• 한국연소학회지
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• 제18권4호
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• pp.37-43
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• 2013

The effects of preferential diffusion of hydrogen in interacting counterflow $H_2$-air and CO-air premixed flames were investigated numerically. The global strain rate was varied in the range $30-5917s^{-1}$, where the upper bound of this range corresponds to the flame-stretch limit. Preferential diffusion of hydrogen was studied by comparing flame structures for a mixed average diffusivity with those where the diffusivities of H, $H_2$ and $N_2$ were assumed to be equal. Flame stability diagrams are presented, which show the mapping of the limits of the concentrations of $H_2$ and CO as a function of the strain rate. The main oxidation route for CO is $CO+O_2{\rightarrow}CO_2+O$, which is characterized by relatively slow chemical kinetics; however, a much faster route, namely $CO+OH{\rightarrow}CO_2+H$, can be significant, provided that hydrogen from the $H_2$-air flame is penetrated and then participates in the CO-oxidation. This modifies the flame characteristics in the downstream interaction between the $H_2$-air and CO-air flames, and can cause the interaction characteristics at the rich and lean extinction boundaries not to depend on the Lewis number of the deficient reactant, but rather to depend on chemical interaction between the two flames. Such anomalous behaviors include a partial opening of the upper lean extinction boundary in the interaction between a lean $H_2$-air flame and a lean CO-air flame, as well as the formation of two islands of flame sustainability in a partially premixed configuration with a rich $H_2$-air flame and a lean CO-air flame. At large strain rates, there are two islands where the flame can survive, depending on the nature of the interaction between the two flames. Furthermore, the preferential diffusion of hydrogen extends both the lean and the rich extinction boundaries.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3452-3457
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• 2007

Experiments were carried out in an atmopheric pressure, lab-scale gas turbine combustor to see the effect of partial premixing on unstable flame structure and $NO_X$ emission characteristics. The swirl angle is 45 deg., fuel-air mixing degrees were varied 0, 50, and 100% respectively at equivalence ration ranging from 0.53 to 0.79. The evaluation of phased-locked OH chemiluminescence images were acquired with an ICCD. $NO_X$ emission characteristics were also investigated at each experimental condition. The effect of the fuel-air mixing degree on the flame structure was obtained from phase-locked $OH^*$ images. And it was obtained from local heat release characteristics that the information about the region which the combustion instability was amplified or damped. It also could be confirmed that ${\sigma}$ has greatly influence on $NO_X $emission characteristics at lean regimes. It would be expected that it could provide invaluable data for understanding the mechanism of combustion instability

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.111-115
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• 1999

In order to enhance the burner performance of household gas fired absorption chiller/heaters, the operating condition(excess air $\approx$ 10%) of the burner currently being used was required to be optimized. In this regard, we examined where the $CO_{\min}$. emission limit was located between blow off and yellow tip limit and how much amount of excess air was exhausted by means of observing blow off and yellow tip limit. It was found that the $CO_{\min}$ limit(excess air ${\approx}$ 4%) was determined near the yellow tip limit. The effect of exhaust pressure on the $CO_{\min}$. limit was that, if exhaust pressure was higher than that in steady condition, higher air blower fan rpm is demanded to maintain the $CO_{\min}$ limit. Therefore, it was necessary to optimize the operating condition of burner in terms of a thermal efficiency and safety.

• 한국분무공학회지
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• 제16권4호
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• pp.167-175
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• 2011

The HCCI engines have been known with high efficiency and low pollution and can be actualized as the new internal combustion engines. However, As for(??) the ignition and combustion depend strongly on the oxidation reaction of the fuel, so it is difficult to control auto-ignition timing and combustion duration. Purpose of this paper is creating the database for development of multi-dimensional simulation and investigating the influence of different molecular structure. In this research, the effect of n-heptane mole ratio in fuel (XnH) on the ignition delay from homogeneous charge compression ignition(HCCI) has been investigated experimentally. By varying the XnH, it was possible to ascertain whether or not XnH is the main resource of ignition delay. Additionally, the information on equivalence ratio for varying XnH was obtained. The tests were performed on a RCM (Rapid Compression Machine) fueled with n-heptane and iso-octane. The results showed that decreasing XnH (100, 30, 20, 10,0), the ignition delays of low temperature reaction (tL) and high temperature reaction (tH) is longer. And the temperature of reaction increases by about 30K. n-heptane partial equivalence ratio (fnH) affect on tL.and TL. When ${\phi}$nH was increased as a certain value, tL was decreased and TL was increased.

• 한국추진공학회지
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• 제20권6호
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• pp.61-69
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• 2016

본 연구는 이중 선회 가스터빈 연소기에서 연소실 길이와 열용량을 변수로 연소불안정 현상과 관련된 결과이다. 특히 열용량이 상대적으로 작은 구간에서 연소실 길이가 길어지면 공진 주파수의 값이 일정하게 유지되는 맥놀이 현상이 발생하는 것이 확인되었다. 이러한 맥놀이 현상은 메인 화염과 파일럿 화염이 각각 다른 주기로 거동하기 때문에 발생되었으며, 연소실 길이가 증가하여도 주파수의 값이 변하지 않는 현상은 메인 화염과 파일럿 화염의 서로 다른 상호작용 결과라고 판단된다.

• 한국연소학회지
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• 제21권2호
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• pp.29-37
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• 2016

This study described the experimental investigations of combustion instability in a model gas turbine combustor. Strong coupling between pressure oscillations and unsteady heat release excites a self-sustained acoustic wave, which results in a loud and annoyed sound, and may also lead to a structural damage to the combustion system. In this study, in order to examine the combustion instability phenomenon of a dual swirling combustor configuration, the information of heat release and pressure fluctuation period with respect to the variation in both thermal power and combustor length was collected experimentally. As a result, the fundamental acoustic frequency turned out to increase with the increasing thermal power without respect to the combustor length. The frequency response to the combustor length was found to have two distinct regimes. In a higher power regime the frequency significantly decreases with the combustor length, as it is expected from the resonance of gas column. However, in a lower power regime it is almost insensitive to the combustor length. This insensitive response might be a result of the beating phenomenon between the interacting pilot and main flames with different periods.

• 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.