Temperature Measurements In Flames 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.

Study of chemiluminescence of methane–air flame stabilized on a flat porous burner

In this work, the spatial distribution and spectral characteristics of the chemiluminescence of chemically excited species, OH∗ and CH∗, are experimentally and numerically studied by using a stationary premixed methane–air flame stabilized on the surface of a flat porous burner for various equivalence ratio and normal pressure. Numerical simulations are carried out using detailed reaction mechanisms, and the experimental study includes high-resolution spatial and spectral optical measurements. Despite the data reported in the literature, it is found that (i) the rotational degrees of freedom of OH∗ and CH∗ are not in thermal equilibrium with the surrounding gas and therefore cannot be used to measure flame temperature; (ii) there is no direct correlation between the heat release rate and the distribution of OH∗ and CH∗; (iii) the detailed reaction mechanisms not only quantitatively, and also qualitatively differ in description of the OH∗ and CH∗ concentrations. Since the chemically excited species are well localized in a direction normal to the flame surface, they are demonstrated to be a very accurate markers of flame location. The shape of the combustion front can be reconstructed and resolved up to the accuracy of tens of microns, which is very important for estimation of blow-off critical parameters and measurement of the laminar burning velocity.Novelty and significance statementCurrently, there is a growing interest in the development of sensors for combustion control systems, including active control and suppression of instabilities, in combustion chambers of various devices and engines based on chemiluminescence of excited reaction species. The possibility of non-invasive determination of parameters such as flame temperature, stoichiometry, heat release rate location, etc. using this technique is discussed. We have found that most of these parameters cannot be estimated either due to fundamental limitations or insufficient knowledge of the reaction kinetics involved in the production of these species. Nevertheless, since OH* and CH* are well localized in the direction normal to the flame surface, they can be used as very accurate markers of flame shape and position, allowing us to reconstruct the flame surface to within tens of microns resolution, which is very important for estimating blow-off critical parameters and measuring laminar burning velocity.

Simultaneous measurement of temperature and C2H4 concentration in hydrocarbon flames using interference-immune differential absorption spectroscopy at 3.3 μm

In diagnostic applications based on tunable diode laser absorption spectroscopy, the measurement of target substances can be influenced by factors such as background thermal radiation in the combustion environment, extinction caused by solid or liquid particles, and other interfering absorptions. In this work, we developed a differential absorption diagnostic technique based on wavelength pairs, utilizing an interband cascade laser near 3.3 μm to simultaneously measure temperature and C2H4 concentration in hydrocarbon flames. Based on a detailed study of the C2H4 spectrum in this region and considering the optimal standard for spectral lines, two wavelength pairs were selected. The temperature is determined by the ratio of the absorption cross-sections of two wavelength pairs, and the C2H4 concentration is inferred based on the wavelength pair with higher differential absorption. In the initial stage, the system’s accuracy was verified in high-temperature static conditions (T = 300–800 K, P = 1 atm), and continuous time series measurements demonstrated the system’s stability. The limit of detection achieved by Allan-Werle variance analysis is 2.5 ppm at the optimal average time of 100 s. Subsequently, measurements were taken in a hydrocarbon flame. The obtained results indicate an average deviation of 1.021 % between the measured temperature in the flame and the reference value, with a standard deviation of 1.381 % for concentration measurement. All the measurements show that the system can be potentially applied to combustion diagnosis.

A simultaneous non-invasive diagnosis method for flame temperature and velocity fields based on radiation self-calibration and optical flow

The measurement of flame temperature and velocity is crucial to combustion research, hence it is of great significance to develop a non-invasive diagnosis technology for the measurement of flame temperature and velocity. In this study, a single-camera simultaneous non-invasive diagnosis technology for flame temperature and velocity field was developed, based on radiation self-calibration and optical flow method. The diagnosis method was applied to two case studies, propane diffusion flame and solid surface spread flame. The reconstructed flame temperature field was compared with measuring results by thermocouples. Results show that the reconstructed temperature field can accurately describe the symmetrical distribution characteristics and the clear high-temperature front. The combustion zone reconstruction temperature was 1250–1380 K for propane diffusion flame and the maximum reconstruction temperature was 1400 K for solid spread flame. The maximum relative error between the reconstructed temperature and the measured values by thermocouples is less than 15 %. Additionally, the flow velocity field at the flame edge was also measured, which could provide a good qualitative characterization of flame kinematic.

Development of compact-modulated absorption/emission technique towards micro-gravity sooting flame measurements

To meet the experimental physical limitations on Chinese Space Station (CSS), three compact-modulated absorption/emission (CMAE) implementations are miniaturized progressively from original MAE layout, which are investigated as potential options for simultaneous soot temperature and volume fraction measurements in the axis-symmetric flames. Contrasted with the original MAE technique, a white LED point light source (diameter of ϕ = 8 mm) and a white LED planar light source (rectangle of 200 × 120 mm2) in turns replaces the laser source, by which the light beam homogeneous implementation is significantly simplified. Moreover, a 3-CMOS prism-based camera enables simultaneously recording flame two color radiations that reduces the detecting complexity. It is found that backlight beam intensity should be more than 2.5 times the flame radiation intensity to avoid abnormal extinction coefficient on the flame edge in this configuration. Moreover, the robustness and consistency of the three CMAEs measurements are validated with a standard Santoro’s flame, and low average standard deviation ranges of ±0.04∼±0.06 ppm and ±65.0∼± 96.3 K for soot volume fraction and temperature respectively is evaluated from error propagation assessment. As such, the proposed CMAE-2 and CMAE-3 layouts are promising candidates for high-fidelity flame soot parameters measurements under limited space, weight and power supply on CSS.

Dual-range emission spectroscopy for temperature measurement of laminar aluminum dust flames

Understanding the temperature fields/profiles in aluminum dust flames is critical to the design of aluminum-based sustainable fuels and the development of aluminum combustion simulation tools. Although emission spectroscopy has been applied in aluminum flames, the signals in most works were integrated along the recording path and over the whole flame and, therefore, the measurements could not provide information of the flame spatial structure. In addition, the details of the diagnostic method were scarcely introduced. This work develops a dual-range emission spectroscopy diagnostic system for 1D measurements of the liquid temperature and the flame temperature of aluminum flames. The important aspects for diagnostics, such as the instrument specifications, signal acquisition strategy, data processing, accuracy and precision, are introduced and quantified in detail. The continuous spectrum from the liquid phase of Al(L) and/or Al2O3(L), rovibrational AlO spectrum from the micro-diffusion flame, and 2D flame luminosity are recorded simultaneously. Based on Planck's law, a linear fitting method is implemented to derive a continuous spectrum temperature. A nonlinear minimization framework based on the stick spectrum is introduced to fit the AlO spectra and derive a AlO temperature. The accuracy and precision are quantified by a comparison of the average temperatures against the equilibrium temperatures and the standard deviations. The effectiveness of this technique for temperature measurements of aluminum dust flames is verified by the agreement of the continuous spectrum temperature and the AlO temperature in the post-flame region. The 1D distribution of the continuous spectrum temperature indicates the boiling of Al and the dissociation/condensation of Al2O3 from upstream to downstream through the flame. The 1D temperature distributions also present a lag of the continuous spectrum temperature compared to the AlO temperature, indicating that the continuous spectrum temperature is dominated by the Al fuel droplets and the Al2O3 caps, instead of the Al2O3 nanometric droplets.

In-situ measurement of potassium and sodium concentrations in a 16 MW MSW incinerator employing the FES system

To comprehensively understand the release characteristics of alkali metals which can cause corrosion and slagging problems in municipal solid waste (MSW) incinerators, the temporal concentrations of sodium (Na) and potassium (K) in a 16 MW MSW incinerator were measured employing a calibrated flame emission spectroscopy (FES) system. The experimental results revealed that the concentrations of alkali metals increased first and then decreased from the left side to the right side of the MSW incinerator. The maximum concentrations of Na and K were 111 ppm and 184 ppm, respectively. The peak and average concentrations of K near the left wall were 27 % and 58 % higher than those near the right wall at the same height of the MSW incinerator, owing to the different combustion stages of the MSW. The differences of the peak and average concentrations of K at the different heights of the MSW incinerator were 33.7 % and 23.5 %, respectively. Moreover, a positive correlation between the concentration of alkali metals and flame temperature was confirmed during the char phase combustion stage. Since the primary air distribution pattern of MSW incinerator decreased form the left side to the right side, the concentration of alkali metals near the left wall was positively correlated with the primary air flow, and that near the right wall exhibited a positive correlation with the garbage caloric value. This research provided an effectual solution for in-situ measurement of alkali metal concentration and flame temperature in MSW incinerators.

The impact of equivalence ratio on the fire characteristics of Kerosene/air flame produced by NexGen burner for aeronautic application

This paper provides an experimental investigation of a Kerosene/air flame (produced by the NexGen burner designed by the FAA, and here calibrated for ISO 2685/AC20-135 standards fire tests conditions), which is used to generate flame/burnt gases impinging on material samples in the field of fire safety. The purpose of this study is to characterize this burner, and experimental means are implemented to better understand the effects of the equivalence ratio on the spatial distribution of the gas temperature (thermocouples) and the heat flux (heat flux gauge). A parametric study was carried out by varying the global equivalence ratio (ER); highlighting a flickering phenomenon, a relation between the ER and the heat flux, and determining empirical correlations. Hence, the measured flame temperature, heat flux, and heat release rate increase up to a critical value of equivalence ratio equal to 1.03 (flame temperature (1101.5 °C) and heat flux (140 kW/m2).

Flame Imaging Technology Based on 64-Pixel Area Array Sensor.

High-resolution flame temperature images are essential indicators for evaluating combustion conditions. Tunable diode laser absorption spectroscopy (TDLAS) is an effective combustion diagnostic method. In actual engineering, due to the limitation of line-of-sight (LOS) measurement, TDLAS technology has the problems of small data volume and low dimensionality in measuring combustion fields, which seriously limits the development of TDLAS in combustion diagnosis. This article demonstrates a TDLAS imaging method based on a 64-pixel area array sensor to reconstruct the two-dimensional temperature field of the flame. This paper verifies the robustness of the Algebraic Reconstruction Technique (ART) algorithm through numerical simulation and studies the effects of temperature, concentration, and pressure on the second harmonic intensity based on the HITRAN database. The two-dimensional temperature field of the flame was reconstructed, and reconstruction accuracy was verified using thermocouples. The maximum relative error was 3.71%. The TDLAS detection system based on a 64-pixel area array sensor provides a way to develop high-precision, high-complexity flame temperature measurement technology.

Effect of CH4 Addition on Soot Formation in C2H4 Diffusion Flame

Abstract Studying the effect of co-combustion of multiple fuels on soot formation has become a hot spot in the investigation of soot particles. In this paper, the influence of methane blending on soot formation in ethylene flame combustion is studied experimentally and numerically. The visible spectrum of flame image processing technology was used for the in situ measurement of laminar flame temperature and carbon smoke volume points in the experiment. The effects of different methane blending ratios on particle nucleation, coalescence, surface growth, and oxidation process of soot were analyzed based on the piecewise particle dynamics soot model of polycyclic aromatic hydrocarbons (PAHs) using CoFlame Code. Results indicate that the synergistic effect promoted the increasing rate of nucleation and addition reaction of hydrogen extraction at a low methane blending ratio, and the increase in the total mass of soot was mainly due to the PAH condensation rate. The total amount of soot generation gradually decreases with increasing blending ratio. The overall trend of condensation, surface growth rate, and soot nucleation in the flame decreases with increasing blending ratio. And the nucleation rate gradually shifts from a single peak to a double peak and increases slightly at the initial stage of the flame combustion reaction. It is worth mentioning that the change of three PAH precursors (secondary benzo(a)pyrenyl, benzo(a)pyrene, and benzo(ghi)fluoranthene) and the temperature explains the change of nucleation rate from unimodal to bimodal.

Multidimensional high-temperature field measurement method for flame based on near infrared radiation spectrum of water vapor

The temperature distribution is an important parameter in the design and optimization of :various engine types, and this paper begins by analyzing the temperature sensitivities of different waveband combinations. Based on an evaluation of the effects of self-absorption phenomena on the temperature measurement accuracy, a multidimensional temperature measurement method based on the integrated ratio of the intensity of the water vapor broadband radiation spectra is proposed. To address the multidimensional temperature inversion problem, the practicality of a nonlinear reconstruction approach is evaluated, and a multiple linear iteration algorithm is proposed. In addition, validation experiments are performed in the form of methane/oxygen laminar flame temperature measurements in combination with parallel rotating beam spectroscopy, and the results show that the method exhibits temperature measurement resolution of 10 K. The method proposed and developed in this work provides a new experimental concept for high-temperature measurements and is expected to provide reliable multidimensional temperature data for combustion chambers and plumes in engine ground experiments.

On the Effects of Flow Swirl on Static Stability Limits and Flow/Flame Characteristics of Premixed Oxy-Methane Flames: An Experimental Study

ABSTRACT An experimental study was performed to investigate the effects of flow swirl on flow/flame characteristics and stability of atmospheric premixed oxy-methane (CH4/O2/CO2) flames. The flames generated by two swirlers of 55° and 45° swirl angles were tested on a test stand for a dry low emission (DLE) model gas turbine combustor at constant inlet flow velocity of 5.2 m/s and over ranges of operating oxygen fraction (OF: 21% to 70% - by volume in the O2/CO2 mixture) and equivalence ratio (: 0.2 to 1.0). Combustor static stability limits (flashback and blow-out) were determined experimentally in the -OF domain to identify the operational ranges of the combustor while varying inlet flow swirl. To understand the mechanisms for flashback and blow-out, the lines representing the stability limits were displayed in the -OF domain against the contours of combustor power density (PD: MW/m3/atm), adiabatic flame temperature (AFT), and inlet flow Reynolds (Re). Comparison of flame macrostructure and measurements of local flame temperatures were performed for the two swirlers over ranges of , OF, and AFT to determine the effects of such operational parameters on flow/flame interactions and flame stability and to serve as a database for validating numerical models for such flames. The results show that, for both swirlers, the flames blow-out at a very similar AFT of ~1600 K indicating the dominant role of AFT in controlling premixed oxy-flame stability near the blow-out limit. Compared to the same combustor with a 55° swirler, the 45° swirler has a wider stable combustion zone. Comparing the flames of the same AFT, at fixed inlet flow velocity, shows almost identical flame macrostructure whatever the operating inlet flow swirl, OF and φ.

Investigation of the flame properties and fire behavior of carbon‐reinforced PEKK, BMI and phenolic composites impacted by Jet‐A1/air flames

AbstractThis paper provides an experimental investigation of a kerosene/air burner (the NexGen burner designed on the FAA's proposed ISO 2685 standard), which is used to generate flame/burnt gases impinging on material samples in the field of fire safety. The purpose of this study is to characterize this burner, and experimental means are implemented to better understand the effects of the equivalence ratio on the spatial distribution of the gas temperature (thermocouples), the heat flux (heat flux gauge), and gas emission species. Hence, the measured flame temperature, heat flux, and heat release rate increase up to a critical value of equivalence ratio equal to 1.03. Furthermore, a pyrolysis test was carried out on composite materials and the results of the comparative analysis of carbon‐phenolic, carbon‐BMI, and carbon‐PEKK materials show that carbon‐PEKK had the lowest mass loss, highest back‐face temperature without significant material delamination, and the lowest concentration of gas emission species.

LIF-imaging of temperature and iron-atom concentration in iron nitrate doped low-pressure aerosol flat flames

To enable the investigation of the flame chemistry of precursor-laden nanoparticle forming spray flames in quasi-one-dimensional geometry, a matrix burner was developed in which a laminar flat flame is uniformly supplied with liquid aerosol. In the present work, the burner was used to study the interaction of iron(III) nitrate as precursor dissolved in 1-butanol with the flame. Distributions of temperature and relative iron-atom concentrations were measured via OH and Fe laser-induced fluorescence imaging, respectively. Elastic laser light scattering was used to determine the spatial distribution of particles and droplets to characterize the burner and to obtain insight into the particle formation process. The matrix burner was operated with hydrogen or methane. The measured flame temperatures were compared with one- and three-dimensional CFD simulations supporting the development of reaction mechanisms for precursor-laden flames.

Enhancing process efficiency through improved temperature measurement: the EMPRESS projects

EMPRESS 2 is a European project to enhance the efficiency of high value manufacturing processes by improving temperature measurement and control capability. This project seeks to address four contemporary thermometry challenges in this sector, and new developments from this and its predecessor project, EMPRESS, will be described:• Below 1000°C many industrial processes require reliable surface thermometry e.g. welding, coating, forging and forming. Conventional non-contact surface thermometry techniques e.g. thermal imaging are prone to large errors (tens of degrees) due to reflected thermal radiation and unknown emissivity. Contact thermometry approaches are prone to similarly large errors. Traceable imaging phosphor thermometry is being developed to overcome these difficulties, and is being combined with quantitative thermography to determine emissivity for thermometry over wide fields of view.• Above 1300°C sensor drift is a significant unaddressed issue for casting, forging and heat treatment, causing large errors. There is a need for more stable sensors and standardisation of at least one new thermocouple type to fill the gap from 1300°C to 1800°C. This is being addressed through improved Pt-Rh thermocouples and optimisation of double-walled mineral insulated, metal sheathed thermocouples by mitigating insulation breakdown and drift effects.• Combustion temperature measurement is very challenging and traceability is almost non-existent; for example, thermocouple measurements of flame temperatures can be in error by hundreds of degrees. A ‘standard flame’ that can be transported to users’ sites has been developed, and is being deployed in several high value manufacturing and industrial applications to a) demonstrate the possibility of reducing flame temperature uncertainties by at least an order of magnitude and b) for the first time to demonstrate in-situ traceability to the International Temperature Scale of 1990 (ITS-90).• Many processes are not amenable to any conventional thermometry techniques due to inaccessibility, ionising radiation, electromagnetic interference, and contamination; here methods based on optical fibres are ideal but there are no traceable calibration techniques for such sensors currently available. A suite of different fibre-optic thermometers and calibration techniques is being developed to address this. In some cases (ionising radiation) darkening of the fibre is a problem, and this is being overcome by the development of novel thermometry approaches based on practical ‘hollow core’ fibres.

Color CCD High-Temperature Measurement Method Based on Matrix Searching

High-temperature processes can have a direct impact on the state and physicochemical properties of materials, making high-temperature measurements important in scientific research, materials processing, and equipment evaluation. A temperature measurement method of color CCD based on matrix search is reported in this paper. In this method, the traditional temperature reverse calculation process is transformed into the forward matrix search process, and the process parameters such as medium absorption gamma correction are incorporated, which saves the calculation resources and is closer to the actual temperature measurement conditions. A temperature measurement process and a temperature visualization procedure are designed for this high-temperature measurement method, the flame temperature measurement experiments are carried out, and the error results are obtained. By comparing the solution results and chrominance deviation distance between the perturbation emissivity model and the non-perturbation emissivity model, the robustness of the solution method is discussed.

The development of a multispectral pyrometer for achievable true temperature field measurements of the explosion flame

The temperature measurement of explosion flames is a key challenge in the field of weapons research. Many pyrometers have been developed to determine the accurate temperature of the explosion flame. However, these pyrometers can only measure the true temperature curve and the brightness temperature field of explosion flames, not their true temperature field. A multispectral pyrometer that measures the true temperature field of the explosion flame is developed in this paper. The multispectral pyrometer acquires brightness temperature field images at four different wavelengths of the explosion flame at the same moment using synchronous spectral-splitting technology. The pixels of the obtained four brightness temperature field images are then aligned using an edge feature-based image matching algorithm. The true temperature value is finally calculated for each pixel using multispectral radiation thermometry to construct the true temperature field of the explosion flame. Based on the experimental results, the true temperature field of the explosion flame can be measured with the proposed multispectral pyrometer.

Emission thermometry of microwave-assisted alkali-doped propellant combustion

Recently, the application of high-power microwave fields to sodium-doped aluminized solid propellants has been shown to increase the atmospheric burning rate by up to 60%. Two main mechanisms have been proposed to increase the burning rate: (1) plasma enhancement by the presence of low-ionization threshold sodium and (2) the dielectric thermal runaway heating of metallic-oxide products. To examine the mechanisms of microwave energy deposition in the solid propellant burning strands, optical emission measurements were made during the application of a 2.46 GHz, 870 W microwave field in a single-mode microwave resonator. Flame temperature measurements are made via gas-phase AlO B2Σ+→X2Σ+(Δv=−1) electronic emission spectroscopy, spatially-resolved two-color imaging pyrometry of the condensed phase, and spatially-resolved two-line sodium emission thermometry. These experiments indicate an increase in the gas phase AlO temperature of ∼130 K, and a ∼1200 K increase in the sodium gas-phase temperature during the application of the microwave field. Gray body condensed-phase temperatures of burning aluminum particles indicated little temperature change, but the product plume temperature increased by ∼700 K. These temperature measurements of the vapor and condensed phase products indicate several important pathways for the thermalization of the field energy throughout the propellant flame structure, offering opportunities for further optimization of electromagnetically tunable energetic material combustion.

Spectroscopic measurement of the two-dimensional flame temperature based on a perovskite single photodetector.

Existing non-contact flame temperature measuring methods depend on complex, bulky and expensive optical instruments, which make it difficult for portable applications and high-density distributed networking monitoring. Here, we demonstrate a flame temperature imaging method based on a perovskite single photodetector. High-quality perovskite film epitaxy grows on the SiO2/Si substrate to fabricate the photodetector. Duo to the Si/MAPbBr3 heterojunction, the light detection wavelength is extended from 400 nm to 900 nm. Then, a perovskite single photodetector spectrometer has been developed using the deep-learning method for spectroscopic measurement of flame temperature. In the temperature test experiment, the spectral line of doping element K+ has been selected to measure the flame temperature. The photoresponsivity function of the wavelength was learned based on a commercial standard blackbody source. The spectral line of element K+ has been reconstructed using the photocurrents matrix by the regression solving photoresponsivity function. As a validation experiment, the "NUC" pattern is realized by scanning the perovskite single-pixel photodetector. Finally, the flame temperature of adulterated element K+ has been imaged with the error of 5%. It provides a way to develop high precision, portable, low-cost flame temperature imaging technology.

AP-HTPB propellant combustion under strain conditions with laser absorption spectroscopy.

Understanding the combustion behaviors of solid propellant with different levels of strains is of practical interest. In this work, an experimental study of the effects of static and dynamic strains on the burning rate, temperature, CO, and C O 2 formation of aluminized ammonium perchlorate (AP)-hydroxyl terminated poly-butadiene (HTPB) propellant combustion was presented at initial pressures of 0.1MPa, 0.2MPa, and 0.5MPa. The strains were being applied onto solid propellant by exerting static and cyclic loadings. The propellant burning rate was acquired by a 4kHz high-speed photography system, and the combustion temperature, CO, and C O 2 column densities were measured at 10kHz through laser absorption spectroscopy (LAS). At atmospheric pressure, it was demonstrated that the propellant burning rate increased with tensile stress and decreased with compressive stress. The measured flame temperature showed a similar correlation with strains as compared to the propellant burning rate. At elevated pressures, the increase of the propellant burning rate due to tensile stress was more evident, while the difference in combustion temperatures was less significant. For the cyclic strain condition, the variations of the measured C O 2 and CO column densities were consistent with the static strain condition.