Flame Radiation Characteristics Research Articles

Flame temperature and emissivity distribution measurement of solid propellant based on clustering analysis of multispectral radiation images.

To measure the combustion parameters of a solid propellant, this Letter researches the fitting method for flame temperature and emissivity based on multispectral images and proposes the particle swarm optimization-K-means (PSO-K-means) clustering optimization algorithm of a flame multispectral image. Considering the difference in flame radiation characteristics in different regions, the flame multispectral image is clustered, and spectra in different regions are analyzed and selected in different fitting bands to inverse temperature and emissivity. On this basis, the method is applied to measure solid propellant combustion parameters with different formulations. The measurement shows that the flame temperature is between 1700 and 2100 K, and the emissivity is concentrated in 0.1-0.5. Compared with temperature measurements obtained from tungsten-rhenium thermocouples, the relative deviation of multispectral imaging thermometry is less than 5%. The distribution characteristics of solid propellant combustion parameters with different formulations were analyzed, which provided important data support for evaluating combustion conditions and optimizing solid propellant formulations.

Effect of flame thickness on the temperature measurement error for bare-bead thermocouple in open pool fires with different fuels

Accurately obtaining the temperature distribution of the flame is crucial for a comprehensive understanding of the combustion behavior of the pool fire. The correction method is needed to compensate the measurement error when the temperature is measured by bare-bead thermocouple in the open pool experiment, but the effect of flame thickness is rarely considered in the current method. Thus, this work develops a coupled heat transfer model of bare-bead thermocouples in open pool fires and modifies the flame radiation characteristics based on the fuel type and flame thickness. The control mechanism of measurement error in the model is identified, and then the effects of main parameters such as flame thickness and flame temperature on measurement error are analyzed. The results show that the flame emissivity decreases exponentially with the decrease of flame thickness, the minimum emissivity of gasoline flame is 0.26 when flame thickness is 0.1 m. The decrease of flame thickness leads to a sharp increase of temperature measurement error. The maximum increment of error can reach 227.3 K. On this basis, the flame thickness limit value, considering the correction of temperature measurement error in different hydrocarbon pool fire experiments is proposed.

Ceiling radiation heat flux and downward received radiation heat flux of methane jet fire with hydrogen addition

Radiation and flame scale characteristics of ceiling jet are important key elements, which are related to the safety of hydrogen energy transport. In this study, the flame radiation characteristics caused by hydrogen-blended natural gas (mixed gas) pipeline leakage fire were investigated experimentally. The effects of heat release rate, hydrogen addition ratio, nozzle diameter and source-ceiling height are considered. The flame shape of the ceiling jet fire is modeled by a cylinder cone and a cylindrical model. The WSGGM model is applied to calculate the flame emissivity. The flame emissivity is quantized by the equivalent diameter and gas type. The flame emissivity, downward received radiative heat flux and radiative heat flux under ceiling increase with the increase of hydrogen addition ratio. The view factor is calculated by the solid flame model. Moreover, the calculated flame radiative heat flux is in a favorable agreement with experimental results. The research results may provide reference for risk assessment of hydrogen mixing.

Experimental and theoretical research on flame emissivity and radiative heat flux from heptane pool fires

This paper presents an experimental investigation on the flame radiation characteristics of pool fire, including the flame emissivity, diameter and temperature. A series of experiments of heptane pool fires with diameters of 0.1–0.4 m were carried out. The flame height, mass loss rate, temperature distribution, flame emissivity and radiative heat flux were measured. A four regions function was used to correlate the centerline temperature rise above the pool surface with the flame height. The variations of the flame diameter against the flame height were formulated for D>0.2 m and D ≤ 0.2 m respectively. The highest flame emissivity is found at the flame base, which decreases with increasing height. Furthermore, a new model predicting the radiative heat flux based on classical solid flame model is developed taking into account the flame emissivity, diameter and temperature variations along the flame height. The comparisons between the new model and other models show that the new model can better predict the thermal radiation from heptane pool fires.

Impacts of N2 and CO2 diluent gas composition on flame emission spectroscopy for fuel concentration measurements in flames

Flame emission spectroscopy (FES) is used to determine methane fuel concentration in a premixed flat-flame burner with varying diluent composition. Spectral profiles of the molecular emission bands of OH* (306.4 nm), CH* (431.5 nm), and C2* (520 nm) in the UV-to-visible range are recorded and analyzed for various equivalence ratios (0.72 < ∅ < 1.25), oxygen concentration (0.19 < XO2 < 0.35), and diluent gas species (N2, CO2). The importance of flame radiation, which is strong and reliable in the UV spectrum, is confirmed particularly for quantitative measurement purposes. In air-methane flames, the band intensity ratios of OH*/CH* and C2*/CH* are shown to be highly sensitive to fuel stoichiometry, and can thus serve as accurate indicators of ∅. In addition, the impact of diluent gas composition on flame radiation characteristics and FES utilizing band intensity ratios is investigated for potential applications such as clean combustion utilizing exhaust gas recirculation (EGR), and oxy-combustion in supercritical CO2 power plants. It is shown that the strength of the underlying broadband emission is strongly dependent on the diluent gas composition, and influences the sensitivity and accuracy of the FES-based ∅ measurement.

Monitoring regenerative steel reheating burners using an intelligent flame diagnostic system

The present paper describes the use of an intelligent Flame Monitoring System on regenerative steel reheating burners based on direct measurement and analysis of the flame radiation signals. A series of experiments were conducted on a 500 kW furnace fitted with two burners firing in a regenerative manner. The experiments covered a wide range of burner operating conditions including variations in the burner firing-rate and excess air levels. Gas supply to one of the burners was manually reduced in order to simulate burner imbalance. The flame radiation signals were acquired using a fibre-optic based optical instrument incorporating broad ultraviolet, visible and infra-red photodiodes. The correlation between the dynamic flame signals with respect to the excess air level and nitrogen oxides emissions were made using neural network models following off-line analysis of the acquired signals using different signal processing methods, to yield a set of flame features. The present work indicates that the measurement of flame radiation characteristics, coupled with advanced data modelling techniques such as neural network, provides a promising means of monitoring and optimising burner performance.

Development of an intelligent flame monitoring system for steel reheating burners

This article describes the development of a system to indirectly monitor the combustion characteristics of individual burners based on measurement and analysis of the signals detected from photodiodes detecting flame radiation signals. A series of experiments were conducted on a 500 kW pilot-scale furnace and on two 4 MW industrial burners located in two steel reheating furnaces. The flame radiation signals were monitored using a lens that transmitted the flame radiation to ultraviolet, visible and infrared photodiodes through a trifurcated optical fibre. The experiments covered a wide range of burner operating conditions including; variations in the burner load and excess air levels and simulations of burner imbalance. The relationships between the dynamic flame radiation signals and the burner operating parameters and conditions were made off-line using neural network models. The present work indicates that the measurement of flame radiation characteristics, coupled with neural networks, provides a promising means of monitoring and adjusting burner performance.

Flame structure and radiation characteristics of CO/H2/CO2/air turbulent premixed flames at high pressure

Experimental study on turbulent premixed flames for a CO/H2/CO2/air mixture as a model of coal gasification syngas in a high pressure environment was performed up to 1.0MPa. CH4/air flames with laminar burning velocity and adiabatic flame temperature identical to those of CO/H2/CO2/air mixture were also employed, and then the flame structure and turbulent burning velocity analyzed using OH-PLIF as well as flame radiation characteristics were compared. Results showed that in the case of the CO/H2/CO2/air flame, very fine cusps were seen, these small cusps being generated on a large scale wrinkled flame front even for low u′/SL. Flame surface density of the CO/H2/CO2/air flame was higher than that of the CH4/air flame, and the mean volume of the turbulent flame region of CO/H2/CO2/air flame was smaller than that of the CH4/air flames at high pressure. Bending of ST/SL with u′/SL for the CO/H2/CO2/air flame was not observed in this experiment, while such bending was clearly seen for the CH4/air flame. The difference in the bending characteristics can be explained based on the scale relation between the smallest scale of flame wrinkles represented by the fractal inner cutoff and characteristic flame instability scale. The spectrum of flame radiation for the CO/H2/CO2/air flame at 0.5MPa showed continuous emission in the visible range of the wavelength, while that for CH4/air flames for the equivalence ratio of unity showed very intense H2O emission in the IR range. When the flames with identical adiabatic flame temperature for the CO/H2/CO2/air flame and the CH4/air flame were compared, the total radiation intensity of the former mixture was observed to be strong. The intense emission from the CO/H2/CO2/air flame is thought to be one of the mechanisms which generate very fine flame cusps as enhanced cellar instability for smaller Lewis number.

Dynamic application of digital image and colour processing in characterizing flame radiation features

In this work, the experimental investigation of the dynamic flame properties of flame flickering and equivalence ratio sensing of a combustion process was done. In particular, the time-varied flame properties were examined using a novel digital image and colour processing methodology. This technique makes use of the observed correlation between a digital image colour signal and physical flame radiation characteristics in the visible wavelength domain. Aspects of RGB and HSV colour modelling principles were applied to show that the addition of colour identification in the image processing of high-speed flame image data could yield three useful parameters which are related to the dynamic behaviour of different flame emanating components. First, the validity of the colour identities for tracking the yellowish-red diffusion and greenish-blue premixed flame colourations were examined by comparing their respective flickering frequency profiles. Then, the usefulness of the extracted Rdiffusion, Gpremixed and Bpremixed colour signals to abstractly represent the behaviour of soot, C2* and CH* emission characteristics in a dynamic flame transition from diffusion to stoichiometric premixed condition was demonstrated. In particular, the colour signal ratio Bpremixed/Gpremixed was correlated to exemplify the approximate time-varied state of the equivalence ratio from the imaged combustion phenomenon.

Flame radiation characteristics in pulsed combustion of liquid motor fuels in a constant-volume combustion chamber

Flame combustion of liquid hydrocarbon fuels occurs in augmented engines of transport vehicles and stationary power installations. Calculation of the radiative heat transfer from the flame to the combustion chamber walls represents a complicated problem whose solution requires reliable data on the in-chamber temperature distribution and flame radiation characteristics. Physically, the flame can be considered a complex disperse system consisting of gases and solid particles of soot carbon. The radiative properties of soot particles depend on a number of factors: their geometry, concentration, and optical properties. The burning in augmented small-size combustion chambers of diesel and gas turbine engines and other similar power units proceeds in either pulsed or strongly nonstationary regimes that differ considerably from stationary combustion. The difference consists in the short time of visible burning, the high rate of change in the main parameters of the combustion process, and the soot particle geometry, as well as the cyclicity of the working process. Radiation from the soot particles predominates over radiation of polyatomic gases in the process of heat transfer between the flame and the chamber walls. For this reason, the radiative properties of soot particles and the peculiarities of the heat transfer inside the chamber are given the most attention in the studying of pulsed combustion of liquid fuels. Experimental evidence and calculations are presented for the radiative characteristics of the flame in pulsed combustion of gasolines, kerosenes, and diesel fuels in a constant-volume chamber. The experimental results, along with literature data on the flame emission characteristics under stationary combustion of liquid fuels, are generalized in the form of empirical formulas that permit estimation of the flame radiation properties depending on combustion conditions (parameters). A comparison of the flame emission properties and radiative heat transfer rate calculated by the method developed by the authors shows satisfactory agreement with the results of measurements of these characteristics in diesel combustion chambers. Therefore the obtained formulas are recommended for an engineering analysis of radiative heat transfer in combustion chambers of internal combustion engines and other similar power installations.