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.     

On the Structure of the Space of States for a Thermal Model of Fluidized-Bed Reactor–Regenerator Units and Control Visualization Principles

Theoretical Foundations of Chemical Engineering - A system of differential equations for the dynamics of thermal states in reactor–regenerator units with finely dispersed catalysts is...     

Thermal Properties of Carbon Nanotube–Copper Composites for Thermal Management Applications

Carbon nanotube–copper (CNT/Cu) composites have been successfully synthesized by means of a novel particles-compositing process followed by spark plasma sintering (SPS) technique. The thermal conductivity of the composites was measured by a laser flash technique and theoretical analyzed using an effective medium approach. The experimental results showed that the thermal conductivity unusually decreased after the incorporation of CNTs. Theoretical analyses revealed that the interfacial thermal resistance between the CNTs and the Cu matrix plays a crucial role in determining the thermal conductivity of bulk composites, and only small interfacial thermal resistance can induce a significant degradation in thermal conductivity for CNT/Cu composites. The influence of sintering condition on the thermal conductivity depended on the combined effects of multiple factors, i.e. porosity, CNTs distribution and CNT kinks or twists. The composites sintered at 600°C for 5 min under 50 MPa showed the maximum thermal conductivity. CNT/Cu composites are considered to be a promising material for thermal management applications.     

A General Hybrid GMDH–PNN Model to Predict Thermal Conductivity for Different Groups of Nanofluids

Theoretical Foundations of Chemical Engineering - In this study, a general model for estimating the nanofluids (NFs) thermal conductivity by using a hybrid group method of data handling polynomial...     

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.     

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...     

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%.     

Analysis of the Critical Conditions for Ignition of Gas–Particle Mixtures by a Heated Body with Pulsed Energy Supply

The critical conditions for the ignition of solid particles suspended in a gas by a heated body with pulsed energy supply are determined using numerical and approximate methods. It is shownthat in the kinetic (onetemperature) ignition regime, the critical duration of the thermal pulse is equal to the time of establishment of a zero gradient on the interface between the heaterand the gas–particle mixture. In the diffusive (twotemperature) ignition regime (small coefficients of heat transfer between the particles and the gas), the critical duration of the thermal pulse is much shorter than the time of establishment of a zero gradient. It is established that the critical duration of the thermal pulse is determined from the condition that the time of complete particle burnout on the interface between the heater and the gas–particle mixture is equal to the time of repeated heating of the gas to the temperature of the transition of the particle oxidation reaction tothe diffusive reaction regime. An approximate method for calculating the critical duration of the thermal pulse for the diffusive ignition regime is proposed. Numerical calculations show that the minimum time of establishment of the hightemperature combustion regime is reached when the thermal pulse duration is equal to the time of attainment of a zero pressure gradient on the interface between the heater and the gas–particle mixture.     

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.     

Particulate Emission Characteristics of a Compression Ignition Engine Fueled with Diesel–DMC Blends

The effect of fuel composition on the combustion characteristics and particulate emissions of a compression-ignition engine fueled with Euro V diesel fuel blended with dimethyl carbonate (DMC) was investigated experimentally. Blended fuels containing 4.48%, 9.07%, 13.78%, and 18.6% by volume of DMC, corresponding to 3%, 6%, 9%, and 12% by mass of oxygen in the blended fuels, were investigated. By analyzing the measured in-cylinder pressure data and the derived heat release rate, it is observed that the addition of DMC increases the ignition delay and the amount of heat release in the premixed combustion duration, but shortens both the diffusive burning duration and the total combustion duration. On the emission side, the smoke opacity, the particulate mass concentration as well as the total number of particulates are all reduced, while the proportion of soluble organic fraction (SOF) in the particulate is increased, by using the blended fuels. The geometric mean diameter of the particles shifts towards smaller size in comparison with that of the diesel fuel. The particulate mass concentration, the total number of particles and SOF can be further reduced by the use of diesel oxidation catalyst (DOC), while the particles shift towards larger geometric mean diameter for each fuel, indicating that the DOC could reduce the finer particles.     

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.     

Thermal analysis of a diesel engine operating with diesel–biodiesel blends

In this paper we study the transient heat conduction in a piston of a diesel engine, subjected to a periodic boundary condition on the surface in contact with the combustion gases. The heat transfer coefficient at the top surface was modeled taking into account the temperature and pressure inside the combustion chamber. Such instantaneous pressure was measured using a special probe for an engine operating with several blends of diesel and biodiesel, and the temperature was obtained through a First Law analysis. The physical properties, including the cetane number were evaluated experimentally for all diesel/biodiesel blends used in this work. An elliptic scheme of numerical grid generation was used, so that the irregular shaped piston in the physical domain was transformed into a cylinder in a computational domain. The timewise variations of the temperature of several points in the piston were examined for different piston materials and various load conditions.     

Thermal conductivity of equiatomic high-entropy diboride ceramics with 5–9 cations

As a new type of high-entropy material, most of the current work has focused on the synthesis and characterization of mechanical properties of high-entropy diboride ceramics (HEBs). In this work, single-phase HEBs with 5–9 cations were prepared by spark plasma sintering with self-synthesized HEB powders through the boro/carbothermal reduction method. The distribution of the metal elements in the obtained HEBs was homogeneous. Due to the phonon scattering caused by the inherent lattice distortion in the HEBs, the thermal conductivity of the ceramics decreased with the increased configurational entropy or the number of cation kinds. However, this study reveals that the degree of reduction in thermal conductivity for the HEBs demonstrate a weakened tendency with cation kinds of more than 6.     

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%.     

On-line Thermal Desorption–Gas Chromatography of Intact Insects for Pheromone Analysis

By using a thermodesorption system (TDS) together with a programmable temperature vaporizer (PTV) injector, we confirmed the composition of the sex pheromone of Adoxophyes orana (Lepidoptera: Tortricidae) and Campylomma verbasci (Heteroptera: Miridae) from a single insect per analysis. Intact females and males or pheromone glands were placed in the oven part of the TDS, which was subsequently heated. The compounds released were transferred to the PTV, which was cooled to –150°C. Injection was on a dual-column GC by heating the PTV rapidly to 250°C. The major sex pheromone compounds of A. orana were found only in the pheromone gland of females. Male and female C. verbasci showed fingerprint-identical chromatograms, except for the two sex pheromone compounds, which were present only in females. No distinct differences were found in compounds released from female and male Lygocoris pabulinus (Heteroptera: Miridae). The advantages of this rapid method are the high sensitivity and the low degree of degradation and contamination. This technique was effective in analyzing small insects by gas chromatography–mass spectrometry (GC-MS) without prior manipulation, such as solvent extraction or distillation.     

Ignition of droplets of coal–water–oil mixtures based on coke and semicoke

To permit expansion of the resource base and utilize industrial waste, coal–water–oil fuels may be prepared on the basis of coke and semicoke, as well as common petroleum derivatives (fuel oil and spent compressor, turbine, and transformer oils). The minimal oxidant temperature corresponding to stable ignition of coal–water–oil slurries is established. Typical variation in fuel temperature in the course of reaction is determined, as well as the delay time of ignition and the total combustion time for individual droplets of such fuel suspensions. For droplets of initial size 0.5–1.5 mm, the influence of the various factors (droplet size, oxidant temperature, and concentration of the components) on the threshold (minimum) temperature and inertia of ignition is studied. It is shown that stable ignition of coke and semicoke in such fuel is possible at moderate oxidant temperatures: 700–1000 K.     

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.