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Investigation of flameholding characteristics in a kerosene-fueled scramjet combustor with tandem dual-cavity
Accepted Manuscript Investigation of flameholding characteristics in a kerosene-fueled scramjet combustor with tandem dual-cavity Yu-hang Wang, Wen-yan Song, De-yong Shi PII:
S0094-5765(17)30981-5
DOI:
10.1016/j.actaastro.2017.08.014
Reference:
AA 6433
To appear in:
Acta Astronautica
Received Date: 17 July 2017 Revised Date:
6 August 2017
Accepted Date: 10 August 2017
Please cite this article as: Y.-h. Wang, W.-y. Song, D.-y. Shi, Investigation of flameholding characteristics in a kerosene-fueled scramjet combustor with tandem dual-cavity, Acta Astronautica (2017), doi: 10.1016/j.actaastro.2017.08.014. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
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Investigation of Flameholding Characteristics in a
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Kerosene-fueled Scramjet Combustor with Tandem
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Dual-Cavity
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Wang Yu-hang, Song Wen-yan, Shi De-yong
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Northwestern Polytechnical University, 710072 Xi’an, People's Republic of China
The flameholding characteristics in a kerosene-fueled scramjet combustor with a tandem
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dual-cavity were investigated experimentally under various inlet stagnation pressure conditions.
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Flame stabilization locations were judged by the pressure distributions and flame luminescence
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images. The results show that at lower and higher equivalence ratios, the flame was stabilized in
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the downstream and upstream cavities, respectively. While at intermediate range of equivalence
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ratio the flame was oscillating between the two cavities. The inlet stagnation pressure has a
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significant impact on the flameholding characteristics by affecting the relative pressure rise and
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the flame speed. The transition of flame stabilization location can occur in a higher local flow
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Mach number in the case of the higher inlet stagnation pressure.
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1. Introduction
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Interest in the flameholding of the supersonic combustor in scramjet has been persistent since
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1950s and it became an active area of research around the world [1]. Compared with hydrogen
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fuel, liquid hydrocarbon fuel has a higher energy density and favorable handling characteristics [2].
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However, their additional atomization, evaporation processes and longer ignition delay time [3]
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pose a significant challenge in flameholding due to the extremely short flow residence times.
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Hence, more attentions are given to the flameholding characteristic of hydrocarbon fuel in
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scramjet combustor [4-7]. Wall-mounted cavities have been considered as preferred flameholding devices since they
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can form large recirculation zones and avoid higher stagnation pressure loss caused by intrusive
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structures [8]. Many studies [7, 9-10] indicated that a combustor with a tandem dual-cavity has
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advantage of mixing, ignition and combustion performance. Smirnov et al. [11-14] analyzed the
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role of cavities in flameholding in supersonic flows. Therefore, the tandem dual-cavity was often
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used as a flameholder for liquid hydrocarbon fuel in the previous investigations [5, 9, 15-17].
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Many studies analyzed the possible influence factors on the flame stabilization of scramjet
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combustor using gaseous fuel. Micka et al. [18] investigated the influence of inlet stagnation
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temperatures to the combustion characteristics of a dual-mode scramjet combustor. They found
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two distinct combustion stabilization locations, the jet-wake stabilized combustion is initiated
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upstream of the cavity leading edge at higher air stagnation temperatures and the cavity stabilized
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combustion is anchored within the cavity shear layer at lower air stagnation temperatures. For an
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intermediate range of stagnation temperature, the reaction zone oscillated between the jet-wake
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and cavity stabilization locations. Wang et al. [19] studied the combustion characteristics in a
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supersonic combustor with several cavity geometries, fuel injection ports and fueling conditions. Three
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combustion modes were observed: cavity assisted jet-wake stabilized combustion, cavity shear layer
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stabilized combustion and combined cavity shear-layer/recirculation stabilized combustion. These
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combustion modes can be shifted by changing the cavity geometry, fuel injection ports or equivalence
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ratio.
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However, the flameholding characteristics of liquid hydrocarbon fuels will be different. Li et
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al. [4] conducted combustion experiment with kerosene fuel in a dual-cavity scramjet combustor.
ACCEPTED MANUSCRIPT Two distinct cavity-organized flame regimes were found: cavity flame and cavity shear layer
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flame. The driving force of the flame stabilization transition is the high pressure environment. Le
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et al. [5] found two kinds of flame stabilizing modes of liquid RP-3 fuel, i.e., the
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shear-layer-stabilized flame and the recirculation-zone-stabilized flame in the upstream injection
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of cavity combustion experiment. Their numerical simulation results showed that the local
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equivalence ratio of the shear layer is a key factor in determining the flame stability.
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In this paper, a tandem dual-cavity was chosen as the flameholder for the kerosene-fueled
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scramjet combustor model. Not too much works has been done for the flameholding
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characteristics of the tandem dual-cavity. More importantly, the previous researches focused on
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the effects of inlet stagnation temperature, cavity geometry, and equivalence ratio. Few studies
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have been done to investigate the influence of the inlet stagnation pressure. For the experiments in
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this paper, the stagnation temperature of the Mach 2.0 inflow was fixed at 800 K and the
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stagnation pressure was varied from 600 to 900 kPa. These test conditions correspond to different
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dynamic pressure trajectories of flight Mach number 4. The influence of the inlet stagnation
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pressure to the flameholding characteristics was investigated and a mapping of flame stabilization
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locations and combustion modes was draw to reflect the decoupling effects of the inlet stagnation
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pressure.
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2. Experimental Apparatus
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All experiments were conducted using Northwestern Polytechnical University electric
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resistance heating direct connected test system, as shown in Fig. 1. This test system includes: air
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source, heating system, combustor model, fueling system, experimental control system and data
ACCEPTED MANUSCRIPT acquisition system. The air can be heated by the electric resistance heater to the stagnation
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temperature between 600 and 1000 K without vitiated species.
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Fig.1 Direct-connect experimental system of NPU
The combustor model is directly connected to the heater through a Mach 2.0 nozzle. It
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consists of three segments: a constant cross section with a height of 0.030 m, a constant cross
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section with a height of 0.040 m and a 2 deg divergent section. The combustor width is constant
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over the whole length at 0.040 m. A backwind step is generated between section I and section II
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and used to resist high backpressure. The tandem dual cavity is located at section III. The
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upstream cavity has a depth of 0.010m and a length-to-depth ratio of 7.3, while the downstream
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cavity has a depth of 0.015m and a length-to-depth ratio of 11. A schematic of the combustor
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model is shown in Fig. 2.
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Fig 2 Schematic of the scramjet combustor model
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Kerosene fuel with a room temperature was injected upstream of the upstream cavity through
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four spanwise 0.3 mm diameter ports and the distance between the injection ports and the cavity
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leading edge was 0.008 m. In this condition, kerosene was injected into the combustor in liquid
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states and break into small droplets through the small orifices. The ignition of the liquid kerosene
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hydrogen was about 0.25. The high temperature and pressure environment induced by hydrogen
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combustion contains a large number of free radicals which significantly improve the ignition
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performance of kerosene. The time sequences of the injected fuel and spark plug is shown in Fig.
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3. The spark plug turned on firstly and then the pilot hydrogen was injected. The spark energy is
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12 J and works at a frequency of 10Hz. The pilot hydrogen can be ignited easily and it would burn
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alone for 2 seconds. After the spark plug turned off, the kerosene was injected into the
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hydrogen-burned environment. The pilot hydrogen and kerosene was injected simultaneously for 2
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seconds to ensure the successful ignition of kerosene. The kerosene fuel would burn alone in the
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next 2 seconds under the flamholding condition.
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Kerosene Pilot H2
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1
2
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9
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Fig.3 Time sequences for the injected fuel and spark plug
In these experiments, 19 pressure-tap ports along the streamwise direction of the combustor
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model on the upperwall were instrumented with transducers which provide an uncertainty of 0.5%.
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The detected wall pressures were sampled at 1.5 kHz using an IDTS-4516U data acquisition
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instrument. Side window (shown in Fig. 2) in the combustor model allowed live observation of the
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flame through a normal video camera with 30 fps, 640×480 pixels and shutter time 1/30 s.
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3. Results and discussion
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3.1 Analysis of flame stabilization location
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One of the most informative observations of the flame stabilization location is the
ACCEPTED MANUSCRIPT distribution of pressure along the streamwise direction of the combustor. Fig. 4 shows the pressure
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distributions of the kerosene combustion experiments which were conducted in the inlet stagnation
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pressure of 800 kPa. The results show that the pressure rose gradually with the increase of
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equivalence ratio (ER). However, it is noticed that the peak pressure position changed in this
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process. An obvious peak pressure position can be seen in the downstream cavity region in the
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cases of ER=0.42, 0.50 and 0.59. But in the case of ER=0.67, peak pressure was in the upstream
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cavity region and a constant high-pressure region appeared from X/m=0.330 to 0.390. When the
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equivalence ratio increased to 0.75, the constant high-pressure region extended upstream to
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X/m=0.270. It is known that the location of peak pressure is related to main heat release region
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[20]. Fotia et al. [21] found that the peak pressure position was at the location of flame
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stabilization in their experiments. Thus, the upstream movement of the peak pressure indicates
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that transition of the flame stabilization location might occur.
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The standard deviations of wall pressures are also shown in Fig. 4. The variations of the
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standard deviations with the increased equivalence ratio are shown in Fig. 5. It is seen that the
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standard deviations of many locations reached the maximum at ER=0.67 and decreased in the
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higher equivalence ratio case. This indicates that a stronger pressure fluctuation occurred at
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ER=0.67.
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ACCEPTED MANUSCRIPT 0.02
ER=0 ER=0.42 ER=0.50 ER=0.59 ER=0.67 ER=0.75
0.016
P/Pt0
Standard Deviation
0.4
0.2
X/m=0.270 X/m=0.290 X/m=0.310 X/m=0.330 X/m=0.350 X/m=0.370
0.012
0.008
0.004
0
0.2
0.4 X/m
0 0.4
0.6
0.5
0.6
0.7
0.8
ER
Fig 4 Wall pressure distributions for Pt0 of 800 kPa
Fig 5 Variations of standard deviation with equivalence ratio for Pt0 of 800 kPa
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In order to obtain the flame stabilization location, normal video camera was used to observe
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the flowfield in the upstream cavity region through the observing window. If the flame was
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stabilized in the upstream cavity, there would be luminosities captured by the camera. If the flame
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was stabilized in the downstream cavity, there would be no luminosity captured but the pressure
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would still remain a high level. In the case of ER=0.59, the average gray-scale of every image was
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calculated and its time history is shown in Fig. 6. The pressure trace at X/m=0.150 is also shown
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in this figure. When the average gray-scale was greater than zero, it means the flame was appeared
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in the upstream cavity region. When the average gray-scale dropped to zero and the pressure still
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remained a high level, it means the flame was stabilized in the downstream cavity. It can be
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determined that the flame oscillated between the downstream and the upstream cavities in this
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case. This flame oscillation phenomenon would cause the fluctuation of wall pressure. It can be
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seen that the pressure fluctuation was associated with the movement of the flame stabilization
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location in Fig. 6.
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ACCEPTED MANUSCRIPT Pressure-X/m=0.150 Average gray-scale
0.05 Intensity
(P-Pavg)/Pt0
20 0
10
-0.05
0 6
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Fig.6 Time histories of pressure and flame image average gray-scale at ER=0.59 for Pt0 of 800 kPa
The time histories of average gray-scale in the cases of ER=0.50, 0.67 and 0.75 are shown in
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Fig. 7. It is seen that the flame was stabilized in the upstream cavity when pilot hydrogen and
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kerosene was injected simultaneously. In the case of ER=0.50, once the pilot hydrogen closed, the
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combustion heat release decreased and it was insufficient to create a suitable condition for the
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upstream cavity to stabilize the flame. Therefore, the upstream cavity only played the role of
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promoting fuel/air mixing. This result agrees with the analysis of Quick et al. [10], the tandem
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dual cavities was regarded as a upstream mixing cavity coupled with a downstream flameholding
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cavity. After a long distance for the kerosene to atomize and evaporate, the kerosene flame can be
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stabilized in the downstream cavity. When the equivalence ratio increased to 0.59, as has been
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given before, the flame oscillated between the downstream and the upstream cavities. A similar
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phenomenon was observed in the case of ER=0.67, but the time when flame appeared in the
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upstream cavity was increased. The oscillation behaviors of the flame at the cases of ER=0.59 and
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0.67 also explains the increased standard deviations of the pressure in these cases. Finally, when
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the equivalence ratio increased to 0.75, the flame was completely stabilized in the upstream cavity,
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and the flame luminosity was constantly appeared in the images during kerosene combustion. In
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this condition, the heat release of kerosene combustion cause a higher pressure rise and decelerate
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ACCEPTED MANUSCRIPT the main flow, hence the upstream cavity was able to stabilize the flame. It is seen that the
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pressure was maintain at a high level in the region of X/m=0.270 to 0.390, which indicated that
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some kerosene still burned in the downstream cavity even the flame was stabilized in the upstream
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cavity. Pilot H2 +Kerosene
6 4 2 0
5
6
7 t/s
Pilot H2 +Kerosene
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Kerosene
Intensity
Intensity
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8
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4 2 5
Kerosene
6
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8
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ER=0.67
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6
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ER=0.50 Pilot H2 +Kerosene
Kerosene
6
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ER=0.75 Fig 7 Time histories of flame image average gray-scale for Pt0 of 800 kPa 147
3.2 The influence of inlet stagnation pressure
Kerosene combustion experiments were conducted in various inlet stagnation pressures to
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investigate the influence of inlet stagnation pressure on the flameholding characteristics. Four
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stagnation pressures of 600, 700, 800 and 900kPa were tested. The tested equivalence ratios of
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each inlet stagnation pressure are shown in Table 1.
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Table 1 Selected experimental case conditions
Pt0
600kPa 700kPa 800kPa 900kPa
0.57 0.48 0.42 0.42
ER 0.67 0.57 0.50 0.50
0.67 0.59 0.57
0.75 0.67 0.60
0.75 0.67
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In the case of a stagnation pressure of 600kPa, the pressure traces at X/m=0.390 in each
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equivalence ratio are shown in Fig. 8. The pressure dropped to unreacting level in the case of
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ER=0.67, which indicates the flame extinction, when pilot hydrogen and kerosene was still
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injected. The reason for the flame extinction may be that the heat absorbed by the kerosene
ACCEPTED MANUSCRIPT evaporation process increased when the equivalence ratio was increased to 0.67, but the
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combustion heat release was not improved significantly because of low combustion efficiency. For
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this stagnation pressure, further increase of the kerosene equivalence ratio would only make its
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ignition process more difficult.
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When the stagnation pressure was increased to 700 kPa, the pressure traces at X/m=0.390 in
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every equivalence ratio are shown in Fig. 9. Blowout was observed in the case of ER=0.67.
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However, in this case blowout occurred in the kerosene combustion duration after successful
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kerosene ignition. When the equivalence ratio of kerosene was increased to 0.75, the kerosene
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flame was stabilized successful again. The pressure distributions for the inlet stagnation pressure
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of 700 kPa are shown in Fig. 10. The pressure distribution at ER=0.67 is the instantaneous
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pressure before blowout. Observing the pressure distribution and the flame luminosity images in
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the case of ER=0.57 and 0.75, the flame was stabilized in the downstream cavity and the upstream
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cavity, respectively. Hence, Blowout in the case of ER=0.67 is probably related to the oscillation
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behavior of flame. The instantaneous pressure distribution shows the peak pressure located at
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X/m=0.390 which means the flame was stabilized in the downstream cavity at that time. It is
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inferred that the blowout occurred when the flame was propagating upstream.
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Pilot H2 + Kerosene
Pilot H2
0.6
0.8
Kerosene ER=0.57 ER=0.67
0.3 0.2
4
0.5 0.4 0.3 0.2
0.1
2
ER=0.48 ER=0.57 ER=0.67 ER=0.75
0.6
P/Pt0
P/Pt0
0.4
0
Kerosene
0.7
0.5
0
Pilot H2 + Kerosene
Pilot H2
0.1 6
8
10
0
0
2
4
6
8
10
t/s
t/s
Fig 8 Pressure traces at X/m=0.390 for Pt0 of 600 kPa
Fig 9 Pressure traces at X/m=0.390 for Pt0 of 700 kPa
ACCEPTED MANUSCRIPT ER=0 ER=0.48 ER=0.57 ER=0.67-instantaneous ER=0.75
0.6
P/Pt0
0.4
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0.2
0
0
0.2
0.4 X/m
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Fig. 10 Wall pressure distributions for Pt0 of 700 kPa
The results under the inlet stagnation pressure of 800kPa have been already introduced in
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Section 3.1, and a similar phenomenon was observed when the stagnation pressure was further
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increased to 900kPa. The pressure distributions and time histories of flame image average
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gray-scale are shown in Fig. 11 and Fig. 12 respectively. When the equivalence ratio increased
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from 0.42 to 0.67, the pressure distributions and time histories of average gray-scale indicated that
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a shift of the flame stabilization location occurred.
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ER=0 ER=0.42 ER=0.50 ER=0.57 ER=0.60 ER=0.67
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0.2
0.4 X/m
0.6
Fig. 11 Wall pressure distributions for Pt0 of 900 kPa Pilot H2 +Kerosene
6 4 2 0
5
6
7 t/s
ER=0.42
Pilot H2 +Kerosene
8
Kerosene
Intensity
Intensity
8
8
9
Kerosene
6 4 2 0
5
6
7 t/s
ER=0.50
8
9
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5
6
7 t/s
Pilot H2 +Kerosene
10
Kerosene
Intensity
Intensity
10
8
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Kerosene
5
0
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6
7 t/s
8
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ER=0.57 ER=0.60 Fig. 12 Time traces of flame image average gray-scale for Pt0 of 900 kPa Fig. 13 shows the influence of inlet stagnation pressure to flame stabilization characteristics.
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Under the inlet stagnation pressure of 600 kPa, the kerosene equivalence ratio of ignition limit was
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between 0.57 and 0.67. It is difficult to ignite in the larger equivalence ratio of kerosene by the
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current pilot hydrogen equivalence ratio. When the inlet stagnation pressure was increased to 700
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kPa, successful ignition was obtained in the equivalence ratios between 0.48 and 0.75, but the
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flame oscillation cause blowout in the equivalence ratio of 0.67. When the inlet stagnation
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pressure was further increased to 800 and 900 kPa, flame oscillation does not lead to the blowout.
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The flame oscillation behaviors were also affected by the inlet stagnation pressure. With the
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increase of inlet stagnation pressure, the downstream-cavity-stabilized flame began to propagate
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upstream at a lower equivalence ratio and the stable upstream-cavity-stabilized flame was
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obtained at a lower equivalence ratio as well. From these experimental results, it is seen that the
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inlet stagnation pressure has a significant influence on the ignition performance and flameholding
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characteristics.
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ACCEPTED MANUSCRIPT Blowout Upstream cavity Downstream cavity Oscillation between dual-cavity
1000
900
Pt0/kPa
800
600
500 0.3
0.4
0.5
0.6
ER
0.7
0.8
0.9
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3.3 Analysis of influence of the inlet stagnation pressure
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Fig. 13 Flame stabilization location mapping relating inlet stagnation pressure and equivalence ratio
The downstream-cavity-stabilized flame tended to propagate upstream with the increase of
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inlet stagnation pressure. Two possible reasons can be explained to this phenomenon. One is that
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the relative pressure rise at the same equivalence ratio becomes higher with the increase of inlet
195
stagnation pressure. The other is that the local flame speed can be improved with the increase of
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inlet stagnation pressure.
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These reasons were further explained from Fig. 14a, in which the flame stabilization location
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was formulated as a function of inlet stagnation pressure and relative pressure rise. The
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non-dimensional pressure at X/m=0.390 was selected to reflect the relative pressure rise of the
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downstream cavity region. In the experiments, the inlet stagnation temperature was fixed at 800 K.
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Hence, the same relative pressure rise means the same local Mach number and flow velocity, and
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the isoline of Mach number is parallel to the y-axis. It is found that the upstream propagating of
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the downstream-cavity-stabilized flame occurred at the non-dimensional pressures of 0.41 and
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0.43 when the inlet stagnation pressures are 900 kPa and 800 kPa, respectively. It means the
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propagation of the flame to the upstream occurred at a higher local Mach number with the increase
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propagating of the downstream-cavity-stabilized flame did not occur until the non-dimensional
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pressure was increased to 0.44. Blowout occurred at a higher non-dimensional pressure. The
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instantaneous non-dimensional pressure before blowout was shown as the red symbol. These
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evidences show that the flame speed was improved with the increase of inlet stagnation pressure
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and hence the upstream propagation of flame can occur at a higher local Mach number.
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The stable upstream-cavity-stabilized flame was also obtained at a lower equivalence ratio
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with the increase of inlet stagnation pressure. The flame stabilization location relating inlet
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stagnation pressure and relative pressure rise was shown in Fig. 14b. Non-dimensional pressure at
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X/m=0.270 was selected to represent the relative pressure rise in the upstream cavity region. It can
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be seen that the non-dimensional pressure at the boundary was about 0.42 at the inlet stagnation
217
pressure of 900 kPa and it increased to 0.45 with the inlet stagnation increased to 800 kPa. Hence,
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flame can stabilize in the upstream cavity at a higher local Mach number in the condition of a
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higher inlet stagnation pressure.
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1000
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900
Ma=1
1000
Oscillation between dual-cavity
Downstream cavity
Ma=0.9
Oscillation between dual-cavity
Upstream cavity
900 Ma=1
Ma=0.8
Ma=0.9
Ma=0.8
Pt0/kPa
800
Pt0/kPa
800
700
700
600
600
Scram mode Ram mode 500 0.25
0.3
0.35
0.4
PX/m=0.390/Pt0
a)
0.45
0.5
500 0.35
0.4
0.45
0.5
0.55
PX/m=0.270/Pt0
b) Fig. 14 Flame stabilization location and combustion mode mapping relating inlet stagnation pressure and relative pressure rise
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4. Conclusions
In this paper, a tandem dual-cavity was chosen as the flameholder for the kerosene-fueled
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scramjet combustor model. The stagnation temperature of the Mach 2.0 inflow was fixed at 800 K
223
and the stagnation pressure was varied from 600 to 900 kPa which are corresponding to different
224
dynamic pressure trajectories in flight Mach number 4. The influence of inlet stagnation pressure
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to the flame stabilization characteristics was investigated.
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The wall pressure distributions show that the peak pressure position moved upstream with
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the increased equivalence ratio. The standard deviations of pressure indicate that the flowfield had
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an obvious oscillation behavior at intermediate range equivalence ratio. Combined with the flame
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luminosity images, it is found that the flame was stabilized in the downstream cavity at lower
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equivalence ratios and it was stabilized in the upstream cavity at higher equivalence ratios. For an
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intermediate range of equivalence ratio, the flame oscillated between the dual cavities.
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The inlet stagnation pressure had a significant influence to the ignition performance and
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flameholding characteristics of the tandem dual-cavity. The ignition performance was improved
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with increased inlet stagnation pressure. The oscillation behavior tends to occur in the case of the
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higher inlet stagnation pressures. With the increase of inlet stagnation pressure, the
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downstream-cavity-stabilized flame began to propagate upstream at a lower equivalence ratio and
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the stable upstream-cavity-stabilized flame was obtained at a lower equivalence ratio as well.
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A mapping of flame stabilization locations was obtained to reflect the influences of inlet
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stagnation pressure. The inlet stagnation pressure was considered to affect the flameholding
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characteristics in two aspects. One aspect is that the same non-dimensional pressure level can be
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obtained at lower equivalence ratio in the cases of higher inlet stagnation pressures. The other
ACCEPTED MANUSCRIPT aspect is that the increased inlet stagnation pressure improves the flame speed and hence the
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upstream transition of flame stabilization location can occur in a higher local Mach number.
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Reference
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[1] Fry, R. S., “A Century of Ramjet Propulsion Technology Evolution,” Journal of Propulsion and Power, Vol. 20, No. 1, 2004, pp. 27-58. [2] Denman, Z. J., Wheatley, V., Smart, M. K., and Veeraragavan, A., “Supersonic Combustion of Hydrocarbons in a Shape-Transitioning Hypersonic Engine,” Proceedings of the Combustion Institute, Vol. 36, No. 2, 2016, pp. 2883-2891. [3] Dagaut, P., and Cathonnet, M., “The ignition, oxidation, and combustion of kerosene: A review of experimental and kinetic modeling,” Progress in Energy and Combustion Science, Vol. 32, No. 1, 2006, pp. 48-92. [4] Li, X. P., Liu, W. D., Pan Y., Yang, L. C., An, B., and Zhu, J. J., “Characterization of Kerosene Distribution around the Ignition Cavity in a Scramjet Combustor,” Acta Astronautica, Vol. 134, 2017, pp. 11-16. [5] Le, J. L., Yang, S. H., Wang, X. Y., and Li H. B., “Analysis and Correlation of Flame Stability Limits in Supersonic Flow with Cavity Flameholder,” 18th AIAA/3AF International Space Planes and Hypersonic Systems and Technologies Conference, AIAA Paper 2012-5948, September 2012. [6] Sun, M. B., Zhong, Z., Liang, J. H., and Wang, H. B., “Experimental Investigation on Combustion Performance of Cavity-Strut Injection of Supercritical Kerosene in Supersonic Model Combust[6] Sun, M. B., Zhong, Z., Liang, J. H., and Wang, H. B., “Experimental Investigation on Combustion Performance of Cavity-Strut Injection of Supercritical Kerosene in Supersonic Model Combustor,” Acta Astronautica, Vol. 127, 2016, pp. 112-119. [7] Yu, G., Li, J. G., Chang, X. Y., Chen, L. H.,and Sung, C. J., “Fuel Injection and Flame Stabilization in a Liquid-Kerosene-Fueled Supersonic Combustor,” Journal of Propulsion and Power, Vol. 19, No. 5, 2003, pp. 885-893 [8] Barnes, F. W., and Segal, C., “Cavity-based Flameholding for Chemically-reacting Supersonic Flows,” Progress in Aerospace Sciences, Vol. 76, 2015, pp. 24-41. [9] Situ, M., Wang, C., Zhuang, F., “Investigation of Supersonic Combustion of Kerosene Jets with Hot Gas Piloted Energy and Dual-Cavity,” 40th AIAA Aerospace Sciences Meeting & Exhibit, AIAA Paper 2002-0804, January 2002. [10] Quick, A., King, P., Gruber, M., Carter, C., Hsu, K-Y., “Upstream Mixing Cavity Coupled with a Downstream Flameholding Cavity Behavior in Supersonic Flow,” 41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, AIAA Paper 2005-3709, July 2005. [11] Smirnov, N. N., Nikitin, V. F., Shurehdely, S. A., “Transient regimes of wave propagation in metastable systems,” Combustion, explosion and shock waves, Vol. 44, No. 5, 2008, pp. 25-37. [12] Smirnov, N.N., Nikitin, V. F., Phylippov Y. G., “Deflagration to detonation transition in gases in tubes with cavities,” Journal of Engineering Physics and Thermophysics, Vol. 83, No. 6, 2010, pp. 1287-1316.
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[13] Smirnov, N. N., Nikitin, V. F., Shurekhdeli S. A., “Investigation of Self-Sustaining Waves in Metastable Systems: Deflagration-to-Detonation Transition,” Journal of Propulsion and Power, Vol. 25, No. 3, 2009, pp. 593-608. [14] Smirnov, N. N., Tyurnikov, M., “Experimental investigation of deflagration to detonation transition in hydrocarbon-air gaseous mixtures. Combustion and Flame,” Vol. 100, No. 4, 1995, pp. 661-668. [15] Pan, Y., Liu, W. D., Wang, Z. G., “Cavities installation schemes affect on the scramjet ignition,” 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, AIAA Paper 2007-5400, July 2007. [16] Zhang, T. C., Wang, J., Fan, X. J., Zhang, P., “Combustion of Vaporized Kerosene in Supersonic Model Combustors with Dislocated Dual Cavities,” Journal of Propulsion and Power, Vol. 30, No. 5, 2014, pp. 1152-1160. [17] Wang, Z.P., Li, F., Gu, H.B., Yu, X.L., Zhang, X.Y., “Experimental study on the effect of combustor configuration on the performance of dual-mode combustor” Aerospace Science and Technology, Vol. 42, 2015, pp. 169-175 [18] Micka, D. J., and Driscoll, J. F., “Combustion Characteristics of a Dual-Mode Scramjet Combustor with Cavity Flameholder,” Proceedings of the Combustion Institute, Vol. 32, No. 2, 2009, pp. 2397–2404. [19] Wang, H. B., Wang Z. G., Sun, M. B., and Wu, H. Y. “Combustion modes of hydrogen jet combustion in a cavity-based supersonic combustor,” International Journal of Hydrogen Energy, Vol. 38, , No. 27, 2013, pp. 12078-12089. [20] Heiser, W. H., and Pratt, D. T., Hypersonic Airbreathing Propulsion, AIAA Education Series, AIAA, Washington, D.C., 1994, Chap. 6. [21] Fotia, M. L., and Driscoll, J. F., “Ram-Scram Transition and Flame/Shock-Train Interactions in a Model Scramjet Experiment,” Journal of Propulsion and Power, Vol. 29, No. 1, 2013, pp. 261–273.
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1. Kerosene flame stabilization location of a dual-cavity flameholder is determined. 2. Effect of inlet stagnation pressure to flameholding characteristics is analyzed. 3. A mapping of flame locations is obtained to reflect the transition boundary.
S0094-5765(17)30981-5
DOI:
10.1016/j.actaastro.2017.08.014
Reference:
AA 6433
To appear in:
Acta Astronautica
Received Date: 17 July 2017 Revised Date:
6 August 2017
Accepted Date: 10 August 2017
Please cite this article as: Y.-h. Wang, W.-y. Song, D.-y. Shi, Investigation of flameholding characteristics in a kerosene-fueled scramjet combustor with tandem dual-cavity, Acta Astronautica (2017), doi: 10.1016/j.actaastro.2017.08.014. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Investigation of Flameholding Characteristics in a
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Kerosene-fueled Scramjet Combustor with Tandem
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Dual-Cavity
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Wang Yu-hang, Song Wen-yan, Shi De-yong
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Northwestern Polytechnical University, 710072 Xi’an, People's Republic of China
The flameholding characteristics in a kerosene-fueled scramjet combustor with a tandem
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dual-cavity were investigated experimentally under various inlet stagnation pressure conditions.
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Flame stabilization locations were judged by the pressure distributions and flame luminescence
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images. The results show that at lower and higher equivalence ratios, the flame was stabilized in
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the downstream and upstream cavities, respectively. While at intermediate range of equivalence
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ratio the flame was oscillating between the two cavities. The inlet stagnation pressure has a
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significant impact on the flameholding characteristics by affecting the relative pressure rise and
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the flame speed. The transition of flame stabilization location can occur in a higher local flow
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Mach number in the case of the higher inlet stagnation pressure.
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1. Introduction
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Interest in the flameholding of the supersonic combustor in scramjet has been persistent since
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1950s and it became an active area of research around the world [1]. Compared with hydrogen
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fuel, liquid hydrocarbon fuel has a higher energy density and favorable handling characteristics [2].
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However, their additional atomization, evaporation processes and longer ignition delay time [3]
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pose a significant challenge in flameholding due to the extremely short flow residence times.
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Hence, more attentions are given to the flameholding characteristic of hydrocarbon fuel in
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scramjet combustor [4-7]. Wall-mounted cavities have been considered as preferred flameholding devices since they
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can form large recirculation zones and avoid higher stagnation pressure loss caused by intrusive
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structures [8]. Many studies [7, 9-10] indicated that a combustor with a tandem dual-cavity has
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advantage of mixing, ignition and combustion performance. Smirnov et al. [11-14] analyzed the
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role of cavities in flameholding in supersonic flows. Therefore, the tandem dual-cavity was often
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used as a flameholder for liquid hydrocarbon fuel in the previous investigations [5, 9, 15-17].
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Many studies analyzed the possible influence factors on the flame stabilization of scramjet
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combustor using gaseous fuel. Micka et al. [18] investigated the influence of inlet stagnation
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temperatures to the combustion characteristics of a dual-mode scramjet combustor. They found
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two distinct combustion stabilization locations, the jet-wake stabilized combustion is initiated
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upstream of the cavity leading edge at higher air stagnation temperatures and the cavity stabilized
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combustion is anchored within the cavity shear layer at lower air stagnation temperatures. For an
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intermediate range of stagnation temperature, the reaction zone oscillated between the jet-wake
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and cavity stabilization locations. Wang et al. [19] studied the combustion characteristics in a
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supersonic combustor with several cavity geometries, fuel injection ports and fueling conditions. Three
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combustion modes were observed: cavity assisted jet-wake stabilized combustion, cavity shear layer
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stabilized combustion and combined cavity shear-layer/recirculation stabilized combustion. These
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combustion modes can be shifted by changing the cavity geometry, fuel injection ports or equivalence
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ratio.
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However, the flameholding characteristics of liquid hydrocarbon fuels will be different. Li et
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al. [4] conducted combustion experiment with kerosene fuel in a dual-cavity scramjet combustor.
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flame. The driving force of the flame stabilization transition is the high pressure environment. Le
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et al. [5] found two kinds of flame stabilizing modes of liquid RP-3 fuel, i.e., the
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shear-layer-stabilized flame and the recirculation-zone-stabilized flame in the upstream injection
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of cavity combustion experiment. Their numerical simulation results showed that the local
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equivalence ratio of the shear layer is a key factor in determining the flame stability.
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In this paper, a tandem dual-cavity was chosen as the flameholder for the kerosene-fueled
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scramjet combustor model. Not too much works has been done for the flameholding
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characteristics of the tandem dual-cavity. More importantly, the previous researches focused on
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the effects of inlet stagnation temperature, cavity geometry, and equivalence ratio. Few studies
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have been done to investigate the influence of the inlet stagnation pressure. For the experiments in
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this paper, the stagnation temperature of the Mach 2.0 inflow was fixed at 800 K and the
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stagnation pressure was varied from 600 to 900 kPa. These test conditions correspond to different
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dynamic pressure trajectories of flight Mach number 4. The influence of the inlet stagnation
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pressure to the flameholding characteristics was investigated and a mapping of flame stabilization
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locations and combustion modes was draw to reflect the decoupling effects of the inlet stagnation
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pressure.
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2. Experimental Apparatus
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All experiments were conducted using Northwestern Polytechnical University electric
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resistance heating direct connected test system, as shown in Fig. 1. This test system includes: air
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source, heating system, combustor model, fueling system, experimental control system and data
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temperature between 600 and 1000 K without vitiated species.
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Fig.1 Direct-connect experimental system of NPU
The combustor model is directly connected to the heater through a Mach 2.0 nozzle. It
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consists of three segments: a constant cross section with a height of 0.030 m, a constant cross
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section with a height of 0.040 m and a 2 deg divergent section. The combustor width is constant
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over the whole length at 0.040 m. A backwind step is generated between section I and section II
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and used to resist high backpressure. The tandem dual cavity is located at section III. The
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upstream cavity has a depth of 0.010m and a length-to-depth ratio of 7.3, while the downstream
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cavity has a depth of 0.015m and a length-to-depth ratio of 11. A schematic of the combustor
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model is shown in Fig. 2.
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Fig 2 Schematic of the scramjet combustor model
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Kerosene fuel with a room temperature was injected upstream of the upstream cavity through
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four spanwise 0.3 mm diameter ports and the distance between the injection ports and the cavity
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leading edge was 0.008 m. In this condition, kerosene was injected into the combustor in liquid
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states and break into small droplets through the small orifices. The ignition of the liquid kerosene
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hydrogen was about 0.25. The high temperature and pressure environment induced by hydrogen
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combustion contains a large number of free radicals which significantly improve the ignition
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performance of kerosene. The time sequences of the injected fuel and spark plug is shown in Fig.
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3. The spark plug turned on firstly and then the pilot hydrogen was injected. The spark energy is
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12 J and works at a frequency of 10Hz. The pilot hydrogen can be ignited easily and it would burn
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alone for 2 seconds. After the spark plug turned off, the kerosene was injected into the
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hydrogen-burned environment. The pilot hydrogen and kerosene was injected simultaneously for 2
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seconds to ensure the successful ignition of kerosene. The kerosene fuel would burn alone in the
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next 2 seconds under the flamholding condition.
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Kerosene Pilot H2
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Fig.3 Time sequences for the injected fuel and spark plug
In these experiments, 19 pressure-tap ports along the streamwise direction of the combustor
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model on the upperwall were instrumented with transducers which provide an uncertainty of 0.5%.
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The detected wall pressures were sampled at 1.5 kHz using an IDTS-4516U data acquisition
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instrument. Side window (shown in Fig. 2) in the combustor model allowed live observation of the
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flame through a normal video camera with 30 fps, 640×480 pixels and shutter time 1/30 s.
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3. Results and discussion
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3.1 Analysis of flame stabilization location
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One of the most informative observations of the flame stabilization location is the
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distributions of the kerosene combustion experiments which were conducted in the inlet stagnation
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pressure of 800 kPa. The results show that the pressure rose gradually with the increase of
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equivalence ratio (ER). However, it is noticed that the peak pressure position changed in this
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process. An obvious peak pressure position can be seen in the downstream cavity region in the
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cases of ER=0.42, 0.50 and 0.59. But in the case of ER=0.67, peak pressure was in the upstream
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cavity region and a constant high-pressure region appeared from X/m=0.330 to 0.390. When the
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equivalence ratio increased to 0.75, the constant high-pressure region extended upstream to
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X/m=0.270. It is known that the location of peak pressure is related to main heat release region
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[20]. Fotia et al. [21] found that the peak pressure position was at the location of flame
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stabilization in their experiments. Thus, the upstream movement of the peak pressure indicates
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that transition of the flame stabilization location might occur.
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The standard deviations of wall pressures are also shown in Fig. 4. The variations of the
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standard deviations with the increased equivalence ratio are shown in Fig. 5. It is seen that the
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standard deviations of many locations reached the maximum at ER=0.67 and decreased in the
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higher equivalence ratio case. This indicates that a stronger pressure fluctuation occurred at
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ER=0.67.
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ER=0 ER=0.42 ER=0.50 ER=0.59 ER=0.67 ER=0.75
0.016
P/Pt0
Standard Deviation
0.4
0.2
X/m=0.270 X/m=0.290 X/m=0.310 X/m=0.330 X/m=0.350 X/m=0.370
0.012
0.008
0.004
0
0.2
0.4 X/m
0 0.4
0.6
0.5
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0.7
0.8
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Fig 4 Wall pressure distributions for Pt0 of 800 kPa
Fig 5 Variations of standard deviation with equivalence ratio for Pt0 of 800 kPa
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In order to obtain the flame stabilization location, normal video camera was used to observe
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the flowfield in the upstream cavity region through the observing window. If the flame was
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stabilized in the upstream cavity, there would be luminosities captured by the camera. If the flame
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was stabilized in the downstream cavity, there would be no luminosity captured but the pressure
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would still remain a high level. In the case of ER=0.59, the average gray-scale of every image was
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calculated and its time history is shown in Fig. 6. The pressure trace at X/m=0.150 is also shown
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in this figure. When the average gray-scale was greater than zero, it means the flame was appeared
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in the upstream cavity region. When the average gray-scale dropped to zero and the pressure still
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remained a high level, it means the flame was stabilized in the downstream cavity. It can be
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determined that the flame oscillated between the downstream and the upstream cavities in this
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case. This flame oscillation phenomenon would cause the fluctuation of wall pressure. It can be
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seen that the pressure fluctuation was associated with the movement of the flame stabilization
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location in Fig. 6.
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0.05 Intensity
(P-Pavg)/Pt0
20 0
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-0.05
0 6
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Fig.6 Time histories of pressure and flame image average gray-scale at ER=0.59 for Pt0 of 800 kPa
The time histories of average gray-scale in the cases of ER=0.50, 0.67 and 0.75 are shown in
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Fig. 7. It is seen that the flame was stabilized in the upstream cavity when pilot hydrogen and
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kerosene was injected simultaneously. In the case of ER=0.50, once the pilot hydrogen closed, the
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combustion heat release decreased and it was insufficient to create a suitable condition for the
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upstream cavity to stabilize the flame. Therefore, the upstream cavity only played the role of
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promoting fuel/air mixing. This result agrees with the analysis of Quick et al. [10], the tandem
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dual cavities was regarded as a upstream mixing cavity coupled with a downstream flameholding
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cavity. After a long distance for the kerosene to atomize and evaporate, the kerosene flame can be
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stabilized in the downstream cavity. When the equivalence ratio increased to 0.59, as has been
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given before, the flame oscillated between the downstream and the upstream cavities. A similar
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phenomenon was observed in the case of ER=0.67, but the time when flame appeared in the
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upstream cavity was increased. The oscillation behaviors of the flame at the cases of ER=0.59 and
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0.67 also explains the increased standard deviations of the pressure in these cases. Finally, when
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the equivalence ratio increased to 0.75, the flame was completely stabilized in the upstream cavity,
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and the flame luminosity was constantly appeared in the images during kerosene combustion. In
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this condition, the heat release of kerosene combustion cause a higher pressure rise and decelerate
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ACCEPTED MANUSCRIPT the main flow, hence the upstream cavity was able to stabilize the flame. It is seen that the
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pressure was maintain at a high level in the region of X/m=0.270 to 0.390, which indicated that
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some kerosene still burned in the downstream cavity even the flame was stabilized in the upstream
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cavity. Pilot H2 +Kerosene
6 4 2 0
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Pilot H2 +Kerosene
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Kerosene
Intensity
Intensity
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4 2 5
Kerosene
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Kerosene
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ER=0.75 Fig 7 Time histories of flame image average gray-scale for Pt0 of 800 kPa 147
3.2 The influence of inlet stagnation pressure
Kerosene combustion experiments were conducted in various inlet stagnation pressures to
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investigate the influence of inlet stagnation pressure on the flameholding characteristics. Four
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stagnation pressures of 600, 700, 800 and 900kPa were tested. The tested equivalence ratios of
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each inlet stagnation pressure are shown in Table 1.
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Table 1 Selected experimental case conditions
Pt0
600kPa 700kPa 800kPa 900kPa
0.57 0.48 0.42 0.42
ER 0.67 0.57 0.50 0.50
0.67 0.59 0.57
0.75 0.67 0.60
0.75 0.67
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In the case of a stagnation pressure of 600kPa, the pressure traces at X/m=0.390 in each
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equivalence ratio are shown in Fig. 8. The pressure dropped to unreacting level in the case of
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ER=0.67, which indicates the flame extinction, when pilot hydrogen and kerosene was still
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injected. The reason for the flame extinction may be that the heat absorbed by the kerosene
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combustion heat release was not improved significantly because of low combustion efficiency. For
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this stagnation pressure, further increase of the kerosene equivalence ratio would only make its
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ignition process more difficult.
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When the stagnation pressure was increased to 700 kPa, the pressure traces at X/m=0.390 in
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every equivalence ratio are shown in Fig. 9. Blowout was observed in the case of ER=0.67.
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However, in this case blowout occurred in the kerosene combustion duration after successful
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kerosene ignition. When the equivalence ratio of kerosene was increased to 0.75, the kerosene
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flame was stabilized successful again. The pressure distributions for the inlet stagnation pressure
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of 700 kPa are shown in Fig. 10. The pressure distribution at ER=0.67 is the instantaneous
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pressure before blowout. Observing the pressure distribution and the flame luminosity images in
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the case of ER=0.57 and 0.75, the flame was stabilized in the downstream cavity and the upstream
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cavity, respectively. Hence, Blowout in the case of ER=0.67 is probably related to the oscillation
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behavior of flame. The instantaneous pressure distribution shows the peak pressure located at
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X/m=0.390 which means the flame was stabilized in the downstream cavity at that time. It is
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inferred that the blowout occurred when the flame was propagating upstream.
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Pilot H2 + Kerosene
Pilot H2
0.6
0.8
Kerosene ER=0.57 ER=0.67
0.3 0.2
4
0.5 0.4 0.3 0.2
0.1
2
ER=0.48 ER=0.57 ER=0.67 ER=0.75
0.6
P/Pt0
P/Pt0
0.4
0
Kerosene
0.7
0.5
0
Pilot H2 + Kerosene
Pilot H2
0.1 6
8
10
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Fig 8 Pressure traces at X/m=0.390 for Pt0 of 600 kPa
Fig 9 Pressure traces at X/m=0.390 for Pt0 of 700 kPa
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0.6
P/Pt0
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Fig. 10 Wall pressure distributions for Pt0 of 700 kPa
The results under the inlet stagnation pressure of 800kPa have been already introduced in
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Section 3.1, and a similar phenomenon was observed when the stagnation pressure was further
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increased to 900kPa. The pressure distributions and time histories of flame image average
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gray-scale are shown in Fig. 11 and Fig. 12 respectively. When the equivalence ratio increased
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from 0.42 to 0.67, the pressure distributions and time histories of average gray-scale indicated that
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a shift of the flame stabilization location occurred.
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Fig. 11 Wall pressure distributions for Pt0 of 900 kPa Pilot H2 +Kerosene
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ER=0.42
Pilot H2 +Kerosene
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Intensity
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Pilot H2 +Kerosene
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Intensity
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ER=0.57 ER=0.60 Fig. 12 Time traces of flame image average gray-scale for Pt0 of 900 kPa Fig. 13 shows the influence of inlet stagnation pressure to flame stabilization characteristics.
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Under the inlet stagnation pressure of 600 kPa, the kerosene equivalence ratio of ignition limit was
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between 0.57 and 0.67. It is difficult to ignite in the larger equivalence ratio of kerosene by the
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current pilot hydrogen equivalence ratio. When the inlet stagnation pressure was increased to 700
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kPa, successful ignition was obtained in the equivalence ratios between 0.48 and 0.75, but the
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flame oscillation cause blowout in the equivalence ratio of 0.67. When the inlet stagnation
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pressure was further increased to 800 and 900 kPa, flame oscillation does not lead to the blowout.
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The flame oscillation behaviors were also affected by the inlet stagnation pressure. With the
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increase of inlet stagnation pressure, the downstream-cavity-stabilized flame began to propagate
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upstream at a lower equivalence ratio and the stable upstream-cavity-stabilized flame was
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obtained at a lower equivalence ratio as well. From these experimental results, it is seen that the
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inlet stagnation pressure has a significant influence on the ignition performance and flameholding
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characteristics.
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1000
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Pt0/kPa
800
600
500 0.3
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3.3 Analysis of influence of the inlet stagnation pressure
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Fig. 13 Flame stabilization location mapping relating inlet stagnation pressure and equivalence ratio
The downstream-cavity-stabilized flame tended to propagate upstream with the increase of
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inlet stagnation pressure. Two possible reasons can be explained to this phenomenon. One is that
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the relative pressure rise at the same equivalence ratio becomes higher with the increase of inlet
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stagnation pressure. The other is that the local flame speed can be improved with the increase of
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inlet stagnation pressure.
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These reasons were further explained from Fig. 14a, in which the flame stabilization location
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was formulated as a function of inlet stagnation pressure and relative pressure rise. The
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non-dimensional pressure at X/m=0.390 was selected to reflect the relative pressure rise of the
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downstream cavity region. In the experiments, the inlet stagnation temperature was fixed at 800 K.
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Hence, the same relative pressure rise means the same local Mach number and flow velocity, and
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the isoline of Mach number is parallel to the y-axis. It is found that the upstream propagating of
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the downstream-cavity-stabilized flame occurred at the non-dimensional pressures of 0.41 and
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0.43 when the inlet stagnation pressures are 900 kPa and 800 kPa, respectively. It means the
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propagation of the flame to the upstream occurred at a higher local Mach number with the increase
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propagating of the downstream-cavity-stabilized flame did not occur until the non-dimensional
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pressure was increased to 0.44. Blowout occurred at a higher non-dimensional pressure. The
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instantaneous non-dimensional pressure before blowout was shown as the red symbol. These
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evidences show that the flame speed was improved with the increase of inlet stagnation pressure
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and hence the upstream propagation of flame can occur at a higher local Mach number.
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The stable upstream-cavity-stabilized flame was also obtained at a lower equivalence ratio
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with the increase of inlet stagnation pressure. The flame stabilization location relating inlet
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stagnation pressure and relative pressure rise was shown in Fig. 14b. Non-dimensional pressure at
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X/m=0.270 was selected to represent the relative pressure rise in the upstream cavity region. It can
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be seen that the non-dimensional pressure at the boundary was about 0.42 at the inlet stagnation
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pressure of 900 kPa and it increased to 0.45 with the inlet stagnation increased to 800 kPa. Hence,
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flame can stabilize in the upstream cavity at a higher local Mach number in the condition of a
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higher inlet stagnation pressure.
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1000
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900
Ma=1
1000
Oscillation between dual-cavity
Downstream cavity
Ma=0.9
Oscillation between dual-cavity
Upstream cavity
900 Ma=1
Ma=0.8
Ma=0.9
Ma=0.8
Pt0/kPa
800
Pt0/kPa
800
700
700
600
600
Scram mode Ram mode 500 0.25
0.3
0.35
0.4
PX/m=0.390/Pt0
a)
0.45
0.5
500 0.35
0.4
0.45
0.5
0.55
PX/m=0.270/Pt0
b) Fig. 14 Flame stabilization location and combustion mode mapping relating inlet stagnation pressure and relative pressure rise
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4. Conclusions
In this paper, a tandem dual-cavity was chosen as the flameholder for the kerosene-fueled
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scramjet combustor model. The stagnation temperature of the Mach 2.0 inflow was fixed at 800 K
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and the stagnation pressure was varied from 600 to 900 kPa which are corresponding to different
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dynamic pressure trajectories in flight Mach number 4. The influence of inlet stagnation pressure
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to the flame stabilization characteristics was investigated.
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The wall pressure distributions show that the peak pressure position moved upstream with
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the increased equivalence ratio. The standard deviations of pressure indicate that the flowfield had
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an obvious oscillation behavior at intermediate range equivalence ratio. Combined with the flame
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luminosity images, it is found that the flame was stabilized in the downstream cavity at lower
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equivalence ratios and it was stabilized in the upstream cavity at higher equivalence ratios. For an
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intermediate range of equivalence ratio, the flame oscillated between the dual cavities.
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The inlet stagnation pressure had a significant influence to the ignition performance and
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flameholding characteristics of the tandem dual-cavity. The ignition performance was improved
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with increased inlet stagnation pressure. The oscillation behavior tends to occur in the case of the
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higher inlet stagnation pressures. With the increase of inlet stagnation pressure, the
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downstream-cavity-stabilized flame began to propagate upstream at a lower equivalence ratio and
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the stable upstream-cavity-stabilized flame was obtained at a lower equivalence ratio as well.
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A mapping of flame stabilization locations was obtained to reflect the influences of inlet
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stagnation pressure. The inlet stagnation pressure was considered to affect the flameholding
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characteristics in two aspects. One aspect is that the same non-dimensional pressure level can be
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obtained at lower equivalence ratio in the cases of higher inlet stagnation pressures. The other
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upstream transition of flame stabilization location can occur in a higher local Mach number.
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Reference
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[13] Smirnov, N. N., Nikitin, V. F., Shurekhdeli S. A., “Investigation of Self-Sustaining Waves in Metastable Systems: Deflagration-to-Detonation Transition,” Journal of Propulsion and Power, Vol. 25, No. 3, 2009, pp. 593-608. [14] Smirnov, N. N., Tyurnikov, M., “Experimental investigation of deflagration to detonation transition in hydrocarbon-air gaseous mixtures. Combustion and Flame,” Vol. 100, No. 4, 1995, pp. 661-668. [15] Pan, Y., Liu, W. D., Wang, Z. G., “Cavities installation schemes affect on the scramjet ignition,” 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, AIAA Paper 2007-5400, July 2007. [16] Zhang, T. C., Wang, J., Fan, X. J., Zhang, P., “Combustion of Vaporized Kerosene in Supersonic Model Combustors with Dislocated Dual Cavities,” Journal of Propulsion and Power, Vol. 30, No. 5, 2014, pp. 1152-1160. [17] Wang, Z.P., Li, F., Gu, H.B., Yu, X.L., Zhang, X.Y., “Experimental study on the effect of combustor configuration on the performance of dual-mode combustor” Aerospace Science and Technology, Vol. 42, 2015, pp. 169-175 [18] Micka, D. J., and Driscoll, J. F., “Combustion Characteristics of a Dual-Mode Scramjet Combustor with Cavity Flameholder,” Proceedings of the Combustion Institute, Vol. 32, No. 2, 2009, pp. 2397–2404. [19] Wang, H. B., Wang Z. G., Sun, M. B., and Wu, H. Y. “Combustion modes of hydrogen jet combustion in a cavity-based supersonic combustor,” International Journal of Hydrogen Energy, Vol. 38, , No. 27, 2013, pp. 12078-12089. [20] Heiser, W. H., and Pratt, D. T., Hypersonic Airbreathing Propulsion, AIAA Education Series, AIAA, Washington, D.C., 1994, Chap. 6. [21] Fotia, M. L., and Driscoll, J. F., “Ram-Scram Transition and Flame/Shock-Train Interactions in a Model Scramjet Experiment,” Journal of Propulsion and Power, Vol. 29, No. 1, 2013, pp. 261–273.
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1. Kerosene flame stabilization location of a dual-cavity flameholder is determined. 2. Effect of inlet stagnation pressure to flameholding characteristics is analyzed. 3. A mapping of flame locations is obtained to reflect the transition boundary.