Flame Temperature Distribution Research Articles

Flame Structure and Combustion Capability of Non-Premixed Rifled Nozzles

The target of this study is to promote combustion capability using a novel rifled nozzle which was set at the outlet of a conventional (unrifled) combustor. The rifled nozzle was utilized to adjust the flow swirling intensity behind the traditional combustor by changing the number of rifles. The rifle mechanism enhances the turbulence intensity and increases the mixing efficiency between the central-fuel jet and the annular swirled air-jet by modifying the momentum transmission. Specifically, direct photography, Schlieren photography, thermocouples, and a gas analyzer were utilized to document the flame behavior, peak temperature, temperature distribution, combustion capability, and gas-concentration distribution. The experimental results confirm that increasing the number of rifles and the annular swirling air-jet velocity (ua) improves the combustion capability. Five characteristic flame modes—jet-flame, flickering-flame, recirculated-flame, ring-flame and lifted-flame—were obtained using various annular air-jet and central fuel-jet velocities. The total combustion capability (Qtot) increases with the number of rifles and with increasing ua. The Qtot of a 12-rifled nozzle (swirling number (S) = 0.5119) is about 33% higher than that of an unrifled nozzle. In addition, the high swirling intensity induces the low nitric oxide (NO) concentration, and the maximum concentration of NO behind the 12-rifled nozzle (S = 0.5119) is 49% lower than that behind the unrifled nozzle.

Spectroscopic Observation of Chemical Species From High-Temperature Air Pulverized Coal Combustion

In situ monitoring of chemical species from the combustion pulverized coal in high-temperature air is examined using several different spectroscopic diagnostic at different equivalence ratios. Two-dimensional (2D) distributions of flame temperature were obtained using a thermal video camera. The experimental results showed the temperatures to range from low to 1400 °C under various conditions of fuel-lean, stoichiometric, and fuel-rich. The highest temperature and flame stability were obtained under fuel-lean combustion condition. The chemical species generated from within the combustion zone were analyzed from the spontaneous emission spectra of the flame in the Ultraviolet–visible (UV-Vis) range. The spatial distribution of NO, OH, and CN were identified from the spectra. The 2D distribution of emission intensity visualized and recorded for NO, OH, and CN revealed high-temperatures close to the root of the flame that rapidly dispersed radially outward to provide very high temperatures over a much larger volume at further downstream locations of the flame.

Soot temperature and volume fraction retrieval from spectrally resolved flame emission measurement in laminar axisymmetric coflow diffusion flames: Effect of self-absorption

The effects of self-absorption on the inverted soot temperature and volume fraction distributions in coflow laminar diffusion flames were investigated using two correction methods. Self-absorption was found unimportant when the optical thickness of the flame is less than 0.3, but can be very important in flames of large optical thicknesses. Due to the uncertainty in soot absorption function E(m), different assumptions of the variation of E(m) with wavelength were investigated. Decreasing E(m) with wavelength leads to largest errors in the recovered soot temperature and volume fraction when self-absorption correction is not accounted for. The assumption of constant E(m) in general results in smallest errors in the inverted soot volume fraction and the increasing E(m) with wavelength gives rise to smallest errors in the recovered soot temperature. Neglect of self-absorption correction in general leads to underestimate of the inverted soot temperature, while the inverted soot volume fraction can be higher or lower than the true value, depending on how E(m) varies with wavelength. The self-absorption correction method of Snelling et al. [D.R. Snelling, K.A. Thomson, G.J. Smallwood, Ö.L. Gülder, E.J. Weckman, R.A. Fraser, AIAA J. 40(9) (2002) 1789–1795] is effective in recovering accurate soot temperature and volume fraction distributions from noise-free emission data even for flames with optical thickness as large as 5. For inversion of emission data containing noise it is still advantageous to account for self-absorption. Multi-wavelength emission data from a laminar coflow ethylene/air diffusion flame at atmospheric pressure and a methane/air diffusion flame at 40atm were reanalyzed to demonstrate how self-absorption affects the reconstructed temperature and soot volume fraction distributions. It is preferred to detect flame emissions at longer wavelengths in the visible spectrum to minimize the self-absorption effect. The effect of self-absorption should in general be taken into account in the reconstruction of soot temperature and volume fraction from the line-of-sight spectral flame emission data using the method of Snelling et al.

Experimental and numerical study of probe-induced perturbations of the flame structure

A study is made of the external flow of an atmospheric-pressure burner-stabilised methane-oxygen-argon flame near an axisymmetric conical sampling probe with an orifice at the centre of the cone tip. The flow is simulated by solving the full set of unsteady Navier-Stokes equations using a recently developed original algorithm. Heat release due to chemical reactions is approximately described by a source term in the energy equation which provides a given temperature distribution in the unperturbed isobaric flame. On the probe orifice surface, the axial gas velocity is assumed to be equal to the local velocity of sound. A qualitative understanding of the nature and magnitude of the perturbing effects of the probe on the flame is obtained by comparing the steady flow near the probe and the unperturbed flame. Probe-induced distortions in the flame mixture composition are simulated by calculating concentration distributions of some species (CH4, CO2, H2O, and O2) in the flow field from the diffusion equation for binary gas mixtures (CH4 – Ar, CO2 – Ar, etc.) in a linear formulation. The effect of chemical reactions is approximately described by a source term in the diffusion equation which provides given concentration distributions in the unperturbed flame. The developed approach based on spatially fixed sources of energy and species concentrations provides more realistic simulations of probe-induced perturbations of the flame structure than the approaches described in the literature. The data demonstrating the nature of the probe-perturbed flame under conditions close to real ones were obtained for the first time.

Theoretical Study on Premixed Flames of Nano Aluminum Particles and Water Mixture

A theoretical model is proposed to investigate premixed combustion characteristics of Nano aluminum particles - water mixture. The effects of particle size, initial pressure, and temperature were considered as well. Computational domain is divided into 3 regions; preheat zone 1, preheat zone 2, and reaction zone. No reaction occurs in either of the preheat zones. Reaction zone, consisting of nano aluminum particles–steam mixture and the combustion products, is the region where reaction and heat-release occurs. Energy conservation is considered separately at each zones. The flame speed and temperature distribution are derived by solving the energy equation in each regime and matching the temperature and heat flux at the interfacial boundaries. Combustion time correlation of nano aluminum particle is also considered to imply complex aluminum combustion kinetics. Normalized flame speed is calculated as a function of pressure, initial particle diameter, and equivalence ratio and compared with experimental data.

Flame temperature distributions of biodiesel fuel in a single-cylinder diesel engine

An experimental investigation was conducted on the effect of injection timings and pressure on flame temperature of biodiesel. To estimate flame temperatures accurately during the combustion processes, an optical HSDI diesel engine composed of an endoscope and a high-speed CCD camera was used. In addition, the AVL-ThermoVision software allowed measurement of discrete flame temperatures from images taken during the combustion processes. NOx and soot concentration, which are directly related to the flame temperature, were also measured using exhaust emission analyzers, in order to study the correlation between emissions characteristics and the temperature under various injection timings.The results of this study show the characteristics of flame temperature values and distribution for biodiesel and ULSD fuel owing to the difference of their physical properties and injection strategies. Additionally, the study of high pressure injection was performed under the same conditions. When the injection pressure increased, more homogeneous combustion was observed.

Auto-ignition and combustion of diesel spray using unsteady laminar flamelet model

This work emphasises the modelling capabilities of the unsteady flamelet/reaction progress variable approach to implement diesel spray flames for capturing the auto-ignition and flame lift-off phenomena. The droplet size distribution based on the moment scheme characterises the poly-disperse spray model [1] employed in this work. The flamelet progress variable solutions embedded in a Reynolds-averaged Navier–Stokes (RANS) framework, together with the probability density function (PDF) approach, signify the turbulence–chemistry interaction. All thermochemical scalars are represented as a function of mean mixture fraction, mixture fraction variance, reaction progress variable and scalar dissipation rate. Mixture fraction is assumed to follow a beta-PDF distribution, because the reaction progress variable and scalar dissipation rate distributions are assumed to be a delta-PDF. In order to assess the capability of this developed model, the predicted results are compared with experimental data [2]. The developed model gives a reasonably good overall prediction performance in terms of auto-ignition, flame development and flame lift-off length. The flame temperature distributions are comparable with the formations of luminous flames. The predicted flame growth rate is consistent with the experimental results but there is a small over-prediction. Therefore, the present approach can accurately and efficiently capture the auto-ignition and flame lift-off phenomena of diesel spray flame.

酸素ガス切断における予熱ガス炎性状と切断性能の関係に関する研究

Plate temperature and heat input in oxyfuel gas cutting process with H2/LP gas and LPG flame are calculated by 3-dimensional FE heat conduction analyses. FE analyses are performed by using moving coordinates, and cutting groove temperature is determined by iterative calculation. The 2-dimensional groove temperature distribution determined by Matsuyama's theory is chosen as the initial values in this iterative calculation. The heat transfer properties of the preheating flame are determined by using the GA-based heat transfer estimation technique proposed in the previous report. The validity of the proposed numerical procedure and the accuracy of the determined groove temperature are examined by comparing the calculated and measured plate temperature and HAZ sizes. Heat input due to preheating, qG, and that due to self burning of steel, qB, are estimated in these analyses, and they are compared with the heat inputs estimated by Wells' and modified Wells' equations. The relation between the heat transfer characteristics of the preheating gas flame and plate temperature distribution is examined, and the cutting performance improvement mechanisms of Hydrogen preheating are discussed. As results, followings are found: 1) The 3-dimensional groove temperature distribution can be calculated by performing the iterative analyses procedure proposed in this study; 2) The critical cutting speed can be estimated once the gas heat transfer parameters are known; 3) It is not appropriate to evaluate the magnitude of cutting thermal deformation only from the preheating gas's total calorific value; 4) Under the conditions chosen, the heat generated by self burning is inadequate to maintain the cutting process, and it is essential to supplement heat by preheating; 5) The faster cutting speed and smaller total heat input of H2/LP gas are results of the larger local heat transfer coefficient below the gas ejection hole. It is supposed that the improvement in oxyfuel gas cutting performance can be achieved by modifying the heating apparatus so that the local heat transfer coefficient becomes larger.

Characterization of hexane pool fires using infrared thermography

This study is an experimental investigation of the influence of shape and diameter on the radiative properties of open pool fires. Circular and square shapes of equivalent surface area are considered. The circular pool diameters are 0.3, 0.5, 0.7, and 1.0 m, and the lengths of the square pools are 0.26, 0.44, 0.62, and 0.89 m. Hexane is used as the fuel in this study. Radiative properties such as flame emissivity, optical thickness, temperature distribution, and emissive power distribution are studied. Mass burning rate of each pool is measured. Flame emissivity values are inferred from the mass burning rate measurements. Using these emissivity values, the temperature and emissive power distributions are computed using infrared thermography. Irradiance values at a distance from pool fires are computed.

Combustion process of JP-8 and fossil Diesel fuel in a heavy duty diesel engine using two-color thermometry

An experimental study was performed to analyze the combustion processes of JP-8 and fossil Diesel fuel in an optically-accessible single-cylinder heavy-duty diesel engine equipped with a high pressure common-rail injection system. In terms of emission, JP-8 emitted less smoke with more HC and NOx. Direct imaging and two-color thermometry were applied to verify the emission trend for both fuels. The combustion process was characterized by means of image analysis focusing on the luminosity intensity and its spatial distribution (flame spatial fluctuation (FSF) and flame non-homogeneity (FNH)). The results from the two-color thermometry were analyzed by the flame temperature and KL factor distribution. From the combustion process analysis of the direct imaging, it was verified that JP-8 had a longer ignition delay compared to fossil Diesel fuel regardless of injection pressure. However, flame luminosity of JP-8 was vanished more rapidly. The flame luminosity intensity analysis showed that fossil Diesel fuel had stronger flame luminosity overall and duration of visible flame luminosity was longer than JP-8. This implies that fossil Diesel fuel had more diffusion dominant combustion. From the flame luminosity variation rate analysis, decreasing rate of flame luminosity for JP-8 was higher compared with fossil Diesel fuel, showing that oxidation rate of JP-8 was much higher than fossil Diesel fuel. From FSF and FNH analysis, JP-8 showed lower value for both FSF and FNH in the later stage of combustion, because the later stage of combustion with JP-8 has less jet structure in comparison with fossil Diesel fuel. The flame temperature field from two-color thermometry showed that locally high temperature region existed with JP-8. KL factor distribution of JP-8 was distributed more uniformly with a relatively lower level of KL intensity in comparison with fossil Diesel fuel in the late stage of combustion.

Analysis of a Micro Gas Turbine Fed by Natural Gas and Synthesis Gas: MGT Test Bench and Combustor CFD Analysis

In recent years, the interest in the research on energy production systems fed by biofuels has increased. Gaseous fuels obtained through biomass conversion processes such as gasification, pyrolysis and pyrogasification are generally defined as synthesis gas (syngas). The use of synthesis gas in small-size energy systems, such as those used for distributed micro-cogeneration, has not yet reached a level of technological maturity that could allow a large market diffusion. For this reason, further analyses (both experimental and numerical) have to be carried out to allow these technologies to achieve performance and reliability typical of established technologies based on traditional fuels. In this paper, a numerical analysis of a combustor of a 100-kW micro gas turbine fed by natural gas and biomass-derived synthesis gas is presented. The work has been developed in the framework of a collaboration between the Engineering Department of the University of Ferrara, the Istituto Motori - CNR (Napoli), and Turbec S.p A. of Corporeno di Cento (FE). The main features of the micro gas turbine Turbec T100, located at the Istituto Motori - CNR, are firstly described. A decompression and distribution system allows the feeding of the micro gas turbine with gaseous fuels characterized by different compositions. Moreover, a system of remote monitoring and control together with a data transfer system has been developed in order to set the operative parameters of the machine. The results of the tests performed under different operating conditions are then presented. Subsequently, the paper presents the numerical analysis of a model of the micro gas turbine combustor. The combustor model is validated against manufacturer performance data and experimental data with respect to steady state performance, i.e., average outlet temperature and emission levels. A sensitivity analysis on the model capability to simulate different operating conditions is then performed. The combustor model is used to simulate the combustion of a syngas, composed of different ratios of hydrogen, carbon monoxide, methane, carbon dioxide and water. The results in terms of flame displacement, temperature and emission distribution and values are analyzed and compared to the natural gas simulations. Finally, some simple modifications to the combustion chamber are proposed and simulated both with natural gas and syngas feeding.

Simultaneous estimation of the 3-D soot temperature and volume fraction distributions in asymmetric flames using high-speed stereoscopic images

An inverse radiation analysis using soot emission measured by a high-speed stereoscopic imaging system is described for simultaneous estimation of the 3-D soot temperature and volume fraction distributions in unsteady sooty flames. A new iterative reconstruction method taking self attenuation into account is developed based on the least squares minimum-residual algorithm. Numerical assessment and experimental measurement results of an ethylene/air diffusive flame show that the proposed method is efficient and capable of reconstructing the soot temperature and volume fraction distributions in unsteady flames. The accuracy is improved when self attenuation is considered.

Two-Dimensional Numerical Study of Temperature, Species Distributions in Coflow Laminar Diffusion Flames

Abstract. temperature and species distributions of an atmosphere coflow laminar CH4/air diffusion flame was studied by numerical simulation. We solve the steady equations for the species mass fraction, energy, momentum with detailed gas-phase reaction mechanism and complex thermal and transport properties to predict the velocity, temperature, species distributions for different dilute level. Results indicated that the predicted temperature and species are in excellent with available experiment date at different dilute level. In addition, it is indicated that adding N2in the fuel has a significant influence on the flame temperature and species distribution.

Heat transfer efficiency evaluation for outward and inward multi-flame-hole gas burner

The purpose of this study is to understand the factor that influence the heating efficiency of the outward and inward multi-hole gas burner. The flame-hole angle and the distance from flame hole to heating object are chosen as the experimental parameters. The measurement of the flame temperature distribution is carried out on each experimental condition. The observation of combustion flame, by the Schlieren method, is done from the purpose to understand the combustion phenomenon on the heating efficiency. LPG (Liquefied petroleum gas) is used for the test fuel gas. The compositions of LPG are propane 97.5vol%, butane 0.2vol% and methane + ethylene 2.3vol%. The optimum ranges of the flame-hole angle and the distance from flame hole to heating object are clarified. The experimental correlation equations for the outward and inward multi-flame-hole gas burner are proposed.

Fuel shape effect on the determinitic properties of turbulent diffusion flames

Measurements of flame height and temperature distribution above fuel surface were made on rectangular propane burners i,.p a huge calm eln~os~72.' Flame height is represented as a function of Q d; Q/ p CpT g AB , where A and B are the length of the shorter and m'1'onger ~ide 0 of a fuel respectively. Vertical distribution of temperature above the center of a fuel is compared with temperature profiles for square fuels and for line fuels. Finally a practical criterion for the approximation of rectangular fuels by square and line source is proposed. key words: turbulent flame, flame height, temperature, aspect ratio.

Modeling of pool fires in cold regions

Fires and especially pool fires are among the most frequent accidents in process facilities. Flame impingement and thermal radiation are the main hazardous characteristics of pool fires. Pool fires have been the subject of numerous modeling and experimental studies covering a variety of areas such as fire and flame structure, emissive power, temperature distribution and fire characteristics. The effects of environmental parameters such as wind velocity, humidity and water/ice droplets in the air have not been studied extensively. Further, the effect of surrounding surface reflectivity has not been studied. This issue is very important for cold regions like the Arctic, where outdoor surfaces are covered with snow and ice for several months of the year. Furthermore, there is no comprehensive fire consequence modeling tool that includes pool fire development, environmental characteristics effects and thermal radiation. This study proposes a new comprehensive model for steady state and fully developed pool fires. This new model takes into account the effects of environmental variables such as temperature, the presence of droplets and surface reflectivity on thermal radiation and subsequently on the fire consequence assessment.

Modeling flame temperature profile on a fire‐engulfed cylindrical tube

ABSTRACTIn this article, experimental measurements of flame temperature profile on a cylindrical tube circumference engulfed in a small‐scale pool fire were carried out. Three models were presented for flame temperature distribution with analytical and numerical based methods. The first model that is based on correlation showed the best agreements with experimental data, and other two models had almost acceptable predictions. The results revealed that the analytical and mathematical based model is more general than correlation methods and may be used to predict flame temperature and have wider‐range application usage. Copyright © 2011 John Wiley & Sons, Ltd.

대형 디젤 엔진에서 JP-8 과 디젤 적용 시의 배기 배출물 특성에 대한 이해

커먼레일 분사 시스템이 장착된 대형 단기통 가시화 엔진에서 디젤과 JP-8 의 연소 및 배기 특성을 분석하였다. 두 연료 적용 시, 배기 배출 경향을 분석하기 위해 직접 화염가시화와 이색법을 적용하였다. 연소과정은 직접 화염 가시화로부터 화염 강도 분석을 통해 이루어 졌다. 이색법 결과는 화염 온도 및 KL 값을 도출하여 분석을 하였다. 직접 화염 가시화 결과, JP-8 연소 시, 점화 지연 기간이 길며, 디젤 연소에 비해 화염이 빠르게 소멸되는 것을 확인하였다. 화염 강도 분석을 통해 디젤 연소의 경우, 연소 전 기간에 걸쳐 높은 화염 강도 수준을 유지하며 화염 지속 기간이 긴 것을 알 수 있었다. 이색법 결과를 통해, JP-8 연소의 경우, 국부적으로 고온의 화염 면이 더 많이 분포하는 것을 확인하였으며, 이는 NOx 가 더 많이 배출된 경향을 설명해준다. 또한 KL 치 분석 결과, JP-8 연소 시 낮은 수준의 KL 값이 더 고르게 분포하는 것을 알 수 있었으며, 이는 JP-8 연소 시 스모크 가 덜 배출된 결과를 뒷받침 해준다.

Experimental and numerical study of thermocouple-induced perturbations of the methane flame structure

In flame temperature measurements by a thermocouple, it is usually assumed that, due to its small size, the thermocouple produces negligible perturbations of the flame structure. Our studies show, however, that this assumption may be incorrect. The temperature of a premixed atmospheric methane/oxygen/argon flame measured by several thermocouples was found to be systematically higher than the theoretical temperature at small distances from the burner (in the region with a high temperature gradient). The external flow of the flame over a thermocouple was simulated using the full set of unsteady Navier–Stokes equations to explain the discrepancy between experimental and theoretical data. An approximate allowance for the heat release due to chemical reactions was made by adding a source term to the energy equation to provide a given temperature distribution in the unperturbed isobaric flame. The observed discrepancy was found to be related to deceleration of the flow in the vicinity of the thermocouple, resulting in additional heat release due to chemical reactions in the flow. In addition, significant additional heating of the thermocouple was observed, when it was placed in the zone with maximum concentrations of H and OH radicals.

Development of a high-speed two-colour system and its application to in-cylinder diesel combustion temperature and soot measurements with split injections

In the present study, a high-speed two-colour system was developed in order simultaneously to investigate the temporal and spatially resolved flame temperature and soot concentration (the KL factor) in the combustion chamber of a diesel engine during the same engine cycle. The new two-colour system features a high-speed video camera and a high-repetition image intensifier. It is capable of capturing images at a high sampling frequency, so as to allow the possibility of investigating the flame temperature and soot distribution throughout a complete engine cycle. The system was calibrated against a tungsten ribbon lamp and tested on a Ricardo Hydra single-cylinder diesel engine for the in-cylinder diesel combustion temperature and soot diagnostics. Videos of combustion were taken through the optical access to the combustion chamber, and the radiation intensity was correlated with the analysed calibration data. The two-colour method was used to study the influence of the injection timing on the nitrogen oxide and soot emissions and the relation between the time histories of the local flame temperature, the soot concentration (the KL factor), and the exhaust emissions.