Acetylene Concentration Research Articles

Quantitative Detection of C<sub>2</sub>H<sub>2</sub> Gas Based on an Infrared Laser Gas Sensor

Detection of C2H2 gas in transformer oil is significant for diagnosing the operating state assessment of power equipment. The paper develops an infrared laser gas sensor to detect the C2H2 gas in transformer oil, and also introduces the system structure in detail. A gas-absorbed laser cell that contains a series of laser reflectors is designed and used in our detection system, which adds the optical path without changing the volume of the cell. 1529.16nm is chosen as the characteristic spectrum line of C2H2 gas, and concentration of C2H2 gas is quantitatively analyzed based on least square method. The experiment result shows that in certain volume fraction range of acetylene, the absorbance has a good linear relationship with the acetylene concentration, and the minimum detection limit for acetylene is 10μL/L. In general, the developed infrared laser gas sensor can detect C2H2 gas in transformer oil effectively.

Effect of hydrogen additives on the kinetics of formation and destruction of acetylene during the ignition and combustion of methane-oxygen mixtures

The kinetics of formation and destruction of acetylene during the self-ignition of methane-oxygen mixtures with and without hydrogen additives in a closed volume have been studied by numerical analysis. The time dependence of the acetylene concentration exhibits a sharp peak at a maximum concentration and slightly descends with increasing initial temperature and hydrogen concentration in the studied range. Ignition delays and the time of concentration decay after maximum significantly decrease with increasing initial temperature, hydrogen concentration, and pressure. It has been speculated that the experimentally observed decrease in the yield and particle size of soot owing to hydrogen additives to a hydrocarbon-oxygen mixture is attributed to a strong decrease in the lifetime of significant acetylene concentrations in the reaction zone which is caused by these additives.

Partial oxidation of JP8 in a distributed reactor

Volume distributed reaction technique was applied to examine the partial oxidation behavior of JP8 with the goal to improve reformate quality. The reactor design was based on previously developed volume distributed combustion, but modified to foster unique reforming conditions. The reactor demonstrated almost colorless reaction zone even at a high equivalence ratio of Φ=3.0 (that is normally a soot formation regime), with no visible soot found on the walls of the reactor.A stable reaction zone was demonstrated at low temperatures of 764–863°C. Reformate concentration consisted of 8.68–9.92% hydrogen and 18.12–18.58% carbon monoxide, which is significantly higher than that available in the literature on partial oxidation at temperatures of 700–800°C (only 4.0–7.5% hydrogen and 5.7–17% carbon monoxide). Acetylene concentrations under distributed reaction regime were 20–23% lower than that in conventional flames. The results show that volume distributed reactions offer significant advantages to produce higher concentrations of hydrogen and carbon monoxide and very low amounts of acetylene that is a well-known precursor to soot formation.

Diamondlike nanocomposite a-C:H:Cr Coatings: Structure, mechanical, and tribological properties

The results from a comprehensive investigation of the structure, phase and chemical composition, microhardness, and nanomechanical and tribological properties of chromium-doped coatings of hydrogenised amorphous carbon a-C:H:Cr are presented. The coatings are deposited via reactive magnetron sputtering in an Ar + C2H2 + N2 gas mixture at various volume concentrations of nitrogen and acetylene. It is found that the carbon in the coatings is formed as disordered mixtures of domains with tetrahedral (sp3) and hexagonal (sp2) carbon coordinations. In addition, the doping metal in the coating consists of nanosized inclusions of metallic chromium and its carbide and nitride phases. Additional nitrogen doping resulting in the formation of chromium nitride is shown to improve the micromechanical and tribological properties of the obtained coatings.

Over 99.6 wt%-pure, sub-millimeter-long carbon nanotubes realized by fluidized-bed with careful control of the catalyst and carbon feeds

To establish a method for sub-second conversion of acetylene to sub-millimeter-long carbon nanotubes (CNTs), we have proposed and developed an internal heat-exchange reactor for fluidized-bed chemical vapor deposition (FBCVD). This reactor enabled sufficient heating of the reaction gas and uniform heating of the bed of alumina beads at a space velocity as high as 3600h−1. The direct feeding of the catalyst vapors (aluminum isopropoxide for the alumina support layer and ferrocene for the iron particles) to the bed separately from the other gases, which were fed through the heat-exchange and preheating zone and the distributer, enabled the careful control of the catalyst particles deposited on the beads. By decreasing the acetylene feed concentration and preventing the deactivation of small Fe particles, we realized semi-continuous production of 99.6–99.8wt%-pure, sub-millimeter-long, few-wall CNTs with an average diameter of 6.5nm at a carbon yield of 42%. The FBCVD reactor with an internal heat-exchanger can be scaled-up for practical mass production with uniform and energy-saving heating.

Chemical interactions between 1,2,4-trimethylbenzene and n-decane in doped counterflow gaseous diffusion flames

The chemical interaction of the two-components of a jet fuel surrogate, n-decane and 1,2,4-trimethylbenzene (TMB), was studied by adding several hundreds ppm of each chemical to two counterflow diffusion flames, one using methane and the other ethylene as baseline fuels. The objective was to look into evidence of synergistic effects due to the interaction of these reference fuels, that are representative of normal alkanes and aromatics, respectively, making up the bulk of practical fuels. The dopants were added in the same proportions as in the Aachen surrogate of jet fuel. The flames presented two distinct environments: the permanently blue methane flame and the incipiently sooting ethylene flame provide well defined temperature–time histories and chemical environments, with the one based on ethylene being relatively more oxygen-deficient. Profiles of critical pyrolysis products and of some stable soot precursors were determined from GC/MS analysis of gas samples extracted from the flames and compared with results from the OPPDIFF model using a lumped chemical mechanism. Mechanistically relevant synergies among the two fuel components are highlighted considering the production rate of aromatics in both flames when adding the two components either simultaneously or separately. The principal observation is that the combined addition of the two components causes an overproduction of methane in the ethylene flame, a decrease in the concentration of acetylene in the methane flame and an acceleration of the aromatic destruction/growth pathways. The model for the most part fails to capture the principal evidence of synergistic effects. Most of the other quantified species reveal no synergy, their concentration being the sum of the contributions of each component used individually, partly because of the small amounts of reactants that were added to the flames.

Experimental and numerical study on soot formation and oxidation by using diesel fuel in constant volume chamber with various ambient oxygen concentrations

The study on effects of exhaust gas recirculation (EGR) on soot behavior is very important to reduce soot emissions and control the low temperature combustion process in diesel engines. In this work, high time-resolved quantitative soot measurements were experimented on a constant volume chamber by using European low-sulfur diesel fuel at three ambient oxygen concentrations (21%, 18%, 15%). Meanwhile, an improved semi-empirical soot model was coupled into computational fluid dynamics (KIVA-3V Release 2) code for in-depth understanding the soot formation and oxidation processes. Results demonstrated that numerical results of the improved semi-empirical soot model showed good agreement with experimental data in the whole processes of soot formation/oxidation and soot distribution under different oxygen concentrations. The mass concentration of acetylene, soot precursor species and soot mass initially increased with decreasing ambient oxygen concentrations from 21% to 15% and then began to decrease at 12% oxygen, while OH radicals reduced monotonically from 21% oxygen to 12%. At 12% oxygen, the concentrations of local rich sooty zone, acetylene and soot precursor species were as high as those under higher oxygen concentrations, but the total area of soot zone shrank remarkably at 12% oxygen. Compared to 21% ambient oxygen concentration, both soot formation and oxidation rates were increased under 18% oxygen, while the higher soot mass under 18% oxygen was the result of stronger soot formation mechanism. At 15% oxygen, both soot formation and oxidation rates were reduced and the maximum peak of soot mass concentration was caused by the suppressed oxidation mechanism. At 12% oxygen, reaction rates of soot formation and oxidation dropped to the very low level and the reduction in soot mass concentration and number density were achieved. Finally, it could be concluded that the retarded and reduced soot mass concentration at low ambient oxygen was the result of suppressed soot inception reaction from precursor species.

Investigation of adsorption and desorption of acetylene on hard coal samples from Polish mines

Acetylene is a mine air component in addition to other hydrocarbons: ethylene, propylene, propane and ethane. Increased acetylene concentrations in the mine atmosphere are associated with its emission from a coal deposit at elevated temperatures caused by the self-heating of coal. This study investigates the sorption capacity of hard coals with respect to acetylene, and the acetylene volume is related to the proportion between carbon and oxygen as well as to moisture and porosity levels. The largest amounts of acetylene are adsorbed by low-rank coals with high oxygen content, highly porous and characterized by large specific surface areas and high moisture content. Higher rank coals displaying lower porosity tend to adsorb significantly smaller amounts of acetylene. These coals have a compact structure, and their behavior is non-polar due to the presence of a layer of chain hydrocarbons surrounding the aromatic coal polymer. The analysis of desorption isotherms indicates that the process of acetylene adsorption is irreversible. Desorption isotherms do not coincide with adsorption isotherms, forming an open hysteresis loop. Certain amounts of acetylene held more firmly to the coal structure are likely to remain there, their actual quantities depending on the coal type. The adsorption of acetylene is a polar process, involving the electron-donor and electron-acceptor centers' interactions with dipolar molecules of acetylene. The heat of the adsorption of acetylene based on the Clausius–Clapeyron equation ranges from 15 to 27kJ/mol, depending on the type of coal and the degree of coverage.In the consequence of acetylene adsorption, its concentration in mine air is reduced, which undermines the reliability of the self-heating hazard assessments.

Analysis of trace compounds generated by pressurized oxygen blown entrained flow biomass gasification

Trace compounds were measured in synthesis gas and waste water from a pilot scale pressurized entrained flow oxygen blown biomass gasifier. The feedstock used was milled soft stem wood powder. Gaseous trace compounds were analyzed by gas chromatography. Up to 20 ppm of hydrogen sulfide was observed in the cold synthesis gas and the concentration seemed to be independent of the oxygen equivalence ratio (ER). Benzene varied from 30 to 1100 ppm, strongly depended on the ER and correlated well with the methane concentration. The concentrations of acetylene and ethylene increased as the ER was reduced and could have acted as precursors for the observed soot particles which were characterized using thermogravimetric analysis, X‐ray diffraction, and scanning electron microscopy. Common polycyclic aromatic hydrocarbons from high temperature biomass gasification such as pyrene, phenanthrene, fluoranthene, and naphthalene were observed in low concentrations in the soot, in the cold synthesis gas and also in the waste water from the quench. Inorganic elements from the feedstock were observed in the waste water. Comparisons were also made with previous results from a black liquor gasifier. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 699–705, 2014

Laser absorption diagnostic for measuring acetylene concentrations in shock tubes

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 (3335.55cm−1) of the tunable diagnostic was typically set at the peak of the 3300cm−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 1720K and 0.8 to 4.0atm. 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.

Tunable fiber laser based photoacoustic gas sensor for early fire detection

A photoacoustic gas sensor using a near-infrared tunable fiber laser and based on wavelength modulation spectroscopy technique is developed. This sensor is capable of quasi-simultaneous quantification of water vapour, acetylene, carbon dioxide, and carbon monoxide (H2O, C2H2, CO and CO2) concentrations in the fire emulator. The feasibility of using this sensor as an early fire detector was demonstrated. The fire warning gases from smoldering paper were measured. The peak concentrations of gases from smoldering paper were 20,300ppm H2O, 2.1ppm C2H2, 756ppm CO, and 1612ppm CO2 after 400s.

From Voyager-IRIS to Cassini-CIRS: Interannual variability in Saturn’s stratosphere?

We present an intercomparison of Saturn’s stratosphere between Voyager 1-IRIS observations in 1980 and Cassini-CIRS observations in 2009 and 2010. Over a saturnian year (∼29.5years) has now passed since the Voyager flybys of Saturn in 1980/1981. Cassini observations in 2009/2010 capture Saturn in the same season as Voyager observations (just after the vernal equinox) but one year later. Any differences in Saturn’s atmospheric properties implied by a comparison of these two datasets could therefore reveal the extent of interannual variability. We retrieve temperature and stratospheric acetylene and ethane concentrations from Voyager 1-IRIS (Δν̃=4.3cm-1) observations in 1980 and Cassini-CIRS (Δν̃=15.5cm-1) ‘FIRMAP’ observations in 2009 and 2010. We observe a difference in temperature at the equator of 7.1±1.2K at the 2.1-mbar level that implies that the two datasets have captured Saturn’s semiannual oscillation (SSAO) in a slightly different phase suggesting that its period is more quasi-semiannual. Elevated concentrations of acetylene at 25°S in 1980 with respect to 2010 imply stronger downwelling at the former date which may also be explained by a difference in the phase of the SSAO and its dynamical forcing at low latitudes. At high-southern and high-northern latitudes, stratospheric temperatures and hydrocarbon concentrations appear elevated in 1980 with respect to 2009/2010. This could be an artefact of the low signal-to-noise ratio of the corresponding observations but might also be explained by increased auroral activity during solar maximum in 1980.

Diamond-like carbon coatings with nanocomposite structure formed by reactive magnetron sputtering of chrome in an Ar + C2H2 + N2 gas mixture and their tribological behavior

Results of a complex study of the structure, the phase and chemical compositions, the microhardness, as well as the nanomechanical and tribological properties of a-C: H: Cr: N hydrogenated amorphous carbon coatings are presented; these coatings were formed by the reactive magnetron sputtering of chromium at various concentrations of nitrogen and acetylene in the active Ar + C2H2 + N2 gas mixture. Raman spectroscopy has shown that carbon in these coatings is represented by a disordered mixture of regions with tetrahedral (sp3) and hexagonal (sp2) coordination of carbon atoms. The alloying metal in the coating formed nanosized inclusions of metal chrome, as well as of its carbide and nitride phases. It has been shown that the additional alloying of a-C: H: Cr coatings with nitrogen, which leads to the formation of chromium nitride, makes it possible to improve their mechanical and tribological characteristics.

Toxicological effects of functionalized Carbon Black Nanoparticles on Type II pneumocytes

Carbon black nanoparticle structures have been shown to influence the integrity of the respiratory tract, especially its surface functionalization is considered to structurally und functionally modulate the lung epithelia. To study the impact of functionalized carbon black nanoparticle surfaces a mouse model was established, applying the following particles by oropharyngeal aspiration: 9-nitroanthracen (NA) and benzo[a]pyren (BaP) functionalized and un-functionalized Printex®90 (7 µg), acetylene black with PAHs (7 and 15 µg) and DQ12 as positive control (7 µg). Saline as well as distilled water with and without BSA were used as controls. As readout lung function was measured after which lungs were excised for histological examinations or used to perform BAL and type II pneumocyte isolation. The grade of oxidative stress and inflammation was examined by changes in lung structure, BAL composition and type II pneumocyte metabolism. All Printex®90 functionalization's and acetylene black concentrations induced no lung injuries as evaluated by picrosirius red staining. However, acetylene black with PAHs (7 µg) provoked a reduced lung function compared to the saline control. Cell proliferation examined by immunohistology revealed elevated cell proliferations induced by Printex®90 in distilled water, BaP-CBNP and 15 µg acetylene black with PAHs respectively. Glutathione peroxidase 3 protein expressions and BAL protein and phospholipid measurements revealed no peculiarities. BAL cell profiles were influenced by treatments with Printex®90 suspended in distilled water with and without BSA and BaP-CBNP. The number of type II pneumocytes was significantly increased by 7 and 15 µg acetylene black with PAHs compared to the saline group. mRNA expression of diverse antioxidant enzymes, the pro-inflammatory cytokine IL-6, surfactant proteins and enzymes of the surfactant synthesis revealed strong deviations between all treatment groups. The short-term experiment results clearly show that small doses of surface functionalized carbon black nanoparticles only provoked marginal effects. We hypothesize long-term periods with repeated inhalations are necessary to induce marked alterations in the respiratory tract. Beside exposure time, nanoparticle dose and chemistry the particle size and the sort of vehicle are considered to be crucial.

Influence of the Oxygen Presence on Polycyclic Aromatic Hydrocarbon (PAH) Formation from Acetylene Pyrolysis under Sooting Conditions

The concentration of sixteen polycyclic aromatic hydrocarbons (PAH), classified by the Environmental Protection Agency (EPA) as priority pollutants, and the soot amount obtained from acetylene conversion for different oxygen concentrations have been determined in a tubular reactor experimental system. The present work also reports concentrations of other products such as light gases, which are known as important in the soot-PAH formation process or because of their abundance in the experiment outlet gas stream. For an acetylene concentration of 30000 ppmv two types of studies have been performed namely a) the effect of reaction temperature was evaluated between 873 and 1323 K in absence and presence of oxygen (0 and 10000 ppmv) and b) the influence of the oxygen concentration between 0 and 50000 ppmv on product formation was considered for temperatures of 973 and 1223 K. Apart from CO as the main product formed from the conversion of C2H2 in the presence of oxygen, benzene, PAH, and soot are also formed in significant amounts. They are encouraged by the presence of oxygen in fuel rich conditions at the lowest temperatures studied but seem to be diminished when the temperature is increased. The results obtained at a reaction temperature of 973 K and different oxygen concentrations showed that the PAH concentration presents a maximum of around 10000 ppmv. Moreover, for a temperature of 1223 K, an increase of oxygen concentration causes a decrease of benzene/PAH/soot formation.

Optimizing the slow light properties of slotted photonic crystal waveguide and its application in a high-sensitivity gas sensing system

To enhance the sensitivity of a gas sensing system, slotted photonic crystal waveguide (SPCW) was introduced as the gas cell, and its structure was properly optimized to obtain slow light with large bandwidth and high group index. Simulation results indicated that a relatively high group index of 110 over 2.2 nm could be achieved and the field enhancement factor would reach 12, by shifting the first and second rows of air holes adjacent to the slot. Combined with the correlation spectroscopy technology for signal processing, a detection limit of 3.15 ppm was achieved for measurement of acetylene concentration. Additionally, the active region was only 300 µm long, which could be of great advantage in the use of miniaturized absorption spectrometers.

Development of a spectrofluorimetry-based device for determining the acetylene content in the oils of power transformers

Power transformers are essential for a functioning electrical system and therefore require special attention by maintenance programs because a fault can harm both the company and society. The temperature inside a power transformer and the dissolved gases, which are primarily composed of acetylene, are the two main parameters monitored when detecting faults. This paper describes the development of a device for analyzing the acetylene content in insulating oil using spectrofluorimetry. Using this device introduces a new methodology for the maintaining and operating power transformers. The prototype is currently operating in a substation. The results presented by this system were satisfactory; when compared to chromatographic data, the errors did not exceed 15%. This prototype may be used to confirm the quality of an insulating oil sample to detect faults in power transformers.

Scalar transport in diffusion flame wrapped up by an air and fuel side vortex

The present work involves a computational study of soot (chosen as a scalar which is a primary pollutant source) formation and transport in a laminar acetylene diffusion flame perturbed by a convecting line vortex. The topology of soot contours resulting from flame vortex interactions has been investigated. More soot was produced when vortex was introduced from the air side in comparison to the fuel side. Also, the soot topography was spatially more diffuse in the case of air side vortex. The computational model was found to be in good agreement with the experimental work previously reported in the literature. The computational simulation enabled a study of various parameters like temperature, equivalence ratio and temperature gradient affecting the soot production and transport. Temperatures were found to be higher in the case of air side vortex in contrast to the fuel side one. In case of fuel side vortex, abundance of fuel in the vortex core resulted in fuel-rich combustion zone in the core and a more discrete soot topography. Besides, the overall soot production was observed to be low in the fuel side vortex. However, for the air side vortex, air abundance in the core resulted in higher temperatures and greater soot production. Probability density functions (PDFs) have been introduced to investigate the spatiotemporal variation of soot yield and transport and their dependence on temperature and acetylene concentration from statistical view point. In addition, the effect of flame curvature on soot production is also studied. The regions convex to fuel stream side witnessed thicker soot layer. All numerical simulations have been carried out on Fluent 6.3.26.

The effect of carbon input on the morphology and attachment of carbon nanotubes grown directly from stainless steel

This work presents a simple, inexpensive and scalable method to grow multi-walled carbon nanotubes (CNTs), using chemical vapor deposition, directly from stainless steel 316mesh, without any pretreatment or the use of an external catalyst. A growth method is proposed based on the generation of particle-like growth sites, which are created as a result of chromium migration to the surface during heating. Acetylene concentrations were modeled within the reactor at various flow conditions and compared to experimental results to show that carbon input can be used as a way of controlling the diameter of the CNTs. All CNTs produced were strongly rooted to the SS substrate, however the larger diameter CNTs were more difficult to break and remove by means of ultrasonication.

STUDY ON THE ACETYLENE HYDROGENATION PROCESS FOR ETHYLENE PRODUCTION: SIMULATION, MODIFICATION, AND OPTIMIZATION

In this study, an industrial acetylene hydrogenation unit is simulated utilizing three available kinetic models. The results are compared against six-day experimental data and the best model is selected. Effects of feed temperature and the amount of injected hydrogen on ethylene selectivity are also studied. According to the simulation results, the unit is not working under its optimum conditions. Furthermore, by reduction of the hydrogen flow rate to 52 kg/h, process selectivity is increased. In addition, a new approach is proposed to modify the hydrogenation process and reduce undesired by-products. In the simulation of the modified process, hydrogenation reactors temperature, hydrogen flow rate, and H-1/H-2 ratio were regulated as adjustable parameters for the process optimization. The simulation shows that ethylene selectivity increases by 12%, while acetylene concentration and hydrogenation reactor temperature remains within acceptable ranges. Such selectivity could be achieved at the hydrogen flow rate of 50 kg/h with H-1/H-2 ratio of 0.1/0.9.