| The distribution of hydroxyl radical(OH)in methane-air jet diffusion flame was studied by planar laser induced fluorescence.The influence of different mass flow ratio of methane and air on flame temperature,OH group fluorescence grayscale value,color change,flame size,emission of NO_X concentration and the relationship between these factors and OH concentration distribution were observed through the OH-PLIF measurement technology in the opening designed burner(cyclone burner).As the intermediate product of combustion chemical reaction,OH group distribution can be approximately regarded as the structure of flame reaction zone.The structure of reaction zone in methane/air jet diffusion flame was studied by planar laser induced fluorescence.The effects of different inlet pressures on the flow field of methane-air diffused combustion were analyzed by using the one-step reaction mechanism.The methane and air in the combustion chamber were injected tangentially at the bottom and the combustion products were discharged axially.The subgrid stress model and the finite-rate/vortex-dissipative combustion model were used to numerically analyze the turbulent combustion process and important phenomena in the swirling combustion chamber and verify the experimental results.According to the numerical simulation,with the increases of air inlet pressure,the temperature distribution at the cross section of the same position becomes more and more uniform,and the momentum generated by methane and air at this time makes the relative static time of air at the methane inlet greater than other positions.Within a certain range,increasing the air intake pressure can effectively improve the combustion temperature of the flame.Since the flame is relatively stable under the condition of high equivalence ratio,the data of the three working conditions with the equivalent ratio of 1.2 for chemical reaction was selected to study the OH distribution of them respectively.In other words,under the condition of the same equivalence ratio,the conclusions are as follows:the distribution of OH group is partially concentrated,and the fluorescence grayscale value on the right side is higher than that on the left side.In the combustion process with an equivalent ratio of 1.2,with the increases of air inlet velocity,the OH group gradually transits from the initial laminar combustion to turbulent combustion.The OH group concentration increased with the increased of the inlet velocity,and its distribution is relatively dense and the fluorescence grayscale value is relatively high,which proved that the combustion is sufficient.The?=0.5-1.5 a wide range of equivalent ratios to study flame temperature and external wall temperature,fluorescence grayscale value,OH-PLIF images aspect ratio,the flame of the front/vertical view and NO_X concentration changes.That is,under different equivalent ratios,the conclusions are as follows:The self-cooling phenomenon on the surface wall appears at the position of 130-240mm.With the increases of the inlet equivalent ratio and the inlet Reynolds number,the cooling effect becomes more obvious.In low equivalent ratio laminar flame,the OH group flame structure in swirl burner is periodic.The average temperature in the main combustion area of the swirl burner is 1200K,and the internal temperature distribution shows a trend of zigzag rise,and there is a concentrated heat area at the top of the swirl combustion area.with the increase of the equivalent ratio,the maximum temperature at the axis of the burner also increases.The temperature changed from 1187.3k to 1207.1k at the beginning,and the equivalence ratio increases from 0.5 to 1 at the same time,and the temperature here is the highest.The mean value normalization of fluorescence signal of OH-PLIF first increases and then decreases with the increases of the equivalent ratio.The highest value occurs at the position of the equivalence ratio of 1 and is normalized to 0.951,while the lowest value occurs at the position of 0.5 and is normalized to 0.869.under the same equivalent ratio,the higher the inlet flow of methane/air is,the smaller the aspect ratio of OH-PLIF image will be.When the methane/air inlet flow remains unchanged,the aspect ratio of OH-PLIF images under three working conditions increases first and then decreases with the increases of the equivalent ratio.in the range of 0.5~0.8equivalent ratio,the height and width of the flame increases with the increases of equivalent ratio,and its length also increase.Equivalent ratio in the range of 0.9 to 1.1,the flame height and width are significantly reduced compared to the last counterclockwise rotation speed with high speed at the same time,in the area of the flame color of blue and white,proving the best combustion status,flame temperature the highest temperature of 1200?,the utilization rate of fuel is the highest.under various working conditions,that is,when the air inlet velocity remains unchanged,the highest value of NO_X concentration appears near the equivalent ratio of 0.9.When the equivalent ratio is constant,the higher the air inlet velocity,the higher the NO_X concentration. |
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