• 한국추진공학회지
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• 제22권6호
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• pp.84-93
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• 2018

냉각제 분사조건이 변화할 때 혼합가스 사출시스템 (또는 가스-스팀 발사체계) 냉각효율 및 발사체 사출성능의 변화를 확인하기 위해 3차원 수치모사를 수행하였다. 선행연구를 참조하여 구축한 1차원 모델을 통해 3차원 단상(single-phase) 계산모델을 검증한 후, Discrete Phase Model을 활용하여 고온의 기체에 냉각제 분사를 모사한 이상(two-phase) 유동 계산을 수행하였다. 냉각제 유량과 분사구 개수를 각각 변화시키면서 계산을 수행한 결과, 분사구 개수를 증가시켰을 경우 냉각효율이 보다 개선되었다. 또한 분사조건에 따라 냉각제 액적 서로간의 coalescence 발생 빈도 및 공간분포 변화가 발생하여 액적의 직경이 달라졌고, 이는 냉각제 증발률에 영향을 미쳤다. 냉각제의 증발은 breech 내부의 온도를 감소시키는 반면에 압력감소를 억제하여 사출시스템 최적화 설계에 있어 중요한 요소임을 확인하였다.

• 대한기계학회논문집B
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• 제37권7호
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• pp.675-682
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• 2013

전단 동축 분사기의 Inner-stage와 Outer-stage의 기체 분사 비율 변화에 따른 축방향 유동 분포 특성과 분무 분열 특성을 실험적으로 연구였다. 무차원 측정 거리를 Z/d=100까지 변화시킴에 따라 운동량 교환, 공기역학적 항력, 점성 혼합의 영향으로 완전 발달된 유동의 형태를 나타내었다. Inner-stage의 기체분사와 Outer-stage의 기체 분사의 영향은 Z/d=5 이내의 영역에서 간섭받지 않고 분무 초기에 Inner-stage에서 분사된 기체 전단력에 의해 분열됨을 파악할 수 있었으며, Z/d=10 이상의 영역에서 완전 발달된 유동으로 변화하며, 유동의 혼합이 진행됨을 관찰 할 수 있었다. Inner-stage의 운동량 플럭스 비 0.84 이내에서 Outer-stage의 운동량 플럭스 비가 증가함에 따라 SMD가 감소하는 경향을 나타내었으며, Inner-stage의 운동량 플럭스 비가 1.38 이상의 조건에서 SMD의 분포가 유사하게 나타나는 경향을 관찰할 수 있었다.

• 한국전기전자재료학회논문지
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• 제27권10호
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• pp.668-672
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• 2014

Carbon nanotubes(CNT) has chemical stability and great sensitivity characteristics. In particular, the gas sensor required characteristics such as rapid, selectivity and sensitivity sensor. Therefore, CNT are ideal materials to gas sensor. So, we fabricated the NOx gas sensors of MOS-FET type using the MWCNT (multi-walled carbon nanotube). The fabricated sensor was used to detect the NOx gas for the variation of $V_{gs}$(gate-source voltage) and electrode changed electrode spacing=30, 60, 90[${\mu}m$]. The gas sensor absorbed with the NOx gas molecules showed the decrease of resistance, and the sensitivity of sensor was increased by magnification of electrode spacing. Furthermore, when the voltage($V_{gs}$) was applied to the gas sensor, the decrease in resistance was increased. On the other hand, the sensor sensitivity for the injection of NOx gas was the highest value at the electrode spacing $90[{\mu}m]$. We also obtained the adsorption energy($U_a$) using the Arrhenius plots by the reduction of resistance due to the voltage variations. As a result, we obtained that the adsorption energy was increased with the increment of the applied voltages.

• 대한기계학회논문집B
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• 제24권3호
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• pp.390-401
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• 2000

In this study, numerical calculation is carried out to investigate the influence of injection timing, fuel amount, intake $O_2$ concentration, and EGR on Nitric Oxide(NO) formation using a two-zone model in a diesel engine. Results can be summarized as follows. The NO formation is very sensitive to the burned gas temperature, so multi-zone model must be applied to combustion process to predict the burned gas temperature exactly. Since the burned gas temperature increases rapidly during the premixed combustion, most NO is formed within 20 crank angle degrees after ignition. As the injection timing is retarded, the combustion occurs later in the expansion process which causes the decrease of burned gas temperature and, as a result, NO formation decrease. The increase of fuel amount results in the increase of earlier formation of NO in the engine. As the intake $O_2$ concentration increases, the maximum pressure and burned gas temperature increase due to activate combustion. And, [O] mole fraction of equilibrium combustion products also increase. Therefore NO exponentially increases. If exhaust gas is recirculated, the burned gas temperature decreases which results in NO decrease. If exhaust gas is cooled, more NO can be decreased.

• 한국가스학회지
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• 제24권1호
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• pp.49-55
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• 2020

산업용 혹은 발전용 가스터빈에 사용되는 이중 콘형 예혼합 연소기의 다단 연소 특성을 이해하기 위하여 실험적연구를 수행하였다. 이를 위하여 기존에 모두 경사면에 공급되는 연료를 콘부분으로 일부 할애하는 방식으로 다단연소 방식을 구성하였으며 콘에서 분사되는 연료공급은 축방향과 콘 경사면 방향으로 하였다. 다단연소 연소특성을 이해하기 위하여 콘에서의 연료 분사 방향과 연료 분배율 변화에 대한 NOx와 CO의 배출 농도 그리고 벽면 온도분포를 측정하였다. 그 결과 총 연료에 대한 콘으로의 분배율이 3%인 경우 콘에서의 연료 분사방향에 관계없이 노즐내의 예혼합 영역에서 연료가 공기와 균일하게 혼합됨으로서 연소영역의 고온점 감소에 의하여 NOx 배출 농도가 감소된다. 그러나 콘에서 축방향으로 분사되는 연료분배율이 8%로 증가하는 경우 노즐 내부 예혼합 영역으로의 화염 역화로 인하여 NOx의 배출농도가 오히려 증가하게 된다.

• 한국자동차공학회논문집
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• 제5권5호
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• pp.97-103
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• 1997

Effects of fuel injection timing on the lean misfire limit of a sequential MPI SI engine has been investigated. To investigate the interaction of injection timing and intake flow characteristics, so called axial stratification phenomena, 4 kinds of different intake swirl port of the same combustion chamber geometry have been teated in a single cylinder engine test bench. And 2 kinds of fuel, gasoline and compressed natural gas(CNG), were used to see the effect of liquid fuel vaporization. Result shows that combination of port swirl and injection timing governs the lean misfire limit and lean misfire limit envelopes remain almost the same for a given ratio regardless of engine speed. It is also found that two phase flow has some effects on lean misfire limit.

• 한국전기전자재료학회논문지
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• 제26권9호
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• pp.707-711
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• 2013

Carbon nanotubes(CNT) has strength and chemical stability, greatly conductivity characteristics. In particular, MWCNT (multi-walled carbon nanotubes) show rapidly resistance sensitive for changes in the ambient gas, and therefore they are ideal materials to gas sensor. So, we fabricated NOx gas sensors structured MOS-FET using MWCNT (multi-walled carbon nanotubes) material. We investigate the change resistance of NOx gas sensors based on MOS-FET with ultra lean NOx gas concentrations absorption. And NOx gas sensors show sensitivity on the change of gate-source voltage ($V_{gs}=0[V]$ or $V_{gs}=3.5[V]$). The gas sensors show the increase of sensitivity with increasing the temperature (largest value at $40^{\circ}C$). On the other hand, the sensitivity of sensors decreased with increasing of NOx gas concentration. In addition, We obtained the adsorption energy($U_a$), $U_a$ = 0.06714[eV] at the NOx gas concentration of 8[ppm], $U_a$ = 0.06769[eV] at 16[ppm], $U_a$ = 0.06847[eV] at 24[ppm] and $U_a$ = 0.06842[eV] at 32[ppm], of NOx gas molecules concentration on the MWCNT gas sensors surface with using the Arrhenius plots. As a result, the saturation phenomena is occurred by NOx gas injection of concentration for 32[ppm].

• 천문학회지
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• 제34권4호
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• pp.293-295
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• 2001

A numerical scheme that incorporates a self-consistent cosmic-ray (CR, hereafter) injection model into the combined gas dynamics and CR diffusion-convection code has been developed. The hydro/CR code can follow in a very cos-effective way the evolution of CR modified shocks by adopting subzone shock-tracking and multi-level Adaptive Mesh Refinement techniques. The injection model is based on interactions of the suprathermal particles with self-generated MHD waves in quasi-parallel shocks. The particle injection is followed numerically by filtering the diffusive flux of suprathermal particles across the shock to upstream region according to a velocity-dependent transparency function, which represents the fraction of leaking suprathermal particles. In the strong shock limit of Mach numbers $\ge$20, significant physical processes such as the injection and acceleration seem to become independent of M, while they are sensitively dependent on M for M < 10. Although some particles injected early in the evolution continue to be accelerated to higher energies, the postshock CR pressure reaches a time asymptotic value due to balance between acceleration and diffusion of the CR particles.

• International Journal of Automotive Technology
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• 제8권1호
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• pp.27-31
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• 2007

The number of vehicles employing diesel engines is rapidly rising. Accompanying this trend, application of an after-treatment system is strictly required as a result of reinforced exhaust regulations. The Diesel Particulate Filter (DPF) system is considered as the most efficient method to reduce particulate matter (PM), but the improvement of a regeneration performance at any engine operation point presents a considerable challenge by itself. Therefore, the present study evaluates the effect of fuel injection characteristics on regeneration performance in a DOC and a catalyzed CR-DPF system. The temperature distribution on the rear surface of the DOC and the exhaust gas emission were analyzed in accordance with fuel injection strategies and engine operating conditions. A temperature increase more than BPT of DPF system was obtained with a small amount fuel injection although the exhaust gas temperature was low and flow rate was high. This increase of temperature at the DPF inlet cause PM to oxidize completely by oxygen. In the case of multi-step injection, the abrupt temperature changes of DOC inlet didn't occur and THC slip also could not be observed. However, in the case of pulse type injection, the abrupt injection of much fuel results in the decrease of DOC inlet temperatures and the instantaneous slip of THC was observed.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.101-102
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• 2014

Rising oil price and environmental problems are causing automotive industry to increase fuel efficiency. Improved fuel efficiency in gasoline engine was made possible by development of DISI gasoline engine. Since fuel is injected inside cylinder directly, in-cylinder temperature can be reduced than multi-port injection engine and this leads to increased compression ratio. However, engine performance is largely dependent on mixture formation process due to in-cylinder fuel injection. Especially for spray guided and air guided DISI gasoline engine, injection direction is important factor to mixture preparation. It is because interaction between intake flow and spray affect fuel-air mixture. Hence, in this study, mixture formation characteristics were analyzed by varying injection direction using KIVA 3V release2 code. Residual gas was considered for assuming combustion. Therefore, initial condition for in-cylinder temperature was set equal to the end state of exhaust stroke of combustion cycle. Since angle between intake air flow direction and spray direction affects fluid flow and evaporation field, mixture distribution was affected by fuel injection direction dominantly.