Oxygen Flame Research Articles

Numerical study of hydrogen–oxygen flame acceleration and deflagration to detonation transition in combustion light gas gun

A large eddy model with detailed chemical reaction mechanism is developed to investigate the interior ballistic process of the combustion light gas gun (CLGG). Flame acceleration and deflagration to detonation transition process with high initial pressure and low initial temperature hydrogen–oxygen mixture in CLGG is numerically studied. Simulation results indicate that the hydrogen–oxygen flame propagation experiences an exponential acceleration stage, a nearly uniform propagation stage and a fast reacceleration stage. Detonation can be triggered through two different mechanisms, which are the amplification between the overlapped shock wave at flame surface, and the elevated flame velocity and shock strength caused by local explosions. Reflected shock waves play an important role in the suppression of the flame propagation when the flame front is close to the chamber throat, leading to a deceleration of the deflagration flame.

Optical fiber pressure sensor based on F-P cavity in the oil and gas well

To meet the need of the measurement in high temperature and high pressure in oil and gas well, an optical fiber pressure sensor based on extrinsic Fabry Perot (F-P) cavity is developed. The sensor is fabricated by hydrogen and oxygen flame thermal bonding in high temperature technique, and the change of the senor’s cavity length is compensated in temperature changing with cascading fiber bragg grating, and the sensor has characteristics of large dynamic range, high resolution, high repeatability, long term operation stability and high temperature resistance. The pressure measuring range is 0∼69MPa, the repeatability is 0.01% F·S,the hysteresis is less than 0.01% F·S, the long term stability is less than 0.02MPa/y, and the sensor can satisfy the requirement of the measurement in the oil and gas well. Practical application proved that the relative deviation of the pressure measurement value is less than 0.01% compared with the traditional electronic pressure sensor.

Tribological analysis of WC–10Co–4Cr and Ni–20Cr2O3 coating on stainless steel 304

Centrifugal slurry pump is widely used for transportation of solids through pipeline in many chemical and mining industries. Erosion wear considered as one of the important parameter which plays significant role in slurry transportation system by affecting both initial cost and life of its components. In the present work, erosion wear due to solid–liquid mixture has been investigated using a slurry erosion pot tester. The erosion tests have been conducted on centrifugal slurry pump material stainless steel (SS304) to establish the influence of rotational speed, particle size, solid concentration and time duration. Sand and fly ash were taken as erodent materials with solid concentrations ranging from 30 to 60% (by weight). The experiments were performed at four different speeds namely 600, 900, 1200 and 1500rpm with time duration of 90, 120, 150 and 180minutes. WC–10Co–4Cr and Ni–20Cr2O3 coating powders were used to increase the erosion wear resistance. Coating powders are deposited on pumping material by supersonic flame of high velocity oxygen fuel (HVOF) coating. Experimental results indicate that erosion wear has high dependence on rotational speed, time duration and nature of erodent solid particles. Significant improvement in erosion wear resistance was also observed by using WC–10Co–4Cr coating over Ni-20Cr2O3.

Neural network analysis for erosive wear of hard coatings deposited by thermal spray: Influence of microstructure and mechanical properties

An artificial neural network (ANN) analysis is used to obtain a model to predict the rate of erosive wear of hard coatings deposited by two different kinds of thermal spray techniques. High Velocity Oxygen Fuel (HVOF) and Flame Spray FlexiCords (FS/FC) techniques were used under various operational conditions. Different microstructural features that control the mechanical and the tribological performances of three groups of deposits: tungsten carbide, chromium carbide and metallic alloy coatings, were analyzed. The ANN technique involves database use to predict erosive wear evolution, having a large number of variables like deposition process, impingement angles and velocity of the erosive particles, porosity, roughness, microhardness and fracture toughness. Commercially available powders were used as feedstock for coatings deposited by HVOF. Commercial cord wires were used in the FS/FC coating deposition. The slurry erosion testing was performed using a laboratory made pot-type slurry erosion tester, at impact velocity of 3,61m/s and 9,33m/s combined with impact angle of 30° and 90°. From the results, it was observed that the microhardness and fracture toughness, as a combination factor, have the greatest influence on erosive rate followed by porosity. Samples coated with WC-CoCr cermet coating with fine WC carbides exhibit higher erosion resistance as compared with the other conventional cermet and metallic alloy coatings, mainly because of its homogenous microstructure and improved properties like low porosity, high microhardness and high fracture toughness. The numerical results obtained via neural network model were compared with the experimental results. The agreement between the experimental and numerical results is considered a good aspect.

Gas dynamics and kinetics of the penetration of methane–oxygen flames through complex obstacles, as studied by 3D spectroscopy and high-speed cinematography

It was experimentally found that, on the penetration of a flame through obstacles, gas dynamic factors such as flame turbulization can determine the kinetics of combustion, for instance, a transition of low-temperature hydrocarbon combustion to the high-temperature mode.

Experimental study on the effects of mixture flow rate, equivalence ratio, oxygen enhancement, and geometrical parameters on propane-air premixed flame dynamics in non-adiabatic meso-scale reactors

In the present study, the effects of reactive mixture flow rate, adding oxygen to propane-air mixture, geometrical parameters, and equivalence ratio on propane-air/oxygen premixed flame dynamics in non-adiabatic meso-scale reactors were experimentally investigated. During the experiments, seven flame regimes of blow-off, blow-out, asymmetric stationary, stationary-repetitive extinction and re-ignition (RERI), forced/self-RERI, RERI-flash-back, and flash-back were observed. The results showed that increasing the reactive mixture flow rate could generally promote variety of the flame regimes and also improve flame stability in the non-adiabatic meso-scale reactors, especially in 40% and 80% oxygen-enhanced cases. Also, the results demonstrated that increasing the reactor inner diameter and equivalence ratio generally extended propane-air- oxygen flame stability and its presence range in the non-adiabatic meso-scale reactors. Moreover, it was shown that increasing the reactor length and also increasing the added oxygen to propane-air mixture more than 40% promoted flame instability and consequently restricted propane-air-oxygen flame presence range in the non-adiabatic meso-scale reactors. Also, it was shown that variations in the mixture flow rate, the reactor length and inner diameter, equivalence ratio, and oxygen concentration in propane-air mixture could significantly influence the flame average propagation speed, acoustic, and chemiluminescence in the non-adiabatic meso-scale reactors.

The bonding strength of powder coatings in gas-flame spraying with the hydrogen–oxygen flame

The equipment, procedure and the results of investigations of the bonding strength of gas-flame coatings with the substrate are described. The dependence of the bonding strength on the conditions of spraying with the powder materials using the hydrogen–oxygen flame is outlined.

Design and Development of Instrumentations for the Preparation of Platinum Single Crystals for Electrochemistry and Electrocatalysis Research. Part 1: Semi-Automated Crystal Growth

In this contribution, we report on a novel design of semi-automated system for the growth of spherical platinum (Pt) single crystals. The system is based on the flame fusion methodology, where the crystal melting/solidification process is controlled by the vertical movement of a hydrogen–oxygen flame by using an actuator. The paper systematically examines the impact of several process variables on the crystal growth. First, the hydrogen–oxygen flame is optimized through control of the gas flow rate and the mixing ratio to ensure the formation of high-quality platinum single crystals. The procedure of crystal growth is documented in a step-by-step manner, starting with cleaning of the Pt wire, followed by the initial formation of metallic sphere, and ending with repetitive zone refining combined with chemical etching. The equilibrium shape of the platinum single crystals is discussed, and the individual low and high Miller index facets identified and visualized. The critical step in the single-crystal growth, the repetitive zone refining, is semi-automated in order to ensure the highest quality crystals and reproducibility, and to minimize any human error.

Thermo-kinetic dynamics of near-limit cool diffusion flames

The dynamics of near-limit cool diffusion flames are investigated experimentally and numerically by studying transient flame evolution and instability. In order to observe the effects of chemistry-transport coupling on ignition and instability in a cool diffusion flame, diffusion flames of n-heptane and pure oxygen are sensitized by ozone in a counterflow burner. First, it is found from experimental observations that the immediate addition of ozone to the oxidizer side of a frozen flow either initiates a cool diffusion flame or triggers a two-stage ignition into a hot flame. Second, a cool flame near its extinction limit can be destabilized by a perturbation of the fuel mole fraction, eventually leading to flame extinction. The recorded flame chemiluminescence signals reveal repeated flame oscillations before extinction. Next, details of the transient dynamics of near-limit cool diffusion flames are explored through numerical calculations by adopting the same perturbation method. Experimental observations of unsteady flame initiation and instability are simulated, and it is found that the ignition process is highly sensitive to the perturbed ozone mole fraction and that the ignition delay times in a counterflow configuration are significantly affected by the diffusive transport of species with high concentration. The instability mechanism of a cool flame is found to be distinct from that of diffusive-thermal instability. The results show that the instability behavior of a cool flame is a thermo-kinetic instability, which is triggered and controlled by the chemical kinetics associated with the OH radical population in the negative temperature coefficient chemical kinetic regime coupled with heat production and loss.

Erosion–Corrosion Property of CeO2-Modified HVOF WC-Co Coating

Rare-earth elements have been widely used in materials manufacturing to improve hardness and toughness. In this work, conventional, nanostructured, and CeO2-modified WC-12Co powders were sprayed using high-velocity oxygen flame spraying. The erosion–corrosion behavior and interaction of erosion and corrosion of the coatings in 3.5 wt.% NaCl solution were investigated. In situ observation was employed to analyze the failure mechanism. The results showed that the CeO2-modified WC-12Co coating possessed the best erosion–corrosion resistance, while the lowest corrosion resistance was exhibited by the conventional WC-12Co coating. The results also suggested that the erosion–corrosion mechanism in the three coatings was dominated by corrosion-accelerated erosion. However, the extent of acceleration of erosion by corrosion differed.

Flammability properties of polypropylene containing montmorillonite and some of silicon compounds

New polypropylene (PP) blends were prepared using phenyltrimethoxysilane (PTMS), glycidoxypropyltrimethoxysilane (GPTMS) and potassium-montmorillonite (K-MMT). Polymers A (K-MMT/PTMS), B (MMT/GPTMS) and C (modified-MMT) were prepared using sol-gel technique then incorporated in the PP matrix by different concentrations. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimeter (DSC) were used to investigate the structure and thermal stability. The mechanical properties (tensile strength/TS and elongation/%) were measured. The flame-retardant properties of the unblended and blended (PP/A, PP/B and PP/C) were estimated by limiting oxygen index (LOI), flame chamber (UL/94) and oxygen bomb calorimeter (OBC) tests, whereas the thermal stabilities were investigated using TGA were carried flammability out to detect the properties of the blended PP.

Research on Characteristic Parameter of Ta-Zro2 Fiber Blackbody Cavity Temperature Sensor

By sputtering and plasma spraying technology, a sapphire optical fiber blackbody cavity temperature sensor of tantalum (melting point is 2997℃) - zirconium oxide (melting point is 2715℃) thin film was developed. Static calibration system for the sensor to measure target temperature 1721 ℃ is also designed by using three oxygen (produced by water electrolysis) flame guns. When its impact resistant capacity is more than 50MPa, the corresponding temperature is 2802 ℃ . A high power and high frequency modulation CO2 laser pulse is used as exciting source to heat it to 1500℃, and the dynamic calibration device is designed independently, thus this sensor in experimental results show a time response on the order of μs. Signal collection and transmission through fiber optic cable are proposed, which can meet the need of transient high temperature measurement in harsh environment.

Experimental investigation of partially premixed methane–air and methane–oxygen flames stabilized over a perforated-plate burner

In this work, two sets of experiments were performed including air and oxy-combustion premixed flames stabilized over a perforated-plate burner. A set of experiments was performed considering air–fuel combustion in order to identify a range of equivalence ratio for stable flame operation at fixed oxidizer Reynolds number and over a range of premixing ratio (namely 7, 25, 45, 67 and 128). Also, effects of premixing ratio (L/D) on lower and upper flammability limits over a range of oxidizer Reynolds number were investigated. Another set of experiments was performed considering oxy-fuel combustion in order to identify a range of equivalence ratio for stable flame operation at fixed oxidizer Reynolds number. The study documents the visual flame length, appearance and color and identifies the extinction mechanism outside the flammability limits for both air and oxy-combustion flames over wide ranges of operating equivalence and premixing ratios. For air combustion flames, the results showed wide ranges of flammability limits at lower premixing ratios and tight ranges of flammability limits at higher premixing ratios. This can be attributed to the increase in the degree of flame diffusivity while reducing the premixing ratio and, as a result, more stable flame is obtained. Reductions in the emissions of NO and CO were observed while increasing the premixing ratio for the air combustion case. For the oxy-combustion flames, the results showed stable flame operation at oxygen fraction of 36%; however, the flammability limits were approximately 20% lower as compared to those of air combustion flames. Flash back was observed when operating oxygen fraction exceeded 40% and flame stability was affected badly with the decrease of oxygen fraction. The visual flame length was longer in cases of oxy-combustion flames as compared to those of air combustion.

Measurements of the concentrations of positive and negative ions along premixed fuel-rich flames of methane and oxygen

The positive and negative ions in fuel-rich, pre-mixed flames of CH4+O2+Ar (0.4 ≤ C/O (atomic basis) ≤0.75) burning at 1 atm have been studied mass spectrometrically. The ions in the most oxygen-rich of these non-turbulent flames were found to be similar to those in more fuel-lean flames, previously studied by Goodings et al. In particular, in this flame, ions are produced in only one chemi-ionisation step in the reaction zone, i.e. by CH+O→CHO++e−. Subsequently a pool of positive ions is then formed rapidly, mainly by protons being transferred from CHO+ to intermediates and final products of combustion. Some negative ions were detected in the reaction zone, but none were found in this flame more than 1mm downstream of the reaction zone, i.e. in the burnt gas. These negatively charged species, like the positive ions, reflect the presence of intermediates in and near the reaction zone. In the burnt gas, the dominant positive ion, H3O+, recombines with free electrons, the principal negatively charged species, in H3O++e−→products. The recombination coefficient was measured to be 2.9 ± 1.5×10−7ml ion−1 s−1 at ∼2250K. However, in the richer oxy-methane flames with C/O ≥ 0.50, another ion-producing step was found to operate from 1 to at least ∼5mm downstream of the reaction zone. This new process is deduced to be CH+C2H2→C3H3++e−, and maybe involves electronically excited CH radicals. Certainly, C3H3+ becomes the major positive ion in the more fuel-rich flames. The richest flame studied, with C/O=0.75, is weakly sooting; in its burnt gas, both positive and negative ions with masses exceeding 170 a.m.u. were formed throughout the first 8 or so mm of the burnt gas. It is likely that the heavy positive ions are produced by proton transfer from a pool of positive ions (with the primary ion being C3H3+) to precursors of soot, including polyaromatic species. Likewise, the pool of massive negative ions reflects these precursors of soot.

Photolytic-interference-free, femtosecond, two-photon laser-induced fluorescence imaging of atomic oxygen in flames

Ultrashort-pulse lasers are well suited for nonlinear diagnostic techniques such as two-photon laser-induced fluorescence (TPLIF) because the signals generated scale as the laser intensity squared. Furthermore, the broad spectral bandwidths associated with nearly Fourier-transform-limited ultrashort pulses effectively contribute to efficient nonlinear excitation by coupling through a large number of in-phase photon pairs, thereby producing strong fluorescence signals. Additionally, femtosecond (fs)-duration amplified laser systems typically operate at 1–10 kHz repetition rates, enabling high-repetition-rate imaging in dynamic environments. In previous experiments, we have demonstrated utilization of fs pulses for kilohertz (kHz)-rate, interference-free imaging of atomic hydrogen (H) in flames. In the present study, we investigate the utilization of fs-duration pulses to photolytic-interference-free TPLIF imaging of atomic oxygen (O). In TPLIF of O, photodissociation of vibrationally excited carbon dioxide (CO2) is known to be the prominent interference that produces additional O atoms in the medium. We have found that through the use of fs excitation, such interferences can be virtually eliminated in premixed laminar methane flames, which paves the way for two-dimensional imaging of O at kHz data rates. Such measurements can provide critical data for validating complex, multidimensional turbulent-combustion models as well as for investigating flame dynamics in practical combustion devices.

石英ガラスの火加工の研究

Quartz glass is a special glass material known as "King of Glass". The silicon purity of the quartz glass is very high, therefore it is excellent in heat resistance, chemical resistance and optical transparency as compared to other glasses, such as borosilicate glass. At present, it is used in the production field of leading-edge. Now researchers are carried out to develop it as key components of special manufacturing equipment, scientific instruments and analysis equipment that require high-precision, high purity, the high light transmittance. However, due to its high heat resistance, it is difficult to process into various shapes. As a result, manufactured Quartz glass products, generally, might be different even in one batch. To respond to such products for precision instruments, it is preferable to select the heat molding process by flame called "fire-process" in many cases. "fire-process" is the process of forming a softening point of heated quartz glass material by a mixed combustion flame of hydrogen and oxygen. Therefore, a technique for forming a glass material softened by heating is required, and now it is done by human hand processing of engineers. Skilled human technique of long time experience is required in order to produce high precision and some efficient products. Therefore, analysis of the work of expert engineers with high level of skill is needed to increase the processing technology of the engineers less skilled and take advantage in the manufacture of high-precision products.

Interaction of the laminar flames of natural gas–oxygen mixtures with planar obstacles, diffusers and confusers

It is experimentally shown that the limit on diameter of an opening of penetration of diluted methane–oxygen flames through a confuser is markedly less than in the case of a plain orifice, and is still less than in the case of a diffuser under the same conditions, i.e . the diffuser is the most effective flame arrester.

Study on combustion characteristics of dimethyl ether under the moderate or intense low-oxygen dilution condition

Experiments and numerical simulations were conducted in this paper to study the combustion behavior of dimethyl ether in the moderate or intense low-oxygen dilution regime, in terms of thermal/chemical structure and chemical kinetics associated with nitrogen oxide and carbon monoxide emissions. Several co-flow temperatures and oxygen concentrations were involved in the experiments to investigate their impacts on the flame behavior systematically. The results show that in the moderate or intense low-oxygen dilution regime, oxygen concentrations in the flame base slightly increased because of the prolonged ignition delay time of the reactant mixture due to oxidizer dilution, which changed the local combustion process and composition considerably. The oxidation rates of hydrocarbons were significantly depressed in the moderate or intense low-oxygen dilution regime, such that a fraction of unburned hydrocarbons at the furnace outlet were recirculated into the outer annulus of the furnace, which changed the local radial profiles of carbon monoxide, methane, and hydrogen partially. Moreover, with the increment in co-flow temperature or oxygen mole fraction, flame temperature, and hydroxyl radical, carbon monoxide, and hydrogen mole fractions across the reaction zone increased gradually. For the dimethyl ether-moderate or intense low-oxygen dilution flame, temperature homogeneity was improved at higher co-flow temperature or lower oxygen mole fraction. The carbon monoxide emission depended on the levels of temperature and hydroxyl radical concentration inside the reaction zone significantly. Emission index of carbon monoxide increased at lower co-flow temperature or oxygen mole fraction; and it was more sensitive to the variation in co-flow oxygen mole fraction. Additionally, the dominant formation pathways of nitrogen oxide in the dimethyl ether-moderate or intense low-oxygen dilution flame were clarified. The contribution of the thermal pathway was fairly unimportant. Emission index of nitrogen oxide increased as co-flow temperature or oxygen mole fraction was increased. The ratio of nitrogen dioxide emission index to nitrogen oxide emission index decreased with the increment in co-flow temperature or oxygen mole fraction.

Effects of thermal radiation heat transfer on flame acceleration and transition to detonation in particle-cloud hydrogen flames

The current work examines regimes of the hydrogen–oxygen flame propagation and ignition of mixtures heated by radiation emitted from the flame. The gaseous phase is assumed to be transparent for the radiation, while the suspended particles of the dust cloud ahead of the flame absorb and reemit the radiation. The radiant heat absorbed by the particles is then lost by conduction to the surrounding unreacted gaseous phase so that the gas phase temperature lags that of the particles. The direct numerical simulations solve the full system of two phase gas dynamic time-dependent equations with a detailed chemical kinetics for a plane flames propagating through a dust cloud. It is shown that depending on the spatial distribution of the dispersed particles and on the value of radiation absorption length the consequence of the radiative preheating of the mixture ahead of the flame can be either the increase of the flame velocity for uniformly dispersed particles or ignition either new deflagration or detonation ahead of the original flame via the Zel'dovich gradient mechanism in the case of a layered particle-gas cloud deposits. In the latter case the ignited combustion regime depends on the radiation absorption length and correspondingly on the steepness of the formed temperature gradient in the preignition zone that can be treated independently of the primary flame. The impact of radiation heat transfer in a particle-laden flame is of paramount importance for better risk assessment and represents a route for understanding of dust explosion origin.

Penetration of methane–oxygen flames through spherical and planar obstacles in a closed cylindrical reactor

The ignition of a dilute methane–oxygen mixture (total pressure, to 200 Torr) after a single obstacle can be observed markedly far from the obstacle surface. The use of meshed sphere as an obstacle leads to an increase in the distance of flame emergence behind the obstacle in comparison with a round opening; two or more close-meshed obstacles strongly suppress flame propagation.