Impact of Vitiation on a Swirl-Stabilized and Premixed Methane Flame

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.

Section: Experimental Apparatusmentioning

confidence: 99%

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

et al. 2018

“…The models and their predicted results are shown in Table 1, where dj is 0.01 m (the diameter of the nozzle throat which is considered as the exit of injector). As displayed in Table 1, the calculated frequencies from the theoretical models are larger than the present measurement of swirl flame (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). This indicates that the puffing frequency of swirl flame does not only depend on the diameter of injector but also relies on the mass flow rate of primary air, that is to say, it was much more sensitive to the variation in ṁpri than the frequency of non-swirl flame.…”

Section: Puffing Frequencymentioning

confidence: 53%

An Experimental Study on Flame Puffing of a Swirl Partially Premixed Combustion under Varying Mass Flow Rate of Primary Air

Sabir

et al. 2018

It is of practical significance to understand the flame puffing behavior under varying mass flow rate of primary air ṁpri. An experiment was conducted to study the impact of ṁpri on flame puffing in a swirl partially premixed combustor, the puffing behavior of six significant flame properties was examined. The results showed that almost every spectrum had two fundamental frequencies, which is different from the single-peak spectrum of non-swirl flame. The flame heat-release rate, flame area, and flame equivalent width had identical dominant frequency and sub-dominant frequency, both decreased with the increasing of ṁpri. It was attributed to the decreased overall flame temperature caused by the improved mixing of fuel and primary air. All measured frequencies were in the range of 3–14 Hz, but the predicted frequencies from the theoretical models based on non-swirl flame were larger than the measured. This indicates the puffing frequency of swirl flame was much more sensitive to the variation in ṁpri than the frequency of non-swirl flame. Moreover, the amplitude of flame length was the smallest in all properties, with the most weakened oscillating intensity. While the amplitude of the flame area and flame equivalent width were the largest, with the strongest oscillation level. Consequently, the flame puffing is mainly attributed to the oscillation in width direction.

“…The signal of flame luminosity is usually employed to study flame flickering [2,3,12,28]. Giving a discrete time luminance signal l(ti) (ti is time instant, i = 1 … N), some oscillation parameters including mean value, flickering weighted average frequency, flickering coefficient of variation, skewness, and kurtosis were determined as follows.…”

Section: Analysis Parametersmentioning

confidence: 99%

“…The signal of flame luminosity is usually employed to study flame flickering [2,3,12,28]. Giving a discrete time luminance signal l(t i ) (t i is time instant, i = 1 .…”

Section: Analysis Parametersmentioning

confidence: 99%

Experimental Analysis on Flame Flickering of a Swirl Partially Premixed Combustion

Sabir

et al. 2018

An experiment was conducted to explore the flickering parameters under varying mass flow rate of fuelṁ F with spatial analysis and global analysis. The parameters include mean value, flickering weighted average frequency F, flickering coefficient of variation c v (firstly introduced), skewness s, and kurtosis k. From the spatial analysis, it was found that the brightest part of flame is located in its core, and the brightness gradually decreased from the inside out. The distributions of high levels of F, c v , s, and k are almost consistent, all lying in the flickering edge, which is a thin layer where the parameters sharply declined. From the global analysis, with the increment oḟ m F , the global F decreased slightly; the global c v declined uniformly, which means the oscillation amplitude diminished and thus the flame became more stable; the global s linearly reduced; and the global k also showed a decreasing trend. The decreasing global s indicates that the number distribution gradually became symmetric, and the decreasing global k indicates that the number distribution progressively became flat. Consequently, the number distribution progressively tends to normal distribution at largerṁ F . Keywords: flame flickering; partially premixed flame; varying mass flow rate of fuel; spatial analysis and global analysis; flickering weighted average frequency; flickering coefficient of variation; skewness and kurtosis