Kihoon Jung

Assessment of planar liquid-laser-induced fluorescence measurements for spray mass distributions of like-doublet injectors

The planar liquid-laser-induced fluorescence (PLLIF) technique has been known to be a useful tool for the measurement of the spray mass distributions for various spray injectors because it can obtain two-dimensional images with high spatial resolutions without any intrusion on the spray field. In the cases of dense sprays, however, it has been known that the extinctions of the incident laser beam or fluorescence signal and the secondary emission can cause errors in quantifying the spray mass distributions. Since a like-doublet injector, which is commonly used in liquid rocket engines, has a locally concentrated spray zone at the spray centre, we investigated the applicability of the PLLIF technique for this injector. From the experimental results, we found out that the extinctions of the incident laser beam and fluorescence signal are not significant because the concentrated spray zone is narrow. Also, we found out an optimal incident laser power which can avoid a nonlinear increase of fluorescence signal at the spray centre as well as obtain a high signal-to-noise ratio, and we measured the spray mass concentration of the like-doublet injector spray using the optimal laser power. In order to assess the accuracy of the PLLIF data, we converted the spray mass concentration into the mass flux distribution and compared it with the data obtained by a mechanical patternator and phase Doppler particle analyser. From the result that the PLLIF data showed good agreement with those of the mechanical patternator, we concluded that the PLLIF technique can be successfully applied to measuring the mass distributions of the like-doublet injectors.

Effects of Orifice Internal Flow on Breakup Characteristics of like-Doublet Injectors

Under cold-flow and atmospheric ambient pressure conditions, the breakup characteristics of liquid sheets formed by a like-doublet injector were investigated. The sheet breakup wavelength, which induces the sheet to be broken into ligaments, and the sheet breakup length, which is important for finding the flame location, were measured using stroboscopic light. After sheet breakup, liquid ligaments are formed intermittently, and their wavelengths are believed to be related to the combustion instability of liquid-rocket engine. Therefore, the wavelength and the breakup length of ligaments broken into fine drops were also measured. Because these spray characteristics are affected by the flow characteristics of the two liquid jets before they impinge on each other, the focus was on the effects of orifice internal flow, such as the cavitation phenomenon that occurs inside a sharp-edged orifice. From the experimental results, it was found that liquid jet turbulence delays sheet breakup and shortens the wavelengths of both sheets and ligaments. Because the turbulence strength of a sharp-edged orifice is stronger than that of a round-edged orifice, the shape of orifice entrance gives large differences in the spray characteristics. With these results, empirical models of the spray characteristics of a like-doublet injector were proposed, and these models can provide useful and practical data for use in designing liquid-rocket combustors.

Development of Quantitative Measurement of Fuel Mass Distribution Using Planar Imaging Technique

The quantified fuel mass distribution of a spray was obtained from laser induced fluorescence images with optical patternation. In the dense spray region, however, the emitted fluorescence signal is significantly attenuated in the path of the detector because of particle scattering. Thus, the fluorescence image obtained with a camera may be different from the true fluorescence image pattern. Therefore, we propose a method of finding the geometric mean of the intensities obtained with two cameras and apply it to a solid-cone spray. We also compared this optical patternation technique with other spray measurement techniques, such as, PDPA (Phase Doppler Particle Analyzer) and the mechanical patternator, to validate the accuracy of the proposed method. Results show that the quantified mass distribution of the optical patternator agrees well with those of the PDPA and the mechanical patternator. Hence, we can estimate the local mass distribution rapidly without determining the entire structure of the spray by using the geometric mean of the signals obtained from two cameras.

Comparison of Mixing Characteristics of Unlike Triplet Injectors Using Optical Patternator

Mixing characteristics of an unlike split triplet fuel-oxidizer-oxidizer-fuel (F-O-O-F) injector, which separates the single oxidizer hole of an unlike triplet fuel-oxidizer-fuel (F-O-F) injector for liquid-rocket engines, were investigated under cold-flow conditions. The spray mass distributions of the fuel and oxidizer were measured using an optical patternator based on the planar liquid laser-induced fluorescence technique, and the mixing mechanism and the mixing efficiency of the F-O-O-F injector were compared with those of the F-O-F injector. Results showed that the mixing efficiency of the F-O-O-F injector is less sensitive to the changes of the momentum ratio or impingement angle than that of the F-O-F injector because the mixing of the F-O-O-F injector is determined by the coalescing process of two liquid sheets, whose impinging momentum is weak. Therefore, the F-O-O-F injector has an advantage in starting injection wherein the momentum ratio is usually different from the operating condition.

BREAKUP CHARACTERISTICS OF LAMINAR AND TURBULENT LIQUID SHEETS FORMED BY IMPINGING JETS IN HIGH PRESSURE ENVIRONMENTS

Breakup characteristics of liquid sheets formed by the impingement of two water jets were investigated as increasing the injection velocity up to 30m/s and the ambient gas pressure up to 4.0MPa. We compared the breakup characteristics between laminar and turbulent sheets, which are formed by round and sharp edged orifices, respectively. The results showed that the aerodynamic force significantly affects the breakup of laminar sheet when the gas based Weber number is higher than unity. It was also found that the turbulent sheets have three breakup regimes, i.e. expansion regime, wave breakup regime and catastrophic breakup regime according to the gas based Weber number. Using the experimental results, we could suggest empirical models on breakup lengths for laminar and turbulent sheets.

The Breakup Characteristics of Liquid Sheet Formed by Like-Doublet Injectors

The atomization process of uni-element like-doublet injector includes formation of liquid sheet, fragment into ligaments, and breakup into fine drops. During the processes, breakup characteristics of the liquid sheet such as breakup length and breakup frequency affect the combustion instability as well as the efficiency of liquid rocket combustor. In this paper we proposed spray models on the breakup characteristics of the liquid sheet based on empirical data. We focused on the effects of the orifice inner flow characteristics such as cavitation phenomenon inside the sharp-edged orifice. From our experimental results, we found that the effects of turbulence inside the sharp-edged orifice are significant for the breakup of liquid sheet, and the cavitation tends to increase the turbulence strength. Since the turbulence strength of jet at the orifice exit increases as the orifice length becomes short, we also considered the effects of orifice length. Our empirical formula for the beakup length and the breakup frequency of liquid sheets formed by like-doublet injectors are believed to give some useful and actual data for designing liquid rocket combustors.

Effect of ambient gas density and injection velocity on the atomization characteristics of impinging jet

On this paper study is concentrated on the breakup and atomization characteristics of spray formed by impinging jet injectors(like-doublet) used in liquid rocket engine(LRE). On the process of breakup and atomization, injection velocity and ambient gas pressure are the main parameters, so that these are used as variables that specify the experimental condition. Injection velocity varied from 3m/s to 30m/s and ambient gas pressure changed from 0.1MPa to 4.0MPa with nitrogen gas. As results, measured physical quantities decreased with increasing injection velocity and ambient gas pressure. But the decreasing ratios are different from those of the theory.

The Mixing Characteristics of F-O-O-F Injector in Liquid Rockets Using PLIF Technique

Each mass distribution of oxidizer and fuel for F-OO-F injector which has been used in liquid rockets was measured in cold-flow condition using optical patternator which overcomes problems of mechanical patternator. Using the mass distributions, we calculated the mixing efficiency of F-O-O-F uni-element. Since F-O-O-F injector is modified from F-O-F which is more general, we compared their mixing efficencies for the momentum ratio and the impingement angle. From the results, we could find that F-O-O-F shows very stable mixing efficiency within the experimental range of momenturm ratio. However, the mixing efficency of F-O-O-F injector was slightly lower than that of F-O-F injector.

The Spray Characterization Using Planar Imaging Technique

The characteristics of spray nozzle have been quantified with the measurement of fluorescence and Mie scattering images. To correct the attenuation of the incident light sheet, a sequential double-pass light sheet system and the geometrical averaging of two images was implemented. Quantitative mass flux distribution of spray was obtained from fluorescence image. 3-D image is reconstructed using 2-D radial images. Sauter mean diameter (SMD) distribution was determined using the ratio of fluorescence signal intensity and Mie scattering signal intensity and the values were quantified with PDP A data. The measurement of mass flux and SMD using planar imaging technique agee with PDP A data fairly well in the low density region. However, in dense region， there are significant errors caused by secondary scattering. It was found that the planar imaging technique provides many advantages over the point measurement technique, such as PDP A, and can be implemented for quantitative measurement, especially in low density region.