Spontaneous Ignition of Methane–Air Mixtures in a Wide Range of Pressures

The ignition delay in methane–air mixtures = 0.5) within the range of temperatures of 1200–1700 K and pressures of 3–450 atm behind reflected shock waves in a shock tube is measured on the basis of emission of the electronexcited OH radical (transition A²⁺ – X²) at the wavelength of 306.4 nm and on the basis of absorption corresponding to the component F₁ ⁽²⁾ (₃ = 1) F₂ ⁽²⁾ (₃ = 0) of the P(7) line of the ₃ mode of the CH₄ molecule at the wavelength of 3.3922 m. The measured ignition delays are compared with those calculated by the GRIMech 3.0 mechanism; good qualitative agreement of results is obtained in a wide range of pressures.     

Kinetic Mechanisms of Ignition of Isooctane–Air Mixtures

A kinetic scheme was developed to describe the autoignition of isooctane in air. The scheme includes 976 reactions and 126 species and adequately describes the process at both low and high initial temperatures of the mixture. The results of numerical modeling agree with experimental data on isooctane pyrolysis and autoignition delay of isooctane–air mixtures at initial pressures of 0.1–4.5 MPa, initial temperatures of 700–1300 K, and a fueltoair ratio of 0.5–2.0 with an accuracy not worse than 30%.     

Effect of Molecular Additives on the Ignition of Methane–Air Mixtures

Combustion, Explosion, and Shock Waves - The ignition of methane–air mixtures with additives of ClF5, ClF3, OF2, and H2O2 (additive content in the mixtures  $$\le$$ 1%) is studied by...     

Numerical Simulation of Spark Ignition of a Coal Dust–Air Mixture

This paper describes the development of a physico-mathematical model of spark ignition of a coal dust–air mixture, which is based on a two-phase two-speed model of reacting gas-dispersion medium. There are the results of numerical solution on the problem of spark ignition of a coal dust–air mixture with allowance for its movement caused by gas expansion during heating. The relationships between the minimal energy of spark ignition of a coal dust–air mixture and the mass concentration and particle size of coal dust are obtained. The particle size increases along with the minimal energy of spark ignition. There is mass concentration of coal dust particles with which the energy of spark ignition is minimal. The comparison of the results of calculations of the minimal energy of spark ignition of coal dust with known experimental data yields their satisfactory agreement.     

Ignition and Combustion of Aluminum–Air Suspensions in a Reactor for High-Temperature Synthesis of Alumina Powder

A method for flame stabilization in a reactor for synthesis of metal oxides is developed by analyzing combustion of dispersions of metal powders. An experimental reactor designed to implement this method is described. Ignition and combustion of commercial aluminum powders (ASD-1 and ASD-4) in air were studied, and their reliable ignition and stable combustion in the reactor combustion chamber were confirmed. It is shown that efficient combustion of an aluminum–air mixture depends on powder dispersity, flow mixing conditions, and combustion chamber pressure. Key words: aluminum, powder, suspension, flame, stabilization, combustion, synthesis, oxide.     

Experimental Study of Ignition of a Gasoline–Air Mixture in a Constant‐Volume Combustion Chamber

The characteristics of flamekernel development in a premixed gasoline–air mixture in a cylindrical constantvolume combustion chamber are measured. The experiments are performed with an initial temperature of 393 K, pressure of 6 bar, and equivalence ratio = 0.8 with the use of various ignition systems and spark plugs. The schlieren pictures of the process are presented, and the measured results for flame velocity, heatrelease rate, and mass fraction of the burnt fuel are analyzed.     

Flammability Limits for Hydrogen–Air Mixtures in the Presence of Ultrafine Droplets of Water (Fog)

Combustion of fog consisting of a hydrogen–air mixture, water vapor, and ultrafine particles of water is studied experimentally. Inflammable fog was generated by sudden expansion of a system hydrogenair + water vapor. It is shown that partial condensation of vapor with the formation of microdroplets constricts the flammability limits. Key words: flammability limits, heterogeneous mixtures, rarefaction wave, IR diagnostics.     

Effect of Diffusion of Coal Pyrolysis Products on the Ignition Characteristics and Conditions of Coal–Water Fuel Droplets

This paper presents a theoretical study of the thermal preparation and ignition of a coal–water fuel droplet under intense radiative-convective heating with diffusion of gaseous pyrolysis products of the solid fuel into the ambient gaseous medium. It has been found that gaseous pyrolysis products are ignited at a distance from the heating surface approximately equal to the radius of the droplet, after which the coke of the main fuel layer is ignited. The time between the ignition of volatiles and the coke residue is less than 0.5 s. Comparison of the ignition delays obtained by mathematical modeling and experimentally has shown satisfactory agreement between theoretical and experimental values.     

Engineering Data of Diameter Change during Air Drying of Milk Droplets with 40 wt% Initial Solids Content

Spray drying of liquid food droplets is one of the primary means of manufacturing food powders today. Modeling this process requires single-droplet drying modeling, and droplet size change during drying is one part of such modeling. Some experimental data of milk droplet diameter change at 20 and 30 wt% are reported in literature.^{[ 1} Lin , S.X.Q. ; Chen , X.D. Changes in milk droplet diameter during drying under constant drying conditions investigated using the glass-filament method . Trans IChemE, Part C 2004 , 82 ( C3 ), 213 – 218 . [Google Scholar] ^] Data are not available at higher solid contents, which are of interest to the industry. We now report the experimental results of the effects of drying conditions on milk droplet size change (using projected area diameter as the parameter) using the glass filament technique, complimented by video imaging analysis software. Under the constant drying air conditions for solids content of 40 wt%, and for both skim and whole milk, the droplet diameter changes were correlated using the previous model of Lin and Chen.^{[ 1} Lin , S.X.Q. ; Chen , X.D. Changes in milk droplet diameter during drying under constant drying conditions investigated using the glass-filament method . Trans IChemE, Part C 2004 , 82 ( C3 ), 213 – 218 . [Google Scholar] ^] With previous data together, the shrinkage coefficients were correlated against solids content.     

Ignition of a two-fuel hydrogen–silane mixture in air

Based on the previously developed model of detailed kinetics, the ignition delay time of two-fuel hydrogen–silane–air mixtures is calculated. The effect of the silane concentration and the temperature of the mixture on the ignition delay time is determined. It is shown that addition of a small (within 20%) amount of silane to the hydrogen–air mixture in the temperature range from 1200 to 2500 K leads to significant reduction of the ignition delay time of the mixture, whereas there is only a minor decrease in mixtures with silane concentrations higher than 20%.     

Simulation of Ignition and Combustion of a Homogeneous Methane–Air Mixture under Local Thermal and Photochemical Impacts

Combustion, Explosion, and Shock Waves - Ignition and combustion of a homogeneous stoichiometric methane–air mixture under simultaneous local thermal and photochemical impacts, resulting in...     

Ignition of the drops of coal–water fuel in a flow of air

The ignition of the drops of coal–water fuel (CWF) in a high-temperature gas (air) flow was experimentally studied. The conditions and fundamental characteristics of the ignition (ignition delay times) were found. The effects of a number of factors (drop sizes and ambient temperatures) on the conditions of ignition were examined. Based on the results of experiments, a physical model was formulated for the processes of thermal preparation and ignition of CWF drops. The experimental delay times of the ignition of CWFs were compared with the theoretical values (obtained with the use of a previously developed mathematical model).     

Catalytic Wet Air Oxidation of oChlorophenol in Wastewater

Catalytic wet air oxidation (CWAO) was investigated in laboratory-scale experiments for the treatment of o-chlorophenol in wastewater. Experimental results showed that wet air oxidation (WAO) process in the absence of catalyst was also effective for o-chlorophenol in wastewater treatment. Up to 80% of the initial CODcr was removed by wet air oxidation at 270℃ with twice amount of the required stoichiometric oxygen supply. At temperature of 150℃, the removal rate of CODCr was only 30%. Fe2(SO4)3, CuSO4, Cu(NO3)2 and MnSO4 exhibited high catalytic activity. Higher removal rate of CODcr was obtained by CWAO. More than 96% of the initial CODcr was removed at 270℃ and 84.6%-93.6% of the initial COD Cr was removed at 150℃. Mixed catalysts had better catalytic activity for the degradation of o-chlorophenol in wastewater.     

Numerical Study of the Problem of Thermal Ignition in a Thick‐Walled Container

A problem of thermal ignition of an exothermic mixture with an inert filler in a thickwalled container is formulated. It was found that synthesis can be performed under conditions of a weakly changing temperature if an inert filler is added to the mixture. Variation of critical conditions separating different thermal regimes with different values of model parameters is examined: ignition and extinction or ignition and slow transformation.     

Ignition Delay Time for Hydrogen–Silane–Air Mixtures at Low Temperatures

A modified physicomathematical model of ignition of hydrogen–silane–air mixtures is applied to calculate the ignition delay time for these mixtures at low initial temperatures (300–900 K) and pressures (0.4–1 atm) of the mixture. It is shown that the diagram of the ignition delay time as a function of temperature contains a region of the so-called negative temperature coefficient. The influence of the pressure in the mixture and of the silane fraction on the length of this region is studied. It is found that an increase in both factors (silane concentration and pressure in the mixture) leads to an increase in the length of the negative temperature coefficient region.     

Ignition Wave in a Two–Velocity Gas Mixture of Magnesium Particles

The theory of a steady ignition wave in a multicomponent mixture of a gas and magnesium particles, which is nonequilibrium in terms of phase velocities, is developed. Conditions where the action of a shock wave on a cloud of particles leads to their ignition or regular heating are determined. Qualitatively different types of behavior of the temperatures of dispersed and gas phases behind the front of the leading shock wave are found. A significant role of interphase friction at the early stages of development of the thermal explosion is demonstrated. Verification of the model is performed on the basis of experimental data on the dependence of the induction period of the oxidation reaction in the cloud of particles on the shock–wave Mach number. It is shown that the numerical data obtained within the framework of the equilibrium and nonequilibrium (in terms of phase velocities) models are in good agreement for small–size particles.     

Preparation of Nano-titanium Dioxide in Propane/Air Diffusion Flame

Titanium dioxide (TiO2) nanoparticles were synthesized by the oxidation of titanium tetrachloride (TiCl4), in propane/air diffusion flame. The propane/air diffusion flame is generated using a multi-port diffusion type burner composed of 4 concentric tubes. Flow rates of TiCl4 and combustion gases such as air, industrial propane and carrier gas were chosen as key experimental variables for the control of the particle size and morphology. Effects of propane/air mole ratio and precursor flow rate on particle size, morphology, structure and carbon dots of titanium dioxide particles were studied.     

Stability of Calcium Chloride in the Air–Steam Gasification of Solid Fuel in Filtration Mode

The emission of HCl from calcium chloride during the air–steam gasification of solid fuel in the filtration combustion mode was studied. The limiting amounts of HCl released into the gas phase under real conditions of a shaft kiln gasifier were estimated. It was shown that the most important factors responsible for the stability of CaCl₂ are the humidity of an oxidant gas and the process temperature.     

Hot–Spot Thermal Ignition in a Porous Medium under Conditions of Natural Gas Filtration

The development of a hot spot in a porous reactive medium with chemical reactions occurring at the inner surface of the pores between a solid skeleton and a gaseous oxidizer is studied by asymptotic methods at large values of the Peclet number, the Frank–Kamenetskii parameter, and the temperature head. It is shown that upon natural gas filtration, the process develops in two stages. In the first stage, the pressure, density, and temperature of the gas are equalized over the entire porous medium, and a hot spot develops on the skeleton in the second stage. The limit of hot–spot ignition and the ignition time for a hot spot are determined. An example of calculation of the critical parameters of the system is given.