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Numerical Study on the Combustion Characteristica of Mixture Fuel Containing CO

Author: LiGuoQiang
Tutor: WangJingFu
School: Beijing University of Technology
Course: Thermal Power Engineering
Keywords: numerical simulation turbulent combustion chemical reaction mechanism radiative heat transfer a statistical narrow band mode
CLC: TK16
Type: Master's thesis
Year: 2010
Downloads: 115
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Abstract

In this paper, the research situation was analyzed. Based on the analysis, the configuration of firebox of mixture fuel containing CO was introduced, and two dimensional (2-D) model including flow, heat transfer, mix, chemistry of combustion and flame radiation in the firebox system was built. The effect on temperature field, flow field and concentration field of combustion productions was numerically analyzed when excessive air coefficient and ratio between CO and CH4 varied respectively with three different kinds of models. Moreover, when mixture fuel containing CO was burned, a large quantity of radiative gas was produced. It is necessary to study the effect of flame radiation and reabsorntion on flame configuration and stability in firebox. It provides a basis for numerical simulation and optimization in designing combustion equipment of mixture fuel containing CO.The main two parts in this dissertation are as follows:(1) The statistical narrow band model that considered the variation of gas radiative properties with the wavelength was established. The effect of the wall temperature, the flame thickness and the volume percentage of mixture fuel on variation of the spectral intensity and transmittances with the wavelength were calculated in the model according to the physical property. In this study, the radiative heat transfer equation was calculated by means of the discrete ordinate method, and the code for the calculation of radiation heat transfer in flames with the DOM(discrete ordinate method)was programmed by FORTRAN language. Results show the discipline of the radiative reabsorption on the radiation heat loss versus the wall temperature, the flame thickness and volume percentage of refuse combustion gas. Based on the calculation, it is concluded that the radiation reabsorption, the variation of the radiative properties with the wavelength should be taken into account in numerical simulation of mixture fuel containing CO.(2) Build two dimensional (2-D) model of mixture fuel containing CO including flow, heat transfer, mix, chemistry of combustion and flame radiation in the firebox system, and model its combustion progress. In this study, the Realizable k ?? model was used to solve the flow problem, DO model(Discrete Ordinates)was adopted to simulate flame radiation, and EDC model was used to compute combustion. Because lots of radiation species was included in the high-temperature gas combustion, the effect of thermal radiation was primary studied. The influence of radiative heat transfer on temperature, flow and concentration field of combustion productions is significantly researched by means of adiabatic model (without considering radiation), optically-thin model, and non -gray gas model; For all of these situations, were used 16 Components in 41-step reaction mechanism in detail, so make the model closer to reality.Studies show that (1) Flame thickness and boundary temperature significantly influence the radiative heat loss. The increasing of volume of CO2 causes to increasing of influence of radiation reabsorption and the heat loss is overestimated in optical thin model. (2) flame radiation obviously influenced the temperature of the firebox. The temperature is the highest in adiabatic model .The temperature is higher than 270K in optically-thin model, and higher than 140K in non-gray gas model.(3) the air speed increases when the excess air coefficient increases. High-temperature gas is blown out of the firebox; this decreases the temperature of the firebox and the flame sheet, and influences the combustion of the flammable gas. Moreover some unburned reactions and intermediate products was also blown out of the firebox, this wastes the energy and resource of the firebox.(2)when the ratio of CO in the mixture fuel decreases , the ratio of CH4 increases , and a large quantity of heat is released because of the combustion of CH4. This makes the temperature of the firebox increase; with the decreasing of CO the quantity of air increase and the air speed also increases. This makes the releasing heat of CH4 be more blown out of firebox. This is a waste of the heat energy. In order to increase the consuming ratio of CO, the more quantity of CH4 does not mean the combustion result of CO is better. We must find the optimal solution , Only then we can reasonably and efficiently make use of the releasing heat of CH4.(4)the flame thickness and the wall temperature have large influence on radiative heat loss, and with the volume percentage of CO2 increasing, the radiative reabsorption effect on flame becomes more important. It is found that the optically thin model significantly overestimates the radiation heat loss, causes error and loses its effectiveness in the prediction of flames with much more radiative species. Therefore, more accurate radiation models such as the statistical narrow-band model (SNB) should be employed to accurately predict flames properties in mixture fuel containing CO combustion process.

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CLC: > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Fuel and combustion
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