Average Flame Temperature Research Articles

Mathematical modeling and model predictive control research on coal powder burners for aggregate dryers

Aggregate drying is a crucial step in asphalt mixture production. Enhancing the model accuracy and controller performance of aggregate dryer burners is essential for consistent flame characteristics, reducing NOx emissions, and minimizing fuel consumption. This paper introduces a second-order nonlinear parametric model for coal powder burners that includes delay and noise. Model parameters were determined through experimental data using the Salp Swarm Algorithm, showing higher accuracy than models based on the least square method. A dual-layer model predictive control (MPC) based on this mathematical model was developed to improve the economic efficiency of the aggregate drying process. Simulation results showed that the dual-layer MPC saves 1.08 tons of coal every 10 h compared to a standard MPC. A full-scale prototype demonstrated average flame length, flame temperature, and NOx emissions of 4242.6 mm, 1729.4 °C, and 460.2 mg/m³, respectively, validating the accuracy of the proposed mathematical model and controller.

Design Optimization of an Improved Mud Cookstove Using Computational Fluid Dynamics

ABSTRACT The present study focuses on optimizing the design and performance of natural draft mud-based cookstove (MBC) using the CFD tool ANSYS Fluent. The study simulates the performance of the MBC over different levels of three key factors, i.e. grate height, pot gap, and secondary hole diameter, against the targeted response parameters, which include average flame temperature, thermal efficiency, and combustion efficiency. Two-dimensional (2D) simulations of a real-world prototype of MBC were performed using ANSYS Fluent, solving governing equations for mass, momentum, energy, and species transport throughout the computational domain and employing a pseudo-transient accelerated solver approach to achieve a steady state. Grid independence was established to ensure reliable simulation results. It was observed that an optimized response was obtained at the grate height of 30 mm, pot gap of 30 mm, and secondary hole diameter of 8 mm, wherein the average flame temperature of 887 K, thermal efficiency of 27.64%, and a modified combustion efficiency of 98.97% was observed. The achieved thermal efficiency complied with the BIS IS 13,152:2013 standard for natural draft cookstoves, classifying it as a Tier 2 cookstove according to the performance targets outlined in ISO/TR 19,867-3:2018. The combustion efficiency exceeded 0.97, indicating pure flaming combustion. A full-scale field prototype was fabricated and successfully validated through laboratory and field experiments.

Combustion behavior of electrically controlled solid propellant with tungsten additive

In recent times, there is a growing interest in utilizing the controllable solid propellant combustion that facilitates multiple start and stop bits of the electrically controlled solid propellant (ECSP) combustion at will. This paper is an attempt to understand the effect of tungsten metal additive in the ECSP. The tungsten metal powder (1 μm size) is blended with the lithium perchlorate (LP) and polyvinyl alcohol (PVA) along with other ingredients. LP and PVA form the baseline composition, and metal content is added between 5 and 15% by weight. Thermal analysis of the ECSP samples were conducted at 5 °C/min utilizing differential scanning calorimetry (DSC) and thermogravimetry (TGA) in the temperature range of 30 °C–600 °C, and the results showed that the dominant exothermic peaks occur around 260 °C. High speed imaging facilitates in understanding the combustion characteristics of the ECSP samples. The ignition is achieved by applying 300 V DC supply across the molybdenum electrodes. ECSP combustion can be divided into two distinct phases of burning that can be designated as the transient burning and the steady phase burning. It is found that the burning rate was 38.2% faster for 15%-metalized ECSP than 5%-metalized. In addition, multi-wavelength pyrometry was used to obtain the average flame temperature, and it was observed that the flame temperature was 9% lower for 15%-metalized than 5%-metalized. Hence, this study enunciates the burning characteristics of tungsten based ECSP and helps in realizing the potential use of tungsten as a metal additive in the ECSP for micro thrust generation.

Design and simulation of a novel top-lit downdraft gasifier cookstove and performance comparison with a conventional top-lit updraft cookstove

This study designed and fabricated a novel top-lit downdraft gasifier stove (TLDDGS), which was compared with a traditional top-lit updraft gasifier stove (TLUDGS) in terms of modeling and performance. The experimental and simulation results demonstrated that the novel TLDDGS exhibits a downward-flow configuration. The average fuel consumption measured in the experiments was 4.57 ± 0.933 g/min. The average flame temperature from the experiment was 608 ± 43 °C. The TLDDGS mean flame temperature remained stable throughout the experiment. The O2, H2, CO2, CO, CH4, and N2 in the diluted syngas from the experiment were 16.07, 0.33, 0.66, 2.56, 0.34, and 80.04% by volume, respectively. The total suspended particulates and CO in TLDDGS and TLUDGS were 15 and 28 mg/m3 and 335 and 69 ppm, respectively, which are within the limits specified by the local standard. Thus, the developed TLDDGS is a promising alternative for sophisticated cooking applications because of its superior performance in terms of flame stability.

Analysis of the Effect of Fe2O3 Addition in the Combustion of a Wood-Based Fuel.

A comparative study was carried out of emissions from the catalytic combustion of pellets made from furniture board waste and pellets made from wood mixed with Fe2O3. The mass content of the Fe2O3 catalyst in the fuel was varied from 0% to 5%, 10%, and 15% in relation to the total dry mass weight of the pellets. The average flame temperature in the boiler was between 730 and 800 °C. The effect of the catalyst concentration in the fuel was analysed with respect to the contents of O2, CO2, CO, H2, and NOx in the flue gas and the combustion quality of the pellets in the heating boiler. Changes in the CO2 content and the proportion of unburned combustible components in the combustion residue were assessed. It was established that an increase in the Fe2O3 content of the prepared fuels had a positive effect on reducing NOx, CO, and H2 emissions. However, the proportion of iron oxide in the tested fuel pellets did not significantly influence changes in their combustion quality. A strong effect of the addition of Fe2O3 on the reduction of the average NOx content in the flue gas occurred with the combustion of furniture board fuel, from 51.4 ppm at 0% Fe2O3 to 7.7 ppm for an additive content of 15%. Based on the analysis of the residue in the boiler ash pan, the amount of unburned combustibles relative to their input amounts was found to be 0.09-0.22% for wood pellets and 0.50-0.31% for furniture board waste pellets.

Flame propagation and temperature distribution characteristics of magnesium dust clouds in an open space

In order to explore the flame propagation behaviors and temperature characteristics of magnesium dust clouds, the measurement system and the two-color pyrometer technique were used to study the spatial-temporal distribution of flame temperature fields and flame propagation behaviors with different particle sizes. The experiment results showed that the flame propagation characteristics largely depended on the particle size and the flame propagation velocity was higher with decreasing particle sizes. The flame temperatures of the leading edges were kept stable between 3100 and 3300 K, and the average flame temperature was related to the dust concentrations and particle sizes. The average flame temperature of −400 mesh magnesium with 830 g/m3 dust concentration was the highest, and the descent speed of the average flame temperature had a negative correlation with the particle size. The two-color pyrometer technique could evaluate the severity of magnesium dust clouds explosion, which provides a theoretical basis for the prevention.

Моделювання якісного складу паливно-повітряної суміші у факельному запальнику камер згоряння ГТД

The qualitative composition of the fuel-air mixture, which is formed in the torch igniter of the combustion chamber of the gas turbine engine (GTE), determines the efficiency and reliability of their work. The main task of the study is to determine the qualitative composition of the fuel-air mixture near the electric spark plug of the GTE torch igniter depending on its geometric features and engine operation condition. The composition of the mixture was evaluated using analytical, experimental, and numerical methods. According to the analytical model, a significant over-enrichment of the fuel-air mixture in the igniter housing was established and confirmed experimentally. A numerical model was used to determine the fields of mass concentration of fuel particles in the fuel-air mixture in the torch igniter housing, considering the peculiarities of airflow and fuel supply for different combinations of GTE design features and operating conditions. The influence of geometric parameters of the housing and external factors was investigated using the numerical model of stationary combustion of fuel-air mixture, which was prepared in the torch igniter housing of GTE combustion chamber by evaporation and spraying of aviation kerosene particles in the air stream. The implementation of a small-factor experiment allowed to establish the degree of influence of each factor under study and their interaction on the excess air coefficient. The correlation coefficient between the coefficient of excess air near the spark plug and the average flame temperature is set. Given the absence of serial designs of controller torch ignites, it is proposed to use a pulsed fuel supply to control the quality of the fuel-air mixture. Further ways of research to increase the reliability of ignition of both the torch igniter from the electric spark plug and the combustion chamber of GTE from the flame is outlined.

Fire Spread Characteristics of Metal-Polyethylene Sandwich Panels

An experimental study was conducted to determine the characteristics of the flame spread and droplets of metal-polyethylene (PE) sandwich panels during combustion. The mass-loss rate, average flame height, temperature, and fire spread rate were investigated. The results showed that the fire spread rate, mass change of the droplets, average flame height, and temperature increased with an increase in the sample length, except for the mass loss rate of the 40 cm-long sample. The time interval between the droplets decreased, and the flame pulsation frequency increased. The relationship between the flame height and sample length was determined. During the combustion process, bending deformation and top flame phenomena occurred due to the shrinkage of the PE, which increased the fire risk. The distance between the outer surface of the expanded metal aluminum layer and the insulation panel increased with an increase in the panel length. A schematic diagram of the fire spread of the metal sandwich panel was established based on the observations and theoretical analysis. The mechanism and combustion behavior of the metal sandwich panels were determined to provide references for the construction of metal sandwich panels of exterior walls.

Effects of Jet Flow Pulsation on Diffusion Flame Performance

he objective of the current research is the experimental investigation of the pulsating flow effects on the combustion performance in terms of the flame temperature distribution, the heat transfer rate, the combustion efficiency and the exhaust gas analysis. The flow pulsation provided through a rotary ball valve in accordance with a variable speed motor arrangement increased the flame temperature fluctuation and the magnitude of heat release. The flow pulsation provides a highly turbulent flame wherein the vortices are enlarged. Increasing Strouhal number [St] of the LPG fuel and air flow increases the time-averaged flame temperature of the pulsating flame up to a saturation level that is dictated by the heat transfer rate enhancement. The maximum average flame temperature is 1263oC at St= 0.041, r= 0 mm and 100 mm from the burner inlet. In addition, increasing the pulsating flow amplitude increases the convection and radiation heat fluxes from the pulsating flame. While increasing the pulsation decreases the exhaust UHC due to increasing the turbulent kinetic energy across the pulsating flame, the exhaust NOx slightly increases due to increasing the heat release rate and the flame temperatures. Pulsation thus enhances the combustion efficiency inside the industrial combustors.

Large Eddy Simulation on the Effects of Coal Particles Size on Turbulent Combustion Characteristics and NOx Formation Inside a Corner-Fired Furnace

Abstract The effects of pulverized coal particles’ sizes on the coal combustion characteristics are numerically studied in a laboratory-scale tangentially fired furnace. The turbulent gas flow and the coal particle motion are solved by employing the large eddy simulation (LES) and the discrete phase model (DPM). The mixture fraction probability density function (MF-PDF) is coupled to simulate the non-premixed pulverized coal combustion. It is found that the coal combustion efficiency is positively affected by the dispersion of coal powders. The particle dispersion and the coal combustion are augmented by the intensive impingement caused by the corner-injected flow. Large coal particles, with their greater inertia, enhance particle agglomerations, which limit the combustion of volatile and char. Accordingly, the average flame temperature decreases with the growing particle sizes. Also, the O2 concentration increases slightly because of the incomplete coal combustion, and the CO2 concentration decreases gradually. In contrast, the CO concentration increases markedly in the furnace center due to the presence of a reducing atmosphere. The NO concentration exhibits an exponential decline with the increased particle size. A relatively stable combustion and a relatively low NOx formation are acquired inside such a corner-fired furnace when the particle Stokes number is a little greater than 1.

ОПТИМІЗАЦІЯ КОНСТРУКЦІЇ ФАКЕЛЬНОГО ЗАПАЛЬНИКА ГТД ЧИСЕЛЬНИМ МЕТОДОМ

Solved the problem of gas-turbine engine combustion chamber flame igniter efficiency increasing by increasing the flame temperature via optimizing the body design. To determine the influence of the igniter body various geometric parameters, affecting the formation and combustion of the fuel-air mixture, a parametric model was developed. This model together with the developed project in the ANSYS Workbench software package made it possible to automate the modeling process. The influence of the geometric parameters of the igniter body and external factors on the average flame temperature has been studied via a numerical model of the stationary combustion process of the air-fuel mixture formed inside the igniter of the combustion chamber of a gas turbine engine by evaporation and spraying particles of aviation kerosene in the air stream. The adequacy of the numerical simulation results was confirmed by the implementation of a series of full-scale experiments using the Fisher criterion.The uniformity of temperature and adequacy of the average temperature estimation algorithm was established using the correlation analysis of the results of measured temperature at various points of the flame. To determine the degree and nature of their influence, sequentially screening (fractional), as well as full-factor experiments with varying factors at two and three levels were implemented. Based on the results of the analysis of variance, the most statistically significant factors were selected. A regression dependence was established that relates the diameter of the air inlet orifice and the air pressure drop to the flame temperature. A qualitative and quantitative assessment of the influence of the considered factors on the process of formation of a hot air mixture and its combustion has been performed. The optimal values of the geometric parameters of the igniter body and its operating conditions are determined under which the maximum flame temperature at the stationary combustion stage is ensured. Relationships between design features, igniter operation mode, and the temperature of the flame are established. This allows expanding the range of stable ignition of gas turbine engine combustion chambers in accordance with the design of the igniter, the starting fuel supply mode, and the air pressure drop.

Comparative study among waste cooking oil blends flame spectroscopy as an alternative fuel through using an industrial burner

The presented experimental investigation aims at providing a microscopic insight into the flame characteristics of the conventional (light/heavy diesel), a renewable fuel (waste cooking oil), and its blends with light/heavy diesel oils. A hyperspectral camera is used to provide detailed information on fuel reactivity and radiation intensities within the flame zones via the analysis of the C2 and CH radiation emissions. The experiments cover four equivalence ratios (Φ) of 0.63, 0.75, 0.96, and 1.1. A coaxial disc stabilized burner having a twin air jet atomizer is employed. The flame images are taken in the open atmosphere and the assessment of the combustion efficiency is obtained through the measurements of the cooling load inside a cylindrical combustor. The calculated values of the spatial cross-sectional average flame temperatures along the different flames are compared with the corresponding values obtained by a type S thermocouple. The processing of the hyperspectral flame images proves to be an extremely useful tool to define the location, size, and characteristics of the flame zones. The burning of HDO/WCO blend at near stoichiometric conditions appears to be a viable renewable alternative to burning standalone HDO. The burning of a standalone waste cooking oil must be avoided.

Flame analysis for prediction of thermocouple temperature and quality of sponge iron at TATA steel long products limited

The temperature profiles of the gas and charge in a coal-fired rotary sponge iron kiln affect both the iron ore reduction process and accretion formation. The temperature profile of charge is estimated from the eleven thermocouples (TC1-TC11) placed along the 80 m length of the kiln. The quality prediction models are heavily dependent upon the accuracy of the measurement of TC10. However, slowly, as the kiln’s campaign life increases TC10, and other thermocouples too, get corrupted due to deposition of material (accretions) on the thermocouples. At the beginning of the campaign, however, there is no accretion on TC10. In the present work, an attempt is made to directly correlate flame characteristics with TC10 and with quality of iron produced so that when TC10 is corrupted due to accretion or breakdown, we can still survive by using flame characteristics as a guide to control quality. The flame inside the rotary kiln has been analysed by using image analysis procedures for the first time in a sponge iron plant. The flame’s estimated average temperature and pixel intensity information are correlated with (a) the temperature measured by the thermocouple TC10 (which is installed at a distance of 20 m from the rotary kiln outlet hood) and (b) with quality of iron produced. It is found that use of average flame temperature for quality prediction has several advantages in terms of increased accuracy of prediction and quicker response time of flame to short-time changes in coal quality (particle size, moisture, ash content, etc) whereas TC10 thermocouple takes much longer to reflect these changes due to slow process of heat transfer to charge. In addition, the adverse effect of accretion formation on TC10 for quality prediction has been overcome.

Experiments for combustion temperature measurements in a sugarcane bagasse large-scale boiler furnace

This work presents a numerical and experimental study to measure local combustion temperature from the combustion reactive zone in an industrial sugarcane. A bagasse boiler furnace is utilized preliminary step towards obtaining online three-dimensional temperature measurements. Two different methods were used for in situ measurement of local temperatures in a sugarcane bagasse flame: Spectral Analysis and Image Processing in the Visible Spectrum. The maximum instantaneous temperatures found in the focused reactive zone area of the bagasse flame were 1623 K and 1520 K by the spectrometric and imaging system respectively and the time average maximum flame temperatures measured were 1443 K and 1496 K. Additionally, a set of flame temperature measurement tests was carried out in a laboratory furnace by the spectrometric method and a time average flame temperature of 1569 K was noted. The flame temperatures found in this work show reasonable agreement with results of CFD simulations and results obtained in laboratory tests which were also reported in the literature. Intensity of emission lines of alkali metal (K) were measured in the flame spectra during the bagasse combustion. Spectral flame emissivity was estimated for an industrial level operating condition.

Physical model of wildland fire spread: Parametric uncertainty analysis

For the physical model of wildland fire spread, errors or discrepancies in the prediction of spread rate may arise from uncertain, imprecise or improper determinations of the model parameters due to unreasonable assumptions, rough approximations, or inaccurate measurements. In this study, a parametric uncertainty analysis is made on a typical model of upslope fire spread that is consistent with many other models in the framework of the heat transfer theory and the major equations of sub-models. The variation ranges of the model parameters are determined based on the experimental data and assumptions, thereby the rate of fire spread (ROS) is used as a target variable of model calculation to evaluate the response of the model to parametric uncertainties. It is found that the values of ignition temperatures and averaged flame temperatures have significant impacts on the predicted values of ROS under lower slopes. Although the impacts decrease with the increase of slope, they are still non-negligible under higher slopes. Especially under lower slopes, the assumed values of both temperatures have significant effects on model prediction. The error in estimating the flame length has a remarkable influence on model prediction, and especially, the flame length variation of the same magnitude results in consistent relative errors under different slopes. A larger fluctuation range around a fixed average flame length results in a greater deviation from the predicted results, while for the same fluctuation range of flame length, the relative errors under higher slope angles are distinctly greater than those under lower slopes. In contrast, the errors for evaluation of the flame tilt angle have negligible effects on model predictions. The flame emissivity has a remarkable effect on model prediction and thus should be adjusted to better characterize the variation of flame intensity under different slopes. Besides, the prediction of ROS is very sensitive to the evaluation of fuel consumption efficiency, especially for higher slope angles. Simulation results indicate that larger heat convection coefficients are required for achieving better prediction results for higher slope angles, which agrees well with the previous experimental finding that with the increase of slope angle, a kind of flame-induced convection plays a more and more important role in fire spread.

Quenching distances, minimum ignition energies and related properties of propane-air-diluent mixtures

The ignition by high voltage inductive-capacitive sparks of the quiescent stoichiometric C3H8-air mixture diluted by various amounts of additives (He, Ar, N2, or CO2) is examined at various initial pressures within 0.5–1.5 bar in a cylindrical vessel of volume ~0.28 L. The quenching distances (QDs) of C3H8-air and C3H8-air-diluent mixtures are determined by means of flanged electrodes technique. Experimental QDs are compared with the computed ones, obtained by a previously described model. Using the QD, the minimum ignition energies (MIEs) are evaluated using a correlation model. At constant pressure, dilution results in the increase of both QD and MIE. Among the examined diluents, CO2 has the most important effect, followed by N2, Ar and He. For each diluted mixture the QDs and MIEs depend on initial pressure, according to a power law. The baric exponents of the QD are further used to determine the overall reaction orders of C3H8-O2 reaction in flames. The overall activation energies of this process are determined from the semi-logarithmic dependence of the QDs versus reciprocal average flame temperatures. The overall kinetic parameters of propane-oxygen reaction are influenced by diluent addition.

Suppression of pulverized biomass dust explosion by NaHCO3 and NH4H2PO4

To effectively mitigate accidental biomass dust explosion, the suppression capacities of NaHCO3 and NH4H2PO4 for biomass dust explosion were determined. Suppression mechanism of biomass flame was further revealed. Poplar sawdust and peanut shell dust with two particle size distributions were employed. A high-speed camera was used for to capture flame propagation behavior and microstructure. Flame temperature was measured by a fine thermocouple. Results showed that the consequences of poplar sawdust explosion are greater than peanut shell dust. By increasing the concentration of NaHCO3 and NH4H2PO4, the average flame velocity and flame temperature of pulverized biomass dust were significantly decreased. The minimum suppression concentration of NaHCO3 was about 30% lower than that of NH4H2PO4. The suppressants could consume key radicals of biomass flame, resulting in lower flame speed and lower flame temperature. The heat absorbed by NH4H2PO4 decomposition was about 6.5 times that of NaHCO3 decomposition. However, the extra heat released from the exothermic reactions of NH4H2PO4 could enhance biomass combustion. Hence, NaHCO3 has a better suppression performance than NH4H2PO4 for biomass dust explosion.

The study of co-combustion characteristics of coal and microalgae by single particle combustion and TGA methods

The co-combustion characteristics of coal and microalgae with different blending ratios and under different atmospheres are studied by single particle combustion and thermogravimetric analysis methods. The combustion processes of coal, microalgae and their blends in the single particle combustion experiment have two stages, while the combustion process of coal in the thermogravimetric analysis experiment only has one stage. With the increasing blending ratio of microalgae, flames of volatiles and char of fuels become dimmer and smaller, and the average flame temperature decreases from about 1400 °C to about 1200 °C. The ignition delay time decreases from 200 ms to 140 ms, and the experimental ignition delay time of blended fuels is lower than the theoretical ignition delay time, which demonstrates that the synthetic effect between coal and microalgae exists. To analyze the influence of oxy-fuel atmosphere on the combustion characteristics, the air is replaced by the O2/CO2 atmosphere. The replacement decreases the luminosity, size and average temperature of flames. The average flame temperature of volatiles decreases from 1449.4 °C to 1151.2 °C, and that of char decreases from 1240.0 °C to 1213.4 °C. The replacement increases the ignition delay time of fuel from 80 ms to 100 ms. Increasing mole fraction of O2 in O2/CO2 atmosphere can offset these influences. With the increasing mole fraction of O2, flames of volatiles and char of fuels become brighter and larger, the average flame temperature increases from about 1100 °C to about 1300 °C, while the ignition delay time decreases from 100 ms to 77 ms.

Direct Writing of a 90 wt% Particle Loading Nanothermite.

The additive manufacturing of energetic materials has received worldwide attention. Here, an ink formulation is developed with only 10 wt% of polymers, which can bind a 90 wt% nanothermite using a simple direct-writing approach. The key additive in the ink is a hybrid polymer of poly(vinylidene fluoride) (PVDF) and hydroxy propyl methyl cellulose (HPMC) in which the former serves as an energetic initiator and a binder, and the latter is a thickening agent and the other binder, which can form a gel. The rheological shear-thinning properties of the ink are critical to making the formulation at such high loadings printable. The Young's modulus of the printed stick is found to compare favorably with that of poly(tetrafluoroethylene) (PTFE), with a particle packing density at the theoretical maximum. The linear burn rate, mass burn rate, flame temperature, and heat flux are found to be easily adjusted by varying the fuel/oxidizer ratio. The average flame temperatures are as high as ≈2800 K with near-complete combustion being evident upon examination of the postcombustion products.

Investigation of Fire Protection Certification for Aircraft Engine Components

Fire protection performance is one of the most important capabilities for aircraft engine, since the result may be hazardous in the case of a fire condition. According to fire protection regulation CCAR 33.17 of China Civil Aviation Regulations, fire-proof tests of a specific pipeline, a fuel tank and a fuel filter assembly were carried out. Test conditions include inlet fluid temperature, fluid pressure, fluid volume flow, fire temperature and heat flux density. The average flame temperature during the fire tests is 2000 degrees Fahrenheit, the heat flux density is 116kW/m2±10kW/m2 and the distance from burner exhaust to the test area is 100mm in these fire tests. Fire test of pipe passed, but the fire test of oil tank failed because of the failure of the oil circulation system and the melting of plastic pipe material in the ventilation pipe separately. The first fire test of the fuel filter failed because of design defect of one oil drainage path, but after design change of the oil drainage path, the second one succeeded. Based on the fire protection tests and results analysis, three essential factors of fire protection performance and type certification were presented: 1. Volume of medium retained in test parts; 2. Mass flow of medium; 3. Pressure in the test parts cavity.