An experimental study was performed to investigate the liquid breakup and atomization characteristics in electrohydrodynamic atomization according to the changing of experimental parameters such as nozzle size, fluid flow, and electrical intensity. An original electrohydrodynamic atomizer equipment was designed and manufactured for the analysis of spray visualization and the exploration of relationship between applied power and the behavior of liquid atomization. The image processing technique by using the back-illumination method was applied to visualize the distilled liquid breakup process and to examine the variation of the droplet size distribution. The results show that the spray modes of electrohydrodynamic atomization are closelyconnected by the strength of the electric stresses at the surface of the liquid film and the kinetic energy of the liquid jet leaving the needle tip.

The objective of this work is to analyze the atomization and evaporation characteristics of dimethyl ether(DME) fuel for the application of HCCI diesel engine. In order to investigate the spray behavior of DME fuel, the macroscopic and microscopic characteristics were investigated in terms of spray development, spray tip penetration, impingement time, SMD, and axial mean velocity under the various injection timing and ambient conditions. For the illumination of spray, the spray visualization system was composed of a Nd:YAG laser and an ICCD camera and laser-sheet method was used. The atomization characteristics of DME fuel are analyzed by using phase Doppler particle analyzer (PDPA) system It was reveal that the spray development of DME is slower and rapidly disappeared as elapsed time after start of injection at the same injection duration. The impingement timing of diesel fuel was fester than that of DME fuel. The comparison of spray atomization characteristics in both fuels shows that diesel fuel has a large SMD value that DME.

A specially designed injector using electric conductivity was used to measure the liquid film thickness accurately. The measurement conducted through the precise calibration, accuracy is demonstrated in comparison with the previous theory and the results using other measurement method. The tendency of liquid film thickness for geometric parameters was examined by the precise measurement. The variation of air core and stability are examined through the visualization of the formation of air core in swirl chamber and the variation of liquid film thickness by the time.

Spray characteristics of charge injected 2-fluid nozzle for non-conducting liquid have been studied. Spray current, specific charge and SMD of diesel have been measured. Spray current and specific charge are proportional to applied voltage. Air flow did not effect on spray current and specific charge. SMD decreases as air flow rate increases and decreases as applied voltage increases additionally. Spray angle increases as applied voltage increases. Fine droplets are obtained by charge injected 2-fluid nozzle without charge loss.

As the exhaustion of petroleum resources and air pollution problems are getting serious recently, there are growing interests in premixed diesel engines which have the potential of achieving a more homogeneous mixture near TDC compared to conventional diesel engines. Early studies have shown that the fuel injection frequency and spray angle affected the mixture formation and combustion in a HCCI(Homogeneous Charge Compression Ignition) engine. Therefore, the purpose of this study is to investigate the relationship between combustion and mixture formations by injection timing and frequency using a narrow angle injector, NADI (Narrow Angle Direct Injection). In this study, we found that the fuel injection timing and injection frequency affect the mixture formations and then affect combustion in the HCCI engine.

The static pressure distribution and flow characteristics inside the high-pressure swirl spray were investigated by measuring the static pressure inside the spray and applying the computational fluid dynamics (CFD). The static pressure difference between inner and outer part of spray was measured at different axial locations and operating conditions using a piezo-resislive pressure transducer. To obtain the qualitative value of swirl motion at different operating conditions, the spray impact-pressure at the nozzle exit was measured using a piezo-electric pressure transducer, and the flow angle was measured using a microscopic imaging system. The flow characteristics inside the high pressure swirl spray was simulated by the 1-phase 3-dimensional CFD model. The effect of pressure alternations on spray development was discussed with macroscopic spray images and a mathematical liquid film model. The results showed that the static pressure drop is observed inside the swirl spray as a result of the dragged air motion and the centrifugal force of the air. The recirculation vortex inside the spray was also observed inside the swirl spray as a result of the adverse pressure gradient along the axial locations. The results of analytical liquid film model and macroscopic spray images showed that the static pressure structure is one of the main parameters affecting the swirl spray development.

In the present study, capability of improving the liquid atomization of a high-speed liquid jet by using wall impingement is explored, and its application to a jet engine atomize. is demonstrated. Water is injected from a thin nozzle. The liquid jet impinges on a wall positioned close to the nozzle exit, forming a liquid film. The liquid film velocity and the SMD were measured with PDA and LDSA, respectively. It was shown that the SMD of the droplets was determined by the liquid film velocity and impingement angle, regardless of the injection pressure or impingement wall diameter. When the liquid film velocity was smaller than 300m/s, a smaller SMD was obtained, compared with a simple free jet. This wall impingement technique was applied to a conventional air-blasting nozzle for jet engines. A real-size air-blasting burner was installed in a test rig in which three thin holes were made to accommodate liquid injection toward the intermediate ring, as an impingement wall. The air velocity was varied from 41 to 92m/s, and the liquid injection pressure was varied from 0.5 to 7.5 MPa. Combining wall impinging pressure atomization with gas-blasting produces remarkable improvement in atomization, which is contributed by the droplets produced in the pressure atomization mode. Comparison with the previous formulation for conventional gas-blasting atomization is also made, and the effectiveness of utilizing pressure atomization with wall impingement is shown.