Thesis MEDICIONES DE TEMPERATURA DE HOLLÍN EN LLAMAS FORZADAS DE DIFUSIÓN LAMINAR
Loading...
Date
2017
Authors
CEPEDA ALFARO, FRANCISCO IGNACIO
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Este trabajo presenta los resultados obtenidos de la medición de la temperatura del hollín en llamas dedifusión laminar, que fueron forzadas acústicamente gracias a la intervención con un altavoz en la línea decombustible el cual genera una perturbación periódica cuya intensidad puede ser controlada.En primer lugar, se presentan las bases teóricas sobre las características de las llamas, el forzamientoacústico y las propiedades más importantes medidas en el estudio: la fracción en volumen de hollín y latemperatura del hollín. La primera corresponde a una medida de la cantidad de hollín local presente en lasdiferentes zonas de la llama, mientras que la segunda corresponde a la temperatura que tienen estas partículasy aglomerados dentro de la llama.Para realizar dichas mediciones, se utilizaron las técnicas no intrusivas de atenuación de luz en elcamino óptico (LOSA) y mediciones de emisión espontánea en dos colores, utilizando además técnicas demodulación, deconvolución y regularización. Se estudiaron llamas en estado estacionario, y también forzadascon dos niveles de intensidad de forzamiento y manteniendo una frecuencia constante de 10 Hz. Para todaslas mediciones se realizó su cálculo del error cometido durante las mediciones experimentales.En primer lugar, se impuso una condición de flujos de combustible y oxidante replicando el trabajode Shaddix et al. [1] con el fin de reproducir sus resultados de fracción en volumen de hollín y generarresultados para la temperatura del hollín. Las mediciones de fracción en volumen de hollín muestran unabuena concordancia entre los resultados del artículo replicado y los de este trabajo, tanto en magnitudescomo en distribución local, encontrándose que crece progresivamente según avanza un ciclo hasta alcanzar unmáximo cercano al momento en que la llama se separa completamente de la base del quemador, para luegocomenzar a extinguirse rápidamente decreciendo su cantidad de hollín total. En cuanto a la temperatura, selogró medir y determinar que para todo un ciclo de la llama la temperatura máxima permanece prácticamenteconstante, pero varía su distribución significativamente.Luego, se impusieron las condiciones para una llama con menos flujo de combustible y oxidante,denominada llama propia en este trabajo. Bajo estas condiciones, se realizó un análisis de sensibilidad conrespecto al índice de oxígeno (OI) entre 21% y 33% con el fin de estudiar la influencia de este parámetro.En el caso de las llamas estacionarias, la cantidad de hollín local integrada radialmente máxima aumentadesde 1;571 ppm cm2 para OI 21% hasta 1;839 ppm cm2 en el OI 33 %. Por otra parte, la cantidad de hollínintegrada radialmente y también en la altura de la llama, disminuye para la condición con el índice de oxígenomás alto hasta cerca de 2=3 a partir de las 3;088 ppm cm3 de la llama con OI 21 %. Para las llamas forzadas,se aprecia un comportamiento similar, en el que el hollín integrado radialmente aumenta al aumentar elíndice de oxígeno, pero la cantidad de hollín total en la llama disminuye conforme aumenta este parámetro.La producción de hollín total de la llama tiene un comportamiento sinusoidal independiente del nivel deforzamiento, pero si este aumenta, se observa un aumento en magnitud y también un desplazamiento delmáximo, observándose además una caída más brusca en esta medida.En el caso de la temperatura del hollín, se aprecia como su máximo aumenta conforme tambiénaumenta el índice de oxígeno tanto en el caso en estado estacionario como en los casos forzados. Para lasllamas fuertemente forzadas, se constata que la temperatura máxima de la llama se mantiene prácticamenteconstante a lo largo del ciclo para un determinado índice de oxígeno, pero que en las llamas moderadamenteforzadas se aprecia un comportamiento cíclico alcanzando un máximo que parece estar desfasado cerca deentre 10 y 20 ms con respecto al máximo de producción total de hollín dentro de la llama. La temperaturamáxima es en general menor en el caso de las llamas forzadas fuertemente que en las de forma moderada, perocon diferencias dentro del margen de error. Independientemente del nivel de forzamiento, las distribucionesde los campos de temperatura del hollín varían a lo largo del ciclo, por lo que en este trabajo se muestranlos perfiles de temperatura a diferentes alturas normalizadas de la llama, entregando información de subase y de sus zonas superiores, la cual podría ser valiosa para otros trabajos tanto experimentales comonuméricos.
This work present the results obtained from the measurement of soot temperature in laminar diusionflames, which were acoustically forced with the intervention of a loudspeaker in the fuel line which generatesa periodic disturbance whose intensity can be controlled.Firstly, the theoretical bases on the characteristics of the flame are presented, then the acoustic forcingand finally the most important measured properties in the study: the soot volumen fraction, correspondondingto a measure of the amount of local soot presented in the dierent flame zones, and the soot temperature,which is the temperature of the soot particles and agglomerates within the flameIn order to perform these measurements, non-intrusive technics of light-of-sight attenuation (LOSA)and two-color spontaneous emission measurements were used, using also modulation, deconvolution andregularization techniques. Steady state flames were studied, and were forced with two levels of forcingintensity mantaining a constant frequency of 10 Hz. The error was calculated for all the experimentalmeasurements.One of the imposed condition for the flame was replicating the work of Shaddix et al. . [1] in orderto replicate their soot volume fraction results and generate results for soot temperature. The soot volumenfraction measurements show a good concordance between the results of the article and those of this work, bothin magnitudes and in local distribution, being found that it grows progressively as it advances a cycle untilreaching a maximum near the moment in which the flame is completely separated from the base of the burner,then it start to extinguish quickly decreasing its amount of total soot. As for temperature, it was possible tomeasure and determine that, for a whole flame cycle, the maximum temperature remains practically constant,but its distribution varies significantly.Then, the other condition, with less flow of fuel and oxidant, was impososed for the flame. Underthese condition, an oxygen index sensitivity analysis was done between 21% and 33% in order to study theinfluence of this parameter. In the case of the steady state flames, the amount of maximum radially integratedlocal soot increases from 1; 571 ppm cm2 for OI 21% to 1; 839 ppmcm2 for OI 33 %. On the other hand, theamount of radially integrated soot and also at the flame height, decreases for the condition with the higheroxygen index to about 2=3 from 3; 088 ppm cm3 of the flame with OI 21 %. A similar behavior is observed forforced flames, in which the radially integrated soot volume fraction increases with the increase of the oxygenindex, but the amount of total soot in the flame decreases as this parameter gets higher. The production of totalsoot of the flame has a sinusoidal behavior independent of the forcing level, but if the forcing increases, anincrease in magnitude and also a displacement of the maximum is found, observing a more sudden decrease.In the case of the soot temperature, it can be seen how its maximum increases as the oxygen indexincreases, both in the steady state and in the forced cases. For strongly forced flames, it is obseved thatthe maximum flame temperature remains practically constant throughout the cycle for a given oxygenindex, but in moderately forced flame a cyclical behavior is observed, reaching a maximum that seems tobe out of phase between 10 and 20 ms regarding to the maximum total soot production in the flame. Themaximum temperature is generally lower in the case of strongly forced than in moderately forced flames,but with dierences within the margin of error. Regardless of the level of forcing, the soot temperature fielddistributions vary throughout the cycle, thus in this work the temperature profiles are shown at dierentnormalized heights of the flame, providing information of the base and superior zones of the flame, whichcould be valuable information for other experimental and numerical works.
This work present the results obtained from the measurement of soot temperature in laminar diusionflames, which were acoustically forced with the intervention of a loudspeaker in the fuel line which generatesa periodic disturbance whose intensity can be controlled.Firstly, the theoretical bases on the characteristics of the flame are presented, then the acoustic forcingand finally the most important measured properties in the study: the soot volumen fraction, correspondondingto a measure of the amount of local soot presented in the dierent flame zones, and the soot temperature,which is the temperature of the soot particles and agglomerates within the flameIn order to perform these measurements, non-intrusive technics of light-of-sight attenuation (LOSA)and two-color spontaneous emission measurements were used, using also modulation, deconvolution andregularization techniques. Steady state flames were studied, and were forced with two levels of forcingintensity mantaining a constant frequency of 10 Hz. The error was calculated for all the experimentalmeasurements.One of the imposed condition for the flame was replicating the work of Shaddix et al. . [1] in orderto replicate their soot volume fraction results and generate results for soot temperature. The soot volumenfraction measurements show a good concordance between the results of the article and those of this work, bothin magnitudes and in local distribution, being found that it grows progressively as it advances a cycle untilreaching a maximum near the moment in which the flame is completely separated from the base of the burner,then it start to extinguish quickly decreasing its amount of total soot. As for temperature, it was possible tomeasure and determine that, for a whole flame cycle, the maximum temperature remains practically constant,but its distribution varies significantly.Then, the other condition, with less flow of fuel and oxidant, was impososed for the flame. Underthese condition, an oxygen index sensitivity analysis was done between 21% and 33% in order to study theinfluence of this parameter. In the case of the steady state flames, the amount of maximum radially integratedlocal soot increases from 1; 571 ppm cm2 for OI 21% to 1; 839 ppmcm2 for OI 33 %. On the other hand, theamount of radially integrated soot and also at the flame height, decreases for the condition with the higheroxygen index to about 2=3 from 3; 088 ppm cm3 of the flame with OI 21 %. A similar behavior is observed forforced flames, in which the radially integrated soot volume fraction increases with the increase of the oxygenindex, but the amount of total soot in the flame decreases as this parameter gets higher. The production of totalsoot of the flame has a sinusoidal behavior independent of the forcing level, but if the forcing increases, anincrease in magnitude and also a displacement of the maximum is found, observing a more sudden decrease.In the case of the soot temperature, it can be seen how its maximum increases as the oxygen indexincreases, both in the steady state and in the forced cases. For strongly forced flames, it is obseved thatthe maximum flame temperature remains practically constant throughout the cycle for a given oxygenindex, but in moderately forced flame a cyclical behavior is observed, reaching a maximum that seems tobe out of phase between 10 and 20 ms regarding to the maximum total soot production in the flame. Themaximum temperature is generally lower in the case of strongly forced than in moderately forced flames,but with dierences within the margin of error. Regardless of the level of forcing, the soot temperature fielddistributions vary throughout the cycle, thus in this work the temperature profiles are shown at dierentnormalized heights of the flame, providing information of the base and superior zones of the flame, whichcould be valuable information for other experimental and numerical works.
Description
Catalogado desde la version PDF de la tesis.
Keywords
FORZAMIENTO ACUSTICO , FRACCION EN VOLUMEN DE HOLLIN , LLAMAS DE DIFUSION , TEMPERATURA DE HOLLIN