Acetylene Air Research Articles

Demonstration of Acetylene–Air Flame by Hydrolysis of Calcium Carbide to Rid Blind Beliefs and Misconceptions Regarding Purported Water Lit Lamp

Demonstration of Acetylene–Air Flame by Hydrolysis of Calcium Carbide to Rid Blind Beliefs and Misconceptions Regarding Purported Water Lit Lamp

Numerical Simulation of Gaseous Detonation Performance and Wall Reflection Effect of Acetylene-Rich Fuel

The efficient utilization of energy in rich fuel detonation processes and the effective control method of soot are important topics in combustion research. In this paper, we numerically study the detonation wave behavior of acetylene–air systems in rich fuel condition by using a reduced reaction mechanism. The non-stiff terms of the governing equations are solved explicitly using the gas kinetic scheme, and the stiff terms are solved implicitly. Our results show that the acetylene pyrolysis is the dominant reaction process. The oxidation reaction is exploited to initiate the reaction induction process, providing the required energy to overcome the potential energy barrier. The secondary detonation structure is due to the stable interaction of the transverse waves and the combined action of the vinyl reaction system, thus effectively improve the energy release rate and providing a powerful solution for the fuel-rich high-energy release of advanced heat engines. The area of the unreacted pocket increases with the acetylene concentration, resulting in an irregular wave-front and detonation cell. The reflected shock wave impacting on the wall induces the secondary reaction of the detonation products. The concentration of polycyclic aromatic hydrocarbons decreases significantly and regenerates near the wall. Our approach provides an effective tool for controlling detonation soot and the preparation of carbon particles.

Turbulent flame propagation mechanism of polymethylmethacrylate particle cloud–ammonia co-combustion

Ammonia is a promising energy carrier for realizing a carbon-neutral society. In particular, solid particle cloud–ammonia co-combustion is considered as an efficient and feasible method to reduce CO2 emissions from the thermal power generation sector by using particle-fuel such as solid waste, biomass, and pulverized coal particles in combustors. However, the fundamental turbulent flame propagation mechanism of solid particle cloud–ammonia co-combustion remains unknow. Therefore, the present study intends to investigate and validate the general turbulent flame propagation mechanism of solid particle cloud–ammonia co-combustion. To achieve this aim, silica particle cloud–ammonia–oxygen–nitrogen mixing combustion, silica particle cloud–acetylene–air mixing combustion, and PMMA particle cloud–ammonia–oxygen–nitrogen co-combustion experiments were conducted. The results showed that the turbulent flame propagation velocity of silica particle cloud–gas-fuel–oxidizer mixing combustion is lower than that of pure gas-fuel–oxidizer combustion. However, the comparison of the turbulent flame propagation velocity of PMMA particle cloud–ammonia co-combustion and that of pure ammonia combustion, showed that whether the flame propagation of the co-combustion was higher than that of the pure ammonia combustion was dependent on the equivalence ratio of the ammonia-oxidizer. Therefore, the consistency of the results between the current study of PMMA particle cloud–ammonia co-combustion and the previous study for coal particle cloud–ammonia co-combustion indicates the turbulent flame propagation mechanism of solid particle cloud–ammonia co-combustion is dominated by the negative effect of the heat sink by unburned particles and the local equivalence ratio increment effect in the preheat zone of the flame front by the addition of the volatile matter, and that the positive effect of radiation from soot particles has little effect on the turbulent flame propagation of co-combustion for small-scale flames. Further, the influence of the heterogeneous combustion of char particles on the turbulent flame propagation of solid particle cloud–ammonia co-combustion is minor because of its slow combustion process. Based on the validated turbulent flame propagation mechanism of co-combustion, new numerical simulation models for solid particle cloud–ammonia co-combustion can be developed in the future.

An experimental study of detonation propagation and re-initiation for acetylene–air mixtures in a narrow channel

Detonation propagation, re-initiation, and flame propagation in acetylene–air mixtures were investigated in a channel with a transverse dimension that is comparable with the width of the detonation cell. Experiments were carried out in a channel with a square cross-section of 5 mm $$\times $$ 5 mm. The detonation wave passed from the driver section into the transparent test section. The trajectories of the propagation of glowing combustion products (high-speed image sequences) were recorded, and high-speed schlieren image sequences of the reaction zone and shock waves were obtained. The flame front velocity was measured. The intensity of the shock waves was measured with piezoelectric pressure transducers. Depending on the equivalence ratio ER, four modes of combustion propagation were detected: (1) steady detonation; (2) decay and re-initiation of detonation; (3) detonation decay and flame acceleration; and (4) detonation decay and the absence of flame acceleration. Quantitative evaluation of the boundary layer thickness was carried out. The intensity of the shock wave and the flame front velocity were analysed for different modes. It was shown that the re-initiation of detonation in a mixture of acetylene and air with $$\text {ER} = 1.6$$ is characterized by a spatial interval of $$1000\pm 50$$ mm and a time interval of $$1300\pm 100~\upmu \hbox {s}$$ .

Decaying modes of propagation of detonation and flame front in acetylene–air mixture

Decaying modes of a flame front propagation in narrow channel for acetylene–air mixtures were investigated experimentally using optical methods of diagnostics. Experiments were carried out using an open detonation channel of square cross section with transverse dimension of 3 mm and length of 1000 mm. It was connected to the detonation tube of 20 mm diameter and length of 3000 mm. A galloping decaying propagation of the combustion inside the narrow channel after the entry of a steady Chapman–Jouguet detonation into the channel was registered. It was shown that the propagation of detonation-like galloping combustion is possible in channels of subcritical size. Evolution of the flame front velocity was obtained. The time intervals of gallops and distance intervals were measured. After the decay of the detonation wave, the average velocity of the flame front decreases first to 1000 m/s, and then to 200 m/s.

Spectra signals of gas pressure pulsations in annular and linear dual-slotted nozzles

ABSTRACTComplex results in experimental and numerical flow dynamics research and spectra signals of gas pressure pulsations in annular and linear dual-slotted nozzles are presented. Experiments are performed in a pulsed aerodynamic setup using acetylene–air mixture combustion products as working gas. Viscous flow calculations are based on the Navier–Stokes equations for multicomponent reactive gaseous medium using single-temperature chemical nonequilibrium model. As a result, the frequency Fourier spectrum of pressure pulsation at the thrust wall center is determined. Typical pulsed pressure signals obtained in the calculations and detected in the experiments are presented.

Effect of active gas mixture composition on tribological behavior of coatings obtained by reactive magnetron sputtering of chromium in acetylene–nitrogen and acetylene–air gas mixtures

The tribological properties of chromium-based coatings deposited by reactive magnetron sputtering in argon–acetylene–nitrogen and argon–acetylene–air mixtures of different volume compositions have been studied. The coatings acquired in acetylene–nitrogen gas mixture have DLC structure and demonstrate high mechanical characteristics and low coefficient of friction values in dry friction. Although the coefficient of friction of these coatings has a tendency to decrease with the increasing nitrogen volume concentration in the mixture (until the values below 0.1 in dry friction in pair with silicon nitride), their performance diminishes at high contact pressures. This decrease was maximal for coatings deposited in acetylene–nitrogen gas mixture, with 80 vol % of nitrogen. The substitution of nitrogen with air is shown to considerably improve the performance, but a further increase in the air volume fraction above 85 vol % provokes a drastic decrease in the efficiency, especially at high contact pressures. The possible mechanisms of these effects and the abilities of their elimination are discussed, as well.

Combustion of boron particles in products of an air–acetylene flame

Boron is an attractive fuel for propellants and explosives because of its high volumetric and gravimetric energy density. However, despite multiple previous studies, burn times and combustion temperatures of fine boron particles in well-characterized environments are not well known. The aim of this work was to characterize the combustion of boron particles injected into air–acetylene flames and to determine their burn times and combustion temperatures as a function of their size. The experiments used 95% pure commercial boron powder with particles in the range of 0.4–30µm. Premixed acetylene–air flames with varying equivalence ratios (0.62 and 1.65) were produced. Boron powder was injected axially into the flame combustion products with a nitrogen jet. The particle size distributions were determined using powder that exited from the injector and captured directly on to microscope slides. Agglomerated particles fed into the flame were observed directly and accounted for in the particle size distributions. Powders were analyzed using scanning electron microscopy (SEM) and particle sizes were corrected accounting for the fractal dimensions of the observed agglomerates. The measured burn times were correlated with the obtained particle size distributions to recover the effect of particle size on its burn time. The environment in which the particles burned was characterized in detail using computational fluid dynamics. Results indicated that for micron-sized amorphous boron particles, their time, tb, in ms, can be described as a function of the particle diameter, d, in µm, as tb ≈ 4.73•d0.75. Average combustion temperatures exceed 2600K in a pre-mixed hydrocarbon flame environment and show no significant correlation with particle size or burn times.

Microwave-assisted plasma ignition in a constant volume combustion chamber

An experimental study was carried out to investigate the effect of microwave-assisted plasma ignition on laminar flame development in a 1.4l constant volume combustion chamber (CVCC). The microwave-assisted plasma ignition system consisted of a commercially available 2.45GHz magnetron (700W), a waveguide, a 3-stub tuner, a mixer and a non-resistor spark plug. The combustion tests were performed using an acetylene–air mixture at a range of equivalence ratios and initial ambient pressures. The ejection timing of the microwave also varied based on the spark event. In-chamber pressure analysis and high speed imaging were combined in a CVCC to compare the results between the microwave-assisted ignition and the conventional spark ignition. The enhancement was evaluated from the combustion phase, combustion index, and the flame kernel size based on the in-chamber pressure results and shadowgraph images. Compared to the conventional spark ignition condition, the microwave-assisted plasma ignition showed an extended lean limit with the advanced combustion phase. The conventional spark ignition had a lean limit at the equivalence ratio of 0.6, while it was extended to 0.5 by the microwave-assisted plasma ignition under the initial ambient pressure of 0.1MPa. The flame development time (time for 0–10% of total net heat release) for the microwave-assisted plasma ignition showed significant advancement especially in the lean mixture condition. The shadowgraph images indicated that the flame speed increased up to 20% with the microwave-assisted plasma ignition. In terms of equivalence ratios and initial ambient pressures, the enhancement was decreased with rich mixture and high initial ambient pressure conditions. In this situation, however, an early microwave ejection strategy was found to be beneficial to combustion showing a higher combustion index than the conventional spark ignition condition.

Experimental investigation of dynamics of premixed acetylene–air flames in a micro-combustor

This paper describes a detailed experimental study performed to investigate the flame propagation behaviour of premixed flames in micro-channels. A novel, modular, stackable micro-combustor was developed for this purpose. For a chosen planar channel geometry, the flow condition and the mixture equivalence ratio of premixed acetylene–air were varied to investigate various modes of operation. Three different modes of operation were observed; they were (i) stable periodic operation – consisting of ignition, flame propagation, flame extinction, and re-ignition, (ii) a-periodic operation, and (iii) anchored flame condition. The present work also aims to provide quantitative information on the dynamics of premixed acetylene–air flames propagating inside micro-channels. A novel measurement approach based on OH * chemiluminescence measurements employing a single photomultiplier unit was developed for this purpose. The data recorded were post processed using an in-house developed MATLAB code to evaluate the mean flame propagation speed measured between three different spatial locations along the length of the micro-channel. The results from the flame propagation speed measurements performed during ‘periodic’ mode of operation indicated that the flame travelled at higher propagation speed in the mid-length region of the channel compared to that at the initial entry point, suggesting flame acceleration. This flame acceleration could be attributed to a situation where the flame experienced different local equivalence ratio conditions at different upstream locations. The results suggest that after completion of a cycle of operation consisting of ignition, flame propagation and flame extinction, the fresh mixture that filled the channel was diluted with the exhaust gas from the previous cycle. This pocket of diluted mixture convected downstream with time, thus enabling the spatial variation in local equivalence ratio along the micro-channel.

Hydrogen addition to acetylene–air laminar diffusion flames: Studies on soot formation under different flow arrangements

Axisymmetric co-flowing acetylene/air laminar diffusion flames have been experimentally investigated to study the effect of hydrogen addition on soot formation and soot morphology. An acetylene–hydrogen jet burning in co-flowing air at atmospheric pressure has been studied under different flow arrangements, i.e., premixed and with separate addition of acetylene and hydrogen. Thermophoretic sampling and analysis by transmission electron microscopy are employed for soot diagnostics. Soot microstructure, primary particle size, soot volume fraction, and fractal geometry results are reported. The effect of hydrogen addition on the temperature field is moderate (maximum increase ∼ 100 K ), the effect being greater when hydrogen is premixed with acetylene. Soot volume fraction decreases with hydrogen addition. A shift was noted in the soot volume fraction peak with change in the Reynolds and Froude numbers at the burner exit. The primary soot particle diameter is in the range of 20–35 nm. Soot particles are larger in size close to the burner for the pure acetylene flame. A reverse trend is observed with hydrogen addition. The fractal dimension of the soot aggregates is about 1.7–1.8. It is unaffected by hydrogen addition and location in the flame. Soot aggregate size tends to decrease with hydrogen addition. The results of the present study on the effect of hydrogen addition on soot volume fraction and mean primary particle size are in good correlation with the results of other investigators for ethylene–, propane–, and butane–air flames, which have been described with regard to the HACA mechanism of soot nucleation and growth and enhanced soot oxidation in fuel-rich flames by increased OH radical concentration.

Pulsed flow modulation of soot production in a laminar jet-diffusion flame

An axisymmetric, co-flow, acetylene–air diffusion flame was driven by an acoustic source at frequencies ranging from 230 to 1000 Hz and powers of 0–10 W. Soot concentration was measured both locally within the flame and globally far downstream of the flame. The acoustic characteristics of the system are detailed in this manuscript. We show that the acoustic velocity at the fuel exit plane strongly affects the soot concentration within the flame and emitted by the flame. When the acoustic velocity magnitudes are much larger than the mean fuel velocity, the average soot number concentration measured far downstream of the flame was reduced by almost three orders of magnitude. A simple scaling analysis is performed to show that a partial premixing mechanism may be responsible for the observed changes to the soot properties of the flame. To test this hypothesis, sooting properties of partially premixed flames were characterized over a range of equivalence ratios in the same burner. While initial addition of air into the fuel stream slightly increased the amount of soot released, further addition of air suppressed soot production. Comparisons of the acoustically forced flames to partially premixed flames support the hypothesis that the acoustic field aids in partially premixing the flame.

In situ monitoring of degradation processes of carbon/carbon composites in an acetylene/air by two-dimensional atomic absorption spectrometry

The purpose of this study is to develop a novel measurement technique for in situ monitoring of the degradation processes of high temperature materials in combustion fields. Spatially, spectrally and temporally resolved images of emission from diatomic molecules in an acetylene–air flame were observed by a spectrovideo camera, which was assembled by combining a monochromator and a high speed UV video camera. Two-dimensional atomic absorption spectrometry (2D-AAS) using the spectrovideo camera was applied to investigate the degradation processes of C/C composites in an acetylene–air flame. The test samples employed in this study were three different C/C composites with Mg-doped oxidation-resistive double coating layer of SiC and glass materials, and C/C substrate. The result indicated that the temporal changes in the spatial distribution of atomic absorption by Mg atoms proved to be a good measure for in situ monitoring of the degradation/oxidation processes of the coating layer and substrate of C/C composites in high temperature fields.

Laser-induced fluorescence excitation spectroscopy of the magnesium oxide B^1Σ^+–A^1Π system

Excitation scans of the MgO B(1)?(+)-A(1)? transition were made in a seeded acetylene-air flame. The combustion of magnesium in oxygen and carbon dioxide is well known and is of significant interest for fire safety, solid propellant applications, and recently for use as an in situ resource propellant for planetary exploration of Mars. This spectroscopic study expands the available data on this electronic transition, particularly data at high rotational states that are lacking in the literature. Rotational parameters of the v = 0, 1, and 2 states of B(1)?(+) are derived.

Background signals in wavelength-modulation spectrometry by use of frequency-doubled diode-laser light II Experiment

In an accompanying paper [Appl. Opt. 40, 783-793 (2001)], we predict the existence of background signals from a frequency-doubled wavelength-modulated diode-laser system. We now demonstrate and characterize various nf harmonics of such background signals from a system producing light in the 422-nm region by use of a single-pass KNbO(3) crystal with respect to the modulation amplitude, the laser center frequency, and the crystal temperature. It is demonstrated that 2f detection is plagued by considerably larger amounts of background signal than is detection at other higher, even harmonics. This result implies that 4f or 6f detection is often to be preferred in comparison with 2f detection when frequency-doubled wavelength-modulation spectrometry (WMS) is to be used. This preference is illustrated by the detection of Ca in an acetylene-air flame. It is also shown that the background signals have a much stronger dependence on the modulation amplitude than do the analytical signals. This difference implies that the optimum detectability for frequency-doubled WMS is often reached for modulation amplitudes lower than those normally used. An analysis of the effect of a finite temperature stability of the doubling crystal on the drift of the background signals as well as on the detectability is included. The results verify the theoretical description given in our accompanying paper.

Numerical simulation of detonation initiation in a flame brush: the role of hot spots

This is the final paper in a series describing numerical simulations of deflagration-to-detonation transition (DDT) for conditions similar to reflected shock-tube experiments in an acetylene–air mixture (100 Torr, 298 K). In the experiments and calculations, the interaction of a shock wave and an expanding flame front leads to the rapid creation of a turbulent flame brush and, for sufficiently high Mach numbers of the incident shock, to the subsequent transition to a detonation. The two-dimensional reactive Navier-Stokes equations, including the effects of viscosity, thermal conduction, molecular diffusion, and chemical reaction, are solved on a high-resolution adapting mesh. Shock-flame interactions, through the Richtmyer-Meshkov instability, create and maintain a highly turbulent flame brush and are responsible for injecting unburned material into the region of burned material. Hot spots are created by pressure fluctuations and shocks generated in the flame brush. At relatively low Mach numbers, hot spots that transition to detonation are created outside of the flame brush. For higher Mach numbers, such hot spots are created in pockets of unreacted material inside the flame brush. In both cases, the hot spots give rise to detonations by the gradient mechanism, in which a gradient in induction time leads to a supersonic spontaneous wave that later becomes a detonation.

Two-dimensional large eddy simulation of soot formation in the near-field of a strongly radiating nonpremixed acetylene–air turbulent jet flame

A numerical study of soot formation in the near-field of a strongly radiating, nonpremixed, acetylene–air planar jet flame is conducted using Large Eddy Simulation in two dimensions to examine coupled turbulence, soot chemistry, and radiation effects. The two-dimensional, Favre-filtered, compressible Navier-Stokes, total sensible energy and mixture fraction equations are closed using the Smagorinsky subgrid-scale (SGS) turbulence model. Major species of gas-phase combustion are obtained using a laminar flamelet model by employing experimentally obtained laminar flame state relationships for the major species mass fractions as a function of gas-phase mixture fraction. A combination of a presumed Beta filtered density function and a scale-similarity model are used to account for SGS mixture fraction and scalar dissipation fluctuations on the filtered composition and heat release rate. A soot transport and finite-rate kinetics model accounting for soot nucleation, surface growth, agglomeration, and oxidation is used. Radiation is modeled by integrating the filtered radiative transfer equation using the discrete ordinates method. Both instantaneous and time-averaged results are presented in order to highlight physical and numerical modeling issues and to examine turbulence, soot chemistry, and radiation interactions. Qualitative comparisons are made to previous numerical results and experimental data.

Numerical simulation of deflagration-to-detonation transition: the role of shock–flame interactions in turbulent flames

Two-dimensional reactive Navier-Stokes equations for an acetylene–air mixture are solved numerically to simulate the interaction of a shock wave and an expanding flame front, the formation of a flame brush, and deflagration-to-detonation transition (DDT). The effects of viscosity, thermal conduction, molecular diffusion, and chemical reactions are included. A new method for adaptive mesh refinement was used to ensure that the structure of the flame front was resolved. The shock–flame interactions, through the Richtmyer-Meshkov instability, create and maintain a highly turbulent flame brush. The turbulence is not Kolmogorov turbulence, but it is driven at all scales by repeated shock–flame interactions. Pressure fluctuations generated in the region of the turbulent flame brush create, in turn, hot spots in unreacted material. These hot spots may then transition to DDT through the gradient mechanism. Repeated shock–flame interactions and merging shocks in unreacted material lead to the development of a high-speed shock that moves out in front of the turbulent flame. The region between this shock and the flame is subject to intense fluctuations generated in the flame. The simulations show that the interactions of shocks and flames create the conditions under which deflagration-to-detonation transition may occur.

Transition from Deflagration to Detonation in an End Multiphase Slug

A transition scenario from deflagration to detonation in an end multiphase slug has been proposed, in which the slug is located near an end wall and is made of a dense combustible dust cloud suspended in a combustible gas. To prove the concept, experiments were carried out in an 80 mm diameter detonation tube filled with an acetylene–air mixture and a slug of dense aluminum dust suspension near the end wall. The experimental results and numerical analysis indicated an enhancement of wall peak pressure by a factor of more than twice that of a transition from deflagration to detonation (DDT) in the gas system alone.

Analysis of degradation processes of carbon/carbon composites in a high temperature chemical flame by a spectrovideo camera

The purpose of this study is to develop a measurement technique for in situ monitoring of the degradation processes of thermal-resistance materials, such as C/C (carbon/carbon) composites, in high temperature fields. Spatially, spectrally and temporally resolved images of emission from diatomic molecules were observed in an acetylene–air flame by a spectrovideo camera, assembled by combining a monochromator and a high speed ultraviolet (UV) video camera. In order to calculate flame temperatures around the given test samples, C/C composite disks, emission intensity images of two Cr lines were observed by spraying a Cr 1000 ppm solution. The emission intensity images of OH, CH and C 2 bands were measured to investigate the degradation processes from their changes. The test samples employed in this study were graphite, two-dimensionally textile C/C composites and oxidation-resistive C/C composites with double layer coatings of SiC and glass materials. Graphite was tested as a reference raw material of the C/C composites. The result indicated that the time dependencies in the spatial distribution of OH and C 2 emissions observed by the spectrovideo camera proved to be an effective measure to monitor the degradation/oxidation processes of the C/C composites in high temperature fields.