• Journal of ILASS-Korea
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• v.11 no.3
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• pp.140-146
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• 2006

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.

• Journal of ILASS-Korea
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• v.14 no.2
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• pp.71-76
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• 2009

The aim of this investigation is to study the effect of the high injection pressure on the dimethyl ether (DME) spray characteristics injected through a common-rail diesel injector under various ambient pressures. In order to investigate the effect of the injection pressure and ambient condition, the common-rail injection system with two high pressure pumps and high pressure chamber pressurized up to 40 bar were used, respectively. Spray images of DME fuel obtained from a visualization system composed of high speed camera and two metal halide lamps as the light source. From the obtained images, the spray behaviors such as a spray development process, spray tip penetration, spray width, and spray cone angle were measured for analyzing the DME spray characteristics under various experimental conditions. It was found that the spray development slowed as the ambient pressure increased and spray tip penetration at injection pressure of 90 MPa is longer than that at 50 MPa. In addition, the spray width at the end stage of injection decreased under the atmospheric conditions due to the evaporation property of DME fuel, and DME spray shows narrow spray cone angle according to the injection pressure increased.

• Journal of Welding and Joining
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• v.26 no.6
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• pp.67-73
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• 2008

Three-dimensional transient simulation of laser-GMA hybrid welding involving multiple physical phenomena is conducted neglecting the interaction effect of laser and arc heat sources. To reproduce the bubble and pore formations in welding process, a new bubble model is suggested and added to the established laser and arc welding models comprehending VOF, Gaussian laser and arc heat source, recoil pressure, arc pressure, electromagnetic force, surface tension, multiple reflection and Fresnel reflection models. Based on the models mentioned above, simulations of laser-GMA hybrid butt welding are carried out and besides the molten pool flow, top and back bead formations could be observed. In addition, the laser induced keyhole formation and bubble generation duo to keyhole collapse are investigated. The bubbles are ejected from the molten pool through its top and bottom regions. However, some of those are entrapped by solid-liquid interface and remained as pores. Those bubbles and pores are intensively generated when the absorption of laser power is largely reduced and consequently the full penetration changes to the partial penetration.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.47-53
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• 2007

To suppress the bubble generated in the liquid LPG direct injector is the most important to develop the LPDi engine. It was found in the previous study that bubbling phenomenon in the injector of the LPDi engine is decisively influenced by pressure of fuel and temperature around the injector. Therefore, in this study, the effect on suppressing the bubbling in the LPDi injector by high pressurization of fuel is analyzed and the spray characteristics are also studied. As a result, it is found that the bubbling in the LPDi injector is radically suppressed when the pressure of fuel is over 50MPa. The bubbling is suppressed when the pressure of fuel is over 3MPa if the inserted position of the injector is considered. Also, it is confirmed that the higher the pressure of fuel is the longer spray tip penetration and is the larger spray angle. As the ambient pressure increases, spray tip penetration decreases and spray angle increases due to the increase of drag force.

• Journal of ILASS-Korea
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• v.15 no.1
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• pp.17-24
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• 2010

The objective of this work is to analyze the macroscopic behavior of spray and injection characteristics on the DME blended biodiesel at different mixing ratios by using spray visualization and injection rate measurement system. The spray images were analyzed to a spray tip penetration, a spray cone angle and a spray area distribution at various mixing ratio of DME by weight. The influence of different injection pressure and ambient pressure on the fuel spray characteristics are investigated for the various injection parameters. In order to analyze the injection characteristics of test fuels, the fuel injection rate is measured at various blending ratio. The variation of viscosity of the blended fuel by the mixing of DME fuel shows the improved effect of spray developments. Also, it was found that the injection quantities of high blended ratio were larger than that of lower blended fuel. Also, higher blending fuel showed a faster evaporation than that of mixing ratio of test fuel because kinetic viscosity was changed by blending ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.672-675
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• 2010

Spray characteristics for the modulation with a pulsed spray in low-frequency region were investigted by performing with additional internal pulsed injection. The 1st perturbative flow was generated by rotating-type pulsed device and the 2nd pulse source generated by the magnetic valve was used to modulate the 1st flow. A pattern of the modulated spray was observed through FFT result and visualization. In case of modulated spray with the 2nd pulse control, the width of up and down motion of the modulated spray is smaller than that of the spray without the 2nd pulse. Also, the depth of penetration of the down stream is higher than that of spray without the 2nd pulse.

• Journal of ILASS-Korea
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• v.25 no.4
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• pp.145-153
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• 2020

The purpose of this study is to compare the injection and spray characteristics of single-hole GDI injectors using injection rate and mie-scattering spray images. Five types of single-hole injectors with different nozzle hole diameters were used, and the spray rate, spray tip penetration, spray area, and spray width were analyzed. As a result, the diameter of the nozzle hole had a direct effect on the injection and spray characteristics. It was confirmed that the larger the diameter of the nozzle hole, the higher the injection quantity, the spray tip penetration, the spray area, and the spray width. In addition, it was confirmed that the near-field spray, which has little influence of ambient air, has a great correlation with the injection rate.

• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.2
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• pp.210-217
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• 2022

Chemical warfare agents(CWA) such as nerve agents and vesicating agents show lethality by skin contamination. Skin protection, therefore, is one of the top priorities to deal with the growing threat from CWA. In an attempt to develop the most effective topical skin protectant(TSP), candidate substances including PFPE(perfluorinated polyether), PTFE(polytetrafluoroethylene), glycerin, and polysaccharides were evaluated in forms of various formulations against nerve agent simulant DMMP(dimethylmethyl phosphonate) penetration. The protective efficacy of the formulation against DMMP penetration was estimated as the onset time of color change of the KM9 chemical agent detection paper. Based on this study, it was found that several PFPE- and glycerin-based formulations exhibit remarkably superior efficacy as a protective cream. This protective cream is expected to be used as TSP for military application after further research.

• Journal of ILASS-Korea
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• v.28 no.1
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.1
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• pp.67-74
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• 2013

A jet in a crossflow (JICF) has been extensively studied because of its wide applications in technological systems, including fuel injection into a ram-combustor. However, in the case of insufficient mixing performance of the liquid jet into the crossflow, the flame in a ram-combustor is unstable. In this study, the nonuniform flame and combustion instabilities due to lack of mixing performance were experimentally investigated. By performing correlations to predict the penetration height and break-up point, the spray and mixing characteristics of JICF have been studied. In particular, the improved correlations of penetration height are proposed in two distinctive domains depending on the X/d location of the crossflow.