• 대한기계학회논문집A
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• 제30권11호
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• pp.1494-1501
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• 2006

Mechanical and physical properties of a copper alloy for a liquid rocket engine(LRE) combustion chamber liner application were tested at various temperatures. All test specimens were heat treated with the condition they might experience during actual fabrication process of the LRE combustion chamber. Physical properties measured include thermal conductivity, specific heat and thermal expansion data. Uniaxial tension tests were preformed to get mechanical properties at several temperatures ranging from room temperature to 600$^{\circ}C$. The result demonstrated that yield stress and ultimate tensile stress of the copper alloy decreases considerably and strain hardening increases as the result of the heat treatment. Since the LRE combustion chamber operates at higher temperature over 400$^{\circ}C$, the copper alloy can exhibit time-dependent behavior. Strain rate, creep and stress relaxation tests were performed to check the time-dependent behavior of the copper alloy. Strain rate tests revealed that strain rate effect is negligible up to 400$^{\circ}C$ while stress-strain curve is changed at 500$^{\circ}C$ as the strain rate is changed. Creep tests were conducted at 250$^{\circ}C$ and 500$^{\circ}C$ and the secondary creep rate was found to be very small at both temperatures implying that creep effect is negligible for the combustion chamber liner because its operating time is quite short.

• 한국방재학회 논문집
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• 제1권1호
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• pp.127-138
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• 2001

CFRCs는 고온에서의 우수한 물성에도 불구하고, 연소에 대한 취약한 성질로 인하여 많은 분야에서 사용에 제약을 받고 있다. 그러므로 EFRCs의 연소저항성을 향상시키기 위해서 수 많은 연구가 수행되어지고 있다. 본 연구에서는 고온에서 보다 개선된 물성과 높은 연소저항성을 부여하고, 다른 도포물질과 비교해서 낮은 열팽창계수의 차이를 보이는 탄화규소를 Pack-Cementation 방법으로 4방향성 CFRCs에 도포하였다. 제작된 탄화규소로 도포된 CFRCs는 광학현미경의 관찰을 통하여 도포 메카니즘을 추정하였으며, TGA 시험을 통하여 개선된 연소저항성을 조사하였다. Arc plasma torch 시험을 통하여 고온 연소특성과 거동을 연구하였다. 그 결과로부터 탄화규소로 코팅된 CFRCs의 기계적 강도와 고온 연소특성이 순수한 4방향성 CFRCs에 비해서 개선되었다는 것을 알았다.

• 에너지공학
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• 제24권4호
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• pp.166-174
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• 2015

본 연구에서는 물성 변화에 따라 자동차 성능 및 환경에 미치는 영향을 살펴보기 위하여 휘발유 대비 물성이 상이한 연료를 선정하여 연소특성을 살펴보았다. 실험은 각 연료에 맞는 점화시기 및 공연비제어를 수행하여 물성변화에 따른 최적의 점화시기와 희박연소에 에서의 연소특성을 살펴보았으며, 그에 따른 배출가스도 평가하였다. 실험을 위해 단기통 엔진을 사용하였으며, 휘발유 물성변화를 위해 "석유 및 석유대체사업법"에 고시된 품질기준을 벗어나는 가짜연료를 선정하여 실험을 수행하였다. 그 결과 선정된 연료의 경우 옥탄가와 증류성상, 증기압에서 차이를 보였으며, 불안정 연소 및 다량의 유해배출가스를 유발함을 알 수 있었다.

• 공업화학
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• 제22권4호
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• pp.439-443
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• 2011

수산화마그네슘이 첨가된 저밀도 폴리에틸렌-에틸렌 비닐 아세테이트 혼합물의 연소성을 시험하였다. 저밀도 폴리에틸렌-에틸렌 비닐 아세테이트에 수산화마그네슘을 40~80 wt% 첨가하여 용융 혼합하고 성형 후 콘칼로리미터(ISO 5660-1)를 이용하여 그의 연소성을 시험하였다. 수산화마그네슘을 첨가한 시험편은 첨가하지 않은 시험편에 비하여 그의 연소성이 감소하였다. 이것은 순수한 저밀도 폴리에틸렌-에틸렌 비닐 아세테이트에 첨가한 수산화마그네슘의 흡열 분해 때문에 연소 억제성이 향상된 것으로 생각된다. 수산화마그네슘을 첨가한 시험편은 첨가하지 않은 시험편에 비해 낮은 최대열방출률과 낮은 유효연소열을 나타내었고, 수산화마그네슘 함량이 증가할수록 착화시간은 길어지고, 최대열방출률은 감소하였다.

• 한국대기환경학회지
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• 제19권4호
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• pp.427-436
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• 2003

This study is to establish a waste bed combustion model that can be available to assist the design of incinerators for efficient operation control of municipal waste incinerators. An unsteady one -dimensional bed combustion modeling was developed which incorporates the various sub-process models and solves the governing equations for both gases and solids in the waste bed combustion phenomena. The combustion characteristics and the properties of the combustion gas released from the bed were investigated by using a developed model. Besides, a sub-model which predicts the formation and destruction of nitrogen oxides in the waste bed was also developed as a post-processor for the waste combustion model. It is found that the reduction rate of nitrogen oxides is enhanced in the char layer.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.242-247
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• 2003

An experimental study presents characteristics of combustion in a combustion chamber by port deactivation valve for economy and emissions standards. In order to use combustion properties data it is necessary to build some data base, which use cylinder pressure sensor, etc. Port deactivation valve has been developed to satisfy requirement of achieving sufficient swirl generation to improve the combustion. A feasibility and necessity of combustion pressure based cylinder spark timing control has been examined. So, this was obtained the Coefficient of Variation(COV) and the mass-burned(MFB). The characteristics of pressure ratio fraction is similar to that of mass-burned fraction. Using the results of the test, the effects of the combustion chamber can be improved combustion stability by port deactivation.

• 한국자동차공학회논문집
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• 제7권6호
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• pp.32-41
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• 1999

Natural gas is an attractive fuel in view of environment benefits due to its flow carbon-to-hydrogen ratio. However, its compositions and properties are varied depending upon production regional groups. Therefore, study on the combustion characteristics of natural gas engines with a variety of compositions has been demanded for the efficient application of gas engines. This study aims to investigate the effects of gas composition on engine combustion characteristics. It was found that , by controlling an engine with fixed fuel nozzle area, power and heat release were subject to Wobbe Index. And at fixed excess air ratios, power and heat release were subject to low heating value of unit mixture . In addition, in case of constant nozzle area, combustion duration was found to be inversely proportional to CP(Combustion Potential), and the condition of fixed excess air ratios showed no change in combustion duration, regardless of CP.

• 한국안전학회지
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• 제14권3호
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• pp.84-92
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• 1999

The effects of air velocity and excess air on combustion characteristics were studied in a fluidized bed combustor. The domestic low-grade anthracite coal with heating value of 2010 kcal/kg and the imported bituminous coal from Australia with heating value of 6520 kcal/kg were used as coal samples. The combustion characteristics of mixed fuels in a fluidized bed combustor could be interpreted by pressure fluctuation properties, ash distribution and gas emission. The properties of the pressure fluctuations, such as the standard deviation, cross-correlation function, dominant frequency and the power spectral density function, were obtained from the statistical analysis. From this study, the combustion region increased with increasing air velocity but decreased with excess air due to combustion characteristics of anthracite and bituminous coal.

• 대한기계학회논문집B
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• 제33권10호
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• pp.737-747
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• 2009

This study is to investigate the effect of the moisture, volatile matter and particle size in the coal on the pulverized coal combustion characteristics using CFD. The results show that as the moisture content in coal increases, flame temperature decreases because of heat loss driven from latent heat of vaporization and reduction of heating value. As the volatile matter content in the coal increases, the temperature in the region near the burner increases, while the temperature in rear region of boiler decreases. The solution to keep the temperature in the rear region of boiler is suggested that particle size is needed to be larger. As the particle size increases, the temperature in the rear region of boiler show tendency to increase, for combustion burning time of coal could be extended.

• 대한기계학회논문집B
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• 제27권11호
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• pp.1595-1603
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• 2003

Droplet combustion at high ambient pressures is studied numerically by formulating one dimensional combustion model in the mixture of n-heptane fuel and air. The ambient pressure is supercritical conditions. The modified Soave-Redlich-Kwong state equation is used in the evaluation of thermophysical properties to account for the real gas effect on fluid p-v-T properties in high pressure conditions. Non-ideal thermodynamic and transport property at near critical and supercritical conditions are also considered. Several parametric studies are performed by changing ambient pressure and initial droplet diameter. Droplet lifetime decreased with increasing pressure. Surface temperature increased with increasing pressure. Ignition time increased with increasing initial droplet diameter. Temporal or spatial distribution of mass fraction, mass diffusivity, Lewis number, thermal conductivity, and specific heat were presented.