Byung Joon Rho

Swirl Effect on the Spray Characteristics of a Twin-Fluid Jet

In the liquid fuel combustion chamber, employed fuel must be atomized before being injected into the combustion zone. Therefore, the complete fuel atomization is the most important condition for the combustion efficiency. The atomization quality strongly affects the combustion performance, exhaust pollutant emissions, and flame stability. Therefore, the whole process of spray atomization is of fundamental significance. During past decades many experimental and theoretical studies in this field have been carried out and some improved results have been obtained. Two-phase atomizers, having a variety of advantages such as spray uniformity, appreciable atomization, and smaller SMD with an increase of ambient gas, are considered to be applied in various industrial processes. The purpose of present study is to investigate the mean velocity, turbulence shear stress, turbulence intensity, mean drop size distribution, and droplet data rate in a two-phase swirling jet using PDPA systems.

Atomization characteristics in pneumatic counterfiowing internal mixing nozzle

In an effort to illustrate the global variation of SMD (Sauter mean diameter, orD32) and AMD (Arithmetic mean diameter, orD10) at five axial downstream locations (i. e., at Z=30, 50, 80, 120, and 170 mm) under the different experimental conditions, the radial coordinate is normalized by the spray half-width. Experimental data to analyze the atomization characteristics concerning with an internal mixing type have been obtained using a PDPA (Phase Doppler Particle Analyzer). The air injection pressure was varied from 40 kPa to 120 kPa. In this study, counterfiowing internal mixing nozzles manufactured at an angle of l5o with axi-symmetric tangential-drilled four holes have been considered. By comparing the results, it is clearly possible to discern the effects of increasing air pressure, suggesting that the disintegration process is enhanced and finer spray droplets can be obtained under higher air assist. The variations inD32 are attributed to the characteristic feature of internal mixing nozzle in which the droplets are preferentially ejected downward with strong axial momentum, and dispersed with the larger droplets which are detected in the spray centerline at the near stations and smaller ones are generated due to further subsequent breakup by higher shear stresses at farther axial locations. The poor atomization around the centre close to the nozzle exit is attributed to the fact that the relatively lower rates of spherical particles are detected and these drops are not subject to instantaneous breakup in spite of the strong axial momentum. However, substantial increases in SMD from the central part toward the edge of the spray as they go farther downstream are mainly due to the fact that the relative velocity of droplet is too low to cause any subsequent disintegration.

Atomization Characteristics of a Double Impinging F-O-O-F Type Injector with Four Streams for Liquid Rockets

This paper presents atomization characteristics of a double impinging F-O-O-F type injector with four streams. A phase Doppler particle analyzer was employed to measure the droplet-size and water was used as the inert simulant liquid instead of reactive propellant liquids. The droplet mean diameter (SMD) and size distribution were measured to investigate the effects of the momentum ratio and pressure drop variations. This experimental results can be used during the preliminary design stage of a impinging stream type injector for liquid rockets.

On the intermittent spray characteristics

The quality of spray atomization ejected from an injector has a definitive influence upon the engine’s performance. Furthermore, considerable attention to the Earth’s environmental pollution is increasing now more than ever before. This experimental investigation has been carried out to clarify the characteristics of the intermittent spray using a pintle type gasoline fuel injector. Both the image processing system and the Phase Doppler Anemometer are utilized for the visualization of a spray behavior and the simultaneous measurements of dropsizes and their velocities, which have been conducted at the axial downstream from the injector exit plane. The fuel injection duration was fixed at 3ms and the injection pressure was varied from 250 kPa to 350 kPa. For a high injection pressure of 350 kPa, the spray tip arrival time was fluctuated at the vigorously disintegrated regions. It evidently shows a linear correlation between the axial velocity and the fuel drop size farther downstream.

Investigation of turbulent spray disintegration characteristics depending on the nozzle configuration

The experimental measurements were carried out to examine turbulent disintegration characteristics ejecting from a counter-flowing internal mixing pneumatic nozzle under variable conditions of swirl angles and air pressures. The air injection pressure was varied from 60 kPa to 180 kPa and four counter-flowing internal mixing nozzles with axi-symmetric tangential-drilled holes at swirl angle of 15°, 30°, 45°, and 60° to the central axis have been specially designed. The experimental results were quantitatively analyzed, focusing mainly on the comparison of turbulent atomization characteristics issuing from an internal mixing swirl nozzle. To illustrate the swirl phenomena, the distributions of mean velocities, turbulence intensities, volume flux, and SMD (Sauter Mean Diameter, or D32) were comparatively analyzed.

LDV Measurements of Turbulent Flow Behavior of Droplets in a Two-Phase Coaxial Jet

Coaxial nozzles are frequently utilized for the atomization of liquids in sprays. The performance of a nozzle is generally evaluated by its atomizing characteristics, which are actually governed by the turbulence interactions of two fluids. With this point of view, this experimental study was carried out to investigate the turbulent behavior of the droplets atomized in a two-phase coaxial jet. Air and water have been used as the working fluids, and the measurements have been made by an on-line data acquisition system connected to a two-channel LDV set(DISA, 5W, Argon laser, blue: 488 nm, green: 514.5 nm). In order to generate a two-phase mixing jet, two types of coaxial nozzles (liquid column type, liquid sheet type) were used. For the investigations of the turbulent flow structure of this two-phase mixing jet, the spreading rates, mean and fluctuating components, intermittency factors and the iso-contours of joint probability densities were measured and analyzed. The results from the both types of nozzles did not show remarkable differences in mean and fluctuating velocity distributions, intermittency factors or the iso-joint probability density contours. Since the measurements were made in the fully developed turbulent mixing regions, the mean velocity distribution profiles showed good similarities and agreed well with the semi-empirical curves. The RMS values were represented as high order levels and so were the intermittency factors. The typical development trends of turbulent components ofu′ andv′ for both types were illustrated in the iso-joint probability density contours.

On the mixing flow structure of a turbulent cross jet

An experimental study on the structure of a turbulent cross jet mixing flow is presented. Diffusion rates, two and three dimensional flow structures, mean velocities turbulence intensities and turbulent shear stresses of the mixing flow were measured as varying the velocity ratio. Self-similar forms for the dimensionless mean velocity and turbulent shear stresses was obtained by correlating the measurement data resulting a remarkable agreement. It was found that the deviation gradient(a) is linearly correlated with the velocity ratio(R), and the cross section of the mixing flow is an elliptic form.

LDV Measurements of Turbulence Characteristics in a Two Phase Coaxial Jet

This experimental study was carried out to investigate the turbulent behavior of the droplets atomized in a two phase coaxial jet. The air and water have been used as working fluids and the mass flow rates (Mr = Ma/Mw) were varied from Mr = 1.0 to Mr = 2.8. The measurements have been made by an on-line data acquisition system connected to a two channel LDV set (DISA, 5W, Argon, blue :488 nm, green : 514.5 nm). And the experiments were performed by using two types of coaxial nozzles (liquid column type, liquid sheet type) and the conditions of turbulent mixing characteristics for both types were compared. A coaxial nozzle is usually utilized as an atomizing kit in the sprays and the performance of the nozzle is normally evaluated by the atomizing characteristics. But the atomization is actually characterized by the turbulent interactions of two fluids. Therefore, the investigations on the turbulent mixing flow structures, developments of fluctuating components, joint probability densities, and intermittency factors have been intensively conducted in this study. The results of both types did not show remarkable differences in mean and fluctuating velocity distributions, intermittency factors and the iso-joint probability density contours. Since the measurements were made in the fully turbulent mixing regions, the mean velocity distribution profiles showed good similarities and agreed well with the semi-empirical curves for single phase jets. The RMS values were represented as high order levels and so were the intermittency factors. The typical development trends of turbulent components of u′ and v′ for both types were illustrated in the iso-joint probability density contours.