| The rapid development of science and technology in contemporary society has brought great convenience to human life,but also caused damage to the environment.The environmental pollution caused by the massive use of coal and oil has become increasingly serious.Natural gas,as a clean energy source,can reduce air pollutants produced by combustion,such as nitrogen oxides and sulfur oxides.The main component of natural gas is methane,which is abundant in resources.It is of great practical value to study the combustion of methane.In order to deal with the challenge of global energy shortage and environmental protection,the research on dilution combustion technology with low pollution and energy consumption has been done.The flue gas recirculation technology,the mild combustion technology,H2O dilution combustion technology and Oxygen-enriched combustion technology have been widely used in industry.At present,domestic and foreign scholars have done a lot of research on the influence of diluent on flame,but there are few studies on the influence of dilution position on flame in the dilution combustion research.Moreover,the coaxial jet flame model is a very typical diffusion combustion form,and it is also the closest to the turbulent multidimensional combustion flame model in industrial application.Therefore,it is of great significance to study the influence of dilution position on the diffusion flame of methane coaxial jet for the understanding of dilution combustion technology.Firstly,the NRC 2D flame simulation program was used to study the flame structure of methane coaxial jet diffusion,and the accuracy of the flame code was verified by combining the experimental data in the references.The flame code incorporates detailed chemical reaction mechanisms to simulate and predict detailed diffusion,flow,heat transfer and chemical reaction processes at low Mach numbers.By means of numerical simulation we studied the influence of CH4 laminar coflow diffusion flames with different dilution ratio of carbon dioxide in the fuel side and air side(hereinafter referred to as the "dilution position),and explained the influence of dilution position on the concentration of OH,flame length,and the temperature of the nozzle form two aspects which include the chemical reaction mechanism and physics.This paper studied the influence of dilution position on flame combustion characteristics under different dilution atmospheres of carbon dioxide and water vapor(Z:0-0.20):the maximum concentration of OH diluted on the air side is lower than that on the fuel side.With C02 dilution the maximum concentration of OH diluted on the air side is 96.8%of that on the fuel side when Z=0.05,while it is 92.6%with H2O dilution.From the perspective of heat release rate,the heat release rate of the flame base diluted on the fuel side is greater than that on the air side when Z=0.05.The heat release rate of the flame base on the fuel side is 110%of that on the air side with CO2 dilution,and 116%with H2O dilution.In terms of flame attachment,when the dilution parameter increases from 0.05 to 0.15,the flame attachment depth of fuel side dilutes from-0.10cm to-0.06cm with CO2 dilution,and the flame attachment depth from-0.09cm to-0.04cm with H2O dilution.The flame attachment depth on the air side is stable at about-0.12cm with CO2 or H2O dilution.In terms of nozzle temperature,when the dilution parameter increases from 0 to 0.20,the nozzle temperature diluted in fuel side decreases from 1218K to 1097K with CO2 dilution,and decreases from 1218K to 1176K on the air side.The nozzle temperature diluted in fuel side decreases from 1218K to 1037K with H2O dilution,and decreases from 1218K to 1136K on the air side,so the nozzle temperature of fuel side dilution is lower than that of the air side dilution.In laminar diffusion flame,the flame length is related to the jet velocity.The jet velocity on the fuel side diluted by carbon dioxide and water vapor is greater than that on the air side,resulting in a larger flame length at the fuel side dilution.In general,this paper is of great importance for deep understanding of combustion phenomenon in complex atmosphere.On the other hand,it has great significance for the practical application of dilution combustion in industrial energy saving and emission reduction,so it has guiding value for industrial application. |
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