Changes In Flame Temperature Research Articles

Studies of the diluent, temperature and pressure effect on the lower and upper flammability limits of ammonia in air

Ammonia safety and environmental protection research forms the basis for its role as a clean energy carrier. In this work, an experimental study was conducted in this work to analyze the effect of different inhibitors (nitrogen, argon and water vapor) on the flammability limits (FLs) of ammonia at elevated temperatures and pressures. In addition, the influence of diluents on the compositions and flame temperature changes was evaluated, and the temperature sensitivity coefficients of the elementary reactions and the ROP of free radicals and partial products at the FL concentrations were analyzed. The findings indicated that water vapor provided the strongest flame retardant effect on ammonia in three inhibitors. Within a certain temperature and pressure range, the FLs of ammonia in ammonia/diluent/air can be predicted using the extended Le Chatelier equation. The flame temperature decreased at the lower flammability limit (LFL) concentrations and increased at the upper flammability limit (UFL) concentrations of ammonia with increasing initial pressure. As the initial temperature increases, the flame temperature decreases during ammonia combustion. The influence of ammonia concentration on flame temperature is greater than that of diluents dilution. The elementary reactions H+O2<=>O+OH (R1) and NH2+NO<=>NNH+OH (R82) were the primary reactions that increased the flame temperature at the FL ammonia concentrations in ammonia/diluent/air. Conversely, NH2+NO<=>N2+H2O (R80) and H+O2(+M)<=>HO2(+M)(R15) were the main reactions that decreased the flame temperature. H, OH and NH2 radicals played a crucial role in the combustion reaction process at ammonia FL concentrations. At the LFL concentrations of ammonia, the molar fraction of the OH radical showed the greatest variation, while at the UFL concentrations of ammonia it was NH2 radical. The elementary reaction NH3+OH<=>NH2+H2O (R158) was the primary reaction that consumed OH radical and promoted the formation of NH2 radical. Free radical concentrations decreased with increasing pressure and temperature, while the change rate of free radical ROP accelerated with increasing pressure. In addition to nitrogen and water, the partial products were mainly nitric oxide at the LFL concentrations, while at the UFL concentrations were mainly hydrogen.

Study on the Inhibition Effect of C6F12O on Charged Particles in the Flame of Transformer Oil Discharge Gas

ABSTRACT The accidental combustion of insulating oil poses a significant risk in the event of transformer failure. The charged particles generated through the combustion ionization reaction exert considerable influence on the combustion speed and stability of the flame. Therefore, the detailed chemical reaction mechanism including neutral matter and charged particle is simplified. The two-dimensional finite rate reaction model is established. The theoretical calculation investigates the suppressive effect of the novel fire extinguishing agent C6F12O on charged particles in the flame resulting from transformer oil decomposition. The analysis encompasses changes in flame temperature, free radicals, and charged particles in the decomposition gas of transformer oil under C6F12O concentrations ranging from 0% to 4%. The findings reveal that the addition of C6F12O exerts a discernible inhibitory effect on the flame temperature of the transformer oil exhaust gas. The large reduction of charged particles in the flame caused by C6F12O is achieved by its consumption of large amounts of O and OH radicals in the flame. It hampers key elementary reactions responsible for charged particle generation. In conclusion, C6F12O demonstrates a pronounced inhibitory effect on charged particles in the flame resulting from transformer oil decomposition.

Effect of single and split injection on combustion process of diesel spray injected into 2D piston cavity

The flame characteristics of wall-impinging diesel fuel spray at single injection and split injection strategies were investigated in a high-temperature high-pressure constant volume combustion vessel. The 2D piston cavity has been used to form the impingement spray flame and the two-color method has been used to analyze the flame process. Results reveal that 2nd ignition delay can be defined in a specific area surrounded by single and split injections when the 1st injection proportion is from 25% to 75%. The KL factor and distribution area of a single injection are smaller than that of a split injection at EOI + 0.2 ms. The soot oxidation area is far away from the wall surface. However, the soot formation area is mainly concentrated along the cavity groove. The soot oxidation area proportion plays a decisive role in the emission of soot. The split injection interval has a key role in the soot formation dominant process at the initial stage of ignition. The initial mean flame temperature changes slightly, the mean flame temperature decreases earlier, the soot oxidation degree becomes higher, no interaction or small interaction between the 1st and 2nd injection, and the maximum degree of soot formation and oxidation dominant process occur when the 1st injection proportion equals 50%. The mean flame temperature drop time of the single injection is advanced. The total flame area and the soot formation and oxidation dominant process before and after EOI + 0.2 ms were also discussed. The total flame area of split injection is larger than single injection after EOI + 0.2 ms.

Hydrogen Co-Firing Characteristics in a Single Swirl Burner: A Numerical Analysis

Hydrogen is gaining traction as an energy carrier in the decarbonisation and net-zero-emissions agenda. Because hydrogen is a clean energy carrier, increasing the percentage of hydrogen in natural gas mixtures aids in the decarbonisation initiatives. Hence, the flame characteristics of the natural gas mixtures, together with hydrogen are explored in the current study through a numerical assessment of a single swirl burner (swirl number, SN 0.78) since the said burner is widely used in gas turbine (GT) combustors. The baseline CFD and experimental cases referred to natural gas compositions primarily composed of methane (CH4). The results reveal that the CFD model can effectively represent the swirling component of the flame as seen in the experiment. A 5% hydrogen addition had virtually no effect on the swirling flame structure, as shown by qualitative evaluation of hydroxyl (OH) behaviour and flame temperature in comparison to the baseline methane flame. Despite this, the addition of hydrogen has increased the OH radical pool during combustion, causing a small change in flame temperature. Overall, the novelty of the current research is the opportunity to fire 5% hydrogen in a CH4-dominated GT combustor without any major retrofitting operations, as the study discovered that 5% hydrogen in a pure CH4 stream has a minor affect. However, more research is needed to properly capture the flame structure and strain for assessing transient-related phenomena like flashback and blow off by increasing the hydrogen proportion and using a higher accuracy turbulence model.

Experimental investigation of the methane combustion assisted by atmospheric pressure oxygen microwave plasma torch

The atmospheric-pressure oxygen microwave plasma is employed to enhance the methane combustion in the jet-diffusion combustor. The plasma-assisted combustion (PAC) is compared with natural combustion without plasma application in terms of the flame morphology, flame temperature, and combustion efficiency. It is found experimentally that the oxygen plasma assistance in combustion is prominent in lean oxygen condition, and the active species generated in the microwave plasma torch contribute to the combustion process more dominantly than the flame temperature change caused by heating of oxygen microwave plasma. The combustion degree of CH4 in PAC is much more enhanced in lean oxygen combustion, and the exhaust gas in combustion is effectively controlled with the use of the oxygen microwave plasma torch.

Research on the Ignition Height and Reaction Flame Temperature of PTFE/Al/Si/CuO with Different Mass Ratios of PTFE/Si

Recent studies have shown that the energy release capacity of Polytetrafluoroethylene (PTFE)/Al with Si, and CuO, respectively, is higher than that of PTFE/Al. PTFE/Al/Si/CuO reactive materials with four proportions of PTFE/Si were designed by the molding–sintering process to study the influence of different PTFE/Si mass ratios on energy release. A drop hammer was selected for igniting the specimens, and the high-speed camera and spectrometer systems were used to record the energy release process and the flame spectrum, respectively. The ignition height of the reactive material was obtained by fitting the relationship between the flame duration and the drop height. It was found that the ignition height of PTFE/Al/Si/CuO containing 20% PTFE/Si is 48.27 cm, which is the lowest compared to the ignition height of other Si/PTFE ratios of PTFE/Al/Si/CuO; the flame temperature was calculated from the flame spectrum. It was found that flame temperature changes little for the same reactive material at different drop heights. Compared with the flame temperature of PTFE/Al/Si/CuO with four mass ratios, it was found that the flame temperature of PTFE/Al/Si/CuO with 20% PTFE/Si is the highest, which is 2589 K. The results show that PTFE/Al/Si/CuO containing 20% PTFE/Si is easier to be ignited and has a stronger temperature destruction effect.

SOME TEMPERATURE CHARACTERISTICS SUB-LAYER AEROSOL EXTINGUISHING OF ALCOHOLS

Problem Statement: Nowadays, the process of sublayer aerosol quenching has not been studied at all, and its basic parameters, such as changes in flame temperature, liquid surface layer, tank sides, and approximate time of alcohol quenching and quenching, are unknown. The purpose of the work is to determine the parameters of sublayer aerosol quenching - flame temperature, the surface layer of liquid, tank sides, and the impact on the efficiency of sublayer quenching of aerosols dispersion – as one of the main parameters characterizing the process of alcohol quenching. The scientific novelty of the work is that for the first time the parameters of sublayer aerosol quenching at different sizes of aerosol bubbles were determined and it was found that at smaller bubbles the surface layer temperature decreases to 15%, aerosol distribution on the liquid surface is more uniform and a heterogeneous system is formed, which contains both aerosol solid particles – K2CO3, KOH, KNSO3, NH4HCO3, gases – CO2, N2, H2O, alcohol vapors, and the alcohol itself in the vapor and liquid phases. The main results of the study: The paper describes the developed installation and methodology for determining the parameters of sublayer aerosol quenching at different stages of the aerosol release process. The values of the flame temperature reduction and its behavior when the aerosol enters the flame are established. The established values are plotted and it is determined that when the aerosol enters the flame, the flame temperature begins to decrease actively and in 40 seconds reaches about 600 degrees Celsium. It was also found that the flame turns orange, which indicates that the combustion zone is the thermal dissociation of potassium salts, the flame size decreases, which indicates a decrease in the amount of alcohol vapor entering the combustion zone. The rate of cooling the sides at the exit of the aerosol from different-sized holes was also determined and it was found that the amount of cooling of the tank side is slightly higher at smaller hole diameters with a more uniform distribution of the aerosol on the surface. The range of reduction of liquid and board temperatures for each of the alcohols is less than the boiling point by 30-40 degrees Celsium. The decrease in temperature occurs at approximately the same rate and slows down until the end of the aerosol release. Analysis of the experimental results showed that the action of fire-extinguishing aerosol when it comes to the surface leads to intensive alcohol cooling due to bubbling of the aerosol through the alcohol layer, with active mixing of alcohol layers and the rise of cold liquids to the surface. This phenomenon leads to further cooling of burning surface of the liquid, which can have a temperature of 60 degrees Celsium to 97 degrees Celsium, as well as the sides of the tank as a result of alcohol on them and its intense evaporation. The result is the establishment of the parameters of the sublayer aerosol quenching – the temperature of the liquid surface, the temperature of the sides of the tank, the rate of aerosol to the surface, and the flame temperature when the aerosol enters the combustion zone.

Thermal and chemical effects of differential diffusion in turbulent non-premixed H2 flames

As a renewable fuel, hydrogen (H2) may play an increasingly important role in the development and control of piston and gas turbine engines to achieve zero carbon emissions. Predictive modeling of H2-fueled combustion processes requires a clear understanding of differential diffusion (DD) due to the high diffusivity of H2. On the assumption that turbulent mixing is a far more dominant process than molecular mixing, DD effects are typically neglected in turbulent combustion simulations to reduce modeling complications. While this assumption is reasonable for hydrocarbon fuels, it is less valid for H2 combustion, where DD is significant. In this work, two three-dimensional direct numerical simulations of temporally evolving turbulent H2 jet flames with and without considering DD are performed and compared with laminar flamelet solutions to assess DD effects under turbulent conditions. The emphasis is placed on assessing the suitability of classical mixture fraction Z and Bilger mixture fraction ZBilger as conditioning variables for non-premixed turbulent combustion modeling through analyzing DD effects on flame structure, chemical reactions, and tangential diffusion (TD). Furthermore, the persistence of DD effects under turbulent conditions and the suitability of a conventional DD parameter are investigated by comparing the turbulent flames to laminar flamelet solutions. It is found that conditioning the thermochemical state on ZBilger helps to capture DD effects and mitigate the relative contribution of TD, which gives ZBilger advantages over Z when employing flamelet modeling. Due to close coupling between DD and local chemical reactions, DD can affect the turbulent/laminar flames in the form of thermal effects due to the change in flame temperature, chemical effects due to the change in chemical reactions, and transport effects due to multiple species with varying diffusivities that could result in the difference between Z and ZBilger. While the transport effects are suppressed, significant chemical and thermal effects of DD still persist under turbulent conditions, which indicates that the DD parameter is probably unsuitable for comprehensively characterizing and assessing DD effects on the structure of turbulent non-premixed flames.

Chemical effects of hydrogen addition on low-temperature oxidation of premixed laminar methane/air flames

Hydrogen addition exhibits its chemical incentive on hydrocarbon flames via its reactivity in elementary reactions and the heat enthalpy release in self-oxidation. In the study, a one-step reaction kinetics was provided to fictitious hydrogen addition for separating the hydrogen reactivity effect on radical formation from the heat release effect on flame temperature change. The numerical investigation was conducted by adding the fictitious hydrogen into premixed flame modeling. The structures of the flame preheat zone were compared in terms of the profiles of flame temperature, the build-up of active radical pool and the consumption rates of methane and hydrogen addition. Comparative analyses showed that the reactivity and the heat release of hydrogen addition could both lead to the early boosting of flame oxidation, but showed different dependences on hydrogen enrichment rate. Reaction path analyses were conducted to explore the kinetic reasons for the above observations. The results suggested that OH + H2 = H + H2O was an apparent reaction route to show the reactivity of hydrogen addition, whereas the enhanced triangular reaction loops between OH, H and HO2 were the key factors for strengthening the low-temperature oxidation of hydrogen-enriched methane/air flames. Besides, the effects of the heat release and the reactivity of hydrogen addition on the early build-up of flame kernel were quantified.

Characteristics of a Methane Jet Flame in Elevated Pressure and Oxy-Fuel Atmosphere Using Large Eddy Simulation with Tabulated Chemistry

ABSTRACT The pressurized oxy-fuel combustion is a promising CO2 capture technology for its further reduction of CO2 capture cost. In order to study the combustion behaviors of hydrocarbons under different pressures and atmospheres, a methane/air jet flame is used as the simulation target, with modifications on its oxidizer species and operating pressure. A Large Eddy Simulation (LES) with a tabulated chemistry model is employed, whose lookup tables are constructed by using a 2-D counterflow diffusion flame under different atmosphere and pressure conditions. The original flame with detailed experimental data is used for the validation of the model accuracy, and the simulation results show good agreement with the experiments. The detailed profiles of the temperature, species, and mixture fraction are analyzed. Compared with the air-fired, the flame in the oxy atmosphere is shorter and thinner. Important species and radicals are compared. The comparison shows that under elevated pressure, the differences caused by oxy atmosphere is similar to those found under atmospheric pressure. With the elevation of pressure from 0.1 MPa to 1.5 MPa, the flame height becomes smaller while the radial width is larger near the inlet, which can be observed in both air-fired and oxy-fired conditions. Under elevated pressures, the flame temperature changes slightly, but CO production increases noticeably in the fuel-rich regions.

Numerical study of the effect of electric fields on the combustion characteristics of PMMA under lateral inflow

To satisfy the demand for thrust control on solid rocket motors and solid ramjet engines, numerical simulation of the effect of high-voltage electric fields on the combustion characteristics of polymethyl methacrylate (PMMA) under lateral inflow was undertaken. The mechanism of the effect of electric fields on the regression rate and mass flow rate of PMMA was analyzed. The results show that PMMA mass flow rate can increase by about 54% when subjected to positive voltages. The PMMA mass flow rate can not only increase by about 5.5% but also decrease by about 14% under the action of negative voltages. When the oxygen mass fraction is 54.5% at 0.101 MPa, the effect of electric fields on PMMA mass flow is weakened as the lateral velocity increases. When the inflow velocity is 1.95 m s−1 and oxygen mass fraction is 23.2%, the effect of electric fields on PMMA mass flow is decreased as the pressure rises. The effect of electric fields on PMMA regression rate is mainly due to the electric-field-induced volumetric body force. It will result in large-scale bulk flow movement, known as ionic wind, which changes the distribution of species and affects the heat of reaction, thus causing the changes in flame temperature, finally altering the thermal feedback to the solid phase.

Synthesis of nanocrystalline Mg0.6Cd0.4Fe2O4 ferrite by glycine-nitrate auto-combustion method and investigation of its microstructure and magnetic properties

Nanocrystalline Mg0.6Cd0.4Fe2O4 ferrite powders were produced by the glycine-nitrate auto-combustion method for the first time. The influence of the different molar ratios of glycine-to-nitrate G.N−1) on the characteristics of the prepared powders was systematically investigated by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometry (VSM). Thermodynamic calculations revealed that the adiabatic flame temperature changes from 598.79K to 1757.97K by increasing the G.N−1 ratios from 0.30 to 0.85. The results confirmed that under fuel-lean combustion (G.N−1 = 0.30), Mg0.6Cd0.4Fe2O4 nanoparticles can be obtained at a significantly lower temperature and shorter synthesis time, compared to other preparation methods like standard ceramic and co-precipitation. The XRD and ICP results showed that the crystallite size of the powders changes in the range of 8–43nm, and their Cd content notably decreases with increasing the G.N−1 values. The FE-SEM results proved that the porosity and size of the as-prepared ferrite nanoparticles drastically change with variations in the G.N−1 ratio. The evolution of phase, crystallite/particle size, and magnetic properties after annealing was discussed in detail. At the optimized annealing condition, the synthesized Mg0.6Cd0.4Fe2O4 ferrite offered a high saturation magnetization of 41.70Am2kg−1 and a coercivity of 1.92kAm−1, indicating noticeably better soft magnetic properties compared to the same ferrite produced by the other wet chemical methods.

Relationship between submicron ash aerosol characteristics and ash deposit compositions and formation rates during air- and oxy-coal combustion

Deposition of ash on heat transfer surfaces is a major factor in determining boiler performance. Deposits so formed consist of tightly bound “inside” deposits close to the heat transfer surface and loosely bound “outer” deposits that are easily dislodged. This paper describes research focusing on both the composition of inner and outer deposits, and also on the rate of deposition of the inner deposit layer. Presented are selected results from a wide ranging study concerned with mechanisms governing the formation of fouling deposits during air and oxy-coal combustion in a 100kW test rig. The primary focus is on establishing a relationship between the size segregated composition of the coal ash aerosol, and the spatially resolved composition of the deposit layer, and this is accomplished by experimentation that addresses the impacts of conversion from air-firing to oxy-firing. Experiments involved three different coals (Powder River Basin or PRB, Illinois and a 60/40 Blend of Illinois and PRB), each burned under air- and oxy-coal combustion conditions. Data for the PRB coal suggested that changes in the composition of the inner deposit layer were caused by variations in sub-micron aerosol compositions, but that these occurred only when there were significant changes in flame temperature. An increase of the latter also led to increasing submicron particle concentrations and deposition rates. Although both aerosol and deposit compositions depended greatly on coal compositions, rates of deposition of the inner deposit layer correlate linearly with the concentration of the submicron aerosol in the flue gas, for all three coals, and under all air- and oxy-firing conditions for which data are available. This result suggests the amount rather than the (variable) composition of the submicron aerosol is important. There was no correlation between deposition rates and total ash concentrations.

Electric field effects in the presence of chemi-ionization on droplet burning

The effects of an externally applied electric field on the burning characteristics of a spherically symmetric fuel drop, including the flame structure, flame standoff distance, mass burning rate and flame extinction characteristics of the diffusion flame are studied. A reduced three-step chemical kinetic mechanism that reflects the chemi-ionization process for general hydrocarbon fuels has been proposed to capture the production and destruction of ions inside the flame zone. Due to the imposed symmetry, the effect of the ionic wind is simply to modify the pressure field. Our study thus focuses exclusively on the effects of Ohmic heating and kinetic effects on the burning process. Two distinguished limits of weak and strong field are identified, highlighting the relative strength of the internal charge barrier compared to the externally applied field. For both limits, significantly different charged species distributions are observed. An increase in the mass burning rate is noticed with increasing the strength of the electric field in both limits, with a small change in flame temperature. Increasing external voltages pushes the flame away from the droplet and causes a strengthening of the flame with a reduction in the extinction Damkhöler number.

Effect of Change in Fuel Compositions and Heating Value on Ignition and Performance for Siemens SGT-400 Dry Low Emission Combustion System

The influence of changes in fuel composition and heating value on the performance of an industrial gas turbine combustor was investigated. The combustor tested was a single cannular combustor for Siemens SGT-400 13.4 MW dry low emission engine. Ignition, engine starting, emissions, combustion dynamics, and flash back through burner metal temperature monitoring were among the parameters investigated to evaluate the impact of fuel flexibility on combustor performance. Lean ignition and extinction limits were measured for three fuels with different heat values in term of Wobbe Index (WI): 25, 28.9, and 45 MJ/Sm3 (natural gas). The test results show that the air fuel ratio at lean ignition/extinction limits decreases and the margin between the two limits tends to be smaller as fuel heat value decreases. Engine start tests were also performed with a lower heating value fuel and results were found to be comparable to those for engine starting with natural gas. The combustor was further tested in a high pressure air facility at real engine operating conditions with different fuels covering WIs from 17.5 to 70 MJ/Sm3. The variation in fuel composition and heating value was achieved in a gas mixing plant by blending natural gas with CO2, CO, N2, and H2 (for the fuel with WI lower than natural gas) and C3H8 (for the fuel with WI higher than natural gas). Test results show that a benefit in NOx reduction can be seen for the lower WI fuels without H2 presence in the fuel and there are no adverse impacts on combustor performance except for the requirement of higher fuel supply pressure, however, this can be easily resolved by minor modification through the fuel injection design. Test results for the H2 enriched and higher WI fuels show that NOx, combustion dynamics and flash back have been adversely affected and major change in burner design is required. For the H2 enriched fuel, the effect of CO and H2 on combustor performance was also investigated for the fuels having a fixed WI of 29 MJ/Sm3. It is found that H2 dominates the adverse impact on combustor performance. The chemical kinetic study shows that H2 has significant effect on flame speed change and CO has significant effect on flame temperature change. Although the tests were performed on the Siemens SGT-400 combustion system, the results provide general guidance for the challenge of industrial gas turbine burner design for fuel flexibility.

Effect of Chemical Kinetics on Concurrent-Flow Flame Spread over Solids: A Comparison Between Buoyant Flow and Forced Flow Cases

The authors employed detailed numerical models with a one-step finite-rate chemical reaction to investigate the kinetic rate effect (through the variation of the pre-exponential factor) on concurrent flame spread rates over thin solids. It is found that flames in forced flow are less sensitive to the change of kinetics than flames in buoyant flow, and narrow samples are more sensitive to the change of kinetics compared with wide samples. The rate of chemical kinetics affects the flame spread rates primarily through two mechanisms: the amount of unburnt fuel vapors escaping from the reaction zone and the variation of induced flow velocity through flame temperature change in the case of the buoyant flames. Detailed analyses of the flame structure and flow pattern are presented for the forced- and buoyant-flow cases to explain their different degrees of sensitivity to the combustion reaction rate.

Strategies for pursuing community involvement in OTIS research studies

Nanocrystalline Mg0.6Cd0.4Fe2O4 ferrite powders were produced by the glycine-nitrate auto-combustion method for the first time. The influence of the different molar ratios of glycine-to-nitrate G.N−1) on the characteristics of the prepared powders was systematically investigated by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometry (VSM). Thermodynamic calculations revealed that the adiabatic flame temperature changes from 598.79 K to 1757.97 K by increasing the G.N−1 ratios from 0.30 to 0.85. The results confirmed that under fuel-lean combustion (G.N−1 = 0.30), Mg0.6Cd0.4Fe2O4 nanoparticles can be obtained at a significantly lower temperature and shorter synthesis time, compared to other preparation methods like standard ceramic and co-precipitation. The XRD and ICP results showed that the crystallite size of the powders changes in the range of 8–43 nm, and their Cd content notably decreases with increasing the G.N−1 values. The FE-SEM results proved that the porosity and size of the as-prepared ferrite nanoparticles drastically change with variations in the G.N−1 ratio. The evolution of phase, crystallite/particle size, and magnetic properties after annealing was discussed in detail. At the optimized annealing condition, the synthesized Mg0.6Cd0.4Fe2O4 ferrite offered a high saturation magnetization of 41.70 Am2 kg−1 and a coercivity of 1.92 kA m−1, indicating noticeably better soft magnetic properties compared to the same ferrite produced by the other wet chemical methods.

A numerical modelling of an influence of CH 4, N 2, CO 2 and steam on a laminar burning velocity of hydrogen in air

The influence of additives of various chemical natures (CH 4, N 2, CO 2, and steam) at a laminar burning velocity S u of hydrogen in air has been studied by numerical modelling of a flat flame propagation in a gaseous mixture. It was found that the additives of methane to hydrogen–air mixtures cause as a rule monotonic reduction in the S u value with the exception of very lean mixtures (fuel equivalence ratio ϕ = 0.4), for which a dependence of the laminar burning velocity on the additive's concentration has a maximum. In the case of the chemically inert additives (N 2, CO 2, H 2O) the laminar burning velocity of rich near-limit hydrogen–air flames drops monotonically with an increase in the additive's content, but no more than 1.5 times, and the adiabatic flame temperature changes slowly in this case. In the case of methane as the additive, the laminar burning velocity is diminished approximately 5 times with an increase in the adiabatic flame temperature from 1200 to 2100 K. Deviations from the known empirical rule of the approximate constancy of the laminar burning velocity for near-limit flames are shown.

A numerical study on the effect of hydrogen/reformate gas addition on flame temperature and NO formation in strained methane/air diffusion flames

This paper investigates the effects of hydrogen/reformate gas addition on flame temperature and NO formation in strained methane/air diffusion flames by numerical simulation. The results reveal that flame temperature changes due to the combined effects of adiabatic temperature, fuel Lewis number and radiation heat loss, when hydrogen/reformate gas is added to the fuel of a methane/air diffusion flame. The effect of Lewis number causes the flame temperature to increase much faster than the corresponding adiabatic equilibrium temperature when hydrogen is added, and results in a qualitatively different variation from the adiabatic equilibrium temperature as reformate gas is added. At some conditions, the addition of hydrogen results in a super-adiabatic flame temperature. The addition of hydrogen/reformate gas causes NO formation to change because of the variations in flame temperature, structure and NO formation mechanism, and the effect becomes more significant with increasing strain rate. The addition of a small amount of hydrogen or reformate gas has little effect on NO formation at low strain rates, and results in an increase in NO formation at moderate or high strain rates. However, the addition of a large amount of hydrogen increases NO formation at all strain rates, except near pure hydrogen condition. Conversely, the addition of a large amount of reformate gas results in a reduction in NO formation.

Numerical anlysis and experimental research in rheological manfacturing process of fibre devices

Based on thermal viscoelastic rheological theory and time-temperature equivalent principle,the thermal viscoelastic model of fiberglass under non-uniform temperature field is set up.By continuously adjusting its stiffness matrix and temper-ature field,the thermo-mechanical coupled numerical analysis of fiber coupler in the process of fused biconical taper is accomplished.The effect of technology parameters such as fused temperature and drawing speed on the manufacturing process is acquired.It is discovered that the maximum stress is in direct proportion to drawing speed,and fused temperature affects extremely on the manufacturing process.The change of fused temperature by 5 ℃ can lead to the change of maximum stress by 30%.It is found by experiment that the flame temperature change by 5~30 ℃,while the drawing speed is rather stable.A conclusion can be drawn by theory analysis and experimental research that it is the shift of fused temperature that induces the defaults of bad performance repeatability and unstable excess loss.