An Experimental Investigation on Flame Pulsation for a Swirl Non-Premixed Combustion

Abstract

Flame pulsation has a significant effect on combustion, and understanding its oscillatory behavior is important to the combustion community. An experiment was performed to analyze the pulsation characteristics of a swirl non-premixed flame under various parameters. The results showed that as fuel mass flow rate increased, the puffing frequency increased due to the decreased flame radiation fraction, and the puffing amplitude became smaller resulting in a more stable flame. With an increase in combustor pressure, the flickering frequency declined because of the increasing soot radiation, while the flickering amplitude uniformly increased, leading to more deteriorative flame stability. With an increment in mass flow rate of primary air, the puffing frequency decreased due to the enhanced mixing between fuel and primary air. Also, the puffing amplitude had an oscillating relationship with the mass flow rate of primary air. When the exit velocity of the injector was increased, the flickering frequency diminished nearly linearly because of the improving swirl intensity, and the flickering amplitude was approximately unaffected by injector exit velocity. Moreover, the measured puffing frequencies summarized over all cases varied within the range of 3-22 Hz, the predicted values from theoretical models based on non-swirl flame also fell within this range. The puffing frequency of swirl combustion was more sensitive to the variation in operating conditions than that of non-swirl combustion. Additionally, the obtained correlations indicated that the Strouhal number St was proportional to Fr −1.4 (the Froude number) and Re −2.9 (the Reynolds number), respectively.

Experimental Analysis on Flame Flickering of a Swirl Partially Premixed Combustion

“…m F . This agrees with the previous observation of normalized peak-to-peak amplitude [26], which also displayed a decreasing tendency with . m F .…”

“…Though this variation in F is not much (in the range of 2 Hz) yet, the spectrums as well as the dominant frequencies are entirely different. As we observed in previous research [26], the most dominant frequency increased with . m F .…”

“…Though this variation in F is not much (in the range of 2 Hz) yet, the spectrums as well as the dominant frequencies are entirely different. As we observed in previous research [26], the most dominant frequency increased with ṁF. However, the weighted average F in the present investigation did not follow this increasing trend because it was determined by all the selected components, therefore, its variation trend can be different from the most dominant frequency.…”

“…For this investigation, a combustion test rig was installed, as shown in Figure 1. This device consists of serval parts, which are briefly introduced as follows, more details can be found in our previous research [26]. The gas holder supplies methane as the fuel, and a mass flow controller (MFC) is used for fuel measurement and control.…”

“…Old vortices shed from the flame tip, new vortices formed at the flame root and continue to travels along the flame surface, leading to the flame flickering. More details of flickering dynamics can be found in previous research [26].…”