Flame Propagation Research Articles

The effect of pressure evolution on flame propagation dynamics of H2/CH4 mixtures explosion in a horizontal closed duct

To investigate the effect of explosion pressure on flame propagation of H2/CH4 mixtures, the pressure dynamics of H2/CH4 mixtures explosion with different volume fractions of hydrogen (0, 0.2, 0.4, 0.6, 0.8, 1 (×100/%)) and equivalence ratios (0.8, 1, 1.2, 1.4) is measured using 2 pressure sensors in a horizontal duct with ignition electrode position not at the end. The flame propagation characteristic is studied using images recorded by a high-speed camera. Through the analysis and discussion of the experimental results, the interaction among explosion pressure, flame front, and flow field are discussed. The results show that when the volume fraction of hydrogen is greater than 0.6, the rate of explosion pressure rises, the flame front position, and the flame front speed are greatly improved. At higher and lower equivalence ratios, it is easier to form distorted “tulip” flames. As the volume fraction of hydrogen increases, the inclination angle of the flame front decreases, and becomes a typical “tulip” flame gradually. The convection of the flow field is an important cause of pressure oscillation, which makes the pressure distribution uneven, and its influence on Pmax, (dP/dt)max, and tc is weak. As the volume fraction of hydrogen increases, the duration of pressure oscillation decreases, and the intensity of pressure oscillation increases. The pressure wave has a substantial impact on the flame front propagation of distorted “tulip” flames and the pressure history of typical “tulip” flames.

Influence of Ambient Pressure on the Jet-Ignition Combustion Performance and Flame Propagation Characteristics of Gasoline in a Constant Volume Combustion Chamber

Based on a constant volume combustion chamber, the initial ambient pressure effect on gasoline combustion performance and flame propagation of the active and passive pre-chamber ignition systems were studied. Compared with the passive pre-chamber, the active pre-chamber can significantly expand the lean combustion limit from 1.2 to 1.5, enhance the ignition and combustion performance, and speed up the combustion of the main combustion chamber. At slightly lean combustion conditions, the heat release performance has a positive correlation with the initial ambient pressure. As the premixed λ increases, the heat release performance and the initial ambient pressure begin to become negatively correlated. Ignition delay can be decreased by approximately 50% at an initial pressure of 0.75 MPa, premixed lambda of 1.2 with APC compared with PPC. The high ambient pressure (1.0 MPa) in the constant volume chamber greatly reduces the mixture entrainment ability of the jet flame at lean combustion conditions, thereby reducing the combustion speed and peak heat release rate.

Based on the strong oxidant AP adjustment strategy to obtain Al/AP@PVDF composite material with excellent energy release performance

In this paper, ammonium perchlorate (AP) as a strong oxidant has been added into Al/polyvinylidene difluoride (PVDF) nanothermites. Based on homogeneous structure of PVDF, shorter reaction contact between components can be obtained for more outstanding ignition and combustion performance. Water contact angle experiments were conducted to evaluate the hydrophobicity of the composite films, indicating that the suitability of composite material has enhanced under wet environment. According to TG-DSC results, the thermal decomposition of AP can improve the whole heat release process, which theoretically has excellent combustion performance advantages. Constant volume pressure tests were conducted to assess the energy release properties of the films compared with Al@PVDF films. Combustion performance in air was evaluated by employing optical sensors and a high-speed camera to measure factors such as the ignition delay time, light intensity and combustion flame propagation. After adding 15 % AP, the maximum pressure of Al/AP@PVDF film is 0.0960 Mpa, and that of Al@PVDF film is 0.0805 Mpa. The maximum pressure of the film is increased by nearly 19.25 %. Compared with Al@PVDF film, the ignition delay time of Al/AP@PVDF film is shortened by 45 ms, and the light intensity is increased by nearly 93.39 %. However, excessive AP content adversely impacted film formation efficiency, leading to the deterioration of various properties. Therefore, an optimal AP content of approximately 15 % in Al/AP@PVDF system was finally identified.

Investigation of lubrication and tribological behaviors in a diesel engine with the new designed flow-guided combustion chamber

Changes to the piston bowl geometry directly affect engine performance, exhaust emissions, combustion characteristics and air/fuel mixture formation. In this study, a new combustion chamber (NCC) geometry for a single cylinder direct injection diesel engine is presented, and experimentally compared with the standard combustion chamber (SCC) geometry. Each combustion chamber was fitted to the engine and performed long-term test for 100 h. The effect of combustion chamber bowl geometry on piston rings and lubricating oil was investigated. Firstly, soot was measured in the engine, and the NCC geometry reduced soot emission by approximately 12.32 % compared to the standard bowl geometry type at part load. With the NCC geometry, homogeneity fresh charge and flame propagation were achieved by providing wall-guided flow. The tribological effect of bowl geometry on the lubricating oil was investigated. In the oil analysis, Al,Ca,Co,Cr,Cu,Fe,Mg,Mn,Mo,Ni and Zn elements were higher in the SCC geometry than in the NCC geometry. Especially at the end of the 100th hour of operation, the presence of elements such as Fe and Al showed an increase in engine wears. The lubricating oil kinematic viscosity for SCC was 111.9 mm2/s at 40 °C and 127.9 mm2/s for NCC. In the new geometry, the flash point temperature of the lubricating oil was measured as 232 °C, while this value in the standard geometry was measured as 222 °C. This showed that the volatility and degree of contamination of the oil was lower with the new geometry. SEM/EDX analysis of the piston rings showed a significant difference between the first and second rings for the two geometries. The wear lines in the standard geometry were found to be deeper and more visible than in the new geometry.

Evaluating potential of increasing flow intensity and reducing crevice volume to improve thermal efficiency and hydrocarbon emission in spark-ignition natural gas engines

Low thermal efficiency and high hydrocarbon emissions caused by slow combustion rates and high methane emissions hinder the development of natural gas (NG) engines. Engine structure modifications have always been an important means of improving the combustion effects of engines. This study investigates the effects of combustion chamber improvements on the thermal efficiency and hydrocarbon emissions of stoichiometric spark-ignition NG engines through numerical simulations. The improvements aimed to enhance squish flow, organize high tumble flow, and reduce crevice volume. The results indicate that strengthening the squish intensity by increasing the squish area of the piston can accelerate flame propagation and reduce exhaust loss. However, this improvement is hindered by a significant rise in heat transfer loss, which limits further gains in thermal efficiency. Compared to the traditional high swirl combustion chamber, a high tumble combustion chamber (dual straight intake port combined with a hemispherical piston) can promote flame propagation in the early stages of combustion and increase thermal efficiency by 1.43%. However, the accelerated flame propagation rate resulting from increased flow intensity has little potential to reduce hydrocarbon emissions due to the small contribution of flame quenching to unburned hydrocarbon production. The primary source of hydrocarbon emissions from NG engines is unburned methane in the piston crevice. Therefore, when addressing hydrocarbon emissions from NG engines, the first consideration should be to minimize the volume of the piston crevice, which will significantly reduce methane emissions and incomplete combustion loss.

Experimental Investigation of Microwave-Assisted Kerosene Supersonic Combustion

ABSTRACT The microwave-assisted kerosene combustion in supersonic flow was invested experimentally using a novel microwave-flame coupling method. The experiment used a direct-connected system, with a horn antenna employed to introduce microwaves into the combustion chamber, generating a traveling wave within the cavity. The microwave field simulation results confirm this coupling method’s feasibility. The experimental results showed that with the influence of the microwave, the flame’s stable position moved upstream by 7.4 mm. The average velocity of flame propagation increased by 64% upstream of entering the cavity and by 61% upon exiting it. The specific impulse of the scramjet was increased by about 4% under a 700W continuous microwave. In the presence of hydrogen, there was a significant increase in the excitation of NO and N2. However, in hydrogen-free combustion processes, the enhancement of radicals was considerably less compared to ignition processes, suggesting a close correlation between microwave-assisted combustion and hydrogen. These experimental results validate the feasibility of the microwave-combustion coupling method, representing a novel exploration into microwave-assisted kerosene combustion that aligns more closely with the practical application scenarios of scramjet engines.

Flame Characterization of Cofiring Gaseous and Solid Fuels in Suspensions.

This work characterizes technical scale flames of suspension firing of gaseous and solid fuel mixtures through in-flame measurements with focus on nitrogen oxide (NOx) formation. The aims are to investigate the impacts of substituting a solid fuel with a gaseous fuel on the important mechanisms for NOx formation and to highlight important considerations for burner design. The investigation was performed in a 100 kW test unit that fires mixtures of propane and lignite. The global emissions levels and in-flame compositions were measured. A detailed reaction model was used to interpret the experimental results. The study highlights the importance of the early release of volatile nitrogen to reduce the levels of NOx. The findings indicate that substituting lignite by propane is advantageous in terms of reducing NO emissions, primarily due to the diminished input of fuel-bound nitrogen to the flame. However, this holds true only if the flame temperature of the gaseous fuel does not increase excessively. Finally, introducing a relatively small quantity of solid fuel to a propane flame appears to alter the flame behavior to resembles that of the "solid fuel," with a longer and wider flame. Despite this, carbon monoxide and nitrogen oxide concentrations remain like gas combustion but more dispersed.

Numerical Research of Flame Propagation Process in a Supersonic Combustor with Multi-Strut

ABSTRACT The flame processes and the influence of different factors on the cross flame propagation width in a supersonic combustor equipped with multi-strut fueled with kerosene were analyzed to deepen the understanding of supersonic flame characteristics. Under the conditions of T t = 1680K, P t = 1.64Mpa, and Ma = 2.7, the numerical calculations using the multi-step combustion reaction mechanism were carried out. The mixing performance and flame propagation width could be improved by increasing the number of struts. In the multi-strut injection method, the cross flame was observed outside the central flame. The mechanism of cross flame formation was revealed. The establishment of the cross flame had a maximum spacing requirement between injection struts, but this limit could be expanded by the high temperature zone formed by the narrow-distance injection strut. The effects of igniter energy and ignition strut equivalence ratio on the flame diffusion process were studied. Then the boundary conditions required for the cross flame propagation were obtained. The results of this study are highly significant for enhancing the performance of large-scale supersonic combustors in the future.

Computational insights into flame development and emission formation in an ammonia engine with hydrogen-assisted pre-chamber turbulent jet ignition

Ammonia, as a promising green fuel for achieving carbon neutrality and zero-carbon emissions, encounters obstacles in practical engine applications due to its intrinsic combustion properties like low burning velocity and high autoignition temperature. Hydrogen-assisted pre-chamber turbulent jet ignition (TJI) technology has recently demonstrated great potential in extending the lean limits and enhancing the stability of ammonia combustion. As such, this study conducts a comprehensive analysis on the flame development and emission formation processes under the active pre-chamber TJI mode fueled with ammonia and hydrogen using computational fluid dynamics (CFD) modeling integrated with detailed chemical kinetics, particularly focusing on the effects of hydrogen energy ratio and spark timing. It is found that the active ammonia-hydrogen TJI engine is typically characterized by four primary physical processes involving H2 mixture preparation in the pre-chamber, flame kernel formation and development within the pre-chamber, the formation and ejection of hot jet across the orifices, and the turbulent flame initiation and propagation in the main chamber. Hydrogen injection holds a scavenging effect on the residuals in the pre-chamber while forms fuel stratification near the spark plug, enhancing the ignition stability. Besides, the current combustion mode is commonly characterized by two-stage heat release in the main chamber, but exhibits a three-stage heat release as increasing the premixed H2 ratio. The first stage is dominated by a hot jet flame, the second stage is characterized by turbulent flame propagation or autoignition, and the third stage is induced by a secondary jet ejected from the pre-chamber, which becomes more prominent as the H2 ratio increases. Hydrogen blending could not only facilitate the turbulent flame propagation of NH3-air mixture in the main chamber but also enhance the initiation of flame kernel in the pre-chamber, thereby promoting the overall combustion process and potentially improving the thermal efficiency. The N2O emission is produced in two distinct stages, wherein N2O is generated and undergoes conversion during the main combustion phase, while unburned crevice gases mix with burned gases and convert into N2O during the expansion stroke. Increasing the premixed hydrogen ratio leads to an increased in-cylinder temperature, which in turn facilitates a reduction in N2O emissions and mitigates unburned ammonia. Furthermore, optimization of the spark timing is required after implementing the hydrogen addition into the intake manifold to achieve desirable combustion phasing and further improve the thermal efficiency. Finally, a novel combustion concept, denoted as TJI assisted compression ignition mode, is proposed for achieving high thermal efficiency in ammonia engines via adopting high compression ratio and premixed ammonia-hydrogen charge under the TJI strategy.

Numerical study on the influence of venting interlayer structure on the explosion venting effects

Catering is an important business format of commercial complexes in Chinese Mainland, and most of its kitchens use natural gas as fuel. However, once natural gas leaks, it is very easy to cause explosion accidents. For kitchens without external windows in large commercial complexes, the horizontally arranged explosion venting interlayers should be installed to lead the explosion vents from the kitchens to the exterior walls of the buildings. The paper conducts modeling research on linear and 90° bend, as well as interlayers containing structural beams (obstacles), and obtains the explosion propagation laws of different explosion venting interlayer structures. After the flame enters the venting interlayer, the presence of obstacles can cause flame acceleration; the peak pressure in the kitchen shows an increasing-sudden decreasing-increasing trend as the distance between obstacles and the explosion outlet decreases. When the obstacle is located 2.5 m away from the interlayer inlet, the maximum flame propagation speed can reach 356.5 m/s. The effects of the bend structure on the propagation process of gas explosion venting have been investigated. The peak overpressure of 90° bend venting interlayer is 1.52 times that of the linear interlayer. However, there is a notable reduction in peak overpressure (approximately 26.6%) observed post-bend. Additionally, an increase in the distance preceding the bend results in an initial rise followed by a decline in peak overpressure, while the shock wave attenuation coefficient displays a trend of first increasing and then decreasing.

Impact of the blockage ratio and void fraction of porous obstacle on gas explosion characteristics in semi-confined channel

This study conducted various explosion experiments under different porous obstacle conditions of blockage ratio (BR) and void fraction (Φf). The impact of porous obstacle on flame propagation velocity (v) and peak overpressure (Pop) were analyzed. The results indicate that an increase in the BR enhances explosion pressure near the blockage area for both porous and non-porous obstacles. However, it also increases the downstream pressure decline gradient. An increase in the Φf weakens the hindrance of porous obstacle on the flame propagation, allowing more flame to pass through the internal void channels of obstacles, thus delaying the downstream pressure decay. Compared to non-porous obstacles, gas explosions disturbed by porous obstacles with both high BR (BR＞75%) and high Φf (Φf＞0.55) exhibit a lower downstream pressure decline gradient and a longer positive pressure duration. As a result, the explosion can produce a broader range of destruction.

Developing highly flame-retardant PA6-based composites via in-situ PPS nanofiber network

This study investigates the enhancement of flame-retardant properties in polyamide 6 (PA6) composites through the incorporation of nanofibrillated polyphenylene sulfide (PPS) and a flame retardant, ammonium sulfamate (AS). By strategically combining a fibrillar PPS component (15 wt%) with a minimal AS concentration (1 wt%), the composite achieves a UL 94-V0 rating and a heightened limiting oxygen index (LOI) of 33.8 %. Rheological analyses reveal the formation of an entangled fibril network, contributing to a solid-like response that effectively suppresses flame propagation and prevents dripping. Micro-combustion calorimetry (MCC) results demonstrate a synergistic effect between the PPS nanofibril network and AS, leading to a significant 17 % reduction in peak heat release rate (PHRR) in PA6-nanofibrillated PPS-AS composites, showcasing improved flame-retardant properties compared to neat PA6. Despite a trade-off in mechanical properties, this research presents a promising strategy for enhancing the flame-retardant performance of PA6 composites, offering valuable insights for addressing fire safety challenges in PA6 applications.

Experimental study of combustion efficiency and outlet temperature distribution characteristics of a combined evaporative flameholder

In ramjet engines and afterburners, combined stabilizers are employed to achieve effective flame stabilization. This paper designs a combined evaporative flame stabilizer, aimed at enhancing combustion performance and flame propagation under sub-atmospheric conditions. Combustion efficiency and outlet temperature distribution were experimentally studied under varying inlet Mach numbers, temperatures, pressures, and equivalence ratios. Results indicate that combustion efficiency increases with temperature from 600 K to 800 K, initially increases and then decreases with Mach number from 0.11 to 0.19, and decreases with pressure from 0.04 to 0.101 MPa. At an inlet temperature of 600 K, combustion efficiency drops from 55.84 % to 19.36 % as the fuel–air ratio (FAR) increases from 0.008 to 0.044, and then rises to 24.74 % at a FAR of 0.055. Similar outlet temperature distribution characteristics were observed under different inlet conditions. As the Mach number increases, the peak position of the outlet temperature gradually moves from the center to the lower wall. This study provides design guidance and engineering value for improving the combustion performance of flameholders in afterburners or ramjet engine combustion chambers.

Visualization study on the ignition and combustion characteristics of methane/hydrogen ignited by diesel

Nowadays, internal combustion engine fuels need to shift from diesel and gasoline to clean fuels. As a low-carbon fuel, methane has attracted widespread attention. Diesel ignition of premixed methane is one of the measures to achieve effective application. However, limited by the equipment and the active reactivity of methane, there are few basic visualization studies on that, resulting in a lack of deep understanding of ignition and flame propagation processes. Therefore, this paper studies the diesel ignition and combustion characteristics of diesel-ignited methane and the promotion of 10 and 20% (volume fraction) hydrogen on combustion performance based on the rapid compression and expansion machine. The experimental results indicate that methane has a suppressive effect on the ignition of diesel. The combustion process can be mainly divided into the diesel ignition stage, the premixed combustion stage, and the fuel burnout stage. Blending 10% and 20% hydrogen has little effect on the diesel ignition stage, but has a relatively great impact on the premixed combustion stage. The flame propagation can be improved with hydrogen blending, but that is limited due to the effects of ignition and wall. The combustion duration can be shortened with hydrogen blending, mainly for the CA50-90, especially at a lower equivalence ratio. The combustion efficiency can be improved with hydrogen blending. Overall, the strategy of blending hydrogen is considered more suitable for large bore engines and the results can deepen the understanding of the combustion process of diesel-ignited methane/hydrogen/air mixtures and have value for the relevant engine development so that the energy shortage and environment pollution issues can be alleviated.

Large eddy simulation investigation of the effect of radiative heat transfer on the ignition progress in a model combustor

Radiation significantly influences turbulent combustion. This paper investigates the impact of radiative heat transfer on the ignition process in a multi-staged model combustor. The ignition process is simulated both without and with consideration of radiation. Large Eddy Simulations based on the Euler-Lagrange description of the liquid spray and the Dynamic Thickened Flame model coupled with a skeletal chemical reaction mechanism are employed. The Weighted Sum of Gray Gases method are employed to solve the spectral properties and the Discrete Ordinates method is employed to solve the radiative transfer equation. The results indicate that radiative heat transfer influences the flame structure during the ignition process. In the flame propagation phase, both the total heat transfer and the exit average temperature are higher, with the radiative heat transfer during ignition being less than 15% of the total heat transfer. During the kernel generation phase, radiative heat transfer leads to a 7.24% increase in the maximum temperature of the flame kernel, a 7.74% expansion of the flame surface area, and outward movement of the position of the maximum heat release rate. Additionally, the ignition delay time extends by 14.91%. In the flame propagation phase, the flame transfers heat to the mixed gas and droplets near the flame surface through radiation, promoting flame spread.

The Heat Flux Method for hybrid iron–methane–air flames

Recently, a cyclic energy storage concept was proposed involving the use of metal powder as CO2-free energy carrier, known as the metal fuel cycle. In this cycle, the burning of iron powder is considered as the discharge agent of the energy carrier. However, for this cycle to be an efficient one, a better understanding of the laminar burning velocity of iron powder is required. This study presents a newly developed burner based on the Heat Flux Method (HFM), which can measure the burning velocities of flat hybrid iron–methane–air flames. Since laminar iron flames are difficult to stabilize and have – even for micron-sized particles – burning velocities in close proximity to their terminal velocity, methane is used as a stabilizing agent. In this paper, the design of the new burner system is presented with results for burning velocities of iron–methane–air flames. The results show a steady decrease in burning velocity when iron is added to a stoichiometric methane–air flame down to 16 cm/s. It is hypothesized that in the case of relatively low iron concentrations, the iron acts as a heat sink within these flames, consequently reducing the flame temperature and laminar burning velocity. For these low concentrations, methane is the governing fuel. At concentrations above 250 g/m3, the reduction of the burning velocity comes to a halt, and the iron becomes the governing fuel in the flame. A comprehensive error analysis reveals that the primary sources of uncertainty stem from fluctuations in the iron content and parabolic fitting of the thermocouple measurements in the HFM.Novelty and Significance statementThe novelty of this study is a newly developed burner based on the well-known Heat Flux Method (HFM). In accordance with the HFM, a new burner was designed to facilitate stable flat adiabatic hybrid iron–methane–air flames for the first time and measure its key parameter, the adiabatic burning velocity. Further, a metered iron powder dispersion system was developed for accurate iron mass flow measurements. The results show a steady decrease in burning velocity when iron is added to a stoichiometric methane–air flame in relatively low concentrations and show a very weak dependence of the burning velocity on the iron content at iron concentrations above 250 g/m3. These findings enable the validation of 1D simulations for iron-laden flames. A detailed assessment of the measurement uncertainties reveals that the largest source of uncertainty can be derived back to the stability of iron mass flow, leading to small flame propagation fluctuations on relatively short intervals.

A novel conductive nano-based flame-retardant coating: Preparation and its application for cotton fabric

A novel coating consisting of polyvinyl alcohol (PVA), folic acid (FA), and polyaniline nanoparticles (PANI) was applied to cotton fabric (CF) to enhance its flame retardancy, thermal stability, and electrical properties. The results from different flammability tests indicated a synergistic effect between FA and PANI to enhance the flame retardancy of CF at low weight gain percentages. The rate of burning data displayed that the new coating stopped the flame propagation in CF. The limiting oxygen index (LOI) of CF increased from 18 % to 26.9 % in the sample coated with PVA/FA/PANI. The new coating improved the thermal stability and char residue formation of CF at high temperatures. Moreover, it succeeded in decreasing the smoke density, and the production of toxic gases during treated CF combustion. The tensile strength and colour strength of CF were improved after the addition of PVA/FA/PANI coating. The surface resistance and the AC conductivity of the coated CF were measured. The addition of PVA/FA/PANI to CF increased the AC electrical conductivity due to the growth of conductive paths between the CF and the new coating material.

A physics-based model of thermodynamically varying fuel moisture content for fire behavior prediction

Fuel moisture content (FMC) is a critical parameter in fire and plume behaviors, showing diurnal and spatial variations influenced by local meteorological conditions, soil characteristics, and fuel properties. In low-intensity fires, small-scale FMC variations intensify, leading to an amplification of their effects on fire physics. In an effort to capture these variations, this paper presents the development of a physics-based model that couples a thermodynamic-based FMC prediction model for dead fuels with the Fire Dynamics Simulator of the National Institute of Standards and Technology. The model accuracy is validated against several existing experimental data, showing improvements over the baseline model which uses the kinetic-based Arrhenius drying approach. A case study of flame propagation in a small fuel bed is also presented, indicating the improved performance of the new model and its novel capabilities in capturing complex processes of fuel drying and moisture flux exchanges between the fuel and ambient atmosphere.

Flame propagation dynamic characteristics and mechanisms of methane–syngas–air mixtures in a semi-enclosed duct

The composition of syngas is complex, often leading to the generation of methane, which impacts the explosive characteristics of syngas. The analysis focused on the kinetic characteristics and mechanisms of flame propagation in methane–syngas–air mixtures in a semi-enclosed duct under various equivalence ratios (φ = 0.8–1.4) and methane volume ratios (R = 0 %–70 %) under ambient temperature and pressure. The results indicated that the flame speed and pressure propagation of methane–syngas–air mixtures could be divided into three stages: a stable stage, an oscillatory increase stage, and an oscillatory decrease stage. In the stable stage, as the methane proportion in the premixed gas increased, the oscillations in the flame and pressure decreased. Turbulent flow of the mixed gas was observed due to restrictions and obstructions within the duct. This led to an increase in the peak pressure and flame speed of the mixed gas, thereby resulting in an oscillatory increase stage. Distorted tulip-shaped flames were also formed in the semi-enclosed duct. The flame of the pure syngas/air mixture exhibited a hemispherical shape and a finger-shaped and slope-shaped propagation structure. When 30 %, 50 %, or 70 % of the methane in the methane–syngas–air mixtures was added, the flame exhibited a propagation structure characterized by a hemispherical shape, finger shape, slope shape, flat shape, tulip shape, or distorted tulip shape. The flame front evolved with time from a linear growth stage to a nonlinear growth stage. The flame front speed of the methane–syngas–air mixtures was closely related to the pressure and flame structure. With the increase in the methane proportion in the methane–syngas–air mixtures, the concentration of key radicals and the rate of OH* generation and consumption gradually decreased. Sensitivity analysis revealed that with increasing methane proportion in the premixed gas, the most important reaction dominating OH* consumption changed from R15 (H + O2(+M) <=> HO2(+M)) to R138 (CH4 + OH <=> CH3 + H2O) and then to R112 (2CH3(+M) <=> C2H6(+M)); moreover, the most important reaction dominating OH* generation remained R1 (H + O2 <=> O + OH). The addition of methane interrupted the hydrogen–oxygen chain reaction of the methane–syngas–air explosion process.

Ignition energy, explosion flame propagation, and particle movement process of coal dust cloud in vertical Hartmann tube

To discuss the ignition energy, explosion flame propagation, and particle movement process of coal dust in vertical glass tube, experimental analysis and numerical simulation methods are used to carry out research. The experimental research results show that the optimal ignition delay time is 1 s, under this condition, the dust cloud near the ignition electrode has the highest turbulence, making it easier to ignite. When the dust cloud mass concentration is 2500 g/m3, the ignition energy is the smallest, resulting in the highest risk of explosion. The simulation results show that the propagation speed of flame is 4 m/s, due to the small amount of suspended dust used, the intensity of the explosion is not significant. The further away from the explosion source, the more energy is lost, the lower the temperature of the flame. Within 30∼50 ms after the ignition, the temperature near the explosion source rapidly increases, from 900 K to 1300 K. During the period of 0.2–0.5 s after dust injection, most particles move upwards along the tube. At 1 s after the dust injection, most particles move downwards and gather near the ignition electrode, forming a suspended dust cloud that is easily ignited, which is consistent with the optimal ignition delay time of 1 s obtained from the experiment.