• 대한기계학회논문집B
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• 제30권6호
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• pp.553-559
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• 2006

Most diesel injector, which is currently used in high-pressure common rail fuel injection system of diesel engine, is driven by the solenoid coil energy for its needle movement. The main disadvantage of this solenoid-driven injector is a high power consumption, high power loss through solenoid coil and relatively fixed needle response's problem. In this study, a prototype piezo-driven injector, as a new injector mechanism driven by piezoelectric energy based on the concept of inverse piezo-electric effect, has been designed and fabricated to know the effect of piezo-driven injection processes on the diesel spray structure and internal nozzle flow. Firstly we investigated the spray characteristics in a constant volume chamber pressurized by nitrogen gas using the back diffusion light illumination method for high-speed temporal photography and also analyzed the inside nozzle flow by a fully transient simulation with cavitation model using VOF(volume of fraction) method. The numerical calculation has been performed to simulate the cavitating flow of 3-dimensional real size single hole nozzle along the injection duration. Results were compared between a conventional solenoid-driven injector and piezo-driven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has short injection delay and a faster spray development and produces higher injection velocity than the solenoid-driven injector. And the predicted simulation results with the degree of cavitation's generation inside nozzle for faster needle response In a piezo-driven injector were reflected to spray development in agreement with the experimental spray images.

• 한국분무공학회지
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• 제25권3호
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• pp.111-118
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• 2020

This paper describes the effect of DME, biodiesel blended fuels on the macroscopic spray characteristics in a high pressure diesel injection system using Background Oriented Schlieren (BOS) method. The BOS method for visualization of impingement evaporation sprays to analyze macroscopic spray properties and evolutionary processes. In this work, the blending ratio of DME in the blended fuel are 0, 50, 100% by weight ratio. In order to investigate the macroscopic impinged spray characteristics under the various injection parameters and blending ratio. In this work, a mini-sac type single-hole nozzle injector with nozzle hole was length 0.7 mm and diameter of 0.3 mm was used. According to the result, the spray area of the collision wall increased as the DME mixing ratio increased, and the evolutionary pattern showed a stepwise increase due to the collision effect of the wall. Also, results of impinged spray area were increased according to increasing injection pressure.

• 한국분무공학회지
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• 제28권1호
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• pp.32-42
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• 2023

In this study, spray characteristics of n-heptane and propane were investigated under different injection pressure using various imaging techniques such as Mie-scattering, DBI (diffuse back-illumination), and Schlieren imaging techniques. NI compact RIO system was used to control a test injector. Spray penetration length, length-to-width ratio and number of black pixels were calculated by using MATLAB software to compare spray characteristics of each fuel. Longer spray penetration length and higher length-to-width ratio were observed in propane spray because of flash boiling caused by high saturated vapor pressure. Spray collapse occurred in propane spray due to the high plume-to-plume interaction. Moreover, rapid evaporation occurred in propane spray, so that nozzle tip wetting could not be observed. Rapid evaporation of propane also caused fewer residual droplets compared to n-heptane spray. Therefore, propane is advantageous in reducing the generation of soot emission from large droplets that are not atomized. However, additional evaluation should be conducted considering combustion efficiency and the possibility of deposits by nozzle tip icing during fuel injection.

• International Journal of Automotive Technology
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• 제6권2호
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• pp.125-131
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• 2005

This article reports the experimental and numerical results for free sprays under ultra-high injection pressure conditions to give us better understandings of spray characteristics and also to make clear a limit pressure condition in diesel sprays. The high pressure injection system developed in this work is devised to reach ultra-high pressure conditions in the range from 150 MPa to 355 MPa. The free spray injected from a single nozzle injector is visualized by the Schlieren technique and the high speed camera. In particular, it is found that the shock waves are present and propagated along the edge of spray in the downstream direction. The measured spray penetration length increases gradually with the injection pressure, but its increasing rate is decreased as the injection pressure increases. The Sauter mean diameter is also no longer augmented for the injection pressures higher than 300 MPa. In addition, the three­dimensional numerical simulations are conducted for comparing the measurements with the predictions based on two different breakup models. The TAB model results show better agreements with experimental data than the WAVE model under ultra-high injection pressure conductions. Moreover, the simulation results show that the gas-phase pressure increases substantially in the vicinity of the spray tip region. It supports the experimental observation that the shock waves are formed at the front of spray tip and are propagated downstream.

• 한국자동차공학회논문집
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• 제8권3호
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• pp.28-36
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• 2000

Spray characteristics of diesel fuel injection is one of the most important factors in diesel combustion and pollutant emissions especially in HSDI (High Speed Direct Injection) diesel engines where the interval between the onset of combustion and the evaporation of atomized fuel is relatively short, An investigation into various spray characteristics from different holes of VCO(Valve Covered Orifice) nozzles was performed and its results were compared to standard sac nozzle. The global characteristics of spray, including spray angle, spray tip penetration, and spray pattern were measured from the spray images which were frozen by an instantaneous photography with a spark light source. For better understanding of spray behavior, SMD of the fuel sprays from multi hole nozzles were measured with back light imaging while the sprays from the other holes are covered by a purpose-built nozzle cap. The investigation manifestly reveals the different spray patterns at the beginning of injection produced by VCO nozzles can be identified as three distinct types with their own macroscopic and microscopic characteristics, while macroscopic non-uniformity disappears at 0.9∼1.0ms from the start of injection.

• 한국분무공학회지
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• 제9권1호
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• pp.8-14
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• 2004

future exhaust emission limits for diesel-driven passenger cars will force the automotive company to significantly develop of the new technologies of diesel engine respectively of the drive assemblies. As we know, the contributions of soot and nitrogen oxide is the main problems in diesel engine. Recently, as a result, the pilot injection of common-rail fuel injection system recognizes an alternative function to solve an environmental problem. This study describes the effect of the nozzle structure and driven characteristic of injector on pilot injection fur a passenger car common-rail system. The pilot spray structure such as spray tip penetration, spray speed and spray angle were obtained by high speed images, which is measured by the Mie scattering method with optical system fur high-speed temporal photography. Also the CFD analysis was carried out for fuel behavior under high pressure in between needle and nozzle of injector for common-rail system to know the condition of initial injection at experiment test. It was found that solenoid-driven injector with 5-hole was faster than 6-hole injector in spray speed at same conditions and piezo-driven injector showed faster response than solenoid injector.

• 한국분무공학회지
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• 제14권3호
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• pp.109-116
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• 2009

The purpose of this study is the experimental and numerical investigation on the DME spray characteristics in the combustion chamber according to the injection timing in a common-rail injection system. The visualization system consisted of the high speed camera with metal halide lamp was used for analyzing the spray characteristics such as spray development processes and the spray tip penetration in the free and in-cylinder spray under various ambient pressure. In order to observe the spray characteristics as a function of injection timing, the piston head shape of re-entrant type was created and the fuel injected into the chamber according to various distance between nozzle tip and piston wall in consideration of injection timing. Also, the spray and evaporation characteristics in the cylinder was calculated by using KlVA-3V code for simulating spray development process and spray tip penetration under real engine conditions. It was revealed that the high ambient pressure of 3 MPa was led to delay the spray development and evaporation of DME spray. In addition, injected sprays after BTDC 20 degrees entered the bowl region and the spray at the BTDC 30 degrees was divided into two regions. In the calculated results, the liquefied spray tip penetration and fuel evaporation were shorter and more increased as the injection timing was retarded, respectively.

• 동력기계공학회지
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• 제18권6호
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• pp.21-28
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• 2014

The studies of the spray characteristics for a CRDI engine had been advancing by many researchers, because the performance and exhaust emission were significantly affected with the spray characteristics. But most experiments of the studies would be done at low ambient pressure conditions under 2MPa. In this study, injection rates were measured with Zeuch's method at various ambient pressures to 5MPa and a constant injection pressure of 130MPa. On the same conditions, non-evaporating spray images were taken with a high speed camera and analyzed carefully with Adobe Photoshop CS3. Macroscopic spray characteristics and breakup processes in the spray could be found from the examined and analyzed data. The initial injection rate, penetration, angle, velocity and breakup of the spray were practically affected with a variation of the ambient pressure, but the injection start time and injection period were scarcely affected. As the ambient pressure was higher, the breakup of a high density droplet region in the spray was happened slowly and the main position of breakup was shifted from a front of the spray to a upstream around a nozzle. The results and techniques of spray visualization and injection rate measurement in this study would be practically effective to study a high pressure diesel spray for a CRDI.

• 한국자동차공학회논문집
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• 제8권2호
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• pp.27-32
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• 2000

The main objective of this work is to investigate the effect of ambient conditions on the spray behavior and spray characteristics of high-pressure fuel injector. For this purpose, the effects of ambient pressure and temperature on the spray characteristics have been studied by applying the analysis of visualization system and phase Doppler particle analyzer. In this experiment, the visualization of spray behavior was performed under various ambient gas conditions and injection parameters such as gas temperature, ambient pressure, injection pressure of injector, and axial distance from the nozzle tip. Based on the investigation results, the spray tip penetration and spray width decrease with the increase of ambient gas pressure in the spray chamber. The effects of the spray parameters on the microscopic characteristics of gasoline spray were discussed.

• 한국분무공학회지
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• 제17권4호
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• pp.210-215
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• 2012

This paper This paper presents effect of nozzle hole number on spray characteristics and engine performance. Experiments were conducted to measure spray penetration and SMD distributions using a spray visualization system and PDPA (phase Doppler particle analyzer) system. In addition, engine performance and emission characteristics were measured using a single cylinder engine and emssion measurement systems. Results showed that 8-hole-injector exhibits improved spray performances. Furthermore, soot emission was decreased with 8-hole-injector, compared to that of 6-hole-injector.