to ultra-lean conditions. Detailed chemical kinetics analysis is also conducted to demonstrate the uncertainty of key reactions. The present work should be valuable to gain insight into the methane ignition characteristics and to facilitate kinetic mechanism optimization of methane combustion., Competing Interests: We declare that we have no financial and personal relationship with other people or organization that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be constructed as influencing the position presented in, or the review of, the paper entitled., (© 2024 The Authors.)

Predicting the onset, style and duration of explosive volcanic eruptions remains a great challenge. While the fundamental underlying processes are thought to be known, a clear correlation between eruptive features observable above Earth's surface and conditions and properties in the immediate subsurface is far from complete. Furthermore, the highly dynamic nature and inaccessibility of explosive events means that progress in the field investigation of such events remains slow. Scaled experimental investigations represent an opportunity to study individual volcanic processes separately and, despite their highly dynamic nature, to quantify them systematically. Here, impulsively generated vertical gas-particle jets were generated using rapid decompression shock-tube experiments. The angular deviation from the vertical, defined as the "spreading angle", has been quantified for gas and particles on both sides of the jets at different time steps using high-speed video analysis. The experimental variables investigated are 1) vent geometry, 2) tube length, 3) particle load, 4) particle size, and 5) temperature. Immediately prior to the first above-vent observations, gas expansion accommodates the initial gas overpressure. All experimental jets inevitably start with a particle-free gas phase (gas-only), which is typically clearly visible due to expansion-induced cooling and condensation. We record that the gas spreading angle is directly influenced by 1) vent geometry and 2) the duration of the initial gas-only phase. After some delay, whose length depends on the experimental conditions, the jet incorporates particles becoming a gas-particle jet. Below we quantify how our experimental conditions affect the temporal evolution of these two phases (gas-only and gas-particle) of each jet. As expected, the gas spreading angle is always at least as large as the particle spreading angle. The latter is positively correlated with particle load and negatively correlated with particle size. Such empirical experimentally derived relationships between the observable features of the gas-particle jets and known initial conditions can serve as input for the parameterisation of equivalent observations at active volcanoes, alleviating the circumstances where an a priori knowledge of magma textures and ascent rate, temperature and gas overpressure and/or the geometry of the shallow plumbing system is typically chronically lacking. The generation of experimental parameterisations raises the possibility that detailed field investigations on gas-particle jets at frequently erupting volcanoes might be used for elucidating subsurface parameters and their temporal variability, with all the implications that may have for better defining hazard assessment. [ABSTRACT FROM AUTHOR]

• New experiemental IDTs for binary bleneded C 2 –C 3 alkanes/alkene are presented. • Newly developed NUIGMech1.1 is evaluated versus the newly taken IDTs. • NUIGMech1.1 predicts the IDTs accurately over the wide range of studied conditions. • Some correlations were derived based on NUIGMech1.1. • The correlations satisfactorily anticipated IDTs data within the studied range. In this work, the ignition delay time characteristics of C 2 – C 3 binary blends of gaseous hydrocarbons including ethylene/propane and ethane/propane are studied over a wide range of temperatures (750 – 2000 K), pressures (1 – 135 bar), equivalence ratios (φ = 0.5 – 2.0) and dilutions (75 – 90%). A matrix of experimental conditions is generated using the Taguchi (L 9) approach to cover the range of conditions for the validation of a chemical kinetic model. The experimental ignition delay time data are recorded using low- and high-pressure shock tubes and two rapid compression machines (RCM) to include all of the designed conditions. These novel experiments provide a direct validation of the chemical kinetic model, NUIGMech1.1, and its performance is characterized via statistical analysis, with the agreement between experiments and model being within ~ 26.4% over all of the conditions studied, which is comparable with a general absolute uncertainty of the applied facilities (~ 20%). Sensitivity and flux analyses allow for the key reactions controlling the ignition behavior of the blends to be identified. Subsequent analyses are performed to identify those reactions which are important for the pure fuel components and for the blended fuels, and synergistic/antagonistic blending effects are therefore identified over the wide range of conditions. The overall performance of NUIGMech1.1 and the correlations generated are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Cyclopentane is a suitable naphthene, or cycloalkane, in a palette for multi-component gasoline surrogate fuels due to its presence in market fuels and its relevance to alkyl substituted cyclopentanes also present. However, the previous oxidation studies of cyclopentane have primarily focused on neat mixtures. Blending cyclopentane with dimethyl ether in this work therefore serves to inform our understanding of, and improve predictive models for, multi-component mixtures. In this work, the auto-ignition of cyclopentane/dimethyl ether blends was studied in a high-pressure shock tube and in a rapid compression machine. A wide range of temperatures (650 – 1350 K) and elevated pressures of 20 and 40 bar were studied at equivalence ratios of 0.5, 1.0 and 2.0 in air for two blending ratios (30/70 and 70/30 mole% cyclopentane/di-methyl ether mixtures). A detailed kinetic model for cyclopentane was revised to capture the measured ignition delay times and apparent heat release rates in this study. Literature ignition delay time, jet-stirred reactor, and laminar burning velocity measurements of neat cyclopentane were used as additional validation. Improvements to the kinetic model were based on recent literature studies related to sub-models including cyclopentene and cyclopentadiene which allowed the removal of previous local rate-constant optimizations. Low temperature reactivity of cyclopentane was found to be controlled by the branching ratio between concerted elimination of HȮ 2 and the strained formation of Q ˙ OOH radicals in agreement with previous studies. In this study, the low branching ratio of Q ˙ OOH formation increases the influence of a competing consumption pathway for cyclopentyl-peroxy (CPTȮ 2 J) radicals. The sensitivity of the simulated ignition delay times to the formation of cyclopentyl hydroperoxide (CPTO 2 H), from CPTȮ 2 J and HȮ 2 , is discussed. The current model is used to analyze the influence of dimethyl ether on the reactivity of cyclopentane in the context of previous literature studies of dimethyl ether binary blends with ethanol and toluene. [ABSTRACT FROM AUTHOR]

We report state-resolved absorption cross-section measurement and oscillator-strength evaluation of the gas-phase iron oxide (FeO) orange system near 611 nm. Intracavity absorption spectroscopy (ICAS) with a homemade broadband dye laser was applied for time-resolved measurements of absorption spectra of shock-activated mixtures of iron pentacarbonyl and carbon dioxide (diluted in argon), generating gas-phase FeO. The measurements were performed with a time resolution of 170 µs in the spectral range of 16,316–16,353 cm−1 that includes a large number of FeO absorption lines. Across the 8-cm diameter of the shock tube, ICAS leads to an effective absorption path length of 260 m. Absorption cross-section values of 0.5 × 10–18–4 × 10–18 cm2 were determined for temperatures around 2200 K and pressures of ∼1.3 bar. Pressure- and temperature-independent oscillator strengths for individual ro-vibronic transitions within the 611-nm band of FeO orange system are reported for the first time. These data are generally applicable for quantitative absorption measurements of flame studies of iron chemistry, where FeO plays a key role as intermediate species. [ABSTRACT FROM AUTHOR]

Shock‐tube detonators, used in the mining industry to initiate charges of blasting explosives, often contain pyrotechnic delay‐lines for controlling the sequence of blasts. Traditionally, delay‐lines consist of pyrotechnic compounds of toxic metals such as lead which are pressed into the metallic tubing. Since lead is well‐known to be a hazard both to people and the environment, lead‐free alternatives were investigated to create a delay‐line composition. Further, to create delay‐lines cheaply and reproducibly, a composition was developed that could be printed onto a substrate. Screen printing was investigated for this purpose. The pyrotechnic ink that we developed consists of two inert inks (a fuel and an oxidiser) so that it can be stored and transported safely and conveniently without being classified as an energetic. After being transported to its destination, the two inks can be mixed to form an energetic (wet) ink, printed, and used as a delay‐line when dry. A silicon‐bismuth trioxide composition bonded together using nitrocellulose was found to be a suitable ink for screen printing. The burning rate was measured as 52±7 mm s−1 for a thickness of 100 μm. This thickness reduces the raw delay‐line material by over 90 % compared to traditional 3D delay‐lines. The target burning rate was 24 mm/s, but the measured rate is sufficiently close to this that changes in geometry could meet this requirement. The critical thickness for a self‐sustainable burn was measured as 40±5 μm. The thermal output and viscosity of the ink were determined as functions of the particle size. The viscosity of the ink was determined as 7.04±0.05 Pa s, which is suitable for screen printing. Milling was used to reduce the particle size below 1 μm. Ignition of the printed delay‐line using shock tubing was achieved through overprinting with a shock‐sensitive ink. The burning rate of a delay‐line is one of its most defining properties when used in mining applications. Thus the effect on the delay‐line's burning rate of the pyrotechnic composition printed thickness, and the ink solvent was investigated. We found that the burning rate could be modified by changing the silicon content in the pyrotechnic, and to some extent, by adding aluminum. Adding a third, slowly evaporating solvent, to the ink vehicle was found to reduce the critical thickness to less than 40 μm, decrease the burning rate to 46±7 mm s−1, and enhance the ink's flow properties. We found that the width of printed lines did not affect the burning rate for widths between 1–5 mm. This is an interesting result and could be used to determine the most cost‐effective shape to produce printed delay‐lines. Ignition of the printed delay‐line using shock tubing was achieved through overprinting with a shock‐sensitive ink. [ABSTRACT FROM AUTHOR]

• A series of HSC beams with 690 MPa bars are tested under blasts and influence of steel/concrete grade is investigated. • Use of high-strength bars increases blast resistance and improves control of displacements. • Results show importance of not exceeding the balanced steel ratio and show HSC is better adapted for beams with HSR bars. • Dynamic inelastic SDOF analysis is used to predict the blast response of the HSC beams with HSR bars. The work reported in this paper is aimed towards better understanding the behavior of reinforced concrete flexural members built with high-strength reinforcement (HSR) under blast loading. As part of the study, a series of high-strength concrete (HSC) beams built with ASTM A1035 Grade 690 MPa bars are tested under simulated blast loads using a shock-tube. Parameters investigated include the effect of steel type (Grade 690 MPa vs. 400 MPa), concrete strength (100 MPa vs. 50 MPa) and reinforcement ratio (ρ = 1%–2.2%). The effect of loading rate is investigated by testing a companion set of beams under slowly applied (quasi-static) loading. The results show that use of high-strength steel in HSC beams results in increased blast capacity and improved control of displacements at equivalent blasts. The use of high-strength concrete is also found to be better suited for beams reinforced with high-strength bars. The results further demonstrate the importance of ensuring beams designed with high-strength bars are under-reinforced and provided with sufficient shear reinforcement. The blast response of the beams is predicted analytically using dynamic analysis. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterize the effects of various UHPFRC strengthening configurations on the blast performance of reinforced concrete (RC) beams. The methodology involved blast tests on eight as-built and UHPFRC-retrofitted RC beams using a pneumatically-driven shock-tube. The 150 mm × 200 mm × 2440 mm beams were first cast with 40 MPa concrete and were retrofitted by replacing the 20 mm cover with UHPFRC. The studied parameters included the influence of UHPFRC applied on the tension face, or in the form of U, Full or localized jackets, under single or repeated blast loads. The first set included one as-built beam and three specimens with tension-sided (T), U-jacket (UJ) or full jacket (FJ) retrofits, and were tested under repeated and gradually increasing blast pressures (P r = 16, 38 and 50 kPa, for Blasts 1, 2 and 3). The second set included one as-built beam and two specimens with full-jacket retrofits applied over the full span (FJ) or in the middle hinge region (FJ-Hinge). The final beam had a hybrid of the T-sided and FJ-Hinge schemes. These beams were tested under single Blast 3 loads, and then tested under static bending to assess their residual capacity. In the first set, all retrofits resulted in reduced displacements (ranging from 30% to 60%) when compared to the as-built beam; however, the repeated blasts ultimately led to crack localization and rupture of the tension steel bars. In the second set, both the full-span and localized hinge schemes led to reductions in damage and displacements (ranging from 20% to 40%), without bar fracture, along with significant residual capacity. Finite element (FE) modelling using LS-DYNA was used to predict the blast behavior of the beams. After validation, the models were used to study the effects of the longitudinal steel ratio and blast load scenario on the behaviour and failure mode of the beams. Increasing the steel ratio was found to be effective in preventing bar rupture, while this failure mode was more likely under repeated blast loading. • Results from blast tests on 8 as-built and UHPFRC-retrofitted beams are presented. • Various retrofits are studied, including T, UJ, FJ and localized FJ-hinge designs. • For repeated blasts, T-UJ-FJ designs reduced displacements, but showed bar rupture. • For single blasts, FJ and FJ-hinge designs improved blast and post-blast response. • FE models were validated and used to study effects of steel ratio and blast scenario. [ABSTRACT FROM AUTHOR]

Highlights • Ten high-strength concrete beams are tested under quasi-static & blast loads. • Effects of concrete strength and steel reinforcement detailing are investigated. • Failure mode and resistance under static and dynamic loading are compared. • HSC beam response is predicted using dynamic inelastic SDOF analysis. Abstract This paper presents the results of study examining the blast performance of reinforced concrete beams constructed with high-strength concrete (HSC). As part of the experimental program, a series of five beams are tested under simulated blast loading using a high-capacity shock-tube at the University of Ottawa. Parameters investigated include the effect of concrete strength, shear reinforcement and longitudinal reinforcement ratio. The effect of loading rate is investigated by testing a companion set of five beams with identical properties under slowly applied (quasi-static) loading. The results show that increasing the reinforcement ratio improves the blast performance of HSC beams by increasing overall blast capacity and reducing maximum and residual displacements at equivalent blast loads. The effect of concrete strength on blast performance is found to be more limited, with companion normal-strength and high-strength concrete beams showing similar performance. The results also confirm the importance of providing transverse reinforcement to prevent blast-induced shear failures in HSC beams. As part of the analytical study, the blast response of the HSC beams is predicted using dynamic inelastic single-degree-of-freedom (SDOF) analysis. [ABSTRACT FROM AUTHOR]

The paper presents the results of studies of low-speed detonation processes in shock-tubes. The complex methodology of experimental studies of basic performance of the tubular detonating waveguide providing a sufficient degree of accuracy with an error of no more than 5% is applied. The mechanism of initiation by an electric explosive, development and low-speed damping of the shock front in the fiber cladding material deposited without explosives and detonation formation process along the length of the waveguide with a deposited layer of explosives is established. The points of its nucleation and growth to maximum velocity of detonation in the area of 0.5 m length and maintaining it at a constant level over the whole length in the range of values (for test samples) of about 1000 m/s are fixed. [ABSTRACT FROM AUTHOR]

The analysis of reactive systems in combustion science and technology relies on detailed models comprising many chemical reactions that describe the conversion of fuel and oxidizer into products and the formation of pollutants. Shock-tube experiments are a convenient setting for measuring the rate parameters of individual reactions. The temperature, pressure, and concentration of reactants are chosen to maximize the sensitivity of the measured quantities to the rate parameter of the target reaction. In this study, we optimize the experimental setup computationally by optimal experimental design in a Bayesian framework. We approximate the posterior probability density functions (pdf) using truncated Gaussian distributions in order to account for the bounded domain of the uniform prior pdf of the parameters. The underlying Gaussian distribution is obtained in the spirit of the Laplace method, more precisely, the mode is chosen as the maximum a posteriori (MAP) estimate, and the covariance is chosen as the negative inverse of the Hessian of the misfit function at the MAP estimate. The model related entities are obtained from a polynomial surrogate. The optimality, quantified by the information gain measures, can be estimated efficiently by a rejection sampling algorithm against the underlying Gaussian probability distribution, rather than against the true posterior. This approach offers a significant error reduction when the magnitude of the invariants of the posterior covariance are comparable with the size of the bounded domain of the prior. We demonstrate the accuracy and superior computational efficiency of our method for shock-tube experiments aiming to measure the model parameters of a key reaction, which is part of the complex kinetic network describing the hydrocarbon oxidation. In the experiments, the initial temperature and fuel concentration are optimized with respect to the expected information gain in the estimation of the parameters of the target reaction rate. We show that the expected information gain surface can change its 'shape' dramatically according to the level of noise introduced into the synthetic data. The information that can be extracted from the data saturates as a logarithmic function of the number of experiments, and few experiments are needed when they are conducted at the optimal experimental design conditions. Furthermore, inversion of the legacy data indicates the validity and robustness of our designs. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A high pressure shock tube “HPST” has been designed and validated for the purpose of chemical kinetics studies at elevated pressures and temperatures. Using this facility, auto-ignition investigations are conducted for methane at 10, 20 and 40 bar and temperatures from 1400 K up to 2000 K. Three equivalence ratios ( ϕ = 0.5, 1 and 2) for a methane/oxygen/argon mixture were studied in this paper under diluted conditions (argon > 90%). Experimental data showed good agreement with previous literature measurements and predictions from three different chemical kinetic models (Aramco Mech 1.3, USC Mech II and GRI Mech 3.0) commonly used in the literature, which confirms the quality of the experimental data obtained with the new high pressure shock tube and allows the expansion of the validation range of the mechanisms for ignition delay times to higher pressures. The investigations performed to explain the differences observed for ignition delay times predictions highlighted an important sensitivity of the USC mechanism predictions to equivalence ratio and an important sensitivity to CH 3 + O 2 reactions. Finally, the impact of pressure and equivalence ratio on ignition delay time is evaluated over a broad range of pressure (1–50 bar) and equivalence ratio ( ϕ = 0.2–3). [ABSTRACT FROM AUTHOR]

The kinematic and thermal coupling between pyroclasts and gas is one of the main controlling factors in the dynamics of explosive volcanic eruptions. Here, we performed rapid decompression experiments in a shock-tube apparatus at eruptive pressures (2–11 MPa) using monodisperse volcanic particles (grain-size 0.063–1.4 mm). We systematically investigated the coupling of these particles with the gas phase by measuring the rarefaction speed and the ejection velocity of the particles front in each experiment. The results are consistent with a theoretical model derived from the pseudogas approximation (i.e. perfect coupling) only for particles smaller than a certain size: ∼ 0.125 mm for rarefaction speed and ∼ 0.5 mm for the particles front ejection velocity, whereas larger particles are significantly decoupled. We present an experimental parameterization to calculate the kinematic Stokes number (St k). We show that: 1) for the ejection process the particles are coupled with the gas if St k < 1, whereas for the rarefaction speed the particles are fully coupled when St k < 0.2; 2) for the rarefaction speed there is a transition when 0.2 < St k < 1; and 3) in both processes particles are decoupled when St k > 1. Furthermore, where the Reynolds number based on the relative velocity between gas and particles (Re p) is larger than 103, the ratio between the timescales required for thermal and kinematic equilibration increases with Re p , such that some particles are coupled with the gas but decoupled from it thermally. These findings represent the first experimental delineation of kinematic and thermal coupling regimes between volcanic particles and gas and contribute thereby to a more robust basis for multiphase explosive eruptive models. • We have measured ejection and rarefaction velocities in rapid decompression experiments. • We experimentally delineated the size of the particles coupled with the gas phase. • Three coupling regimes were delineated in terms of the Stokes number. • The thermal relaxation time is longer than the kinematic for high Reynolds numbers • Our results strengthen the experimental basis enabling multiphase eruptive models. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study examining the blast load performance of ultra-high performance fiber reinforced concrete (UHPFRC) columns. As part of the experimental program nine full-scale columns constructed with compact reinforced composite (CRC), a proprietary UHPFRC, were tested under simulated blast loading and exposed to varying blast pressure–impulse combinations using a shock-tube. Parameters considered in this study include concrete type, fiber content, fiber properties, transverse reinforcement spacing and longitudinal reinforcement ratio. The results demonstrate that the use of UHPFRC significantly improves the blast performance of reinforced concrete columns by reducing maximum and residual displacements, enhancing damage tolerance, and eliminating secondary blast fragments. The results also indicate that fiber content, fiber properties, seismic detailing and longitudinal reinforcement ratio are important factors that can affect the blast load behavior and failure mode of UHPFRC columns. The analytical investigation examines the suitability of using single-degree-of-freedom (SDOF) analysis to predict the blast response of the UHPFRC columns tested in the research program. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new characterization technique for air-coupled ultrasound probes is presented. [•] A dedicated shock tube is designed to generate a controlled pressure wave. [•] A shock wave with low pressure and high frequency content is generated. [•] A quantitative transfer function for air-coupled ultrasound probe is measured. [Copyright &y& Elsevier]

Abstract: A discrete equation method (DEM) for the simulation of compressible multiphase flows including real-gas effects is illustrated. A reduced five equation model is obtained starting from the semi-discrete numerical approximation of the two-phase model. A simple procedure is then proposed for using a more complex equation of state, thus improving the quality of the numerical prediction. Classical test-cases well-known in literature are performed featuring a strong importance of thermodynamic complexity for a good prediction of temperature evolution. Finally, a computational study on the occurrence of rarefaction shock waves (RSW) in a two-phase shock tube is presented, with dense vapors of complex organic fluids. Since previous studies have shown that a RSW is relatively weak in a single-phase (vapor) configuration, its occurrence and intensity are investigated considering the influence of the initial volume fraction, initial conditions and the thermodynamic model. [Copyright &y& Elsevier]

New CO and H 2 O time histories were measured for 2-Methyl-1-Butene (2M1B) behind reflected shock waves. The experimental setup was developed to simultaneously obtain carbon monoxide and water time histories from the oxidation of 2M1B in 99.5% He/Ar (20% He and 79.5% Ar). The experiments were carried out at three different equivalence ratios (ɸ = 0.5, 1.0, and 2.0) at pressures and temperatures ranging from 1.15 atm to 1.32 atm and 1414 K to 1894 K, respectively. A very limited number of studies focusing on 2M1B are available in the literature, and no model is designed specifically for this C5 alkene, as opposed to its other isomers: 1-pentene (1-C 5 H 10), 2-pentene (2-C 5 H 10), 3-Methyl-1-Butene (3M1B), and 2-Methyl-2-Butene (2M2B). Experimental profiles were compared to recent literature models containing a 2M1B sub-mechanism. Numerical predictions using the AramcoMech 3.0 and Ruwe et al. mechanisms show that the combustion behavior of 2M1B is not well captured by these recent detailed kinetics models. More importantly, Cheng et al. proposed a modified version of AramcoMech 3.0 with improvements on the 1-C 5 H 10 and 2M2B sub-mechanisms, which deteriorates the mechanism's performance for 2M1B. Similarly, Power et al. had modified AramcoMech 3.0 on the sub-mechanisms for 1-C 5 H 10 and 2-C 5 H 10 , but it does not reproduce H 2 O and CO time histories any better. The Dong et al. model is accurate within 10% when considering only the induction delay times, but it shows discrepancies for the concentration levels. The present study used an updated, detailed chemical kinetics model, and this mechanism was able to capture the experimental results with suitable precision, giving the best predictions. [ABSTRACT FROM AUTHOR]

Correct evaluation of the hydrodynamic loads induced by large and rapid pressure waves propagating with the speed of sound along the reactor piping systems and Reactor Pressure Vessel (RPV) is an important and difficult issue in nuclear power plant safety. The pressure shock transients and resulting hydrodynamic loads on the pipes and RPV structures are commonly calculated with one-dimensional thermo-hydraulic system codes such as RELAP5, TRACE, DRAKO and ROLAST. In Sweden, the most widely used computer code for this purpose is RELAP5. This code needs, therefore, to be assessed for its capability to predict pressure wave behavior. The conducted assessment involves simulations of single- and two-phase shock-tube problems and two-phase blowdown as well as water hammer experiments. The performed numerical experiments clearly show that RELAP5, with the proper time step and spatial mesh size, is capable of predicting the complex dynamics of single- and two-phase pressure wave phenomena with good to reasonable accuracy. [ABSTRACT FROM AUTHOR]

In this work, the authors introduce the shock-tube model for a hydrothermal eruption in a geothermal reservoir. The governing equations, based on the multiphase Euler equations and a Darcy-type law, are solved using a three-phase weighted sub-system numerical solver. Results are then presented which show the importance of the geometry of the geothermal reservoir in predicting the initiation of a hydrothermal eruption. In particular, the porosity, permeability, and cohesion of the reservoir are shown to significantly affect the pressure difference required to initiate an eruption. Finally, the authors show the importance of the initial liquid water/water vapour volume fractions in determining the size of an eruption, and further show boiling to be of major importance. [ABSTRACT FROM AUTHOR]

Abstract: Because of a wide number of applications, the potential hazards of H2-CH4-air mixtures have to be characterised. For hazard evaluation, an important element is a reliable detailed kinetic scheme. In the present study, three modern kinetic models, those of Konnov, of Dagaut and the GRI-mech 03, have been evaluated with respect to a large set of experimental data, including species profiles obtained in jet-stirred reactor, laminar flame speed, ignition delay time and detonation cell size, for hydrogen-methane-air mixtures. For jet-stirred reactor data, the model of Dagaut provides significantly better results. For flame speed data modeling, the three models are as reliable. For ignition delay times, the model of Dagaut seems the most reliable. For detonation cell size predictions, the model of Konnov is the best. Important chemical reactions are underlined through sensitivity and reaction pathway analysis and are discussed in the frame of rate constant values recommended by Baulch et al. [Copyright &y& Elsevier]

Abstract: The dynamics of magma fragmentation is a controlling factor in the behavior of explosive volcanic eruptions. If porous magma is sufficiently decompressed, a fragmentation front develops and travels through the magma at a certain speed (fragmentation speed) while the resulting particles are being ejected. To investigate the influence of the fragmentation process on eruption dynamics, we have performed fragmentation experiments in a shock-tube apparatus using natural volcanic samples with diverse porosities and different applied pressures (4–20MPa). For each experiment, we simultaneously measured the fragmentation speed and ejection velocities. The results are consistent with a theoretical model based on a 1-D shock-tube theory considering the conservation laws across the fragmentation front. Our results show that a certain pressure threshold has to be exceeded for fragmentation and ejection of the particles to take place and that the fragmentation speed determines the initial conditions of the expansion of the gas–particle mixture. The fragmentation process has a controlling influence on the velocity, density and mass discharge rate per unit area of the gas–particle mixture, all factors which can affect eruption dynamics significantly. The model presented herein may help describe the dynamics of Vulcanian eruptions and improve hazard assessment. [ABSTRACT FROM AUTHOR]

Abstract: Oxidation of n-nonane (n-C9H20) under conditions of high dilution (>97% inert) has been studied over a broad range of temperature (530< T (K)<1591) and equivalence ratio (ϕ =0.5, 1.0, 2.0) at pressures near 1 and 10atm using shock-tube and jet-stirred reactor facilities. Excited-state hydroxyl radical (OH∗) time histories were measured using emission spectroscopy of the A2Σ+ →X2Π transition of OH behind reflected shock waves from which ignition delay and peak formation times were extracted. Temperature-dependent species concentrations were measured using gas chromatography, FTIR, TCD, and FID of jet-stirred reactor combustion products. Ignition delay times show a strong dependence on equivalence ratio, increasing by a factor of nearly 5 at both 1 and 10.4atm. An overall ignition delay time correlation was constructed, revealing a pressure dependence of P −0.48. Experimental data from both facilities were utilized to develop and validate a chemical kinetics mechanism for n-nonane oxidation. Kinetic model predictions of ignition delay time compare well, particularly for the lean and stoichiometric mixtures. Jet-stirred reactor data show excellent overall agreement with major species, as well as alkanes and alkenes present in the combustion products. Alkenes up to C9 were produced from n-nonane oxidation and ethylene, a dominant product of n-nonane thermal decomposition, is identified as the most abundant among them. The present study provides an extensive series of fundamental measurements on n-nonane oxidation, resulting in the formulation of a mechanism used to describe and predict associated reaction kinetics. [ABSTRACT FROM AUTHOR]

Abstract: Rapid compression machine and shock-tube ignition experiments were performed for real fuel/air isobutane mixtures at equivalence ratios of 0.3, 0.5, 1, and 2. The wide range of experimental conditions included temperatures from 590 to 1567K at pressures of approximately 1, 10, 20, and 30atm. These data represent the most comprehensive set of experiments currently available for isobutane oxidation and further accentuate the complementary attributes of the two techniques toward high-pressure oxidation experiments over a wide range of temperatures. The experimental results were used to validate a detailed chemical kinetic model composed of 1328 reactions involving 230 species. This mechanism has been successfully used to simulate previously published ignition delay times as well. A thorough sensitivity analysis was performed to gain further insight to the chemical processes occurring at various conditions. Additionally, useful ignition delay time correlations were developed for temperatures greater than 1025K. Comparisons are also made with available isobutane data from the literature, as well as with 100% n-butane and 50–50% n-butane–isobutane mixtures in air that were presented by the authors in recent studies. In general, the kinetic model shows excellent agreement with the data over the wide range of conditions of the present study. [Copyright &y& Elsevier]

Abstract: During the last decade, the laser desorption/ionization time-of-flight mass spectrometry (LDIToFMS) development has provided the opportunity to improve the understanding of the soot formation process. Combining LDIToFMS and shock-tube allows the study of adsorbed compounds on aged soot formed at constant and well defined temperature. The present work investigates effects of fuel structure (with 2-methyl-2-butene (2M2B)), fuel molecular composition (with thiophene, C4H4S) and the presence of oxygen (with toluene in pyrolysis and at an equivalence ratio of 18) on the composition of the adsorbed phase. The evolution, with the temperature behind reflected shock waves, of the soot induction delay time and the soot yield was also investigated from highly diluted mixtures in argon. LDIToFMS results show that PAHs were detected on soot. The mass range of PAHs is dependant on the fuel and on the temperature. The amount of species adsorbed on soot surface was found to be inversely proportional to the soot yield. A dominant sequence of benzenoid PAHs, with a 24-amu increment between peaks, is observed whatever the initial fuel or condition (temperature, presence of oxygen). A second sequence of five membered ring PAHs was also observed with a 12-amu increment between peaks of the benzenoid sequence. The signal intensity of this five membered ring PAHs sequence depends strongly on the temperature, the presence of oxygen and the structure the fuel. The presence of a sulphur atom in the structure of the initial fuel leads to the detection of small amounts of compounds adsorbed on soot which contain sulphur atom(s) and with a PAH-like structure. [Copyright &y& Elsevier]

New experimental results were obtained for the oxidation of 1,2-dimethylbenzene in a jet-stirred reactor (JSR) at atmospheric pressure in dilute conditions over the temperature range 900-1400 K, and variable equivalence ratio (0.5 ≤ ϕ ≤ 1.5). The data consisted of concentration profiles vs. temperature for the reactants, stable intermediates and final products, measured by sonic probe sampling followed by on-line GC-MS analyses and off-line GC-TCD-FID and GC-MS analyses. The ignition of 1,2-dimethylbenzene-oxygen-argon mixtures was measured behind reflected shock waves over the temperature range 1400-1830 K, at 1 atm, and variable equivalence ratio (0.5 ≤ ϕ ≤ 2.0), using a shock tube (ST). The oxidation and ignition of 1,2-dimethylbenzene under respectively JSR and ST conditions were modeled using a detailed chemical kinetic reaction mechanism (219 species and 1545 reactions, most of them reversible) deriving from a previous scheme proposed for the ignition, oxidation, and combustion of simple aromatics (benzene, toluene, styrene, n-propyl-benzene, 1,3-dimethylbenzene, and 1,4-dimethylbenzene). Sensitivity analyses and reaction path analyses, based on rates of reaction, were used to interpret the results. This study showed the reactivity of 1,2-dimethylbenzene is higher than that of 1,3-dimethylbenzene and 1,4-dimethylbenzene under the above conditions. [ABSTRACT FROM AUTHOR]

A unique hand-held needle-free powder injection system, using a transient shock-tube flow to deliver powder genes and drugs into human skin for a wide range of treatments, has been proposed. In the development of such devices, a strong non-linear phenomenon, possibly shock process instead of unsteady expansion waves, was observed in the driver portion of the shock-tube flow in the presence of a gas micro-cylinder. In this paper, we further investigate effects of a model micro-cylinder in the driver on the gas dynamics of a prototype clinical device numerically. To accurately simulate such complex shock-tube flows, an efficient numerical solver, MIFVS, is extended to incorporate with a transition-modified turbulence model. Comparison with experimental measurements shows that the extended MIFVS accurately predicts pressure traces in both laminar and turbulent regimes. The separation zone due to a strong non-linear process is properly captured via such transition-modified turbulence model. Numerical investigations and discoveries are presented and discussed. [Copyright &y& Elsevier]

Abstract: The present work addresses the soot formation parameters behind reflected shock waves and the identification of adsorbed species on their surface. Soot induction delay times and yields have been experimentally determined in the case of toluene pyrolysis highly diluted in argon for the following conditions: the initial carbon atoms concentration was kept constant around 1×1018 C atomscm−3, reflected shock pressure and temperature ranges of 1135–1600kPa and 1470–2230K, respectively. The decrease of the induction time, as the temperature is raised, was described using an Arrhenius type expression while, for the bell-shaped evolution of the soot yield versus the temperature, a modified Gaussian expression was derived. Using TEM analysis, the mean particle diameter was found to decrease from 35 to 20nm as the temperature is raised from 1475 to 2135K. The micro-texture of the soot sample was found to vary as the temperature is raised, leading to a more organised structure. The adsorbed species on these soot were characterized using laser desorption/ionization time of flight mass spectrometer. Results indicate that for temperatures below 1600K, PAHs in the 178–572 atomic mass units (amu) range were identified. PAHs range was limited to 178–374amu above 1900K and they were of benzenoid type above 1600K. The amount of species adsorbed on the soot surface was found to be inversely proportional to the soot yield with a maximum for the lower temperature domain. [Copyright &y& Elsevier]

The combustion kinetics of n-pentane was fully investigated for the first time. Ignition delay times of n-CH and Oxygen diluted in Argon mixtures were measured over a wide range of compositions, pressures and temperatures. The 240 shocks were statistically correlated and this correlation was compared to two known kinetic schemes, those of Warnatz and of Westbrook. The schemes needed corrections which are discussed here. [ABSTRACT FROM AUTHOR]