摘要
Most of the experimental examinations on laminar flame characteristics of a diluted combustible mixture have simulated combustion residuals with one of the main exhaust gases (N2, H2O, and CO2) or a mixture of two. However, flue gases have quite different thermodynamic properties and chemical reactivities. Therefore, simulating the post combustion products used for dilution with only one or two of the main exhaust gases may yield erroneous laminar flame characteristic data. In the present study, the laminar burning velocities and burned gas Markstein lengths of diluted methane/air mixtures at 1 bar and 473 K were measured with spherically expanding flames under constant pressure in an optically accessible constant volume combustion chamber. The mixtures were diluted with N2, H2O, and CO2 individually as well as with a mixture of 71.49% N2 + 19.01% H2O + 9.50% CO2 by volume, which represents the main product concentrations from stoichiometric methane/air combustion. Experimental results show that the laminar flame speed values of methane/air mixtures diluted with actual combustion residuals are between those of N2 and H2O dilution, whereas the laminar burning velocities of methane flames diluted with CO2 are considerably slower. The effects of different combustion residuals on the burned gas Markstein length were not found to be significant. At the experimentally-investigated initial conditions, CHEMKIN analyses were performed with the GRI-Mech 3.0, San Diego, and USC Mech II mechanisms to inquire about the performances of the kinetic schemes. The GRI-Mech 3.0 results were the closest to the experimental data. This mechanism was also utilized to numerically quantify the dilution, thermal diffusion, and chemical effects of combustion residuals. The dilution effect was the leading effect in decreasing the laminar burning velocity, while the thermal diffusion effect had the smallest contribution. Nevertheless, the thermal diffusion effect changes the thermal and mass diffusivities, and, as a result, the Lewis number, making it a vital parameter for flame stability and stretch. As the thermodynamic properties and chemical reactivities of the combustion residuals vary with temperature, pressure, equivalence and dilution ratios, real combustion residuals cannot be accurately represented with only one or two of the main exhaust gases, as shown in the current study.
摘要译文
在稀释的可燃混合物的层流火焰特性的大多数实验检查中，模拟燃烧残渣与一种主要废气（N 2，H 2 O和CO 2）或两种的混合物混合。但是，烟气具有完全不同的热力学性质和化学反应性。因此，仅用一种或两种主要排气来模拟用于稀释的后燃烧产物可能会产生错误的层流火焰特性数据。在本研究中，在光学可访问的恒定体积燃烧室中，在恒定压力下用球形膨胀火焰在1 bar和473 K下测量了稀释的甲烷/空气混合物的层流燃烧速度和燃烧气体Markstein长度。分别用N 2，H 2 O和CO 2以及按体积计71.49％N 2 + 19.01％H 2 O + 9.50％CO 2的混合物稀释混合物，其代表来自化学计量甲烷的主要产物浓度/空气燃烧。实验结果表明，用实际燃烧残留物稀释的甲烷/空气混合物的层流燃烧速度值介于N 2和H 2 O稀释率之间，而用CO 2稀释的甲烷火焰的层流燃烧速度则要慢得多。没有发现不同的燃烧残留物对燃气Markstein长度的影响是显着的。在经过实验研究的初始条件下，使用GRI-Mech 3.0，圣地亚哥和USC Mech II机制进行了CHEMKIN分析，以查询动力学方案的性能。 GRI-Mech 3.0结果最接近实验数据。该机制还被用来对燃烧残渣的稀释，热扩散和化学作用进行数值量化。稀释作用是降低层流燃烧速度的主要作用，而热扩散作用的贡献最小。然而，热扩散效应改变了热扩散系数和质量扩散系数，结果是改变了刘易斯数，这使其成为火焰稳定性和伸展性的重要参数。由于燃烧残留物的热力学性质和化学反应性随温度，压力，当量和稀释比的变化而变化，如本研究所示，实际燃烧残留物不能仅用一种或两种主要废气精确地表示出来。
Berk CanDuva;Lauren ElizabethChance;ElisaToulson. Dilution effect of different combustion residuals on laminar burning velocities and burned gas Markstein lengths of premixed methane/air mixtures at elevated temperature[J]. Fuel, 2020,267