乙醇小尺度射流扩散火焰燃烧温度及稳燃特性

Combustion Temperature and Stability Characteristics of Ethanol Small-scale Jet Diffusion Flame

对自由射流和受限射流乙醇小尺度扩散火焰的燃烧温度及稳燃特性进行了实验研究。结果表明:火焰在静止空气中燃烧会经历淬熄前火焰、稳燃火焰、振荡前火焰、振荡火焰4个不同的状态。受限空间和自由空间下,火焰峰值温度随雷诺数增大均会经历增大,稳定和减小3个阶段,自由空间下,其温度最高可达1300K。尾部烟气温度随雷诺数先增大后保持稳定,其温度最高可达480K。只有当内径小到一定程度,玻璃管壁温才会随雷诺数有较大增加,其温度最高可达370K。随着受限空间内径的减小,火焰的燃烧上限明显降低,且均比自由空间时的低,而燃烧下限几乎均与自由空间时相同。在本实验范围内,热熄火是淬熄的主要因素,而燃料的不完全燃烧则是火焰由稳定燃烧转变为振荡燃烧的主要因素。

The experimental studies were carried out on the combustion temperature and stability of small-scale diffusion flames using ethanol as fuel both for free jet flow and confined jet flow. Results show that there are four conditions for the jet flow flames in the quiescent air, namely the quenching flames, stable combustion flames, quasi-oscillatory flames, and oscillatory flames. As Reynolds numbers increase, the flame peak temperatures increase firstly and then will decrease. For the free jet flow, the flame peak temperatures reach 1300K, and the exhaust gas temperatures increase, then keep stable, and may reach the maximum value of 480K. When using the quartz glass tube with a certain small diameter, the wall temperatures increase quickly with the increasing of Reynolds numbers, and may reach the maximum of 370K. The upper combustion limits of confined flow are all less than that of free flow, but the lower combustion limits are very close. As the inner diameters of the quartz glass tubes decrease, the upper combustion limits decrease sharply. In the present parameter ranges, thermal quenching is the main factor for flame quenching, and the main reason causing the transition from stable flames to oscillatory flames is the fuel incomplete combustion.