• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.04a
• /
• pp.9-9
• /
• 1998

가스터빈 연소기의 난류유동장을 구성하는 기본적인 유동형태는 크게 밀폐관내의 돌연 확대를 가지는 동축제트, 선회유동, 그리고 연소공기공 및 회석공기공을 통해 연소실에 수직방향으로 유입되는 제트유동 등으로 분류할 수 있다. 실제 가스터빈 연소기내의 난류유동장을 수치해석하기 위해서는 임의의 형상을 갖는 3차원 유동장을 모사할 수 있는 수치해석법과 고차정확도를 유지하면서도 수렴안정성을 만족시키는 대류항 처리기법 등과 같은 수치모델의 개발이 선행되어야 하며, 이와 함께 복잡한 난류연소유동장을 정확히 묘사할 수 있는 난류모델 및 난류연소모델의 개발 및 검증이 가장 중요한 요인이 된다. 또한 가스터빈 연소기의 최적 설계는 넓은 작동구간에서 높은 효율, NOx 및 CO 배기량의 저감, 희박연소 가연한계의 확장, 연소계통에서의 낮은 압력강하, 낮은 연소벽면온도와 온도구배를 유지시키기 위한 공기에 의한 충분한 냉각 같은 서로 상충되는 설계조건을 만족해야 한다. 그리고, 이러한 상충된 연소설계조건들을 충족시키는 최적 연소기의 설계를 위해서는 실험적인 연구뿐만 아니라 연소기내의 물리적인 현상을 잘 반영할 수 있는 물리적 모델을 바탕으로 한 연소유동의 해석적인 연구를 필요로 한다. 본 연구에서는 원통형 가스터빈 연소기의 등온 및 연소유동장, 그리고 연소기와 연결되는 Scroll 내부의 난류유동장에 대한 수치해석을 수행하여 수치 및 물리모델의 예측능력을 검증하였고, 가스터빈 연소유동장 해석에 관련된 중요 논점들에 대하여 심도있게 분석하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.68-77
• /
• 2017

High-frequency combustion instability results from a feedback coupling between the unsteady heat release rate and the acoustic waves formed resonantly in the combustion chamber. It can be modeled as thermoacoustic problems with various degrees of the assumptions and simplifications. This paper presents numerical analysis of self-excited combustion instabilities in a variable-length lean-premixed combustor and designs of passive control devices such as baffle and acoustic resonators in a framework of 3-D FEM Helmholtz solver. Nonlinear behaviors such as steep-fronted shock waves and a finite amplitude limit cycle are also investigated with a compressible flow simulation technique.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2012.05a
• /
• pp.65-69
• /
• 2012

An oxygen rich preburner was tested and the responses from the pressure sensors were studied with FFT analysis. Since the limited capability of the static sensor, less than 250 Hz frequency domain was investigated and compared to the results of the dynamic sensors. As a result, 60 Hz harmonics were presented dominant in the combustion pressure and oxygen inlet pressure. While similar harmonics were shown with the dynamic sensor, it indicated that harmonics less than 60 Hz were very minor and the high frequency is more important.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.3
• /
• pp.251-257
• /
• 2012

This work presents an experimental investigation of NOx emissions according to inlet air temperature (550-660 K), stoichiometric air ratio (${\lambda}$, 1.4-2.1), and elevated pressure (2-5 bar) in a High Press Combustor (HPC) equipped with a double cone burner, which was designed by Pusan Clean Coal Center (PC3). The exhaust-gas temperature and NOx emissions were measured at the end of the combustion chamber. The NOx emissions generally decreased as a function of increasing ${\lambda}$. On the other hand, NOx emissions were influenced by ${\lambda}$, inlet air temperature and pressure of the combustion chamber. In particular, when the inlet air temperature increased, the flammability limit was extended to leaner conditions. As a result, a higher adiabatic temperature and lower NOx emissions could be achieved under these operation conditions. The NOx emissions that were governed by thermal NOx were greatly increased under elevated pressures, and slightly increased at sufficiently low fuel concentrations (${\lambda}$ >1.8).

• Journal of the Korean Institute of Gas
• /
• v.20 no.6
• /
• pp.23-30
• /
• 2016

The conventional natural gas engine realized lean combustion for the improved efficiency. However, in order to cope with exhaust gas regulations enforced gradually, the interest has shifted at the stoichiometric mixture combustion system. The stoichiometric mixture combustion method has the advantage of a three-way catalyst utilization whose purification efficiency is high, but the problem of thermal durability and the fuel economy remains as a challenge. Hydrogen-natural gas blend fuel (HCNG) can increase the rate of exhaust gas recirculation (EGR) because the hydrogen increases burning speed and lean flammability limit. The increase in the EGR rate can have a positive impact on heat resistance of the engine due to the decreased combustion temperature, and further can increase the compression ratio for efficient combustion. In this study, to minimize the exhaust emission developed HCNG engine with stoichiometric combustion method, developed three-way catalyst was applied to evaluate the conversion characteristics. The tests were carried out during the steady state and transient operating conditions, and the results were compared for both the conventional and proto-three-way catalyst of HCNG engine for city buses.

• Journal of the Korean Institute of Gas
• /
• v.17 no.1
• /
• pp.7-12
• /
• 2013

As emission regulation for vehicle has been reinforced, many researches carried out for HCNG(hydrogen-natural gas blends) fuel to the conventional compressed natural gas (CNG) engine. However, abnormal combustion such as backfire, pre-ignition or knocking can be caused due to high combustion speed of hydrogen and it can result in over heating of engine or reduction of thermal efficiency and power output. In the present study, improvement of combustion performance was observed with HCNG fuel since it can extend a flammability limit. Knocking characteristics for CNG and HCNG fuel were investigated. Feasibility of HCNG fuel was evaluated by checking the knock margin according to excess air ratio. The operation of engine with HCNG was stable at minimum advance for best torque(MBT) spark timing and knock phenomena were not detected. However, it is necessary to prepare higher knock tendency since possibility of knock is higher with HCNG fuel.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.19 no.4
• /
• pp.37-44
• /
• 2015

An experimental study was performed for the analysis of frequency-equivalence ratio correlation in the methane-air premixed flame influenced by ultrasonic standing wave. Evolutionary features of the propagating flame were caught by high-speed camera, and the variation of flame-behavior including local velocities was investigated in detail using a post-processing analysis of the high-speed images. It was found that propagation-velocity augmentation of the methane-air premixed flame by the intervention of ultrasonic standing wave was made in leaner mixture, but the velocity diminished when the strength of chemical reaction was saturated around the slightly fuel-rich side of stoichiometry.

• Polymer(Korea)
• /
• v.34 no.5
• /
• pp.415-423
• /
• 2010

Poly(vinyl alcohol)(PVA) with high degree of hydrolysis of above 98% was dissolved in dimethyl sulfoxide(DMSO), and the shear viscosity was measured up to $C{\simeq}0.14\;g/mL$ in the semi-dilute solution regime. Next, as probe particle, polystyrene(PS) latex was introduced into this matrix system and its delayed diffusion due to polymer concentration was investigated by means of dynamic light scattering. When the solution viscosity of PVA/DMSO was plotted against the reduced concentration $C[{\eta}]$, which is scaled by the intrinsic viscosity, the molecular weight dependence was strongly appeared at C$[{\eta}]$ >2. Some heterogeneties in polymer solution were considered as its source. Contrary, the diffusion of probe particle in the matrix solution was observed as a single mode motion at whole concentration range but its ratio of its diffusion coefficient at solution to that at solvent, D/Do did not show any molecular weight dependence at all. However, the application limit of the stretched exponential function was disclosed at C$[{\eta}]$ >2.5.

• 한국벤처창업학회:학술대회논문집
• /
• 2018.04a
• /
• pp.61-64
• /
• 2018

우리나라 특성화고는 산업사회의 각 분야에서 종사할 유능한 인재를 양성하고 합리적이며 능률적인 직업인을 육성하려는 목표로 1998년에 도입되었다. 2010년에는 독일, 스위스, 오스트리아 등에서 자리 잡은 마이스터고 제도를 도입하여 변화를 시도하였다. 유럽에서의 마이스터고는 창업 성공률이 98%에 이를 정도로 창업의지가 높은 학생들로 구성되었다. 우리나라 또한 특성화고 학생들의 창업의지를 높이기 위해서 정부와 민간 기관에서 다양한 시도를 하였다. 창업진흥원의 기업가 마인드 확산 교육 비즈쿨(2002년), 한국시민자원봉사회의 특성화고 대상 창업 마인드 확산 경진대회 Be the CEO(2004년), 아산나눔재단과 어썸스쿨의 앙트러프러너십 교육 히어로스쿨(2014년) 등이 사례이다. 본 저자도 2011년부터 중소벤처기업부와 SK가 공동으로 주최하는 고교생 앱 개발경진대회를 직접 운영하면서 특성화고 학생들의 창업의지를 높이기 위한 방안에 대해 오랫동안 고민하였다. 본 연구에서는 특성화고 학생들의 앙트러프러너십이 창업의지에 미치는 영향을 연구하였다. 앙트러프러너십의 구성요소는 Miller(1983)가 주장한 위험감수성, 혁신성, 진취성에 기회인지를 추가하였다. 또한, 특성화고 학생들이 학교 교육과 다양한 외부활동을 통하여 접하고 있는 창업멘토링이 앙트러프러너십 구성요소와 창업의지간에 조절효과가 있는지 밝히고자 하였다. 이를 위해 전국 491개(2017년 말) 특성화고등학교 중 지역별로 안배하여 14개 학교 학생들을 대상으로 설문을 시행하였으며, 설문서 287부를 실증분석에 활용하였다. 연구분석 결과 특성화고 학생의 기회인지, 위험감수성, 혁신성, 진취성은 모두 창업의지에 긍정적인 영향을 미치는 것으로 나타났다. 한편 기회인지, 위험감수성 등 앙트러프러너십 요소와 창업의지 관계에서 창업멘토링의 조절효과는 진취성에만 긍정적인 영향을 미치는 것으로 나타났다. 창업멘토링의 조절효과가 진취성에만 국한된 것은 특성화고는 창업보다는 취업 중심의 정책을 운영 중이어서 앙트러프러너십은 높으나 창업의지가 희박한 학생이 많았고, 기존의 창업멘토링 내용이 학생들의 창업의지를 높이는데 실제적인 도움이 되지 못하였으며, 창업을 가로막는 제도 때문에 멘토링 만으로는 창업의지를 높이는데 한계가 존재하였다. 본 연구의 결과가 우리나라 특성화고 학생들의 창업의지를 높이는 방안에 대한 연구를 촉발하는데 조그만 보탬이 되기를 바란다. 또한, 창업의지가 높은 특성화고 학생들이 창업을 실행할 수 있는 환경이 구축되고, 특성화고가 취업중심의 정책에서 창업친화적인 정책으로 개선하는 데 촉매제가 되기를 바란다.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.6
• /
• pp.98-106
• /
• 2011

This paper reviews the state-of-the-art thermoacoustic(TA) modeling techniques and research trend to predict major parameters determining combustion instabilities in lean premixed gas turbine combustors. Linear TA modeling results give us an information on eigenfrequencies and initial growth rate of the instabilities. For the prediction, linear relation equation between acoustic waves and heat release oscillations should be derived in the determined system. Key information for this analysis is to determine the heat release fluctuations in the combustor, which is typically obtained by using n-${\tau}$ function from flame transfer function measurements and/or predictions. Great advancement in the linear TA modeling has been made over a couple of decades, and some successful prediction results have been reported in actual gas turbine combustors. However nonlinear TA model developments which are required to analyze nonlinear system behaviors such as limit cycle saturation and transition phenomena are still limited in a very simple system. In order to fully understand combustion instabilities in a complicated real system, nonlinear flame dynamics and acoustic wave interaction with nonlinear system boundary conditions should be explained from the nonlinear TA model developments.