• 대한기계학회논문집B
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• 제34권12호
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• pp.1043-1050
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• 2010

HCCI엔진에는 농도성층화와 열적성층화가 존재하고, 이것들은 착화와 연소과정에 영향을 미치고 있다. 본 연구에서는 예혼합기의 불균질성이 HCCI연소과정에 미치는 영향에 대해서 조사하였다. 우선 4행정광학엔진을 이용하여 잔류가스가 있는 경우와 급속압축장치를 이용하여 잔류가스가 없는 경우의 예혼합기의 불균질성에 대하여 비교분석하였다. DME를 연료로 이용하고 프래밍카메라를 사용하여 2차원화학발광이미지를 취득하였다. 그 결과, 잔류가스가 있는 불균질 한 경우에 4행정엔진실험에서는 연소현상이 공간적으로 연소현상의 시간차이가 발생하였다. 잔류가스가 없는 급속압축장치의 실험에서는 4행정기관의 결과에 비해서 더 적은 공간적인 변화가 존재하는 것을 알 수 있었다.

• 한국자동차공학회논문집
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• 제18권5호
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• pp.1-8
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• 2010

The introduction of mixture heterogeneity has been considered to be one of the ways to avoid knocking, as it reduces the pressure rise rate in HCCI Combustion. The purpose of this research was to investigate the effects of heterogeneity, in particular thermal stratification and fuel strength stratification, on HCCI Combustion fueled with DME and n-Butane. Thermal stratification is formed in the Combustion Chamber of a Rapid Compression Machine with three kinds of pre-mixture, each with different properties. The stratified charge mixture was adiabatically compressed, throughout which cylinder gas pressure and two-dimensional chemiluminescence images were measured and analyzed.

• 대한기계학회논문집B
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• 제34권12호
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• pp.1035-1042
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• 2010

HCCI 엔진연소에서 열적성층화 효과는 노킹을 회피하는 수단으로서 생각되고 있다. 본 연구에서는 DME 와 n-Butane 을 연료로 하는 HCCI 엔진연소의 열적성층화 효과를 조사하였다. 예혼합기가 연소실내부에 투입되고 부력의 효과를 이용하여 연소실 내부에 열적성층화를 형성한다. 그 뒤에 피스톤의 압축에 의해서 단열압축 시킨 후 연소실압력과 2 차원화학발광법을 계측하여 해석하였다. 열적성층화가 존재하는 경우에는, 저온산화반응과 고온산화반응의 시작시기가 균질한 경우에 비해서 진각되었고 연소기간은 길어졌다. 발광의 시작은 온도가 높은 곳에서부터 시작하여 온도가 낮은 곳으로 전파 되는 것을 확인하였고 발광기간도 길어짐을 확인하였다.

• 한국자동차공학회논문집
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• 제17권3호
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• pp.8-14
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• 2009

Effect of heterogeneity of combustion chamber has been thought as one of the way to avoid dramatically generating heat in HCCI Combustion. The purpose of this research is to investigate the effect of heterogeneity, especially thermal stratification and fuel strength stratification on HCCI Combustion fueled with DME and n-Butane. Thermal stratification is formed in Combustion Chamber of Rapid Compression Machine with 3 Kinds of pre-mixture has different properties. The stratified charge mixture is adiabatic compressed and on that process, in cylinder gas pressure and two-dimensional chemiluminescence images are measured and analyzed.

• 대한기계학회논문집B
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• 제24권1호
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• pp.68-74
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• 2000

Experimental investigation on flame spread along suspended droplet arrays have been conducted with various droplet spacings and ambient air velocities. Especially, an opposed air stream is introduced to simulate fundamental flame spread behaviors in spray combustion. High-speed chemiluminescence imaging technique of OH radicals has been adopted to measure flame spread rates and to observe various flame spread behaviors. The fuel used is n-Decane and the air velocity varies from 0 to 17cm/s. The pattern of flame spread is grouped into two: a continuous mode and an intermittent one. It is found that there exists droplet spcings, above which flame spread does not occur. The increase of ambient air velocity causes the limit droplet spacing of flame spread to become small due to the increase of apparent flame stretch. As the ambient air velocity decreases, flame spread rate increases and then decreases after taking a maximum flame spread rate. This suggests that there exists a moderate air flowing to give a maximum flame spread rate due to enhanced chemical reaction by the increase of oxidizer concentration.

• 한국연소학회지
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• 제3권2호
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• pp.1-11
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• 1998

Experimental investigation on flame spread of blended fuel droplet arrays has been conducted for droplet diameters of 1.0mm and 0.75mm using high-speed chemiluminescence images of OH radical. The flame spread rate is measured with blended fuel composition, droplet diameter, and droplet spacing. Flame spread is categorized into two: a continuous mode and an intermittent one. There exist a limit droplet spacing, above which flame does not spread, and a droplet spacing of maximum flame spread, which is closely related to flame diameter. It is seen that flame spread rate is mainly dependent upon the relative position of flame zone within a droplet spacing. In case of large droplet, the increase of % volume of Heptane induces the shift of limit droplet spacing to a larger spacing since volatile Heptane plays a role of an enhancer of flame spread rate. In case of small droplet, the increase of % volume of Heptane leads to the shift of limit droplet spacing to a smaller droplet spacing. This is so because of the delayed chemical reaction time by the rapid increase of mass flux of fuel vapor for small droplet.

• 한국자동차공학회논문집
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• 제16권5호
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• pp.157-163
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• 2008

The HCCI combustion mode poses its own set of narrow engine operating by knocking. In order to solve this, inhomogeneity method of mixture and temperature is suggested. The purpose of this research is to get fundamental knowledge about the effect of thermal stratification on HCCI combustion of PRF -Air mixture. The temperature stratification is made by buoyancy effect in combustion chamber of RCM. The analysis items are pressure, temperature of in-cylinder gas and combustion duration. In addition, the structure of flames using the two dimensional chemiluminescence's images by a framing camera are analyzed. Under stratification, the LTR starting time and the HTR starting time are advanced than that of homogeneous. Further, the LTR period of homogeneous conditions became shorter than that of the stratified conditions. With the case of homogeneous condition, the luminosity duration becomes shorter than the case of stratified condition. Additionally, under stratified condition, the brightest luminosity intensity is delayed longer than at homogeneous condition.

• 대한기계학회논문집B
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• 제23권1호
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• pp.131-139
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• 1999

Experimental investigations on flame spread in droplet arrays have been conducted under supercritical ambient pressures of fuel droplet. Flame spread rates are measured for n-Decane droplet of diameters of 0.75 and 1.0mm, using high speed images of OH chemiluminescence up to 3.0MPa. The pattern of flame spread is categorized into two: a continuous mode and an intermittent one. There exists a limit droplet spacing, above which flame spread does not occur. Flame spread rate with the decrease of droplet spacing increases and then decreases after takin& a maximum. It is also seen that there exists a limit ambient pressure, above which flame spread does not occur. Flame spread rate decreases monotonically with the increase of ambient pressure. Exceptionally, In the case of a small droplet spacing, flame spread with the increase of ambient pressure is extended to supercritical pressures of fuel droplet. This is caused by enhanced vaporization with the increase of ambient pressure. Consequently, in flame spread with droplet droplet spacing, the relative position of flame to droplet spacing plays an important role. The monotonic decrease with ambient pressure is mainly related to the reduction of flame radius in subcritical pressures and the extension to supercritical pressures of flame spread is caused by the reduction of ignition time of unburnt droplet due to the enhanced vaporization at supercritical pressures.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.362-367
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• 2003

It is shown that the effect of variable parameters on flame structures and NOx emissions in the laminar partially premixed methane-air flames with a co-axial Bunsen burner. Objectives of this paper is to understand the effects of flow variables on NOx emissions and the flame structure with OH chemiluminescence, including reconstructed image by abel inversion processing at each conditions. A fuel flowrate of 200 [cc/min] was fixed and the amount of air was varied from 400 to 1200 [cc/min]. The experimental variables were equivalence ratio(${\Phi}$ fuel split percentage(${\sigma}$ and inner tube recess(x/D). Flow conditions were ranged from $1.36{\sim}4.76$(equivalence ratio), $50{\sim}100$(fuel split percentage) and $0{\sim}20$(inner tube recess). NOx analyzer and ICCD camera with a OH filter were used as a main experimental apparatus. In addition, Abel inversion, which is a kind of tomography and valuable to estimate a two-dimensional structure of co-axial flames from cubical information, was employed for combustion diagnostics. Results from this study indicate that the main effects depend on equivalence ratio and next sigma, x/D for NOx production and OH formation. Throughout Abel inversion, we could affirm the maximum position and the tendency of OH radical intensity by variants at five axial heights above the burner exit.