乙醇-氢气-空气混合燃气的层流燃烧速度测定

Measurement of Laminar Combustion Velocity of Ethanol-Hydrogen-Air Mixed Gas

为了研究乙醇的层流燃烧特性,在定容燃烧弹内,分别研究了初始压力为0.3 MPa,氢气比例为50%时,不同初始温度(370 K和450 K)和当量比(0.7~1.4)下,氢气-乙醇混合燃气的火焰传播规律。计算得到了混合燃气的层流燃烧速度和马克斯坦长度,分析了拉伸率对火焰传播速度的影响,同时将研究结果与文献数据进行了比较,验证了计算模型的可靠性。结果表明:随着初始温度的增加,混合燃气的层流燃烧速度也会随之提升;当量比的增加也会提升混合燃气的层流燃烧速度,在当量比为1.2时达到了峰值,随后开始降低。初始温度的增加会在一定条件下会导致火焰的不稳定;在初始温度370 K下,马克斯坦长度始终大于0,火焰一直处于稳定状态;初始温度450 K、0.7~0.9当量比下的马克斯坦长度小于0,火焰出现了不稳定状态,因为较高的初始温度会产生强烈的对流和湍流效应,这些效应会使火焰的边界层受到扰动,造成火焰不稳定;不同初始温度下的马克斯坦长度都随当量比的增加而增加,火焰的稳定性不断提升。对计算得到的层流燃烧速度进行数据拟合,得到了计算乙醇-氢气-空气混合气层流燃烧速度的关系式。

In order to study the laminar combustion characteristics of ethanol,the flame propagation rules of hydrogen and ethanol mixed gas in a constant combustion bomb at different initial temperatures(370 K and 450 K)and equivalence ratios(0.7-1.4)under the conditions of 0.3 MPa initial pressure and 50%hydrogen mixing ratio were researched.The laminar combustion velocity and Markstein length of mixed gas were calculated and the influence of stretching rate on flame propagation velocity was analyzed.The research results were further compared with the literature data and the reliability of calculation model was verified.The results indicate that the laminar combustion velocity of mixed gas increases with the increase of initial temperature.Moreover,the increase of equivalence ratio will increase the laminar combustion velocity of mixed gas,which reaches the peak at an equivalence ratio of 1.2 and then begins to decrease.However,the increase of initial temperature will lead to flame instability under certain conditions.At the initial temperature of 370 K,the Markstein length is always greater than zero and the flame remains in a stable state.The Markstein length is less than zero at the initial temperature of 450 K and the equivalence ratio of 0.7-0.9 and the flame appears unstable state.The higher initial temperature will produce strong convection and turbulence effects,which will disturb the boundary layer of flame and finally cause flame instability.The Markstein lengths at different initial temperatures increase with the increase of equivalence ratio and the stability of flame continuously improves.The data fitting was performed for the calculated laminar combustion velocity and the relationship equation for calculating the laminar combustion velocity of ethanol-hydrogen-air mixture was obtained.