• 대한기계학회논문집B
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• 제26권6호
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• pp.805-810
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• 2002

Development of a small gas-turbine combustor for 100㎾ class APU(Auxiliary Power Unit) has been performed. This combustor is a reverse-annular type and has a tangential swiller in the liner head to improve the fuel/air mixing and flame stability. Three main and three pilot fuel injectors of the simplex pressure-swirl type are used. The performance target at the design condition includes a turbine inlet temperature of l170k, a combustion efficiency of 99%, a pattern factor of 30%, and an engine durability of 3000 hours. Under developing the combustor, we conducted the performance test of our first prototype(TS1) with some variants. As a result of the test, the performance targets of the combustor are satisfied except that the pattern factor is about 4% higher than the target value. Therefore, the second prototype(TS2) was redesigned and the performance test was conducted with the critical focus on the pattern factor and the exit mean temperature. We adopted TS2 four variants to check the improvement of the pattern factor. As a result, the pattern factors of several variants were satisfied with the performance target. Finally, the TS2A variant was chosen as a final combustor fur our APU model.

• 에너지공학
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• 제11권2호
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• pp.90-98
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• 2002

본 연구는 선회유동과 연소인자가 9.4L인 터보과급 디젤엔진의 성능과 배기가스특성에 미치는 영향을 실험적으로 고찰하였다. 일반적으로 디젤엔진의 연소과정에서 선회유동은 분사되고 있는 연료와 흡칩공기의 혼합을 촉진시켜 줌으로써 엔진성능을 향상시키는데 매우 중요한 인자가 된다. 특히 터보과급 디젤엔진에서는 실린더내의 고온.고압가스로 인하여 연비와 NO$_{x}$ 농도는 서로 상반관계를 가지므로 적절한 용량의 과급기선정으로 흡.배기시스템, 분사시스템 및 연소실의 설계 등을 고려할 필요가 있다. 본 연구의 결과로서, 정상유동실험을 통하여 선회비가 증가함으로써 평균유량계수가 감소하고, 반면에 걸프 펙터가 증가함을 알 수 있었다. 또한 엔진실험을 통하여 흡기포트의 선회비 2.43, 분사시기 BTDC 13$^{\circ}$ CA, 압축비 16, 리앤트란트 5$^{\circ}$형 연소실, 노즐분공경 $\Phi$0.28*6 및 과급기 GT40(압축기 A/R 0.58, 터빈 A/R 1.19)의 적용인자가 최적의 성능 및 배기가스를 만족시킬 수 있었다.

• 한국자동차공학회논문집
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• 제21권4호
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• pp.135-143
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• 2013

In this study, we suggested effective countermeasure of biodiesel oxidation problems by investigating the oxidation degradation of biodiesels derived from variable resources and the level of oxidation stability of current distributing biodiesel blended fuels (2%) in Korea, and oxidation stability change according to storage time (for 3 month) and biodiesel blending ratio (2, 5, 7, 10%). By the composition analysis results of biodiesel from various resources which are possible to distribute in Korea, the biodiesel from animal fat has poor oxidation stability and cold performance, while the biodiesel from coconut and palm kernel which are considered as future potential raw material showed good oxidation stability and cold performance. The oxidation stability level of current distributing biodiesel blended fuels in Korea was excellent with showing over 30 hours (average 68 hours) stability, but the oxidation stability of the blended fuel with animal fat biodiesel having poor oxidation property (1.22 hours) was rapidly decreased to below 32 hours by mixing only 2%. Therefore, we have to pay attention to quality control of oxidation property, because the oxidation stability problem can be caused by increasing biodiesel blending ratio and diversifying raw materials those have worse property.

• 한국항공우주학회지
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• 제34권12호
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• pp.59-66
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• 2006

하이브리드 로켓 연료의 연소율 향상을 위한 나선형 홈이 유동 특성에 미치는 영향을 규명하기 위하여 난류 증가와 선회 유동 발생에 대한 수치계산을 수행하였다. 나선형 튜브의 열전달 관계식을 이용하여 여러 형상의 나선형 홈이 있는 연료의 열전달 향상을 예측하였으며 연소율 측정값과 비교하여 상호 연관성을 확인하였다. 실험 결과와 열전달 향상 예측 값은 동일한 경향을 나타내더라도 수치는 큰 차이를 나타냈는데 이것은 연료가 연소하기 위하여 기화할 때 발생하는 분출속도가 존재하기 때문이다. 분출효과를 고려하여 RANS 계산을 수행한 결과, 난류에너지는 상당히 증가한 반면 선회 수는 조금 증가하는 결과를 보여 주었다. 그럼에도 불구하고 나선형 홈에 의한 난류 증가 또는 선회유동 생성은 연소율을 증가시키는 중요한 메커니즘임이 밝혀졌다. 그러나 분출로 인하여 난류에너지가 증가되어도 열전달 향상에 기여하지 못하는 것으로 확인되었는데 이것은 분출 속도가 표면의 경계층을 밀어내어 대류 열전달이 증가되는 것을 차단하기 때문인 것으로 밝혀졌다.

• Tribology and Lubricants
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• 제22권5호
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• pp.260-268
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• 2006

The dielectric constants of used gasoline engine oils were obtained at a few temperatures and a frequency. Through analyzing the characteristics of dielectric constant, the related correlation between the changes in dielectric constants of oil and the degree of oil deterioration is going to be found. The dielectric constant was calculated using cross capacitances measured by a sensor tube. As results of the measurement of the fresh engine oil's dielectric constant, it was found that the value of dielectric constant was set down below $60^{\circ}C$ regardless changing frequency. Further, above 6 kHz, the dielectric constant was set down even if temperature was above $100^{\circ}C$ Therefore, for the measurement of used oils, it was selected the frequency of 6 kHz,,and the temperature of $80^{\circ}C$ preventing a certain ionic-conduction effects on the measured dielectric constant and the evaporation of a certain fluid mixed with engine oil. Specially, the effects of the mixing fluid like coolant, water and fuel on the fresh engine oil's dielectric constant were studied. It was found that the oil mixed with coolant showed the highest value, next water, and the lowest fuel. As results of the measurement of the used engine oil's dielectric constant, it was found that the possible changed rate of the used engine oil's dielectric constant based on the warning limit for engine oil in service was below 4% for gasoline engine oil.

• Tribology and Lubricants
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• 제22권5호
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• pp.290-300
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• 2006

The dielectric constants of used diesel engine oils were obtained at a few temperatures and a frequency. Through analyzing the characteristics of dielectric constant, the related correlation between the changes in dielectric constants of oil and the degree of oil deterioration is going to be found. The dielectric constant was calculated using cross capacitances measured by a sensor tube. As results of the measurement of the fresh engine oil's dielectric constant, it was found that the value of dielectric constant was set down below $60^{\circ}C$ regardless changing frequency. Further, above 6 kHz, the dielectric constant was set down even if temperature was above $100^{\circ}C$. Therefore, for the measurement of used oils, it was selected the frequency of 6 kHz, and the temperature of $80^{\circ}C$ preventing a certain ionic-conduction effects on the measured dielectric constant and the evaporation of a certain fluid mixed with engine oil. Specially, the effects of the mixing fluid like coolant, water and fuel on the fresh engine oil's dielectric constant were studied. It was found that the oil mixed with coolant showed the highest value, next water, and the lowest fuel. As results of the measurement of the used engine oil's dielectric constant, it was found that the possible changed rate of the used engine oil's dielectric constant based on the warning limit for engine oil in service was below 10% for diesel engine oil.

• Asian Journal of Atmospheric Environment
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• 제8권1호
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• pp.15-24
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• 2014

The capital city of Himalayan Country Nepal, Kathmandu Valley is surrounded by consecutive high mountains, which limits the air distribution and mixing effects significantly. It in turn generates steady air flow pattern over a year except in monsoon season. The air shed in the Valley is easily trapped by the surrounded mountains and the inversion layer formulated as the cap. The $PM_{10}$ concentration was noticeably higher than the standard level (120 ${\mu}g/m^3$) in urban and suburban area of Kathmandu valley for all seasons except monsoon period. The Valley area experiences similar wind patterns (W, WWS, and S) for a year but the Easterly wind prevails only during the monsoon period. There was low and calm wind blows during the winter season. Because of this air flow structure, the air emission from various sources is accumulated within the valley air, high level of air pollution is frequently recorded with other air polluted cities over the world. In this Valley area, brick kilns are recognized as the major air pollution source followed by vehicles. Mostly Bull Trench Kiln (BKT), Hoffman Kiln and Vertical Shaft Brick Kiln (VSBK) are in operation for brick firing in Kathmandu valley where the fuels such as crushed coal, saw dust, and natural gas are used for processing bricks in this study. Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) was used for screening and quantifying the potential impacts of air emission from firing fuels. The total Environmental Performance Score (EPS) was estimated and the EPS of coal was approximately 2.5 times higher than those of natural gas and saw dust. It is concluded that the crushed coal has more negative impact to the environment and human health than other fuel sources. Concerning the human health and environment point of view, alternative environment friendly firing fuel need to be used for brick industry in the kiln and the air pollution control devices also need to be applied for minimizing the air emissions from the kilns.

• 한국항공우주학회지
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• 제35권9호
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• pp.792-798
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• 2007

촉매 연소는 통상의 연소 방식과는 달리 촉매 표면에서 연료와 산화제의 화학 반응에 의한 연소 방식이다. 따라서 연소 영역 이전에 연료와 공기가 잘 혼합되어야 하며, 균일한 공급이 이루어져야 한다. 만약 불균일한 유동 분포가 발생하게 되면, 국부적인 고온 지역이 발생하게 되고 이는 촉매와 지지체에 손상을 초래하게 된다. 본 연구에서는 촉매 연소기의 혼합 및 유동 균일도를 향상시키기 위해 다공판을 사용하였으며, 다양한 파라메터의 변화에 따른 유동 특성의 변화를 조사하기 위해 수치적인 방법을 사용하였다. 각각의 조건하에서 촉매부의 입구에서 유동의 균일도를 조사하고 평가하였으며, 그 결과 적절히 설계된 다공판을 사용하였을 경우 대부분의 해석 조건에 대해 효과적인 균일도 향상을 나타냄을 확인할 수 있었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.233-236
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• 2009

산화제는 $LN_2O$, 고체연료는 HDPE(High Density PolyEthlene)를 사용하여 산화제의 상 및 연료포트 직경에 따른 하이브리드 로켓 모터의 연소특성을 비교 분석하였다. 불완전한 액적의 기화와 연료와 산화제의 혼합으로 인해 산화제로 $GN_2O$ 보다 $LN_2O$를 적용했을 때, 연소효율이 낮게 나타났다. O/F비에 따른 화염온도변화 및 끝 단면적에서의 연소반응으로 인해 $LN_2O$와 $GN_2O$를 사용하였을 경우 고체연료의 초기 포트 직경에 따른 후퇴율의 경향이 달리 나타났다.

• 대한기계학회논문집B
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• 제35권6호
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• pp.625-632
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• 2011

[ $CH_4$ ]고온공기 대향류 확산화염의 점화특성을 화염제어 연속계산법을 이용하여 수치해석적으로 검토하였다. 화학반응의 계산에는 GRI-v1.2 반응기구를 이용하였으며, 화염 최고온도를 총괄 스트레인율의 역수에 대해 나타내어 점화 및 소화특성에 관한 화염 최고온도의 S-곡선을 얻을 수 있었다. 총괄 스트레인율 변화에 따른 화염구조를 고찰하기 위해 S-곡선에서 Upper Branch와 Middle Branch의 화염 온도 분포와 속도구배를 비교하였다. 총괄 스트레인율값은 화염면과 혼합층의 연료과 공기측 경계에서 정의되는 국소 스트레인율값과도 비교하였다. 연료측과 공기측의 국소 스트레인율은 총괄 스트레인율과의 좋은 상관관계에 있음을 알 수 있었다. 화염제어 연속계산법이 확산화염의 점화, 소화특성을 검토하는 데 매우 유용한 방법임을 확인하였다.