• 한국자동차공학회논문집
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• 제12권3호
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• pp.10-18
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• 2004

It is well known that the stratified charge combustion has many kind of advantages to combustion characteristics, such as higher thermal efficiency and less CO, NOx levels than conventional homogeneous mixture combustion. Although this combustion can be caused low fuel consumption, it is produced the high unburned hydrocarbon and soot levels because of different equivalence ratio in the combustion chamber. Moreover it has a lot of possibility of low output and misfire if the mixture gas would not be in existence around the spark plug. In this paper, fundamental studies for stratified combustion were carried out using a constant volume combustion chamber. The effect of locally mixture gas distribution according to control the direct injection and premixed injection in the chamber were examined experimentally. In addition, the effects of turbulence on stratified charge combustion process were observed by schlieren photography.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.265-266
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• 2015

The multi-environment PDF model coupled with flamelet generated manifolds(FGM) has been developed for a large eddy simulation of turbulent partially premixed lifted flame. This approach has a capability to realistically account for the transport and evolution of probability density function for mixture fraction and progress variable with the manageable computational burden. Using the tabulated chemistry, it is possible to track radical distributions which is important to predict autoignition process with the vitiated coflow environment. Numerical results indicate that the present yields the good agreement with experimental data in terms of mixture fraction, temperature, and species mass fractions.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1436-1448
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• 2006

This paper describes the effects of injection rate shaping on the combustion, fuel consumption and emission of $NO_x$ and soot of a medium duty diesel engine. The focus is on the influence of four different injection rate shapes, square type 1, square type 2, boot and ramp, with a variation of maximum injection pressure and start of injection (SOI). The experiments were carried out on a 1 liter single cylinder research diesel engine equipped with an amplifier-piston common rail injection system, allowing the adjustment of the injection pressure during the injection event and thus injection rate as desired. Two strategies to maintain the injected fuel mass constant were followed. One where rate shaping is applied at constant injection duration with different peak injection pressure and one strategy where rate shaping is applied at a constant peak injection pressure, but with variable injection duration. Injection rate shaping was found to have a large effect on the premixed and diffusion combustion, a significant influence on $NO_x$ emissions and depending on the followed strategy, moderate or no influence on soot emission. Only small effects on indicated fuel consumption were found.

• 한국산업융합학회 논문집
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• 제18권2호
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• pp.110-118
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• 2015

In this study, it is designed and used the test engine bed which is installed with turbocharger, and in addition to equipped using by oxygen adder. It has been controlled the oxygen volumetric fraction of intake air chrge, and supercharged flow rate into the cylinder of SI 4-stroke engine, and then, has been analyzed engine performance, combustion characteristics, and exhaust emission as analysis parameters. The tested parameters were the oxygen fraction and the variation of engine speed and air-fuel ratio.

• 한국안전학회지
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• 제23권6호
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• pp.38-43
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• 2008

Significant portion of the fire accident is caused by some troubles in electric circuits. To prevent the fire induced by those electric trouble, some indications of electric fire need to be suitably detected at the first stage of the fire development. With this background, the characteristics of soot yielding of electric cables have been investigated using a light extinction method. In this study, a light scattering method was compared with the light extinction method. A slot-type premixed-flame combustor was traversed to bum three types of electric cables by compulsion, then the mass decrease rate and the soot densities were measured. According to the experimental results, the light scattering method is preferred to the light extinction method when the soot yield ratio is relatively small. Thus the former method is more suitable to detect the occurrence of an electric fire in a power distributer box.

• 대한기계학회논문집B
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• 제31권11호
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• pp.926-935
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• 2007

The NOx emission characteristics of DME in laminar coaxial jet and counterflow nonpremixed flames were investigated using experimental and numerical approaches, respectively. The flame structure and NOx emission of DME were compared with those of $C_2H_6$ and $C_3H_8$. The DME flame was calculated using the Kaiser's mechanism, while the $C_2H_6$ and $C_3H_8$ flames were calculated using the $C_3$ mechanism. These mechanisms were combined with the modified Miller-Bowman mechanism for the analysis of NOx. Experimental results show in coaxial jet flame that DME flame has the characteristics of partial premixed flame and the flame length decreases up to 1/3 than that of $C_3H_8$ in the same condition of fuel mass flowrate. Then, the NOx emission of DME decreases to 40% approximately, comparing with that of $C_3H_8$. In the calculated results of counterflow nonpremixed flame, DME flame shows the $EI_{NO}$ decreases up to 50% approximately than those of$ C_2H_6$ and $C_3H_8$ flames when the equivalent fuels are consumed per unit mass and time. Although the overall NOx reaction path of DME is similar with other hydrocarbon fuels, it can be identified that DME flame has a distinct NO reduction mechanism due to the reburning NO chemistry in fuel rich region. From these results, we can conclude that the different NOx emission characteristics of DME flame with other hydrocarbon fuels are attributed to not the temperature increase and the activation of NO reactions due to O atom in DME fuel but the rapid processes of pyrolysis/oxidation.

• 한국화재소방학회논문지
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• 제13권1호
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• pp.37-47
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• 1999

부유중인 분진의 화재 및 용기 또는 파이프의 미세한 균열에서 비산되는 가연성 액체의 분무화재의 위험성은 착화후의 고속 확산과 높은 열방출율로 인하여 매우 높은 것으로 알려졌다. 이에 대한 연구는 주로 실험적으로나 또는 거시적인 관점의 해석으로 제한되어 왔다. 본 연구는 미시적인 관점의 해석으로서 분진 및 분무를 가연성 미세 액적으로 가정하여 그의 증발과 착화에 대하여 연구하였다. 첫 단계로서 일열의 액적 배열을 계산영역으로 하여, 비정상 이차원 보존방정식들을 적용하였다. 수치해석은 일반화된 비직교 좌표계를 사용하였고, 화학반응은 Arrhenius의 법칙에 의하여 반응속도가 제어되는 일단계 반응을 고려하였다. 계산결과는 액적 주위의 온도와 반응물질의 농도분포를 시간에 따라 보여준다. 주위의 산소가 증발하는 액적의 연료와 섞이기 시작하고 착화 조건에 다다르면, 급격한 발열반응이 예혼합된 가스로부터 일어나기 시작한다. 최대온도 영역은 점차적으로 액적 표면으로 이동하며 최대온도는 착화이후 급격히 상승한다. 연료와 산소의 농도는 최대온도 영역 근처에서 최소값을 보인다. 따라서 착화순간에는 예혼합연소의 양상을 띠는 것으로 나타났다. 이후에는 예혼합 가스의 소멸로 확산연소의 양상을 띠게 된다. 액적간의 거리는 중요한 요소로서 멀리 떨어져 있는 경우부터 액적간의 거리가 가까워지면 착화지연 시간이 줄여들어 착화가 빨리 일어나는 것으로 관찰되었다. 또한 착화 후에는 최대온도 영역이 일열의 중심선으로부터 멀어지는 것으로 나타났는데 이것은 중심부근의 산소가 먼저 소모되고 외부로부터의 산소공급도 화염에 의해 차단되어 나타나는 현상이다. 이번 연구로 미세적인 착화현상에 대한 이해를 높이게 되었고 추후 복잡한 배열에 대한 연구도 가능할 것이다.