Experimental studies of the oscillatory combustion of hydrogen in a stirred flow reactor

1991 ◽  
Vol 337 (1646) ◽  
pp. 199-210 ◽  
Keyword(s):  
Maximum Concentration ◽  
Flow Reactor ◽  
Multiphoton Ionization ◽  
Experimental Studies ◽  
Oh Radicals ◽  
Hydrogen Atoms ◽  
Numerical Studies ◽  
Electronically Excited ◽  
Combustion Of Hydrogen ◽  
Oscillatory Combustion

Experimental studies of the phase relations between H atoms, OH radicals and reactant temperature during the gas-phase, oscillatory combustion of hydrogen in a well-stirred flow reactor are reported. Absolute concentrations of the OH radical and the reactant temperature were measured in absorption from the vibrational-rotational structure of the laser-induced, electronically excited, OH spectrum . Relative concentrations of H atoms were obtained by multiphoton ionization, also induced by a laser. The hydrogen atoms reached their maximum concentration first during the oscillatory combustion, rising to a sharp peak followed by a rapid decay within several milliseconds. The OH radicals reached their maximum concentration about 1 ms after the H atoms. The maximum of the reactant temperature was in phase with the hydroxyl radicals. Experimental and numerical studies of the interaction that occurs between oscillations in a pair of coupled reactors are also presented.

The application of resonance enhanced multiphoton ionization to the detection of hydrogen atoms during the oscillatory combustion of hydrogen

1991 ◽  
Vol 434 (1891) ◽  
pp. 399-412 ◽  
Keyword(s):  
Numerical Analysis ◽  
Flow Reactor ◽  
Multiphoton Ionization ◽  
Laser Wavelength ◽  
Time Profile ◽  
Experimental Result ◽  
Oh Radicals ◽  
Hydrogen Atoms ◽  
Experimental Conditions ◽  
Concentration Time

The relative concentrations of hydrogen atoms were measured during the oscillatory ignition of hydrogen in a well stirred flow reactor. Comparisons were made with the experimental concentration—time profiles of the hydroxyl radical obtained previously under similar experimental conditions. The predicted concentration profiles obtained from numerical analysis of a thermokinetic model were also compared with the experimental results. Experiments were performed in a 600 cm 3 Pyrex glass, jet-stirred reactor with the reactants, 2H 2 + O 2 , at a total pressure of 16 Torr ( ca . 2132.8 Pa) and at a vessel temperature of 753 K. The mean residence time was 1.2 s. Oscillatory ignition was established at a period of 3 s in which high radical concentrations were attained and in which the temperature rise was almost adiabatic. The concentration-time profile of hydrogen atoms was obtained by a resonance enhanced multiphoton ionization (rempi) which was induced by a laser pulse at energies in the vicinity of 364 nm, with ion collection at a stainless steel probe inserted into the reactor. Supplementary studies were made to characterize the signals and to identify effects of the probe within the reaction volume. A measurement of the relative concentrations of hydrogen atoms was obtained from an integration of the area of the rempi spectrum determined over the laser wavelength range 363.8-364.6 nm. The spectrum was measured at successive times in the oscillatory cycle by imposing a variable delay on the laser firing signal. The results show that, during oscillatory ignition, the maximum concentration of hydrogen atoms was reached and a sharp decay was already well advanced before that of the hydroxyl radicals was attained. The numerical analysis was in very good quantitative accord with this experimental result. The phase difference of the cyclic variation in the H atoms relative to that of OH radicals is a key feature of the kinetic mechanisms which control the oscillatory oxidation of hydrogen.

IGNITION DELAY REDUCTION IN THE SYNGAS-O2 MIXTURE DUE TO EXCITATION OF O2 MOLECULES TO THE A1-G STATE

2020 ◽  
Author(s):  
V. D. Kobtsev ◽  
◽  
S. A. Kostritsa ◽  
V. V. Smirnov ◽  
N. S. Titova ◽  
...  
Keyword(s):  
Ignition Delay ◽  
Flow Reactor ◽  
Experimental Studies ◽  
Low Pressure ◽  
Oxygen Mixture ◽  
Ignition Process ◽  
Delay Reduction ◽  
Temperature Range ◽  
Numerical Studies ◽  
Discharge Cell

Experimental studies of the influence of singlet delta oxygen on the ignition delay of syngas-oxygen mixture are performed in a low-pressure flow reactor at a pressure of 16 mbar in a temperature range of 860-930 K. Glow discharge is used for the production of O2(a1As) molecules. The discharge cell and ducts for oxygen plasma supply are covered by HgO in order to decrease the concentrations of oxygen atoms and ozone molecules which are the effective deactivators of O2(a1As) molecules. Diagnostics of O2(a1 -g) and O3 concentrations both in the mixer and along the flow reactor is executed. It is shown that the presence of a small amount of O2(a1As) molecules (4% of the total oxygen) result in the 10%-20% reduction of the induction length in the temperature range 860-930 K. The effect of such an amount of O2(a1 -g) molecules is equivalent to the 30-kelvin heating of the whole mixture. It is revealed on the basis of combined experimental and numerical studies that at low pressure (at least at ~ 10-20 bar), the deactivation of O2(a1As) molecules on the reactor walls contributes significantly to a decrease in the singlet oxygen concentration along the reactor. This effect should be taken into consideration during modeling of the ignition process at low-pressure conditions.

Stationary-state and oscillatory combustion of hydrogen in a well-stirred flow reactor

1988 ◽  
Vol 73 (2) ◽  
pp. 163-185 ◽  
Author(s):  
D.L. Baulch ◽  
J.F. Griffiths ◽  
Amanda J. Pappin ◽  
Anne F. Sykes
Keyword(s):  
Stationary State ◽  
Flow Reactor ◽  
Combustion Of Hydrogen ◽  
Oscillatory Combustion

scholarly journals Large contribution to secondary organic aerosol from isoprene cloud chemistry

2021 ◽  
Vol 7 (13) ◽  
pp. eabe2952
Author(s):  
Houssni Lamkaddam ◽  
Josef Dommen ◽  
Ananth Ranjithkumar ◽  
Hamish Gordon ◽  
Günther Wehrle ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Flow Reactor ◽  
Secondary Organic Aerosol ◽  
Cloud Droplet ◽  
Organic Aerosol ◽  
Global Scale ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Large Contribution ◽  
Cloud Processing

Aerosols still present the largest uncertainty in estimating anthropogenic radiative forcing. Cloud processing is potentially important for secondary organic aerosol (SOA) formation, a major aerosol component: however, laboratory experiments fail to mimic this process under atmospherically relevant conditions. We developed a wetted-wall flow reactor to simulate aqueous-phase processing of isoprene oxidation products (iOP) in cloud droplets. We find that 50 to 70% (in moles) of iOP partition into the aqueous cloud phase, where they rapidly react with OH radicals, producing SOA with a molar yield of 0.45 after cloud droplet evaporation. Integrating our experimental results into a global model, we show that clouds effectively boost the amount of SOA. We conclude that, on a global scale, cloud processing of iOP produces 6.9 Tg of SOA per year or approximately 20% of the total biogenic SOA burden and is the main source of SOA in the mid-troposphere (4 to 6 km).

Multiphoton-ionization of hydrogen atoms in intense laserfields

1988 ◽  
Vol 10 (1) ◽  
pp. 35-43 ◽  
Author(s):  
B. Wolff ◽  
H. Rottke ◽  
D. Feldmann ◽  
K. H. Welge
Keyword(s):  
Multiphoton Ionization ◽  
Hydrogen Atoms

Film thickness in elastohydrodynamically lubricated slender elliptic contacts: Part I – numerical studies of central film thickness

2021 ◽  
pp. 135065012110477
Author(s):  
Marius Wolf ◽  
Sergey Solovyev ◽  
Fatemi Arshia
Keyword(s):  
Film Thickness ◽  
State Of The Art ◽  
Experimental Studies ◽  
Elastohydrodynamic Lubrication ◽  
Large Parameter ◽  
Numerical Studies ◽  
Minimum Film Thickness ◽  
Subsequent Publication ◽  
New Formula ◽  
Increasing Load

In this paper, analytical equations for the central film thickness in slender elliptic contacts are investigated. A comparison of state-of-the-art formulas with simulation results of a multilevel elastohydrodynamic lubrication solver is conducted and shows considerable deviation. Therefore, a new film thickness formula for slender elliptic contacts with variable ellipticity is derived. It incorporates asymptotic solutions, which results in validity over a large parameter domain. It captures the behaviour of increasing film thickness with increasing load for specific very slender contacts. The new formula proves to be significantly more accurate than current equations. Experimental studies and discussions on minimum film thickness will be presented in a subsequent publication.

scholarly journals Investigations on Torsion of the Two-Chords Single Laced Members

2017 ◽  
Vol 25 (2) ◽  
pp. 147-160
Author(s):  
Paweł Lorkowski ◽  
Bronisław Gosowski
Keyword(s):  
Cross Sections ◽  
Experimental Studies ◽  
The Finite Element Method ◽  
Second Moment ◽  
Steel Columns ◽  
Numerical Studies ◽  
Traction Network ◽  
Railway Traction ◽  
Parametric Analyses ◽  
The Relationship

Abstract The paper presents experimental and numerical studies to determine the equivalent second moment of area of the uniform torsion of the two-chord steel single laced members. The members are used as poles of railway traction network gates, and steel columns of framed buildings as well. The stiffness of uniform torsion of this kind of columns allows to the determine the critical loads of the spatial stability. The experimental studies have been realized on a single - span members with rotation arrested at their ends, loaded by a torque applied at the mid-span. The relationship between angle of rotation of the considered cross-section and the torque has been determined. Appropriate numerical model was created in the ABAQUS program, based on the finite element method. A very good compatibility has been observed between experimental and numerical studies. The equivalent second moment of area of the uniform torsion for analysed members has been determined by comparing the experimental and analytical results to those obtained from differential equation of non-uniform torsion, based on Vlasov’s theory. Additionally, the parametric analyses of similar members subjected to the uniform torsion, for the richer range of cross-sections have been carried out by the means of SOFiSTiK program. The purpose of the latter was determining parametrical formulas for calculation of the second moment of area of uniform torsion.

scholarly journals Structural Pounding Detection by Using Wavelet Scalogram

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Shutao Xing ◽  
Marvin W. Halling ◽  
Qingli Meng
Keyword(s):  
Experimental Studies ◽  
Shake Table Tests ◽  
Rigid Barrier ◽  
Single Degree Of Freedom ◽  
Structural Pounding ◽  
Numerical Studies ◽  
Bridge Model ◽  
On Line ◽  
Potential Damage ◽  
Bridge Responses

Structural pounding can cause considerable damage and even lead to collapse of structures. Most research focuses on modeling, parameter investigation, and mitigation approaches. With the development of structural health monitoring, the on-line detection of pounding becomes possible. The detection of pounding can provide useful information of potential damage of structures. This paper proposed using wavelet scalograms of dynamic response to detect pounding and examined the feasibility of this method. Numerical investigations were performed on a pounding system that consisted of a damped single-degree-of-freedom (SDOF) structure and a rigid barrier. Hertz contact model was used to simulate pounding behavior. The responses and pounding forces of the system under harmonic and earthquake excitations were numerically solved. The wavelet scalograms of acceleration responses were used to identify poundings. It was found that the scalograms can indicate the occurrence of pounding and occurrence time very well. The severity of the poundings was also approximately estimated. Experimental studies were carried out, in which shake table tests were conducted on a bridge model that underwent pounding between its different components during ground motion excitation. The wavelet scalograms of the bridge responses indicated pounding occurrence quite well. Hence the conclusions from the numerical studies were verified experimentally.

scholarly journals Falling weight impact test of a new-type flexible rock-shed

2018 ◽  
Vol 38 (2) ◽  
pp. 242-252
Author(s):  
Jianrong Yang ◽  
Zhiyu Zhang
Keyword(s):  
Experimental Studies ◽  
Steel Tube ◽  
Time Interval ◽  
Explicit Finite Element ◽  
Numerical Studies ◽  
Structural Details ◽  
Tensile Forces ◽  
New Type ◽  
Falling Weight ◽  
The Impact

A new concept of a flexible rock-shed is presented for protection of the railway from falling rocks. The flexible rock-shed is made of flexible nets connected by specific spring spacer bars to an array of reinforced concrete portable frames which are linked by a longitudinal steel tube truss. To evaluate the performance of the flexible rock-shed, experimental and numerical studies are carried out in the present study. Impact tests are conducted on a full-scale partial model of the prototype structure when it is subjected to a falling block of 340 kg. The impact time interval, maximum deflection of the flexible net, tensile forces in the supporting ropes, and axial strains of spring spacer bars are recorded. To further examine the dynamic behavior of the flexible rock-shed, numerical simulations are also carried out by using the explicit finite element code ANSYS/LS-DYNA. It is found that the numerical results coincide well with the experimental data and both the numerical and experimental studies reveal that the structure can withstand impact energy of 50 kJ with all the materials working in the elastic range. The structural details are improved and the basis for the design and construction of similar structures in the future is provided.<br>

scholarly journals Controlled nitric oxide production via O(<sup>1</sup>D)+N<sub>2</sub>O reactions for use in oxidation flow reactor studies

2017 ◽  
Author(s):  
Andrew Lambe ◽  
Paola Massoli ◽  
Xuan Zhang ◽  
Manjula Canagaratna ◽  
John Nowak ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Flow Reactor ◽  
Branching Ratio ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Ionization Mass ◽  
Flow Reactors ◽  
Oxidative Aging ◽  
Gas Phase Oxidation

Abstract. Oxidation flow reactors that use low-pressure mercury lamps to produce hydroxyl (OH) radicals are an emerging technique for studying the oxidative aging of organic aerosols. Here, ozone (O3) is photolyzed at 254 nm to produce O(1D) radicals, which react with water vapor to produce OH. However, the need to use parts-per-million levels of O3 hinders the ability of oxidation flow reactors to simulate NOx-dependent SOA formation pathways. Simple addition of nitric oxide (NO) results in fast conversion of NOx (NO + NO2) to nitric acid (HNO3), making it impossible to sustain NO at levels that are sufficient to compete with hydroperoxy (HO2) radicals as a sink for organic peroxy (RO2) radicals. We developed a new method that is well suited to the characterization of NOx-dependent SOA formation pathways in oxidation flow reactors. NO and NO2 are produced via the reaction O(1D) + N2O→ 2NO, followed by the reaction NO + O3 → NO2+ O2. Laboratory measurements coupled with photochemical model simulations suggest that O(1D) + N2O reactions can be used to systematically vary the relative branching ratio of RO2 + NO reactions relative to RO2 + HO2 and/or RO2 + RO2 reactions over a range of conditions relevant to atmospheric SOA formation. We demonstrate proof of concept using high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) measurements with nitrate (NO3−) reagent ion to detect gas-phase oxidation products of isoprene and α-pinene previously observed in NOx-influenced environments and in laboratory chamber experiments.

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