ABSTRACT

Biogas is a renewable fuel predominantly composed of carbon dioxide (CO₂) and methane (CH₄) in varying proportions. The effects of the varying CO₂ proportion need to be clarified for the development of engines. The laminar burning velocity and the burned gas Markstein length of premixed CH₄/CO₂/Air were measured with CO₂ concentration ranging from 0.3 to 0.7 dilution ratios. The equivalence ratio was varied from 0.8 to 1.2, the initial pressure was set at 0.5 MPa, and the temperature was set to 298 K. The experiment was performed using a high-pressure constant volume combustion chamber. One-dimensional simulation of the flames was conducted using GRI-Mech 3.0. The results showed a reduction in the laminar burning velocity of CH₄/CO₂/Air mixtures with an increase in CO₂ dilution ratio. A non-monotonic relationship was discovered between measured Markstein length and CO₂ dilution ratio with different equivalence ratios. It was found that an increase in the CO₂ dilution increased the response of the flames to stretch. For the lean and stoichiometric flames, the Markstein length was nearly constant with CO₂ dilution of 0–0.5 and decreased with CO₂ dilution of 0.7, suggesting an increase in susceptibility of the flame to the intrinsic flame instability. This was found to be mainly due to an increase in the Zel’dovich number and a decrease in the effective Lewis number with CO₂ dilution. The Markstein length of the rich flame increased with CO₂ dilution as it was more sensitive to CO₂ dilution. Thermo-diffusive effects and pure stretch effects had similar influences on the burning velocity of the rich flames with an increase in stretch rate.

摘要

沼气是一种可再生燃料，主要由不同比例的二氧化碳 (CO ₂ ) 和甲烷 (CH ₄ ) 组成。对于发动机的开发，需要阐明不同 CO ₂比例的影响。层流燃烧速度和预混 CH ₄ /CO ₂ /Air的燃烧气体 Markstein 长度是在 CO ₂浓度范围为 0.3 至 0.7 稀释比的情况下测量的。当量比从 0.8 到 1.2 变化，初始压力设置为 0.5  MPa，温度设置为 298  K. 使用高压定容燃烧室进行实验。火焰的一维模拟使用 GRI-Mech 3.0 进行。结果表明，随着CO ₂稀释比的增加，CH ₄ /CO ₂ /空气混合物的层流燃烧速度降低。在测量的 Markstein 长度和具有不同当量比的CO ₂稀释比之间发现了非单调关系。发现CO ₂稀释度的增加增加了火焰对伸展的响应。对于稀薄火焰和化学计量火焰，Markstein 长度在 CO ₂稀释度为 0–0.5时几乎恒定，并随着 CO ₂降低0.7 的稀释，表明火焰对固有火焰不稳定性的敏感性增加。发现这主要是由于随着 CO ₂稀释，泽尔多维奇数增加和有效路易斯数减少。富火焰的马克斯坦长度与CO增加₂稀释，因为它是对CO更敏感₂稀释。随着拉伸速率的增加，热扩散效应和纯拉伸效应对富火焰燃烧速度的影响相似。