• International Journal of Automotive Technology
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• 제7권7호
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• pp.763-768
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• 2006

Emission reduction in the cold start period of SI engines is crucial to meet stringent emission regulations such as SULEV Emissoin reduction is the starting point of the study in the which the variable valve timing (VVT) technology may be one promising method to minimize cold start emissions while maintaining engine performance. This is because it is possible to change valve overlap and residual gas fraction during cold start and idle operations. Our previous study showed that spark timing is another important factor for reducing cold-start emissions since it affects warm-up time of close-coupled catalysts (CCC) by changing exhaust gas temperature. However, even though these factors may be favorable for reduction of emissions, they may deteriorate combustion stability in these operating conditions. This means that the two variables should be optimized for best exhaust emissions and engine stability. This study investigated the effects of valve and spark timings in idle performance such as combustion stability and exhaust emissions. Experiments showed that valve timings significantly affected engine stability and exhaust emissions, especially CO and $NO_x$, due to change in residual gas fraction within the combustion chamber. Spark timing also affects HC emissions and exhaust gas temperature. Yet it has no significant effects on combustion stability. A control strategy of proper valve timing and spark timing is suggested in order to achieve a reduction in exhaust emissions and a stable operation of the engine in a cold start and idle operation.

• 한국항공우주학회지
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• 제31권8호
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• pp.69-76
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• 2003

액체로켓 연소기 내의 막냉각 특성 분석을 위한 비회체 분무연소에 대한 수치해석을 수행하였다. 막냉각 연료의 특성에 따른 연소기 벽면의 온도변화를 살펴보기 위하여 막냉각용 연료의 유랑, 막냉각용 액적의 직경, 그리고 공기/연료 혼합비를 매개변수로 한 수치해석을 수행하여 연소기 벽면의 온도는 막냉각용 연료 액적 직경의 변화에는 큰 영향을 받지 않지만 막냉각용 연료 유량 및 공기/연료 혼합비에 영향을 받고 있음을 확인하였다. 또한, 추진기관 벽면으로 전달되는 전도 및 복사열유속을 고찰함으로서 이러한 액체 추진기관의 연소특성을 이해하기 위해서는 열복사 및 물성치의 적절한 고찰이 필요함을 지적하였다.

• International Journal of Automotive Technology
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• 제7권4호
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• pp.391-397
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• 2006

The soot yield has been studied by a premixed propane-oxygen-inert gas combustion in a specially designed disk-type constant-volume combustion chamber to investigate the effect of pressure, temperature and turbulence on soot formation. Premixtures are simultaneously ignited by eight spark plugs located on the circumference of chamber at 45 degrees intervals in order to observe the soot formation under high temperature and high pressure. The eight converged flames compress the end gases to a high pressure. The laser schlieren and direct flame photographs with observation area of 10 mm in diameter are taken to examine the behaviors of flame front and gas flow in laminar and turbulent combustion. The soot volume fraction in the chamber center during the final stage of combustion at the highest pressure is measured by the in-situ laser extinction technique and simultaneously the corresponding burnt gas temperature by the two-color pyrometry method. The changes of pressure and temperature during soot formation are controlled by varying the initial charging pressure and the volume fraction of inert gas compositions, respectively. It is found that the soot yield increases with dropping the temperature and raising the pressure at a constant equivalence ratio, and the soot yield in turbulent combustion decreases as compared with that in laminar combustion because the burnt gas temperature increases with the drop of heat loss for laminar combustion.

• 대한기계학회논문집B
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• 제39권2호
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• pp.125-134
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• 2015

본 논문은 대형 상용기관을 모사한 정적연소실에서 매립지 가스의 연소 특성에 대한 복수의 논문 중 세 번째로, 정적 연소실에서 토치를 적용하여 그 효과를 분석하였다. 실험 결과 토치의 체적에 관계없이 연소를 개선시키는 최적의 오리피스 면적 비율이 존재하며 오리피스가 매우 작은 경우 압력 상승비율은 직경 변화에 무관하게 일정 수준을 유지하거나 소폭 감소한다. 아울러 토치의 효과는 일차적으로 연소 시간단축에 영향을 주고 시간단축에 따른 전열량의 감소가 이후 압력상승에 기여한다. 마지막으로 메탄 분율이 적어 연소 조건이 나쁠수록 토치는 주로 주 연소 기간을 단축시키고, 반면 연소 조건이 좋은 경우 주로 초기 연소를 단축시키는 효과가 있다.

• 한국대기환경학회지
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• 제24권2호
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• pp.238-248
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• 2008

This study investigated mercury emission at various combustion conditions and analyzed mercury species in flue gas from coal combustion at a laboratory scale furnace in coal. The results of this study can be used to predict and to assess mercury emission at coal boilers and power plants. The coal used in the plants generally contains about $0.02{\sim}0.28\;mg$ of mercury per kg. Bituminous and anthracite coal used for the experiment contained 0.049 and 0.297 mg/kg of mercury, respectively. Mercury emissions during coal combustion at temperatures range of $600^{\circ}C$ to $1,400^{\circ}C$ was measured and analysed using Ontario Hydro method; the speciation changes were also observed in mercury emissions. The results showed higher fraction of elemental mercury than that of oxidised mercury at most temperatures tested in this experiment. The fraction of elemental mercury was lower in combustion of anthracite coal than in bituminous combustion. As expected, equilibrium calculations and real power plants data showed good similarity. The distribution of particle size in flue gas had the higher peak in size above $2.5\;{\mu}m$. However the peak of mercury enrichment in dust was at $0.3\;{\mu}m$, which could be easily emitted into atmosphere without filtration in combustion system. When the CEA(Chemical equilibrium and Application) code was used for combustion equilibrium calculation, Cl was found to be the important component effecting mercury oxidation, especially at the lower temperatures under $900^{\circ}C$.

• 대한기계학회논문집B
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• 제41권6호
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• pp.389-395
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• 2017

본 연구는 정적 연소 조건에서 Octane 단일 연료 액적의 매연 생성 거동에 관한 정보를 제공하기 위해 수행하였다. 이를 위해 동일한 분위기 압력($P_{amb}$) 1.0 atm과 산소 농도($O_2$) 21%, 질소 농도($N_2$) 79% 조건에서 초기 액적 직경($d_0$) 변화에 따른 Octane 액적의 매연 생성 특성 실험 결과를 제시하였다. Octane 액적 연소 가시화는 초고속 카메라를 사용하여 촬영하였고, 분위기 조건은 제어 시스템에 의해 동일한 조건을 유지하였다. Octane 액적 연소 결과, 매연 생성량은 동일한 분위기 조건에서 초기 액적 직경 변화의 영향이 크게 나타나지 않았다. 또한, 매연 체적 분율 최댓값($f_{vmax}$)은 $135^{\circ}{\sim}315^{\circ}$ 측정 방향에서 높은 결과를 보였다. 이는 액적 점화 이후 Igniter의 이동 과정에서 생성된 Soot-tail로 인해 매연 체적분율 결과가 증가된 것으로 나타났다.

• 한국자동차공학회논문집
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• 제11권4호
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• pp.29-36
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• 2003

A cylindrical constant volume combustion chamber was used to investigate the flow characteristics at spark plug and the combustion characteristics of inhomogeneous charge methane-air mixture under several parameters. The flow characteristics such as mean velocity and turbulence intensity was analyzed by hot wire anemometer. Combustion pressure development measured by piezoelectric pressure transducer was used to investigate the effect of initial charge pressure, excess air ratio and ignition times on combustion pressure and combustion duration. Mean velocity and turbulence intensity had the maximum value at 200 or 300ms and then decreased to beneath 0.05m/s gradually at 3 seconds. Second mixture is accompanied by an increase in the combustion rate, and that the higher the mass which is added in the second stage injection, the faster the burn rate.

• 한국연소학회지
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• 제14권4호
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• pp.17-24
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• 2009

Reburning is one of the most useful technologies for reducing nitric oxide in economically and technically. The reburning process was demonstrated as an effective NOx reduction method through injection of a secondary hydrocarbon fuel. An experimental study has been conducted to evaluate the effect of biomass reburning on NOx and CO formation in a light oil flamed combustion furnace. Reburning tests on NOx reduction of air-carried rice husk powder as the reburn fuel and light oil as the main fuel were performed in flames stabilized by a co-flow swirl and fuel staged burner, which was mounted at the front of the furnace. The results included flue gas emissions and temperature distribution in the furnace for several kinds of experimental conditions. It was observed clearly that NOx concentrations in the exhaust have considerably decreased due to effect of biomass reburning. The maximum NOx reduction rate was 42% when the reburn fuel fraction was 0.18. The CO emissions were kept under 42 ppmv in all experimental tests. And this paper makes clear that in order to decrease NOx concentration in the exhaust when the biomass reburning system is adapted, the control of some factors such as reburn fuel fraction and reburn zone fraction is very important.

• 한국자동차공학회논문집
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• 제14권5호
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• pp.172-180
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• 2006

This study was to analyze the effect of mixed fuel composition and mass fraction on the characteristics of evaporating diesel spray and combustion under the various ambient conditions. The characteristics of vaporization distribution and combustion were visualized by laser induced fluorescent method and direct photography. The experiments were conducted in the constant volume vessel and rapid compression expansion machine with optical access. Multi-component fuels mixed i-octane, n-dodecane and n-hexadecane were injected the vessel and rapid compression expansion machine with electronically controlled common rail injector. Experimental results show that fuel vapor formed stratified distribution. And vaporization and diffusion are become actively increasing in mass fraction of low boiling point component. Consequently multi-component fuels were expected to control the evaporating behavior according to their suitable mass fraction.

• 한국분무공학회지
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• 제19권4호
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• pp.211-215
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• 2014

The main purpose of this study is to provide basic information of droplet soot generation of decane fuel. To achieve this, this paper presents the experimental results on the decane droplet combustion conducted under various ambient pressure($P_{amb}$), and oxygen concentration($O_2$) conditions. At the same time, the experimental study was conducted in terms of soot volume fraction($f_v$) and its maximum value. Also, visualization of single fuel droplet was conducted by high resolution CCD camera and ambient pressure($P_{amb}$) and oxygen concentration($O_2$) was changed by control system. It was revealed that higher ambient pressure($P_{amb}$), and oxygen concentration($O_2$) enhanced the soot generation and improved the maximum soot volume fraction( $f_v$).