Flame Temperature Distribution Research Articles

Numerical Modeling of Biomass Co–combustion with Pulverized coal in a Small Scale Furnace

Co-combustion of Biomass is a promising greenhouse gases (GHG) abatement technology. This study presents a numerical modeling of co-combustion of coal and Biomass firing under air and oxy-fuel conditions in a small scale furnace. Co-firing conditions are varied with the Biomass sharing considering 20%, 40% on mass basis. Level of confidence is achieved by comparing the model-predicted peak radiative heat flux against the experimental data. Results are presented comparing the flame temperature distribution, species concentration for different cases. Unburned Carbon in ash (CIA) is predicted for different cases and reasonable agreement has been obtained. An improved burnout was observed in oxy-fuel cases. No significant change in CO2 concentrations with the increase of biomass contribution to the total fuel input proves that biomass is CO2-neutral energy source.

Fuel Bed에서의 지표화 확산에 관한 연구

본 연구에서는 Fuel bed를 이용한 실험을 통하여 지표화 확산에 의한 온도 분포, 화염 높이, 복사열, 확산속도 등을 측정하였다. 실험 변수로는 수종, 풍속 및 경사도 등을 사용하였다. 수종으로는 침엽수종인 소나무 낙엽과 활엽수종인 굴참나무 낙엽을 사용하였다. 풍속은 터널식 방 구조에서 간이풍속 장치를 이용하여 1 m/s, 3 m/s, 5 m/s 풍속을 조절하여 실험하였다. 경사도는 Fuel bed의 기울기를 <TEX>$0^{\circ}$</TEX>, <TEX>$10^{\circ}$</TEX>, <TEX>$20^{\circ}$</TEX>, <TEX>$30^{\circ}$</TEX>로 변화시켜 가며 조절하였다. 온도 분포 및 확산속도를 측정하기 위하여 K-type 1.6 mm 열전대를 35개를 격자모양으로 배치하였다. 측정을 위하여 복사열량계를 사용하였으며 이외에도 비디오 카메라 및 열화상 카메라를 사용하였다. In this study a Fuel bed where surface fire spreads through is made to measure the data such as the flame height, radiation, spread rate and temperature distribution of Fuel bed. As experimental variables species of trees, wind velocities and slop are chosen. Fallen leaves of Quercus Variabilis (Q.V.) and Pinus Densiflora (P.D.) are used as fuel. Wind velocity is controlled by simply designed wind turnnel from 1 to 5 m/s. Slope of fuel bed is changed from <TEX>$0^{\circ}$</TEX> to <TEX>$30^{\circ}$</TEX>. For the measurements of temperature distribution and spread rate total 35 of K-type 1.6 mm thermocouples are positioned as a lattice design. Radiant heat flow meters are used besides video camera and thermovision camera.

Study on the relationship between the heat transfer characteristics of preheating gas and cutting performance of oxyfuel gas cutting

Plate temperature and heat input in an oxyfuel gas cutting process with H2/LP gas and LPG flame are calculated by three-dimensional FE heat conduction analyses. FE analyses are performed by using moving coordinates, and cutting groove temperature is determined by iterative calculation. The two-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 genetic algorithm-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 heat-affected zone 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 a result, the followings are found: (1) the three-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.

FLAME BEHAVIOR OF BIFURCATED JETS IN A V-SHAPED BLUFF-BODY BURNER

A plane fuel jet bifurcated into two streams of jets by a V-shaped bluff-body burner with co-flowing air streams was studied. The flame behavior, length, and temperature distributions of the bifurcated jets were experimentally examined. Flame behavior was characterized by flame visualization and instantaneous photograph. The flame length characteristics was obtained by using the long-exposure flame images. The temperatures distributions were measured by using a finewire thermocouple. Three characteristic flame modes were revealed-＂attached flame, transitional flame,＂ and ＂lifted flame＂. The flame length and width of the bifurcated jets increase with the increase of the Re_c in fixed Re_a. The length of the bifurcated flame was significantly shorter than that of the plane jet flame. The reduction was induced by the enhancement in the mixing and entrainment effects of the bifurcated flame. The maximum temperature of the bifurcated-jets flame decreases with the increase of the Re_c. The bifurcated jets enhanced the mixing of the fuel and the air and improved the combustion efficiency. The flame behavior and combustion characteristics of the bifurcated jets changed drastically due to the effects of entrainment and recirculation.

NEPE Propellant Ignition and Combustion under Laser Irradiation

An experimental study was conducted to get the ignitibility of NEPE propellant under different CO2 laser heat fluxes. The combustion flame temperature distribution of NEPE propellant was measured using an infrared thermometer. Results show that the ignition delay time tends to decrease with the increase of laser heat flux, and there exists a significant value. The ignition delay time decreases fast when the heat flux is less than this value, but varies little when the heat flux is greater than this value. Laser irradiation had a significant effect on the combustion of NEPE propellant and after the laser unloading, the flame temperature of the propellant dose not decline immediately, but fall rapidly after a short delay.

Model Analysis of Syngas Combustion and Emissions for a Micro Gas Turbine

The purpose of this study is to investigate the combustion and emission characteristics of syngas fuels applied in a micro gas turbine, which is originally designed for a natural gas fired engine. The computation results were conducted by a numerical model, which consists of the three-dimension compressible k–ε model for turbulent flow and PPDF (presumed probability density function) model for combustion process. As the syngas is substituted for methane, the fuel flow rate and the total heat input to the combustor from the methane/syngas blended fuels are varied with syngas compositions and syngas substitution percentages. The computed results presented the syngas substitution effects on the combustion and emission characteristics at different syngas percentages (up to 90%) for three typical syngas compositions and the conditions where syngas applied at fixed fuel flow rate and at fixed heat input were examined. Results showed the flame structures varied with different syngas substitution percentages. The high temperature regions were dense and concentrated on the core of the primary zone for H2-rich syngas, and then shifted to the sides of the combustor when syngas percentages were high. The NOx emissions decreased with increasing syngas percentages, but NOx emissions are higher at higher hydrogen content at the same syngas percentage. The CO2 emissions decreased for 10% syngas substitution, but then increased as syngas percentage increased. Only using H2-rich syngas could produce less carbon dioxide. The detailed flame structures, temperature distributions, and gas emissions of the combustor were presented and compared. The exit temperature distributions and pattern factor (PF) were also discussed. Before syngas fuels are utilized as an alternative fuel for the micro gas turbine, further experimental testing is needed as the modeling results provide a guidance for the improved designs of the combustor.

Analysis of Azimuthal Thermo-acoustic Modes in Annular Gas Turbine Combustion Chambers

Modern gas turbine combustors operating in lean-premixed mode are prone to thermo-acoustic instabilities. In annular combustion chambers, usually azimuthal acoustic modes are the critical ones interacting with the flame. In case of constructive interference, high amplitude oscillations might result. In this paper, the azimuthal acoustic field of a full-scale engine is investigated in detail. The analyses are based on measurements in a full-scale gas turbine, analytical models to derive the system dynamics, as well as simulations performed with an in-house 3d nonlinear network model. It is shown that the network model is able to reproduce the behavior observed in the engine. Spectra, linear growth rates, as well as the statistics of the system's dynamics can be predicted. A previously introduced algorithm is used to extract linear growth rates from engine and model time domain data. The method's accuracy is confirmed by comparison of the routine's results to analytically determined growth rates from the network model. The network model is also used to derive a burner staging configuration, resulting in the decrease of linear growth rate and thus an increase of engine operation regime; model predictions are verified by full-scale engine measurements. A thorough investigation of the azimuthal modes statistics is performed. Additionally, the network model is used to show that an unfavorable flame temperature distribution with an amplitude of merely 1% of the mean flame temperature can change the azimuthal mode from dominantly rotating to dominantly standing. This is predicted by the network model that only takes into account flame fluctuations in axial direction.

Numerical modelling of oxy fuel combustion, the effect of radiative and convective heat transfer and burnout

In this study, a numerical investigation on the radiative and convective performance of the combustion of pulverised Russian coal having higher Calorific value in a 0.5MWth combustion test facility (CTF) has been conducted for air and CO2-rich oxy-fired environment considering an IFRF Aerodynamically Air Staged Burner (AASB) configured with the furnace. This study is carried out considering a finite volume method (FVM) tool using AVL Fire version 2009.2 coupled with the user defined subroutines especially for the coal devolatilisation and char combustion modelling. This code is validated comparing the experimental radiative heat flux with the numerically predicted data and results show that reasonable agreement has been found with the measured radiative heat flux on the furnace wall. Different combustion environments were investigated including an air-fired as reference case and three recycled flue gas (RFG) fired combustion environments. The different cases are composed of varying recycled ratio (RR) between 65% and 75%. It was found that the flame temperature distribution for the reference case (air fired) and RR72% case were found to be similar. The flame temperature increased with O2 concentration and decreasing RR. With the decrease of RR, the length of the flame is also shortened. The ignition condition improved with enriched O2 concentration in the RR65% (O2 30.9%, CO2 69.2% by mass) case. The results show that radiative and convective heat flux is significantly manipulated by the RR. The position of peak radiative flux moves downstream with increasing RR due to increased mass flow rate and reduced O2 at higher RR. With the increase of normalised total flow (NTF), mean flame temperature and exit temperature decreased whereas with the increase of normalised O2 flow (NOF), mean flame temperature and exit temperature increase. The presented working range for the Russian coal, suggests that the air equivalent radiative heat flux can be obtained at a RR of ≈71% while air equivalent flame temperature were observed at RR of 72%. Reasonable agreement has been obtained for unburned carbon in ash (CIA). An improved burnout was observed in RR conditions.

Investigation of Syngas Combustion at Variable Methane Composition in Can Combustor Using CFD

This paper describes the analysis of the fundamental effect of synthetic gas combustion in a can-type combustor using Computational Fluid Dynamic(CFD). Emphasis is given towards the effect of variation of methane to the flame profile, temperature distribution and heat flux in the combustor. In this study, the composition of hydrogen in the syngas was fixed at 30% while methane and carbon monoxide were varied. Results show that the flame temperature and NOx emissions are highly dependent on the composition of methane in the syngas fuel. Nevertheless, the overall NOx emission for all cases is relatively lower than the conventional pure natural gas combustion.

Experimental study of multispecies gas combustion in a several-section porous media burner

Experiments with combustion of diluted liquefied petroleum gases used as a fuel premixed with air are performed. From the experiment results, one can see that low-heat-value gases are capable of stable burning in a porous media burner. Distributions of species concentrations and flame temperature are measured. Based on these data, the flame is found to be most stable if the equivalence ratio is equal to 0.8. To improve the burner performance, experiments with different characteristics of porous media are performed. Optimal parameters of porous media are confirmed by subsequent numerical simulations. It is demonstrated that the properties of combustion in the porous media burner are superior as compared to those in the free flame burner.

The effect of azeotropism on combustion characteristics of blended fuel pool fire

The effect of azeotropism on combustion characteristics of blended fuel pool fire was experimentally studied in an open fire test space of State Key Laboratory of Fire Science. A 30cm×30cm square pool filled with n-heptane and ethanol blended fuel was employed. Flame images, burning rate and temperature distribution were collected and recorded in the whole combustion process. Results show that azeotropism obviously dominates the combustion behavior of n-heptane/ethanol blended fuel pool fire. The combustion process after ignition exhibits four typical stages: initial development, azeotropic burning, single-component burning and decay stage. Azeotropism appears when temperature of fuel surface reaches azeotropic point and blended fuel burns at azeotropic ratio. Compared with individual pure fuel, the effect of azeotropism on main fire parameters, such as flame height, burning rate, flame puffing frequency and centerline temperature were analyzed. Burning rate and centerline temperature of blended fuel are higher than that of individual pure fuel respectively at azeotropic burning stage, and flame puffing frequency follows the empirical formula between Strouhal and Froude number for pure fuel.

Characteristics of Lean Premixed Flame in Various Oxygen Concentrations Measured by Laser Imaging Techniques

For heavy-duty gas-turbine engines, one of the promising approaches to reducing NOX emissions is the adoption of lean premixed combustion. This technique could be combined with the conventional technique of exhaust gas recirculation (EGR). However, the reduction in the oxygen concentration will influence the burning velocity and reaction zone characteristics of the lean premixed flame. To elucidate this effect, in this study, we measured the lean premixed flame temperature and OH concentration distributions for various oxygen concentrations instantaneously and simultaneously using laser imaging techniques. Based on the results, we investigated the characteristics of a lean premixed flame under various oxygen concentrations and found that the OH laser-induced fluorescence (LIF) intensity in the reaction zone decreased with the oxygen concentration, as did the flame temperature at a given axial distance from the exit nozzle. The characteristics of the premixed flame changed from a small-scale convexo-concave surface to a smoother one, leading to a decrease in the ratio of turbulent to laminar burning velocity. In addition, local extinction of the premixed flame was observed under conditions with a high air ratio and low oxygen concentration.

In-situ spectroscopic monitoring of Jatropha oil combustion properties

In-situ monitoring of chemical species emitted from the combustion of Jatropha oil in a practical Semawar burner were performed by means of several spectroscopic diagnostics. A practical burner commonly used in Indonesia having a built-in preheating system, called semawar, used for illumination purposes with the combustion of Jatropha oil. Non-intrusive two-dimensional (2-D) distributions of flame temperature were obtained using a thermal video camera. The experimental results showed the flame temperatures to range from 500 to 1400 °C. Chemical species generated from within the combustion zone were also determined in the Ultraviolet–visible (Uv–Vis) range from the spontaneous emission spectra of the flame. Spatial distribution of NO, C2 and OH were identified from the spectra. The 2-D distribution emission intensity visualized and recorded for NO, C2 and OH revealed high temperatures close to the root of the flame that rapidly dispersed radially outwards to provide very high temperatures over much larger volume at downstream locations. The radial stretch of the reaction zone is important for improved performance of the burner with light emission form a much wider zone. In addition, in-situ monitoring of CO2 emission of Jatropha oil was performed by using infrared (IR) spectroscopy. The presence of CO, H2O and NO were also investigated in this research. Moreover, 2D distribution of CO2 emission intensity was also visualized using an IR camera.

Effect of flue gas recirculation during oxy-fuel combustion in a rotary cement kiln

The effect of Flue Gas Recirculation (FGR) during Oxy-Fuel Combustion in a Rotary Cement Kiln was analyzed by using a CFD model applied to coal combustion process. The CFD model is based on 3D-balance equations for mass, species, energy and momentum. Turbulence and radiation model coupled to a chemical kinetic mechanism for pyrolysis processes, gas–solid and gas–gas reactions was included to predicts species and flame temperature distribution, as well as convective and radiation energy fluxes. The model was used to study coal combustion with air and with oxygen for FGR between 30 and 85% as controller parameter for temperature in the process. Flame length effect and heat transfer by convection and radiation to the clinkering process for several recirculation ratios was studied. Theoretical studies predicted a located increase of energy flux and a reduction in flame length with respect to the traditional system which is based on air combustion. The impact of FGR on the oxy-fuel combustion process and different energy scenarios in cement kilns to increase energy efficiency and clinker production were studied and evaluated. Simulation results were in close agreement with experimental data, where the maximum deviation was 7%.

Simultaneous LII and TC optical correction of a low-sooting LPG diffusion flame

Two color emission and Laser-Induced-Incandescence techniques were performed simultaneously upon a diffusion laminar LPG bunsen flame. In order to reduce the measuring error, the acquired images were filtered, perspective corrected and post-processed. For quantitative measurements of the soot volume fraction and temperature, a tungsten lamp calibration method was used. As TC and LII are affected by self-absorption and laser attenuation through the flame errors, a correction method was developed using the laser extinction technique. Flame temperature distribution measured with the two-color method was validated with the corrected temperature measured with a fast thermocouple along the flame axis. Soot volume fraction was calculated with the two-color emission and LII and a good agreement was found. For quantitative measurements the influence of self-absorption and laser attenuation were found to be not negligible and an error of 12% was found as sum of the self-absorption and laser attenuation along the optical path.

CFD Analysis of Temperature Distribution in Can-Type Combustor Firing Synthetic Gas

This paper presents CFD analysis of the effect of syngas combustion in a full scale gas turbine combustor with specific emphasis given to the flame and flue gas temperature distribution. A base case solution was first established using conventional natural gas combustion. Actual operating boundary conditions such as swirl, diffusion and fuel mass flow were imposed on the model. The simulation result is validated with the flame temperature of typical natural gas combustion. Result from flow and combustion calculation shows reasonable trend of the swirl mixing effect. The maximum flame temperature was found to be the highest for syngas with the highest H2/CO ratio. However, the flue gas temperature was found to be approximately identical for all cases. The prediction of temperature distribution in the combustor would enable further estimation of pollutant species such as CO2and NOxin complex regions within the combustor.

Hydroxyl and Nitric Oxide Distribution in Waste Rice Bran Biofuel-Octanol Flames

Two-dimensional (2-D) visualization of hydroxyl (OH) radical in combustion of biofuel made of waste rice bran oil (called W) mixed with octanol (called O) at different mixture ratios were examined in a laboratory scale facility using planar laser-induced fluorescence (PLIF) diagnostics. Rice bran oil has a composition similar to that of peanut oil, with 38% monounsaturated, 37% polyunsaturated, and 25% saturated fatty acids. The ratio of this biofuel to octanol fuel examined was W90/O10, W75/O25, and W60/O40. The chemical species generated from within the combustion zone were analyzed from the spontaneous emission spectra of the flame in the ultraviolet to visible (Uv-Vis) range. The spatial distribution of Nitric Oxide (NO) and OH, denoted as OH*, were identified from the spectra. Two-dimensional (2-D) distributions of flame temperature were obtained using a thermal video camera. The experimental results showed the temperatures to range from 600 °C to 1400 °C. The highest temperature was obtained using W60/O40 waste/octanol fuel mixture. A practical burner commonly used in Indonesia, called semawar, that have a built-in preheating system was used for the combustion of biofuels.

Visualizations of combustion and fuel/air mixture formation processes in a single cylinder engine fueled with DME

The purpose of this study is to investigate the effects of various engine conditions on the combustion, flame temperature and emission characteristics of dimethyl ether (DME) fuel compared with ultra-low sulfur diesel (ULSD) fuel through experimental and numerical analyzes. In order to analyze the temperature distribution, the KIVA-3V code and an optical HSDI diesel engine equipped with a visualization system were employed. The numerical validation was conducted with the experimental results from a DME-fueled compression ignition engine. In addition, measurement of the flame temperature from images captured during the combustion processes was performed using AVL-ThermoVision software.This investigation showed that the combustion pressure and heat release rate attained their peak value at the lowest engine speed condition for DME and ULSD fuels. The characteristics of the flame temperature value and distribution due to the differences in engine speed conditions and fuel properties were clearly revealed. When the engine speed increased, an inhomogeneous and low combustion temperature was observed. Furthermore, the nitrogen oxides (NOx) emissions, which are related to the combustion temperature, decreased as the engine speed increased.

Three-dimensional reconstruction of flame temperature and emissivity distribution using optical tomographic and two-colour pyrometric techniques

This paper presents an experimental investigation, visualization and validation in the three-dimensional (3D) reconstruction of flame temperature and emissivity distributions by using optical tomographic and two-colour pyrometric techniques. A multi-camera digital imaging system comprising eight optical imaging fibres and two RGB charged-couple device (CCD) cameras are used to acquire two-dimensional (2D) images of the flame simultaneously from eight equiangular directions. A combined logical filtered back-projection (LFBP) and simultaneous iterative reconstruction and algebraic reconstruction technique (SART) algorithm is utilized to reconstruct the grey-level intensity of the flame for the two primary colour (red and green) images. The temperature distribution of the flame is then determined from the ratio of the reconstructed grey-level intensities and the emissivity is estimated from the ratio of the grey level of a primary colour image to that of a blackbody source at the same temperature. The temperature measurement of the system was calibrated using a blackbody furnace as a standard temperature source. Experimental work was undertaken to validate the flame temperature obtained by the imaging system against that obtained using high-precision thermocouples. The difference between the two measurements is found no greater than ±9%. Experimental results obtained on a laboratory-scale propane fired combustion test rig demonstrate that the imaging system and applied technical approach perform well in the reconstruction of the 3D temperature and emissivity distributions of the sooty flame.

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.