低频声波激励下乙醇池火燃烧特性研究

Combustion Characteristics of an Ethanol Pool Fire Perturbed by Low-Frequency Acoustic Waves

为发展灭火技术,以乙醇为池火火源,采用20~80 Hz的声频率,研究了不同响应距离下的池火燃烧特性。模拟计算了声波诱导下池杯周围的流场特性;采用图像分析得到了火焰关键参数,分析了不同声波频率和响应距离下火焰形态动态特性、火焰特征参数及火焰吹熄的演变规律。结果表明:池杯周围的流场呈周期性变化,但时均速度不为0,池杯上方存在明显的速度剪切,池杯下方速度与压力变化较小;声波激励下,火焰脉动变得极不规则,较低频率声波作用下火焰易直接被吹熄,较高频率声波作用下易出现复燃;声波对火焰的冲击作用、燃烧区化学当量比的调节和燃烧区温度的改变是声波熄灭火焰的主要原因。此外,不同声波激励频率下火焰衰减阶段的平均高度、复燃频次和熄灭时间都呈波动变化趋势。火焰复燃频次与火焰熄灭时间大体呈正比例关系。

To develop fire fighting technology, the characteristics of pool fire under different response distances were studied with ethanol as the fire source and sound frequency of 20 ~ 80 Hz.The flow field around the pool cup induced by acoustic wave were simulated firstly. The key parameters of pool fire flame were extracted by image analysis. The dynamic characteristics of flame shape,flame characteristic parameters and the evolution law of flame blowing out under different acoustic frequency and response distance were analyzed. The results showed that the flow field around the pool cup changed periodically, but the time-averaged velocity was not 0. There was obvious velocity shear above the pool cup. The velocity and pressure changed little below the pool cup. When excited by acoustic waves, the flame pulsation became very irregular. The flame was easy to be extinguished directly under the action of low frequency acoustic wave, and it was easy to reignite under the action of high frequency acoustic wave. The impact effect on flame, the adjustment of chemical equivalence ratio in combustion zone and the change of combustion zone temperature are the main reasons to extinguish flame caused by acoustic waves. In addition, the average flame height, reburning frequency and extinction time at different acoustic excitation frequencies are fluctuating. There is a positive proportion between the frequency of flame reburning and the time of flame extinction.