• Journal of Welding and Joining
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• 제13권1호
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• pp.127-137
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• 1995

The possibility of new GMAW process using economic shielding gases including CO$_{2}$ gas was investigated on the effect of shielding gas on weldabilty. In the optimum welding condition using 600A power source, FCAW process showed low depositions rate, 114 g/min at 300A, but new GMAW using other mixed shielding gases exhibited high deposition rate, 208-224 g/min at 450A. TIME gas, Ar+CO$_{2}$ gas and Ar+CO$_{2}$+O$_{2}$ gas as a shielding gas were able to be used to the very high welding current(450A), moreover TIME gas and Ar+CO$_{2}$ gas showed the highest arc stability among shielding gases studied in this experiments. The weld penetration was performed by axial spray transfer mode of weld droplet. On the basis of workability, weldability and economic point of view, Ar mixture (80%Ar+20%CO$_{2}$) gas was recommended as a shielding gas for the development and application of new GMAW process. This shielding gas showed the low spatter, good weld quality, stable arc and low cost at the region of high welding current.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년 추계학술발표대회 개요집
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• pp.63-65
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• 2006

The paper deals with the effect of hydrogen or helium in argon as a shielding gas on GTA welding of austenitic stainless steel. The studies were carried out in GTA(Gas Tungsten Arc) welding with a non-consumable electrode in case with different volume additions of hydrogen or helium to the argon shielding gas, i.e $5%H_2,\;10%H_2$, 30%He and 67%He. The penetration, welding voltage, microstructure and mechanical property were examined. The deepest penetration was obtained from the sample which was welded under shielding gas of $10%H_2$. The studies showed that hydrogen or helium addition to argon changes the static characteristic of the welding arc. The hydrogen or helium addition to argon increases arc power and the quantity of the material melted. The weld metal penetration depth and its width increased with increasing hydrogen or helium content. Additionally, welding voltage increased with increasing hydrogen or helium content.

• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.2040-2052
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• 2005

The present paper centers on the establishment of a quantified relationship between the macroscopic visual parameters of a Diesel spray and its most influential factors. The factors considered are the ambient gas density, as an external condition relative to the injection system, and nozzle hole diameter and injection pressure as internal ones. The main purpose of this work is to validate and extend the different correlations available in the literature to the present state of the Diesel engine, i.e. high injection pressure, small nozzle holes, severe cavitating conditions, etc. Five mono-orifice, axi-symmetrical nozzles with different diameters have been studied in two different test rigs from which one can reproduce solely the real engine in-cylinder air density, and the other, both the density and the pressure. A parametric study was carried out and it enabled the spray tip penetration to be expressed as a function of nozzle hole diameter, injection pressure and environment gas density. The temporal synchronization of the penetration and injection rate data revealed a possible explanation for the discontinuity observed as well by other authors in the spray's penetration law. The experimental results obtained from both test rigs have shown good agreement with the theoretical analysis. There have been observed small but consistent differences between the two test rigs regarding the spray penetration and cone angle, and thus an analysis of the possible causes for these differences has also been included.

• Journal of Welding and Joining
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• 제16권1호
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• pp.77-87
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• 1998

This paper deals with the effect of laser welding parameters on the weld formation. Thin steels for automotive application were prepared so as to be welded with high power carbon dioxide laser system. Major process parameters were position of focus and travel speed. The effect of shielding gas was also discussed by employing the high speed photometry. Test results showed that the optimal position of focus varied in accordance with the joint configuration; bead-on-plate, butt or lap welding. It was recommended that the position of focus for the lap welding be located at slightly inner part of the material to be welded. In this case, however, it was noticeable that the weld penetration ratio, d/t$_{0}$ dropped drastically at the critical region. Results also demonstrated that both the bead width and penetration reduced as the travel speed increased. The penetration ratio showed two distinct regions; stabilized zone at the lower range of the travel spped and sudden drop zone at the higher range of travel speed. Lower limit of the penetration for acceptable weld was proved to be about 90% of the parent metal thickness based on the physical properties of the weld. Mixed gas application for both the shielding of molten metal and laser induced plasma control was recommended as far as the penetration was concerned.d.

• 동력기계공학회지
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• 제13권6호
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• pp.13-21
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• 2009

This basic study is required to examine spray or jet behavior depending on fuel phase. In this study, analyses of diesel fuel(n-Tridecane, $C_{13}H_{28}$) spray and natural gas fuel(Methane, $CH_4$) jet under high temperature and pressure are performed by a general-purpose program, ANSYS CFX release 11.0, and the results of these are compared with experimental results of diesel fuel spray using the exciplex fluorescence method. The simulation results of diesel spray is analyzed by using the combination of Large-Eddy Simulation(LES) and Lagrangian Particle Tracking(LPT) and of a natural gas jet is analyzed by using Multi-Component Model(MCM). There are two study variables considered, that is, ambient pressure and injection pressure. In a macroscopic analysis, the higher ambient pressure is, the shorter spray or jet tip penetration is at each time after start of injection. And the higher injection pressure is, the longer spray or jet tip penetration is at each time after start of injection. When liquid fuel is injected, droplets of the fuel need some time to evaporate. However, when natural gas fuel is injected, the fuel does not need time to evaporate. Gas fuel consists of minute particles. Therefore, the gas fuel is mixed with the ambient gas more quickly at the initial time of injection than the liquid fuel is done. The experimental results also validate the usefulness of this analysis.

• 한국가스학회지
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• 제24권4호
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• pp.25-31
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• 2020

산업용 혹은 발전용 가스터빈에 사용되는 이중 콘형 예혼합 연소기의 연소 특성을 이해하기 위하여 실험적 연구를 수행하였다. 노즐의 여러 연료 분사 방식에 대하여 NOx와 CO의 배출 특성, 화염 안정성 및 연소실 온도 분포에 대한 연소특성을 비교하였다. 주 연구 결과로는 연료홀 개수가 동일하고 연료 홀 직경이 감소하는 경우와 연료 홀면적이 동일하고 연료 홀 수가 감소되는 경우 연료의 연소용 공기층 침투가 커지기 때문에 NOx의 배출은 감소하지만 화염 안정성은 감소하게 된다. 그리고 동일 연료 홀 면적을 이용하는 분사방식에 있어서 연료 홀을 교차 변경하는 경우 연료의 평균 침투거리 증가로 NOx의 배출이 감소되며 연료 침투거리가 적은 연료가 화염을 안정화시키는 역할을 한다.

• 한국분무공학회지
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• 제10권1호
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• pp.35-42
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• 2005

The present study has numerically and experimentally investigated the spray behavior of liquid jet injected in subsonic cross-flow. The corresponding spray characteristics are correlated with jet operating parameters. The spray dynamics are known to be distinctly different in the three regimes: the column, the ligament and the droplet regimes. The behaviors of column, penetration and breakup of liquid jet have been studied. Numerical and physical models are base on a modified KIVA code. The primary atomization is represented by a wave model base on the KH(Kelvin-Helmholtz) instability that is generated by a high interface relative velocity between the liquid and gas flows. In odor to capture the spray trajectory, CCD camera has been utilized. Numerical and experimental results indicate that the breakup point is delayed by increasing gas momentum ratio and the penetration decreases by increasing Weber number.

• 한국산업보건학회지
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• 제10권1호
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• pp.160-169
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• 2000

Daily indoor and outdoor nitrogen dioxide ($NO_2$) concentration for 30 days were measured in 28 houses with questionnaire of housing characteristics in Brisbane, Australia. Using mass balance equation and regression analysis, penetration factors and source strength factors were calculated. The penetration factors of 27 houses except one house were between zero and 1, though penetration factor should be between zero and 1 by means of mass balance equation. Relationship between indoor and outdoor concentrations in each 27 house was calculated using regression analysis. According to the obtained linear regression equation, the slope means penetration factor and the intercept means source strength factor. Calculated mean and standard deviation of coefficients of determination ($R^2$) in electric and gas range houses were $0.70{\pm}0.13$ and $0.57{\pm}0.21$, respectively. The source strength factors were more than zero in 27 houses. Mean and standard deviation of slopes in electric and gas range houses were $0.65{\pm}0.18$ and $0.56{\pm}0.12$, respectively. Mean and standard deviation of intercepts in electric and gas range houses were $1.49{\pm}1.25$ and $5.77{\pm}3.55$, respectively. Air exchange rate and source strength were calculated from penetration factor and source strength factor, respectively. Geometric mean and standard deviation of calculated air exchange rates in 27 houses were $1.1/hr{\pm}1.5$. Presence of gas range was the most significant factor contributing to indoor $NO_2$ level in house characteristics (p=0.003). In gas range houses, source strengths ranged from 4.1 to $33.1cm^3/hr{\cdot}m^3$ with a mean $12.7cm^3/hr{\cdot}m^3$ and a standard deviation 9.8. The source strengths of gas range houses were significantly different from those of electric range houses by t-test (p<0.001)

• 한국연소학회지
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• 제22권2호
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• pp.36-41
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• 2017

Aero gas turbine engines must demonstrate their ability to be ignited on ground conditions or relighted in flight. The electric spark ignition is usually used in current aero gas turbine engines. Experiments on ignition characteristics relating to spark igniter penetration depth under atmospheric pressure and temperature conditions were conducted on the model combustor which is scaled in 1/18. Exciter was operated during 2 seconds, and successful ignition phenomena were confirmed by the pressure rising sharply in combustor. In addition, instantaneous ignition images were captured by a high-speed camera. It showed kernel propagation and successful ignition events in the sector model combustor. Ignition test results showed that ignition limit with increase in penetration depth of the igniter plug was wider. When the penetration depth of the igniter plug increased under the same fuel injection pressure condition, successful ignition events were obtained in higher differential pressure conditions between inlet and outlet of the combustor. The results demonstrate that the ratio of the combustible mixture, which is exposed to the high temperature environment around the igniter plug tip, increases. Thereby affect the combustor ignition performance.

• Journal of Advanced Marine Engineering and Technology
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• 제29권1호
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• pp.17-24
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• 2005

The characteristics of diesel spray have effect on the engine Performance such as power. fuel consumption and emissions. Therefore, This study was Performed to investigate the effect of various injection parameters. In this study. the experiment is performed by using the high temperature and high pressure chamber. Spray behaviors are visualized by using the high speed camera and spray angle. Penetration etc. are measured. Experimental results are summarized as follows ; 1) Correlations of spray Penetration is expressed as follows $$0 $$t_b 2) Correlations of spray Angle is expressed as follows $$T_a=293K \;;\; tan({\theta}/2)=0.59({\rho}_a/{\rho}_f)^{0.437}$$ $$T_a=473K\;;\; tan({\theta}/2)=0.588({\rho}_a/{\rho}_f)^{0.404}$$ 3) The measured macro characteristics - spray tip penetration and spray angle agreed well with established correlations.