Jinkwan Song

Effects of Orifice Internal Flow on Liquid Jets in Subsonic Crossflows

The effects of orifice internal flow on the spray plume characteristics of the liquid jet injected perpendicularly into subsonic crossflows were investigated experimentally. The internal flows are classified into threemodes: steady flow, cavitationflow, andhydraulic flipflow.Thesemodes aremainly determined by the ratio of the injector lengthL to the injector diameter d and by the shape of the orifice internal edge. To study the spray plume characteristics corresponding to each mode, three measurement techniques were applied: mass-flow-rate measurement, direct photography of internal injector orifices, and planar liquid laser-induced fluorescence. From the results of themassflow-rate measurement and direct photography, each mode of orifice internal flow without air crossflow was classified through the discharge coefficient patterns and internal–external flow shape. Steady flow shows no significant change on the flow pattern, and the discharge coefficient increases as the pressure differential increases. However, unsteady flows, including cavitation and hydraulic flip, have strong bubble envelopes due to a sudden reduction of flow passage, and these phenomena affect the discharge coefficient patterns. The penetrations and the width of the liquid spray plume were analyzed using the images obtained from the planar liquid laser-induced fluorescence method, and they were compared with the previous results. The penetrations and width were formulated with the liquid–air momentum flux ratio q and the ratio of the distance from the injector exit to the injector diameter x=d. It is found that the spray plume trajectory is determined by the liquid column diameter of the orifice exit and the liquid–air momentum flux ratio using the jet velocity at the orifice exit. It is also found that it is better to use the nominal parameters in the case of cavitationflow, and it is better to use the effective parameters in the case of hydraulic flip flow.

Liquid Jets in Subsonic Air Crossflow at Elevated Pressure

The breakup, penetration, droplet size and size distribution of a Jet A-1 fuel in air crossflow has been investigated with focus given to the impact of surrounding air pressure. Data has been collected by Particle Doppler Phased Analyzer (PDPA), Mie-Scattering with high speed photography augmented by laser sheet, and Mie-Scattering with ICCD Camera augmented by nano-pulse lamp. Nozzle orifice diameter, do, was 0.508 mm and nozzle orifice length to diameter ratio, lo/do, was 5.5. Air crossflow velocities ranged from 29.57 to 137.15 m/s, air pressures from 2.07 to 9.65 bar and temperature held constant at 294.26 K. Fuel flow was governed to provide a range of fuel/air momentum flux ratio q from 5 to 25 and Weber number from 250 to 1000. From the results, adjusted correlation of the mean drop size has been suggested using drop size data measured by PDPA as follows; Display Formula(1)D0D32=0.267Wea0.44q0.08ρlρa0.30μlμa-0.16 This correlation agrees well and shows roles of aerodynamic Weber number, Wea, momentum flux ratio, q, and density ratio, ρl/ρa. Change of the breakup regime map with respect with surrounding air pressure has been observed and revealed that the boundary between each breakup modes can be predicted by a transformed correlation induced from above correlation. In addition, the spray trajectory for the maximum Mie-scattering intensity at each axial location downstream of injector was extracted from averaged Mie-scattering images. From these results correlations with the relevant parameters including q, x/do, density ratio, viscosity ratio, and Weber number are made over a range of conditions. According to spray trajectory at the maximum Mie-scattering intensity, the effect of surrounding air pressure becomes more important in the farfield. On the other hand, effect of aerodynamic Weber number is more important in the nearfield.Copyright

An Experimental Study on the Flame Dynamics with V- Gutter Type Flameholder in the Model Combustor

The flame dynamics and the longitudinal combustion instability in the duct combustor with the v-gutter type flameholder were investigated experimentally. The combustor has a long duct shape with a cross section area of 40 x 40 mm. The v-gutter type flameholder is mounted at the side wall of combustor. CNG were used as fuel, and the fuel was injected transversely into air crossflow. In order to study flame characteristics related to longitudinal combustion instability, various measurement techniques were applied: direct-photography, dynamic pressure measurement, Schlieren technique, CH and OH radical chemiluminescence and article image velocimetry (PIV). First, it is observed that the unstable flame shows a very different shape compared with a typical flame generated behind the flameholder. This longitudinal combustion instability is affected by the air mass flow rate, the flameholder geometry and nozzle open ratio. Flame dynamics near the flameholder was observed when the longitudinal combustion instability occurs in the duct combustor having a bluff-body flameholder. All images obtained from various imaging techniques shows flame moves back and forth near the flameholder due to the mixture velocity fluctuation near the flameholder.. Therefore, it is considered that it is liable to induce the longitudinal combustion instability in the duct combustor with a bluff-body flameholder. Nomenclature Aduct = duct area Anozzle = nozzle throat area f = frequency ma = air mass flow rate mf = fuel mass flow rate Va = inlet air velocity Vmixture = mixture velocity Φ = equivalence ratio

An Experimental Study on the Flame Dynamics in Ducted Combustor

The characteristics of flame dynamics occurring near the bluff body was experimentally investigated in a model combustor with V-gutter bluff body. Measurements of chemiluminescence with high speed camera and PIV were performed for visualization of flame structure. Flashback occurs due to the change of pressure gradient in the combustor, and the flashback distance depends on equivalent ratio. Unstable flames can be classified into three types depending on the flashback distance and structure. When the flame goes over the bluff body, an unusual flame structure occurs at the front of the bluff body. Re-stabilization takes place as the flame moves downstream of the combustor. This process is supported by a strong vortex structure behind the bluff body.

Response of Liquid Jet to Modulated Crossflow

Experimental results on the response of spray formed by the liquid (Jet-A) jet injection into a crossflow (Air) is presented with a special emphasis on its response to the modulating crossflow. The pressure of the chamber is up to 3.5 atm and the corresponding Weber number is up to 510. The spray of a liquid jet for steady and oscillating crossflow is characterized. The flow field at the injector location in the crossflow direction is determined using PIV (Particle Image Velocimetry) for oscillating as well as steady crossflow case. Planar Mie-scattering measurement is used to characterize the response of spray formed under oscillating crossflow and supplementary phase-averaged PDPA measurements are used to understand the response behavior. The global response of spray to the oscillating crossflow is characterized using the planar Mie-scattering imaging. It shows that there exist very little differences in the heights of the maximum-pixel intensity trajectory for the non-oscillating and oscillating crossflow conditions and the trajectory under oscillating crossflow is lower than that of steady crossflow, suggesting the oscillating crossflow affects the atomization (i.e. the oscillating crossflow enhances atomization process, results in smaller droplets and penetrates less transversely). The response of spray to the oscillating crossflow characterized in terms of the spray transfer function (STF) shows that the gain of the STF increases linearly (at least monotonically) as the liquid-air momentum flux ratio increases but does not change as much with respect to the change of the Weber number for a fixed liquid-air momentum flux ratio. This also indicates that the liquid jet atomization under oscillating crossflow is enhanced much more with the increase of liquid-air momentum flux ratio than with the increase of Weber number. The phase-averaged PDPA measurements confirm that the oscillating crossflow indeed enhances the atomization process in that the oscillating crossflow results in relatively greater number of smaller droplets and the mean droplet size.Copyright

Effects of Angled Injection on the Spray Characteristics of Liquid Jets in Subsonic Crossflow

The liquid column trajectory and column breakup length characteristics have been experimentally studied in angled jets injected into subsonic crossflow. Pulsed shadowgraph photography and Planar Liquid Laser Induced Fluorescence measurements were used to determine the angled effects. And the main objectives of this research are to get a empirical formula of liquid column trajectory and breakup length with below the degree injection angle conditions, and were compared with previous results. It was also found that the empirical formula, which reversed injection conditions of air stream. As the result, This has been shown that liquid column trajectories and column breakup length were spatially dependent on various injection angle, normalized injector exit diameter, air-stream and fuel injection velocity. Furthermore, the empirical formula of liquid column trajectories and breakup length has been some different of drag coefficient results between normal angled injection and reversed injection in subsonic crossflow.

Flame dynamic behavior stabilized by a V-gutter type flameholder

Mechanism of combustion frequencies occurring during combustion is experimentally investigated in model combustor with v-gutter flame-holder. This combustor has a long duct shape with a cross section area of 40 x 40 mm. The v-gutter type flameholder with 14mm width is mounted at the bottom of combustor. Kerosene and methane were used as fuel, and these fuel were injected transversely into air cross-flow. It is found that combustion frequencies were considered as 1L longitudinal mode caused by combustor geometry and vortex shedding mode of flame-holder. And fuel phase effect and nozzle effect were also observed in the low frequency range.

Spray Plume Characteristics of Liquid Jets in Subsonic Crossflows

The effect of internal liquid flow on spray plume characteristics was performed experimentally in subsonic cross flows. The injector internal flow was classified as three modes such as a normal, cavitation, and hydraulic flip. The objectives of the research are to investigate the effect of internal liquid flow on the spray plume characteristics and compare the trajectory of spray plume with previous works. The results suggest that the trajectory and width of spray plume can be correlated as a function of liquid/air momentum flux ratio(q), injector diameter and normalized distance from the injector exit(x/d). Its also found that the injector internal turbulence influences the spray plume characteristics significantly.