Download THE TITLE OF YOUR PAPER GOES HERE

The 25th National Conference on Combustion and Energy
Kaohsiung, Taiwan, April 24~25, 2015.
Paper ID: XX-XX
The Effect of Inert Dilution on Flickering Motions of Jet Diffusion Flames
Shuhn-Shyurng Hou1, Ta-Hui Lin2,3*
1Department of Mechanical Engineering, Kun Shan University
2
Department of Mechanical Engineering, National Cheng Kung University
3
Research Center for Energy Technology and Strategy, National Cheng Kung University
*
Corresponding Author, Email: [email protected]
NSC Project No: NSC97- 2221-E-168-043
Abstract
In this study, we aimed at investigating the instability of jet flames caused by the buoyancy effects called
“axial flickering.” The results showed that the flickering frequency in the high velocity range was lower
than that in the low velocity range.
Keywords: Jet Diffusion Flame, Flame Flickering, Inert Dilution
1. Introduction
Buoyancy has strong impacts on the
mechanisms of flame stabilization such as flame
flash back, lift-off and blow-off for premixed
flames, and lift-off, and blow-out for diffusion
flames [1-4]. The low-frequency oscillation or
“flickering’’ of laminar diffusion flames induced
by buoyancy effects is a well-known combustion
phenomenon. The buoyant interaction of the hot
burnt gases and the cold ambient air causes flame
front to regularly oscillate at a low frequency. This
buoyancy-driven oscillation is associated with the
Kelvin-Helmholtz instability and the large vortices
formed in the shear layer between the flame sheet
and surroundings.
Fig. 1 Schematic of jet flow system.
In addition, the dimensionless Froude number
is defined as
2. Experimental apparatus and method
The experimental apparatus consisted of a
coaxial jet burner system, a gases supply system, a
high speed camera, and an exhaust suction system,
as shown in Fig. 1.
In dimensional analysis, Strouhal number is
used to describe oscillating flow mechanism:
St 
fd
V
Fr 
V2
gd
(2)
where Fr is the dimensionless Froude number,
which compares the inertial and gravitational
forces, V is the burner tube exit velocity, g is the
acceleration due to gravity, and d is the burner tube
diameter.
(1)
where St is the dimensionless Strouhal number, f is
the flickering frequency, d is the hydraulic
diameter, and V is the velocity of the fluid. The
Strouhal number is the ratio of the local inertia
force to the convective inertia force.
3. Results and discussion
Low frequency flame oscillation is known as
the flame flicker, and it is caused by the instability
of the laminar-jet flows. The instability is due to a
buoyancy-induced velocity field which surrounds a
forced convective flow. There are two distinct
vortical structures, i.e., large vortices outside the
luminous flame and small roll-up vortices inside
The 25th National Conference on Combustion and Energy
Kaohsiung, Taiwan, April 24~25, 2015.
the flame. The vortices outsides the luminous
flame are due to buoyancy-induced KelvinHelmholtz type instability and are also responsible
for low frequency flame oscillations. The
frequency of these vortices is related to the flame
bulge and the flame oscillation frequency.
4. Conclusions
Vortices outside the luminous flame are formed
due to buoyancy-driven instability and are
responsible for the low frequency flame oscillation.
The frequency of the vortical structure outside the
luminous flame is correlated with the flame
flickering frequency. The flicker is a consequence
of the hydrodynamic instability of the buoyancyinduced flow field, the essential characteristic of
which are independent of the flow rate, burner size,
or choice of gases, as recognized in the past.
However, some different and interesting results
were obtained in this study, which are shown as
follows.
Acknowledgments
This work was supported by the National
Science Council, Taiwan, ROC, under contract
NSC97- 2221-E-168-043.
References
[1] Williams F. A., Combustion Theory, 2nd
Ed., Benjamin/Cummings, 1985.
[2] Gardon A. G., and Wolfhard H. G., FlameTheir
Structure,
Radiation,
and
Temperature, 4th Ed., Chapman and Hall,
London, 1979.
[3] Jones, H. R. N., The Application of
Combustion Principles to Domestic Gas
Burner Design, British Gas, 1989.
[4] Kanury A. M., Introduction to Combustion
Phenomena, Gordon and Breach, New
York, 1975.
[5] Sato, H., Amagai, K., and Arai, M.,
Diffusion Flames and Their Flickering
Motion Related with Froude Number Under
Various Gravity Levels, Combustion and
Flame, Vol.123, pp.107-118, 2000.
Paper ID: XX-XX
鈍氣稀釋對噴流擴散火焰擺動現象
的影響
侯順雄 1、林大惠 2,3*
1
崑山科技大學機械工程系(所)
2
國立成功大學機械工程學系
3
國立成功大學能源科技與策略研究中心
*
通訊作者，Email:
[email protected]
摘 要
本研究之目的在於藉由不同比例的鈍氣混
入甲烷，模擬製程的副產可燃氣，分析製程氣
中鈍氣含量對噴流擴散火焰燃燒特性的影響。
研究中主要針對單管噴流火焰進行穩定性分
析，擷取不同操作條件下的火焰影像，分析火
焰的擺動現象與擺動機制。
關鍵字：噴流擴散火焰、火焰擺動、鈍氣稀釋