The Experts below are selected from a list of 3795 Experts worldwide ranked by ideXlab platform
Ronald K Hanson - One of the best experts on this subject based on the ideXlab platform.
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single ended sensor for thermometry and speciation in Shock Tubes using native surfaces
IEEE Sensors Journal, 2019Co-Authors: Wen Yu Peng, Christopher L Strand, Yu Wang, Sean J Cassady, Ronald K HansonAbstract:A single-ended laser absorption sensor for time-resolved measurements of temperature and H2O, CO2, and CO concentrations was designed and deployed on a cylindrical Shock tube operating at combustion-relevant conditions. The sensor transmitted four monochromatic laser beams probing strong species-specific mid-infrared absorption transitions through a single optical port and measured the backscattered laser radiation from the native surface across the 13.97-cm-diameter Shock tube. Despite the non-ideal concave reflective surface and the long optical path relative to the port diameter (1.37 cm), an optimal optical configuration that maximized signal-to-noise ratio and was free of physical blockage was found and implemented using a numerical ray-tracing optimization algorithm. Wavelength-modulation spectroscopy was employed to further compensate for interference sources in the Shock tube environment. The four lasers were sinusoidally injection-current modulated at various frequencies near 100 kHz to yield a measurement rate of 44 kS/s. Demonstration measurements involving non-reacting mixtures of the target species and reacting mixtures of ethane and oxygen in a N2 bath were performed in a Shock tube facility at temperatures between 1100 and 1800 K and pressures between 2 and 9 atm, with measured quantities demonstrating excellent agreement with the expected values. Despite experiencing strong vibrations induced by the dynamic Shock tube environment, the sensor resolved sub-millisecond transients during ethane oxidation and detected H2O, CO2, and CO mole fractions as low as 0.025%, 0.012%, and 0.005%, respectively, representing highly sensitive detection limits suitable for single-port low-concentration multi-species sensing in Shock Tubes and other flow channels of comparable dimensions.
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Demonstration of non-absorbing interference rejection using wavelength modulation spectroscopy in high-pressure Shock Tubes
Applied Physics B, 2018Co-Authors: Wei Wei, Shengkai Wang, Wen Yu Peng, Yu Wang, Rishav Choudhary, Jiankun Shao, Ronald K HansonAbstract:We experimentally demonstrate the non-absorbing interference rejection capabilities of wavelength modulation spectroscopy (WMS) speciation in Shock tube experiments by directly comparing WMS measurements against direct-absorption spectroscopy (DA) measurements. The improved capability is demonstrated by probing the P(20) transition of the CO fundamental band using a quantum cascade laser in Shock-heated mixtures of CO and N $$_2$$ 2 across a wide range of pressures between 3.5 and 18 atm. In the WMS measurements, the second harmonic (2 f ) served as the detection signal, while the first harmonic (1 f ) provided normalization to counteract intensity drift and fluctuations. These perturbations occur in Shock Tubes because of significant beam-steering noise and imperfect optical alignment when experiments are conducted at elevated pressures. The WMS detection system was evaluated at reflected Shock pressures of 3.5 atm, 8.5 atm, and 18 atm, demonstrating improvement in signal-to-noise ratio over concurrent DA measurements. To the authors’ knowledge, this work represents the first direct experimental quantification of the intensity-fluctuation rejection capabilities of a WMS-based TDLAS sensor at high pressures.
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high sensitivity interference free diagnostic for measurement of methane in Shock Tubes
Journal of Quantitative Spectroscopy & Radiative Transfer, 2015Co-Authors: Ritobrata Sur, David F Davidson, Shengkai Wang, Kai Sun, Jay B Jeffries, Ronald K HansonAbstract:Abstract A sensitive CW laser absorption diagnostic for in-situ measurement of methane mole fraction at high temperatures is developed. The selected transitions for the diagnostic are a cluster of lines near 3148.8 cm−1 from the R-branch of the ν3 band of the CH4 absorption spectrum. The selected transitions have 2–3 times more sensitivity to CH4 concentration than the P-branch in the 3.3 μm region, lower interference from major interfering intermediate species in most hydrocarbon reactions, and applicability over a wide range of pressures and temperatures. Absorption cross-sections for a broad collection of hydrocarbons were simulated to evaluate interference absorption, and were generally found to be negligible near 3148.8 cm−1. However, minor interference from hot bands of C2H2 and C2H4 was observed and was characterized experimentally, revealing a weak dependence on wavelength. To eliminate such interferences, a two-color on-line and off-line measurement scheme is proposed to determine CH4 concentration. The colors selected, i.e., for on-line (3148.81 cm−1) and off-line (3148.66 cm−1), are characterized between 0.2–4 atm and 500 K–2100 K by absorption coefficient measurements in a Shock tube. Minimum detectable levels of CH4 in Shock tube experiments are reported for this range of temperatures and pressures. An example measurement is shown for sensitive detection of CH4 in a Shock tube chemical kinetics experiment.
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laser absorption diagnostic for measuring acetylene concentrations in Shock Tubes
Journal of Quantitative Spectroscopy & Radiative Transfer, 2014Co-Authors: Ivo Stranic, Ronald K HansonAbstract:Abstract A fixed-wavelength direct absorption laser diagnostic for high-temperature measurements of acetylene concentration was developed. The diagnostic, based on a tunable continuous wave distributed feedback diode laser, was optimized primarily for studying chemical kinetics behind reflected Shock waves. The center wavelength (3335.55 cm −1 ) of the tunable diagnostic was typically set at the peak of the 3300 cm −1 absorption band of acetylene at high temperatures. The absorption spectrum of acetylene diluted in argon was characterized using scanned-wavelength direct absorption measurements from 1070 to 1720 K and 0.8 to 4.0 atm. Line fitting of the measured absorption spectra was not possible due to the large number of transitions overlapped by pressure broadening that contribute to the spectrum. Instead, empirical fits for the peak absorption coefficient and its corresponding wavelength as a function of temperature and pressure were generated. Furthermore, in order to allow for characterization of interference absorption in kinetic studies, empirical fits for the acetylene absorption coefficient in the region around the primary absorption feature were developed. Absorption coefficient measurements of propyne and 1-butyne, which may be the primary interference candidates, reveal that their absorption coefficients are constant in the wavelength range of interest, and are much smaller than those of acetylene. Therefore, the acetylene concentration in the presence of these interfering species can be inferred using two-color techniques. The utility of the acetylene diagnostic was demonstrated by measuring acetylene mole fraction time-histories during the pyrolysis of propene and 1-butene.
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uncertainty quantification analysis of the effects of residual impurities on hydrogen oxygen ignition in Shock Tubes
Combustion and Flame, 2014Co-Authors: Javier Urzay, David F Davidson, Nicolas Kseib, Gianluca Iaccarino, Ronald K HansonAbstract:Abstract This study addresses the influences of residual radical impurities on the computation and experimental determination of ignition times in H2/O2 mixtures. Particular emphasis is made on the often-times encountered problem of the presence of H-atoms in the initial composition of H2/O2 mixtures in Shock Tubes. Two methods are proposed for quantifying experimentally H-residual impurities in Shock Tubes, namely, an a priori method that consists of detecting OH traces upon Shocking unfueled mixtures, and a posteriori method in which the amount of impurities is inferred by comparing fueled experimental autoignition data with calculations. A stochastic Arrhenius model that describes the amount of H-radical impurities in Shock Tubes is proposed on the basis of experimental measurements as a function of the test temperature. It is suggested that this statistical model yields a probability density function for the residual concentration of hydrogen radicals in standard Shock Tubes. Theoretical quantifications of the uncertainties induced by the impurities on autoignition times are provided by using the 5-step short chemistry of Del Alamo et al. [1] . The analysis shows that the relative effects of H-impurities on delay times above crossover become more important as the dilution increases and as the temperature and pressure decrease. Below crossover, the effects of H-impurities on the ignition delay vanish rapidly, and are negligible compared to the departures produced by the non-ideal pressure rise that is seen in some Shock-tube experiments at such low temperatures. The influences of kinetic uncertainties on the ignition time are typically negligible compared to the effects of the uncertainties induced by H-impurities when the short mechanism is used, except for air at high temperatures for which kinetic uncertainties dominate. Furthermore, calculations performed with the short mechanism show that correlations between the uncertainties in the rates of branching and termination steps have only some small influences on the ignition-time variabilities near crossover, where a global sensitivity analysis shows an increasing importance of the recombining kinetics. Computational quantifications of uncertainties are carried out by using numerical simulations of homogeneous ignition subject to Monte-Carlo sampling of the concentration of impurities. For the conditions analyzed, these computations show that the variabilities produced in ignition delays by the uncertainties in H-impurities are comparable to the experimental data scatter and to the effects of typical uncertainties of the test temperature when the Stanford chemical mechanism [2] is used. The calculations also unveil that the utilization of two other different chemical mechanisms, namely San Diego [3] and GRI v3.0 [4] , yields variations in the ignition delays which are within the range of the uncertainties induced by the H-impurities. Finally, the effects of residual impurities in kinetic-isolation experiments and in supersonic-combustion ramjets are briefly discussed.
Henry J. Curran - One of the best experts on this subject based on the ideXlab platform.
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a six compound high performance gasoline surrogate for internal combustion engines experimental and numerical study of autoignition using high pressure Shock Tubes
Fuel, 2020Co-Authors: Leonel R Cancino, Mustapha Fikri, Christof Schulz, A K Da Silva, A R De Toni, Amir A M Oliveira, Henry J. CurranAbstract:Abstract This paper presents experimental and modeling data for the autoignition of a novel, six-component, high performance gasoline surrogate fuel comprising ethanol, n-heptane, i-octane, 1-hexene, methylcyclohexane, and toluene (AL-P-I-O-N-A). Experimental tests are conducted in two high-pressure Shock Tubes to determine the ignition delay time as a function of pressure, temperature and equivalence ratio. Ignition delay times were measured at 10 and 30 bar in the temperature range from 749 to 1204 K and equivalence ratios ranging from 0.35 to 1.30 . A modified Arrhenius equation is defined to mathematically describe the ignition delay time of the proposed surrogate. For experimental data with temperatures higher than 900 K, a multiple linear regression identified the pressure dependence exponent of 0.72 and stoichiometry dependence exponent of 0.62 , as well as a global activation energy of ≈ 109 kJ/mol. A simplistic approach to mechanism reduction based on the elimination of reactions with no relevant rate of progress was used in order to reduce an extensive detailed kinetics model (hierarchically constructed with more than 17800 reactions). The reduced detailed kinetics model with 4885 elementary reactions among 326 chemical species was used for numerical simulations. Comparisons between the experimental and numerical data are favorable, with the predictions using the reduced kinetics model differing by less than 0.056% when compared to the complete mechanism. It was observed that for low temperatures the proposed reduced kinetics model agrees only qualitatively with the measurements. In order to understand the likely cause of this discrepancy a brute force sensitivity analysis on IDT was performed, elucidating the more influencing reactions on the ignition delay times. The experimental data obtained in this research was compared to available data in the literature in terms of anti-knock index (AKI) and for a scaled pressure of 30 bar ( τ 30 ) at a stoichiometric composition. A modified Arrhenius equation was then fitted and an AKI dependence exponent of - 1.11 was obtained, inferring that the higher the AKI the higher the IDT, independent of fuel composition at temperatures lower than the NTC region. This trend should be confirmed by further studies.
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an experimental and modeling study of the ignition of dimethyl carbonate in Shock Tubes and rapid compression machine
Combustion and Flame, 2018Co-Authors: Katiuska Alexandrino, Maria U Alzueta, Henry J. CurranAbstract:Abstract Ignition delay times of dimethyl carbonate DMC were measured using low- and high-pressure Shock Tubes and in a rapid compression machine (RCM). In this way, the effect of fuel concentration (0.75% and 1.75%), pressure (2.0, 20, and 40 atm) and equivalence ratio (0.5, 1.0, 2.0) on ignition delay times was studied experimentally and computationally using a chemical kinetic model. Experiments cover the temperature range of 795–1585 K. Several models from the literature were used to perform simulations, thus their performances to predict the present experimental data was examined. Furthermore, the effect of the thermodynamic data of the CH3O(C O)Ȯ radical species and the fuel consumption reaction CH3O(C O)OCH3 ⇄ CH3O(C O)Ȯ + ĊH3, on the simulations of the ignition delay times of DMC was analyzed using the different models. Reaction path and sensitivity analyses were carried out with a final recommended model to present an in-depth analysis of the oxidation of DMC under the different conditions studied. The final model uses AramcoMech 2.0 as the base mechanism and includes a DMC sub-mechanism available in the literature in which the reaction CH3O(C O)OCH3 ⇄ CH3O(C O)Ȯ + ĊH3has been modified. Good agreement is observed between calculated and experimental data. The model was also validated using available experimental data from flow reactors and opposed flow diffusion and laminar premixed flame studies showing an overall good performance.
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an ignition delay time and chemical kinetic modeling study of the pentane isomers
Combustion and Flame, 2016Co-Authors: John Bugler, Brandon Marks, Alejandro Camou, Claire Gregoire, Karl Alexander Heufer, Eric L. Petersen, Rachel Archuleta, Olivier Mathieu, Henry J. CurranAbstract:Abstract Ignition delay times of n -pentane, iso -pentane, and neo -pentane mixtures were measured in two Shock Tubes and in a rapid compression machine. The experimental data were used as validation targets for the model described in detail in an accompanying study [14]. The present study presents ignition delay time data for the pentane isomers at equivalence ratios of 0.5, 1.0, and 2.0 in ‘air’ (additionally, 0.3 in ‘air’ for n -, and iso -pentane) at pressures of 1, 10, and 20 atm in the Shock tube, and 10 and 20 atm in the rapid compression machine, as well as data at an equivalence ratio of 1.0 in 99% argon, at pressures near 1 and 10 atm in a Shock tube. An infrared laser absorption technique at 3.39 µm was used to verify the composition of the richest mixtures in the Shock-tube tests by measuring directly the pentane isomer concentration in the driven section. By using Shock Tubes and a rapid compression machine, it was possible to investigate temperatures ranging from 643 to 1718 K. A detailed chemical kinetic model was used to simulate the experimental ignition delay times, and these are well-predicted for all of the isomers over all ranges of temperature, pressure, and mixture composition. In-depth analyses, including reaction path and sensitivity analyses, of the oxidation mechanisms of each of the isomers are presented. To the authors’ knowledge, this study covers conditions not yet presented in the literature and will, in conjunction with the aforementioned accompanying study, expand fundamental knowledge of the combustion kinetics of the pentane isomers and of alkanes in general.
Eric L. Petersen - One of the best experts on this subject based on the ideXlab platform.
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impact of Shock tube facility dependent effects on incident and reflected Shock conditions over a wide range of pressures and mach numbers
Combustion and Flame, 2020Co-Authors: Damien Nativel, Eric L. Petersen, Mustapha Fikri, Sean P Cooper, Timo Lipkowicz, Christof SchulzAbstract:Abstract In real Shock Tubes, deviations from the ideal gas-dynamic behavior can affect experiments and complicate data analysis and interpretation. These non-ideal effects depend on the Shock-tube geometry and therefore, results (e.g., ignition delay times) may vary between different experimental facilities. To clarify the influence of geometry and operating procedures, these effects were investigated in four geometrically different Shock Tubes located in two laboratories, Texas A&M University and the University of Duisburg-Essen. Incident Shock-wave attenuation and pressure rise (dp*/dt) were measured behind reflected Shock waves over a 2.1–4.1 Mach number and a 0.1–3.0 MPa post-reflected-Shock pressure range. A strong influence of the Mach number on dp*/dt was observed for all facilities and conditions, whereas only a slight influence was found for Shock-wave attenuation. Both dp*/dt and attenuation were higher by about a factor of two for the Shock Tubes with approximately half the inner diameter (8.0 vs. 16.2 cm). These findings are analyzed through correlations with initial pressure, inner diameter, Mach number, and specific heat ratio. The implication of non-ideal effects on experiments with reactive mixtures and related combustion experiments is discussed. Extreme conditions of dp*/dt were derived from the correlations and used to understand the effects of an equivalent dT*/dt on simulated ignition delay times of two reactive systems (CH4/air and C7H16/air). It was found that smaller Shock-tube diameters with respectively larger dp*/dt show shorter ignition delay times (especially at temperatures below 1000 K for the C7H16/air case). Therefore, the geometry constraints must be considered in simulations through dp*/dt inputs in the chemical kinetics simulation for the extreme cases to account for non-ideal effects.
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an ignition delay time and chemical kinetic modeling study of the pentane isomers
Combustion and Flame, 2016Co-Authors: John Bugler, Brandon Marks, Alejandro Camou, Claire Gregoire, Karl Alexander Heufer, Eric L. Petersen, Rachel Archuleta, Olivier Mathieu, Henry J. CurranAbstract:Abstract Ignition delay times of n -pentane, iso -pentane, and neo -pentane mixtures were measured in two Shock Tubes and in a rapid compression machine. The experimental data were used as validation targets for the model described in detail in an accompanying study [14]. The present study presents ignition delay time data for the pentane isomers at equivalence ratios of 0.5, 1.0, and 2.0 in ‘air’ (additionally, 0.3 in ‘air’ for n -, and iso -pentane) at pressures of 1, 10, and 20 atm in the Shock tube, and 10 and 20 atm in the rapid compression machine, as well as data at an equivalence ratio of 1.0 in 99% argon, at pressures near 1 and 10 atm in a Shock tube. An infrared laser absorption technique at 3.39 µm was used to verify the composition of the richest mixtures in the Shock-tube tests by measuring directly the pentane isomer concentration in the driven section. By using Shock Tubes and a rapid compression machine, it was possible to investigate temperatures ranging from 643 to 1718 K. A detailed chemical kinetic model was used to simulate the experimental ignition delay times, and these are well-predicted for all of the isomers over all ranges of temperature, pressure, and mixture composition. In-depth analyses, including reaction path and sensitivity analyses, of the oxidation mechanisms of each of the isomers are presented. To the authors’ knowledge, this study covers conditions not yet presented in the literature and will, in conjunction with the aforementioned accompanying study, expand fundamental knowledge of the combustion kinetics of the pentane isomers and of alkanes in general.
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an experimental and modeling study of propene oxidation part 2 ignition delay time and flame speed measurements
Combustion and Flame, 2015Co-Authors: Sinead M Burke, Eric L. Petersen, Olivier Mathieu, Ultan Burke, Reuben Mc Donagh, Irmis Osorio, Charles L Keesee, Anibal Morones, Weijing Wang, Trent A DeverterAbstract:Experimental data obtained in this study (Part II) complement the speciation data presented in Part I, but also offer a basis for extensive facility cross-comparisons for both experimental ignition delay time (IDT) and laminar flame speed (LFS) observables. To improve our understanding of the ignition characteristics of propene, a series of IDT experiments were performed in six different Shock Tubes and two rapid compression machines (RCMs) under conditions not previously studied. This work is the first of its kind to directly compare ignition in several different Shock Tubes over a wide range of conditions. For common nominal reaction conditions among these facilities, cross-comparison of Shock tube IDTs suggests 20-30% reproducibility (2 sigma) for the IDT observable. The combination of Shock tube and RCM data greatly expands the data available for validation of propene oxidation models to higher pressures (2-40 atm) and lower temperatures (750-1750 K). Propene flames were studied at pressures from 1 to 20 atm and unburned gas temperatures of 295-398 K for a range of equivalence ratios and dilutions in different facilities. The present propene-air LFS results at 1 atm were also compared to LFS measurements from the literature. With respect to initial reaction conditions, the present experimental LFS cross-comparison is not as comprehensive as the IDT comparison; however, it still suggests reproducibility limits for the LFS observable. For the LFS results, there was agreement between certain data sets and for certain equivalence ratios (mostly in the lean region), but the remaining discrepancies highlight the need to reduce uncertainties in laminar flame speed experiments amongst different groups and different methods. Moreover, this is the first study to investigate the burning rate characteristics of propene at elevated pressures (>5 atm). IDT and LFS measurements are compared to predictions of the chemical kinetic mechanism presented in Part I and good agreement is observed. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)
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improved turbulent boundary layer model for Shock Tubes
AIAA Journal, 2001Co-Authors: Eric L. Petersen, Ronald K HansonAbstract:A viscous boundary-layer model was assembled to help describe the nonideal gas dynamics within Shock Tubes operating at high densities. The analytical model is based primarily on the landmark work of Mirels, who used the Blasius relation for the turbulent skin friction. The main improvement was the incorporation of a modern friction model for compressible, turbulent boundary layers via changes to the constants and exponents of Mirels's original boundary-layer relations. For example, the wall shear stress now depends on a Reynolds number to the -0.14 power as compared to -0.25 in the original model. As a result, the boundary layer at higher densities is thicker in the present model than in the original one, thus increasing the incident-Shock attenuation and related nonuniformities. Even in borderline cases, the boundary-layer transitions to turbulent very quickly, usually within 100 μs for incident-Shock pressures greater than about 2 atm. Because a turbulent boundary layer is thicker than a laminar one at the same conditions, the boundary-layer thickness in higher-pressure Shock Tubes is expected to be a larger fraction of the tube diameter than normally seen in lower-pressure Shock Tubes
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nonideal effects behind reflected Shock waves in a high pressure Shock tube
Shock Waves, 2001Co-Authors: Eric L. PetersenAbstract:Abstract. Shock Tubes often experience temperature and pressure nonuniformities behind the reflected Shock wave that cannot be neglected in chemical kinetics experiments. Because of increased viscous effects, smaller tube diameters, and nonideal Shock formation, the reflected-Shock nonidealities tend to be greater in higher-pressure Shock Tubes. Since the increase in test temperature ( $\Delta T_5$ ) is the most significant parameter for chemical kinetics, experiments were performed to characterize $\Delta T_5$ in the Stanford High Pressure Shock Tube using infrared emission from a known amount of CO in argon. From the measured change in vibrationally equilibrated CO emission with time, the corresponding d $T_5/$ dt (or $\Delta T_5$ for a known time interval) of the mixture was inferred assuming an isentropic relationship between post-Shock temperature and pressure changes. For a range of representative conditions in argon (24–530 atm, 1275–1900 K), the test temperature 2 cm from the endwall increased 3–8 K after 100 $\mu$ s and 15–40 K after 500 $\mu$ s, depending on the initial conditions. Separate pressure measurements using a shielded piezoelectric transducer confirmed the isentropic assumption. An analytical model of the reflected-Shock gas dynamics was also developed, and the calculated $\Delta T_5$ 's agree well with those obtained from experiment. The analytical model was used to estimate the effects of temperature and pressure nonuniformities on typical chemical kinetics measurements. When the kinetics are fast ( $<300\mu$ s), the temperature increase is typically negligible, although some correction is suggested for kinetics experiments lasting longer than 500 $\mu$ s. The temperature increase, however, has a negligible impact on the measured laser absorption profiles of OH (306 nm) and CH $_3$ (216 nm), validating the use of a constant absorption coefficient. Infrared emission experiments are more sensitive to temperature and density changes, so $T_5$ nonuniformities should be taken into account when interpreting ir-emission data.
Herbert Olivier - One of the best experts on this subject based on the ideXlab platform.
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a high pressure ignition delay time study of 2 methylfuran and tetrahydrofuran in Shock Tubes
Combustion and Flame, 2014Co-Authors: Yasar Uygun, Sakiko Ishihara, Herbert OlivierAbstract:Abstract Ignition delay time studies for tetrahydrofuran (THF) and 2-methylfuran (2MF) as well as optical investigations of combustion for 2MF have been carried out using two Shock Tubes. The experiments with undiluted THF/air mixtures were performed at 20 and 40 bar in a high pressure Shock tube (HPST) at an equivalence ratio of Ф = 1 covering an overall temperature range of 780–1100 K and 691–1006 K, respectively. Undiluted 2MF/air mixtures ( Ф = 1) were also investigated in the HPST at 40 bar in the temperature range of 820–1215 K. The experimental data of 2MF obtained at 40 bar were supported with kinetic simulations of existing models from literature. Additionally, sensitivity analyses of 2MF at several temperatures were performed for finding out the most sensitive reactions. Schlieren imaging was employed in a rectangular Shock tube (RST) utilizing a high speed video camera through which the ignition process was captured for a stoichiometric 2MF/O 2 /Ar mixture at pressures of about 10 bar and in the temperature range of 871–1098 K. The pressure signals of THF and 2MF at 40 bar indicate two types of pre-ignition at low temperatures: a short two-stage ignition for THF and a relatively long and smooth increase in pressure before main ignition for 2MF. Furthermore, in case of 2MF at 40 bar, far-wall ignitions at low temperatures could be observed. The deviation between simulation and experiment as well as the presence of pre-ignitions in the low temperature regime were the main reasons for undertaking optical investigations of 2MF. The Schlieren images show that the ignition process at low temperatures ( T ⩽ 940 K) begins as a deflagrative phase in the form of flame kernels and ends in a strong ignition (explosion in explosion). The current study analyzes the auto-ignition of THF and 2MF at engine relevant pressures and temperatures. The optical investigations have been conducted to analyze the ignition behavior of 2MF.
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a numerical investigation of the flow through a new fast acting valve for diaphragmless Shock Tubes
International Symposium on Shock Waves, 2013Co-Authors: Manuel Gageik, Alexander Weiss, Igor Klioutchnikov, Herbert OlivierAbstract:In Shock Tubes, driver and driven section are usually separated by a diaphragm, which produces nearly ideal Shock waves due to its instant rapture. However, known disadvantages of diaphragms motivate the investigation of diaphragmless Shock Tubes. One of these concepts is to replace a diaphram by a rapidly opening piston.
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determination of ignition delay times of different hydrocarbons in a new high pressure Shock tube
Shock Waves, 2010Co-Authors: K A Heufer, Herbert OlivierAbstract:The impending scarcity of fossil fuel in the future requires continued development in hydrocarbon combustion research. Biofuels offer a promising alternative to traditional fossil fuel-based combustion. To optimize engine design for biofuels, adequate combustion characteristics for new fuels have to be known. In this study, a new high pressure stainless steel Shock tube for measuring ignition delay times is presented. When compared with other Shock Tubes for investigating ignition delays, the new tube provides superior maximum working pressures and geometric properties. Shock tube performance is determined by reference experiments with air as driven gas. These experiments allow to determine the available test time and the influence of Shock attenuation. Owing to the large inner diameter of the Shock tube, Shock attenuation is <1% as it is typical for low pressure Shock Tubes. However, contrast to typical low pressure Shock Tubes, non-diluted fuel–air mixtures at high pressures can be investigated in the new Shock tube due to the high allowable working pressure. First experiments concerning the ignition delay time have been performed with methane and n-heptane. The results of these experiments show a good agreement to literature data. As a first biofuel ethanol has been investigated at elevated pressures up to 40 bar.
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detonation driven Shock Tubes and tunnels
2008Co-Authors: Herbert OlivierAbstract:A more than 40 years, high-enthalpy facilities suitable for aerodynamic testing are still mostly based on the Shock tunnel principle. Recent use of these facilities involves the development of space planes and reentry vehicles for studying the complex aerothermochemistry associated with flight at high velocities. The effects of thermal and chemical relaxation in air become important for flight velocities greater than approximately 4km/s. In addition, high-enthalpy, aerodynamic-impulse facilities are not only used to study high-temperature effects but are also suitable for generating high Mach number, high Reynolds number flows to investigate viscosity-dominated effects at low-enthalpy conditions. In aiming at higher-flow velocities, that is, higher stagnation enthalpies, it became obvious quickly that a technological barrier exists that would be very hard to overcome with conventional Shock Tubes. Therefore, Stalker modified the conventional Shock tunnel to a free-piston Shock tunnel. In these facilities, the driver gas is compressed by a heavy piston accelerated to nearly sonic speed. Between the piston and the main diaphragm, high values of temperature and pressure are achieved to generate a strong Shockwave propagating along the driven section of the Shock tunnel. Before the diaphragm opens, the piston is decelerated by the increasing driver gas pressure. Sophisticated techniques were developed for controlling and tuning this deceleration process because of its great importance for driver
Rubbel Kumar - One of the best experts on this subject based on the ideXlab platform.
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using gas driven Shock Tubes to produce blast wave signatures
Frontiers in Neurology, 2020Co-Authors: Rubbel Kumar, Ashish NedungadiAbstract:The increased incidence of improvised explosives in military conflicts has brought about an increase in the number of traumatic brain injuries (TBIs) observed. Although physical injuries are caused by shrapnel and the immediate blast, encountering the blast wave associated with improvised explosive devices (IEDs) may be the cause of traumatic brain injuries experienced by warfighters. Assessment of the effectiveness of personal protective equipment (PPE) to mitigate TBI requires understanding the interaction between blast waves and human bodies and the ability to replicate the pressure signatures caused by blast waves. Prior research has validated compression-driven Shock tube designs as a laboratory method of generating representative pressure signatures, or Friedlander-shaped blast profiles; however, Shock Tubes can vary depending on their design parameters and not all Shock tube designs generate acceptable pressure signatures. This paper presents a comprehensive numerical study of the effects of driver gas, driver (breech) length, and membrane burst pressure of a constant-area Shock tube. Discrete locations in the Shock tube were probed, and the blast wave evolution in time at these points was analyzed to determine the effect of location on the pressure signature. The results of these simulations are used as a basis for suggesting guidelines for obtaining desired blast profiles.
