Showing papers on "Shock tube published in 2019"

Ignition delay times of methane and hydrogen highly diluted in carbon dioxide at high pressures up to 300 atm

Abstract: The need for more efficient power cycles has attracted interest in super-critical CO2 (sCO2) cycles. However, the effects of high CO2 dilution on auto-ignition at extremely high pressures has not been studied in depth. As part of the effort to understand oxy-fuel combustion with massive CO2 dilution, we have measured shock tube ignition delay times (IDT) for methane/O2/CO2 mixtures and hydrogen/O2/CO2 mixtures using sidewall pressure and OH* emission near 306 nm. Ignition delay time was measured in two different facilities behind reflected shock waves over a range of temperatures, 1045–1578 K, in different pressures and mixture regimes, i.e., CH4/O2/CO2 mixtures at 27–286 atm and H2/O2/CO2 mixtures at 37–311 atm. The measured data were compared with the predictions of two recent kinetics models. Fair agreement was found between model and experiment over most of the operating conditions studied. For those conditions where kinetic models fail, the current ignition delay time measurements provide useful target data for development and validation of the mechanisms.

Effect of shock waves on thermophysical properties of ADP and KDP crystals

Abstract: Ammonium Dihydrogen Phosphate (ADP) and Potassium Dihydrogen Phosphate (KDP) crystals are grown by slow evaporation method at ambient temperature. The said crystals are utilized as a test specimen and subjected to one-dimensional ‘loading of shock waves’ generated by rupturing a paper diaphragm with Mach number of 1.9 using supersonic low energy table-top shock tube. Thermal diffusivity of crystal is measured using Photoacoustic spectrometer (PAS) for the normal and shock loaded crystals, thermal conductivity and thermal effusivity are computed for the given volumetric specific heat capacity of the crystals. XRD characterization studies reveals that KDP crystal has better immunity to shock wave than ADP crystal.

High-pressure oxidation of propane

Abstract: The oxidation properties of propane have been investigated by conducting experiments in a laminar flow reactor at a pressure of 100 bar and temperatures of 500–900 K. The onset temperature for reaction increased from 625 K under oxidizing conditions to 725 K under reducing conditions. A chemical kinetic model for high pressure propane oxidation was established, with particular emphasis on the peroxide chemistry. The rate constant for the important abstraction reaction C3H8 + HO2 was calculated theoretically. Modeling predictions were in satisfactory agreement with the present data as well as shock tube data (6–61 bar) and flame speeds (1–5 bar) from literature.

Structural, optical, and morphological stability of ZnO nano rods under shock wave loading conditions

Abstract: Shock wave recovery experiment on crystalline materials is a hot research topic for aerospace applications. In this research article, authors present and demonstrate the stability of physical properties of ZnO nano rods (ZnO NRs) under shock wave loaded conditions. The test sample is synthesized by hydrothermal method and the shock waves were generated using a table top semi automatic pressure driven shock tube. A shock wave of 2.2 Mach number which has a transient pressure of 2.0 MPa and temperature 864 K was made to strike four test samples for the counts of 50,100,150 and 200, respectively. The shock loaded samples were subjected to XRD and optical analysis so as to understand the influence of shock waves in the structural and optical properties. The results show that ZnO NRs have magnificent molecular, optical, structural and morphological stability for 50,100 and 150 shocks. Though, when the number of shock pulses was increased to 200 and a blue shift was observed in UV-vis spectrum, no changes in structural properties took place which was evidenced from XRD. From this shock wave recovery experiment, it is clear that ZnO NRs are highly stable against shock waves and hence this material is suggested for the aerospace and military applications.

Single-Laser Krypton Tagging Velocimetry Investigation of Supersonic Air and N 2 Boundary-Layer Flows over a Hollow Cylinder in a Shock Tube

Abstract: The titular technique, KTV, is an important development in the field of laser diagnostics for supersonic and hypersonic flows, as it gives access to unexplored regimes. KTV is not plagued by the fundamental limitations of traditional tracer-particle techniques. The authors investigate the boundary-layer profiles that form over a sharp, hollow cylinder in supersonic flows of air and N${}_{2}$ via a single-laser scheme. With the use of high-repetition-rate lasers, this simple, cost-effective evaluation tool for large facilities will allow for time-resolved measurements of turbulent flows, for $e.g.$ the development of high-speed vehicles such as bullet trains.

Shock-tube study of methane pyrolysis in the context of energy-storage processes

Abstract: The thermal decomposition of methane (10 mol% in inert gases) was investigated behind reflected shock waves. Product spectra were measured via GC/MS after reactions with initial temperatures between 1285 and 2400 K at pressures of 1.5 bar in a single-pulse shock tube and of 30 bar in a high-pressure shock tube with rapid gas sampling via a fast opening valve. In the 1.5-bar experiments, additional time-resolved absorption measurements in the mid-IR were carried out. The temporal variation in CH4 concentration was measured at 836–2495 K and 1.8 bar with interband-cascade lasers near 3.39 µm. Time-resolved temperatures were determined via CO two-line thermometry with two quantum-cascade lasers near 4.56 and 4.85 µm for initial post-shock temperatures of 1715–2573 K at 2.2 bar. The results were compared to simulations based on three different literature mechanisms (Cai and Pitsch, 2015; Porras et al., 2017; Wang et al., 2007) as well as with the new rate constant of methane dissociation from Wang et al. (2016).

Influence of shock waves on structural and morphological properties of copper oxide NPs for aerospace applications

Abstract: The present work is focused on stability of shock wave-exposed copper oxide (CuO) nanoparticles. CuO nanoparticles are synthesized by chemical reduction method and exposed to 100 shock pulses having Mach number 2.4. The table top semiautomatic pressure-driven shock tube is used to generate shock waves for the present experiment. The influence of shock waves on the treated and untreated CuO nanoparticles are explored and characterized by a variety of properties like structural, molecular and morphological details observed using powder XRD, FTIR and SEM, respectively. The powder XRD profile confirmed that there are no lattice defects or any deformation except negligible changes in grain size. SEM images established that the shock wave-loaded CuO nanoparticles have good structural and morphological stability. The obtained results showed that CuO nanoparticles can be used in aerospace, nuclear reactors and high-pressure applications which undergo extreme conditions. The details are presented intensely in the following sections.

Effect of shock waves on structural and dielectric properties of ammonium dihydrogen phosphate crystal

Abstract: Abstract In this research article, the authors pay attention to investigate the effect of structural and dielectric properties of ammonium dihydrogen phosphate (ADP) crystal under pre and post shock loaded conditions. A shock wave of Mach number 1.9 was utilized for the present investigation which was generated by a table-top pressure driven shock tube. The crystalline nature and grain size variations were estimated by powder X-ray diffraction technique. The grain size of post shock wave loaded ADP crystal is found to be larger than that of the pre shock wave loaded ADP crystal. The dielectric properties of the pre and post shock loaded crystals were analyzed by impedance analyzer as a function of frequency (1 kHz–1 MHz) at ambient temperature. The dielectric constant is observed to be varying from 346 to 362 at the frequency of 400 kHz for pre and post shock wave loaded ADP crystals, respectively. The obtained results suggest that shock waves can be an alternate tool to tailor the physical properties of materials without creating any change in the original crystal system and surface morphology.

Shock-tube study of the ignition and product formation of fuel-rich CH4/air and CH4/additive/air mixtures at high pressure

Abstract: Higher-value chemicals can be produced from methane with small exergy losses by partial oxidation if the chemical conversion proceeds in an internal combustion engine (ICE) as a polygeneration process (Gossler and Deutschmann, 2015). Kinetics models are not sufficiently validated for the very fuel-rich and high-pressure conditions relevant for this process. Therefore, ignition delay times of fuel-rich methane/(additive)/air mixtures were measured in a shock tube at about 30 bar and temperatures between 600 and 1650 K. n-heptane and diethylether were used as additives to increase the reactivity of the fuel so that the polygeneration process can be realized in an ICE at HCCI conditions at lower compression temperatures. At ϕ = 2, measured ignition delay times agree well with simulations using different mechanisms from literature. Synthesis gas (CO, H2) is the main product at these conditions (Sen et al., 2016). For the production of higher hydrocarbons, the equivalence ratio must be increased. Very fuel-rich mixtures (ϕ = 10) were used because the temperature increase during the reaction of these mixtures is quite low (

Nonlinear behaviour of convergent Richtmyer-Meshkov instability

Abstract: A novel shock tube is designed to investigate the nonlinear feature of convergent Richtmyer–Meshkov instability on a single-mode interface formed by a soap film technique. The shock tube employs a concave–oblique–convex wall profile which first transforms a planar shock into a cylindrical arc, then gradually strengthens the cylindrical shock along the oblique wall, and finally converts it back into a planar one. Therefore, the new facility can realize analysis on compressibility and nonlinearity of convergent Richtmyer–Meshkov instability by eliminating the interface deceleration and reshock. Five sinusoidal interfaces with different amplitudes and wavelengths are considered. For all cases, the perturbation amplitude experiences a linear growth much longer than that in the planar geometry. A compressible linear model is derived by considering a constant uniform fluid compression, which shows a slight difference to the incompressible theory. However, both the linear models overestimate the perturbation growth from a very early stage due to the presence of strong nonlinearity. The nonlinear model of Wang et al. (Phys. Plasmas, vol. 22, 2015, 082702) is demonstrated to predict well the amplitude growth up to a normalized time of 1.0. The prolongation of the linear increment is mainly ascribed to the counteraction between the promotion by geometric convergence and the suppression by nonlinearity. Growths of the first three harmonics, obtained by a Fourier analysis of the interface contour, provide a first thorough validation of the nonlinear theory.

Shock-wave-induced nucleation leading to crystallization in water

Abstract: It is well known that super-cooled materials can be crystallized under the application of shock waves. This is the first report describing crystallization from unsaturated liquids. Shock-wave-induced crystallization of salts from environmental ground and sea water samples is explored. A table-top pressure-driven shock tube is utilized so as to produce the required shock waves of Mach numbers 1.1, 1.2, 1.4, 2.2 and 4.7. The demonstration comprises a train of acoustic shock pulses applied to the water samples. As a consequence of the impact of the shock waves, the colourless water becomes turbid, following which tiny crystallites are precipitated at the bottom of the vessel after a few minutes. The obtained precipitate is subjected to powder X-ray diffraction and energy-dispersive X-ray spectroscopy analysis to confirm the nature of the settled particles and the elements present in them, respectively. From the observed results, it is concluded that shock-wave-induced crystallization in water provides an alternative method for removing dissolved salts from both ground and sea water samples.

Pyrolysis of Furan and Its Methylated Derivatives: A Shock-Tube/TOF-MS and Modeling Study.

Abstract: In this study, the pyrolysis of furan (F) and its two methyl-substituted derivatives 2-methylfuran (2-MF) and 2,5-dimethylfuran (2,5-DMF) was investigated behind reflected shock waves at pressures ...

Shock Tube Measurement of the C2H4 + H ⇔ C2H3 + H2 Rate Constant.

Abstract: The rate constant for the reaction C2H4 + H ⇔ C2H3 + H2 was studied behind reflected shock waves at temperatures between 1619 and 1948 K and pressures near 10 atm in a mixture of C2H4, CH4, H2, and...

Analysis of mild ignition in a shock tube using a highly resolved 3D-LES and high-order shock-capturing schemes

Abstract: A highly resolved three-dimensional large-eddy simulation (LES) is presented for a shock tube containing a stoichiometric hydrogen–oxygen ( $$\hbox {H}_2$$ / $$\hbox {O}_2$$ ) mixture, and the results are compared against experimental results. A parametric study is conducted to test the effects of grid resolution, numerical scheme, and initial conditions before the 3D simulations are presented in detail. An approximate Riemann solver and a high-order interpolation scheme are used to solve the conservation equations of the viscous, compressible fluid and to account for turbulence behind the reflected shock. Chemical source terms are calculated by a finite-rate model. Simultaneous results of pseudo-Schlieren, temperature, pressure, and species are presented. The ignition delay time is predicted in agreement with the experiments by the three-dimensional simulations. The mechanism of mild ignition is analysed by Lagrangian tracer particles, tracking temperature histories of material particles. We observed strongly increased temperatures in the core region away from the end wall, explaining the very early occurrence of mild ignition in this case.

High-Pressure Oxy-Syngas Ignition Delay Times With CO2 Dilution: Shock Tube Measurements and Comparison of the Performance of Kinetic Mechanisms

Abstract: In this study, syngas combustion was investigated behind reflected shock waves in CO2 bath gas to measure ignition delay times (IDT) and to probe the effects of CO2 dilution. New syngas data were taken between pressures of 34.58–45.50 atm and temperatures of 1113–1275 K. This study provides experimental data for syngas combustion in CO2 diluted environments: ignition studies in a shock tube (59 data points in 10 datasets). In total, these mixtures covered a range of temperatures T, pressures P, equivalence ratios φ, H2/CO ratio θ, and CO2 diluent concentrations. Multiple syngas combustion mechanisms exist in the literature for modeling IDTs and their performance can be assessed against data collected here. In total, twelve mechanisms were tested and presented in this work. All mechanisms need improvements at higher pressures for accurately predicting the measured IDTs. At lower pressures, some of the models agreed relatively well with the data. Some mechanisms predicted IDTs which were two orders of magnitudes different from the measurements. This suggests that there is behavior that has not been fully understood on the kinetic models and is inaccurate in predicting CO2 diluted environments for syngas combustion. To the best of our knowledge, current data are the first syngas IDTs measurements close to 50 atm under highly CO2 diluted (85% per vol.) conditions.

R-branch line intensities and temperature-dependent line broadening and shift coefficients of the nitric oxide fundamental rovibrational band

Abstract: Two quantum cascade lasers were used to measure line intensities and line shape parameters of nitric oxide rovibrational transitions in the R-branch of the fundamental band near 1900 cm − 1 in a heated static cell with temperatures from 294 to 802 K and in a shock tube from 1000 to 2500 K. Pressure in the static cell and shock tube experiments ranged from 0.025 to 1 atm and 1.5 to 3.2 atm, respectively. Collision broadening and pressure shift coefficients along with their temperature dependence were determined for nitrogen, argon, and air collision partners. The line shapes of high J” rovibrational transitions (i.e. R(39.5)–R(43.5)) were measured for the first time at elevated temperatures, where these transitions become sufficiently strong. Additionally, several hot band transitions were measured. Measured line intensities show good agreement with those measured by other researchers and tabulated in the HITRAN databases. Comparisons between the temperature exponents measured in the static cell and shock tube provide evidence that the power law often used to define the temperature dependence of collisional effects does not hold outside the temperature range studied.

Effects of operator splitting and low Mach-number correction in turbulent mixing transition simulations

Abstract: Transition and turbulence decay with the Taylor–Green vortex have been effectively used to demonstrate emulation of high Reynolds-number ( R e ) physical dissipation through numerical convective effects of various non-oscillatory finite-volume algorithms for implicit large eddy simulation (ILES), e.g. using the Godunov-based Eulerian adaptive mesh refinement code xRAGE. The inverse-chevron shock tube experiment simulations have been also used to assess xRAGE based ILES for shock driven turbulent mixing, compared with available simulation and laboratory data. The previous assessments are extended to evaluate new directionally-unsplit high-order algorithms in xRAGE, including a correction to address the well-known issue of excessive numerical diffusion of shock-capturing (e.g., Godunov-type) schemes for low Mach numbers. The unsplit options for hydrodynamics in xRAGE are discussed in detail, followed by fundamental tests with representative shock problems. Basic issues of transition to turbulence and turbulent mixing are discussed, and results of simulations of high- R e turbulent flow and mixing in canonical test cases are reported. Compared to the directional-split cases, and for each grid resolution considered, unsplit results exhibit transition to turbulence with much higher effective R e —and significantly more so with the low Mach number correction.

A high pressure shock tube study of pyrolysis of real jet fuel Jet A

Abstract: A typical Jet A fuel was pyrolyzed in a high-pressure shock tube at 25 and 90 atm under highly diluted conditions from 900 to 2200 K. The key species produced from the pyrolysis process were measured by gas chromatography as a function of the shock temperature. It was found that despite the compositional complexity of the fuel, the major pyrolysis products include a handful of species. They are ethylene, methane, hydrogen, propene, 1-butene, iso-butene, benzene, toluene, acetylene, 1,3-butadiene, allene and propyne, etc. Among them, ethylene is the most dominant species. The HyChem model recently proposed for the same fuel was used for prediction and comparison with the experimental data. Considering that the HyChem model was developed using shock tube and flow reactor data collected over a range of conditions significantly different from those of the current study, the agreement between the current experiment and model prediction is satisfactory. A Monte Carlo analysis was carried out that examined the sensitivities of the model predictions to the rate parameters. The results indicate that the effects of the uncertainties of A factors and those of activation energy are of significance in different temperature regions. Moreover, the low temperature region is dominated by the fuel pyrolysis reactions, while the high temperature region is dominated by the foundational chemistry which describes the pyrolysis and oxidation of fuel pyrolysis products.