• 한국가스학회지
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• 제15권2호
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• pp.15-20
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• 2011

도심 대기오염을 줄이고자 도입된 CNG 버스는 현재의 배기규제 기준을 만족시켜 도시 대기환경 개선에 많은 기여를 했지만 추가적인 후처리 장치의 도움 없이는 차기 배기기준인 유로6 배기규제를 만족시키기 매우 어렵다. 수소는 매우 활발하고 빠른 반응성을 가지고 있으며 희박가연한계 또한 매우 넓어 기존 연료와 함께 사용 시 개선된 연소 및 배기성능을 기대할 수 있다. 따라서 본 연구에서는 시내버스용 대형 CNG 엔진에 수소를 일정 부분 CNG와 혼합한 HCNG 연료를 공급하여 희박연소를 시킴으로서 연소 및 배기성능을 개선하는 실험을 수행하였다. 수소혼합비율, 공연비, 점화시기 변화에 따른 연소 및 배기성능을 살펴보고 최적운전조건을 찾아내었으며 산화촉매 성능평가를 통해 11리터 버스용 HCNG 엔진의 상용화 가능성을 검토하였다.

• 산업기술연구
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• 제26권B호
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• pp.21-28
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• 2006

A diesel truck of 1 ton is re-powered by a gasoline engine and the fuelling system of gasoline engine modified to gasoline/CNG bi fuel system. The engine characteristics such as fuel economy and power are evaluated by driving rest, sloping test and dynamometer. The driving test prove the driving cost is saved by 55% and the maximum speed is raised by 13%, which is mainly due to the higher calorific value of CNG. The sloping test is done on the road of which slope is 15%. The truck shows the mean velocity of 88km/h, which means that a re-powered truck is working fine. The BHP are measured by dynamometer. The power and torque produced by a re-powered truck are reduced by 13% and 14% respectively from the power of gasoline engine. The BHP reduction is one of main problems which one has to solve in near future.

• 한국자동차공학회논문집
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• 제15권1호
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• pp.193-200
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• 2007

Natural gas is one of the most promising alternatives to gasoline and diesel fuels because of its lower harmful emissions, including $CO_2$, and high thermal efficiency. In particular, natural gas is seen as an alternative fuel for heavy-duty Diesel Engines because of the lower resulting emissions of PM, $CO_2$ and $NO_x$. Almost all CNG vehicles use the PFI-type Engine. However, PFI-type CNG Engines have a lower brake horse power, because of reduced volumetric efficiency and lower burning speed. This is a result of gaseous charge and the time losses increase as compared with the DI-type. This study was conducted to investigate the effect of injection conditions (early injection mode, late injection mode) on the combustion phenomena and performances in the or CNG Engine. A DI Diesel Engine with the same specifications used in a previous study was modified to a DI CNG Engine, and injection pressure was constantly kept at 60bar by a two-stage pressure-reducing type regulator. In this study, excess air ratios were varied from 1.0 to the lean limit, at the load conditions 50% throttle open rate and 1700rpm. The combustion characteristics of the or CNG Engine - such as in-cylinder pressure, indicated thermal efficiency, cycle-by-cycle variation, combustion duration and emissions - were investigated. Through this method, it was possible to verify that the combustion duration, the lean limit and the emissions were improved by control of injection timing and the stratified mixture conditions. And combustion duration is affected by not only excess air ratio, injection timing and position of piston but gas flow condition.

• 한국분무공학회지
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• 제24권4호
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• pp.171-177
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• 2019

This paper describes numerical study of combustion characteristics in CNG(compressed natural gas) DI(direct injection) engine using gaseous sphere injection model. Simulations were conducted using KIVA-3V Release 2 code. Gaseous sphere injection model, which is modified model of liquid fuel injection, was used to simulate the CNG direct injection. Until now, a very fine mesh smaller than the injector nozzle has been required to resolve the gas-jet inflow boundary. However, the gaseous sphere injection model simulates gaseous fuel injection using a coarse mesh. This model injects gaseous spheres as in liquid fuel injection and the gaseous spheres evaporate together without the latent heat of evaporation. Therefore, it does not require a very fine mesh and reduce calculation time. Combustion simulation were performed under various injection timings and injection pressures.

• 한국가스학회지
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• 제20권4호
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• pp.1-6
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• 2016

버스와 같은 대형 차량에서 사용되는 대형 CNG 엔진에는 가스 연료 분사를 위한 인젝터가 6개 가량의 단위로 모듈 형태를 구성하고 있다. 이러한 인젝터 모듈은 연료 공급을 위한 입출구가 각각 한 곳으로 구성되어 있으며 쓰로틀 후단을 통하여 흡기관으로 연료를 공급하는 방식이므로 과도 운전에 대한 응답성이 매우 낮은 구조를 형성하고 있다. 본 연구에서는 이러한 인젝터 모듈의 내부 유로에 대한 유동 해석을 통하여 응답성을 개선할 수 있는 방안을 제시하고자 한다. 결론에 따르면 내부 유로의 체적을 감소시킴으로써 가스 연료의 공급 응답성을 개선할 수 있었고, 각각의 인젝터에서 모듈의 출구까지의 거리를 동일하게 하는 방안도 응답성과 연료 공급량의 선형성을 확보할 수 있는 것을 확인하였다. 다만 각 인젝터의 분사 순서 시기에는 큰 영향을 받지 않는 결과를 보였다.

• 에너지공학
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• 제9권2호
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• pp.83-88
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• 2000

In this study, the performance and pollutant emission of CNG engine using diesel oil as a source of ignition, so called CNG dual fuel diesel engine is considered by experiment. One of the unsolved problems of the natural gas dual fuel engine is that there is too much exhaust of total hydrocarbon (THC) at a low equivalent mixture ratio. To fix it, a natural gas mixed with hydrogen was applied to engine test. The results showed that the higher the mixture ratio of hydrogen to natural gas, the higher the combustion efficiency. and when the amount of the intake air is reached to 90% of WOT, the combustion efficiency was promoted. But, like a case making the injection timing earlier, the equivalent mixture ratio for the knocking limit decrease and the produce of NOx increases.

• International Journal of Automotive Technology
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• 제2권3호
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• pp.93-101
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• 2001

Distribution of fuel-air mixture has a strong influence on performance and emissions of a compressed natural gas (CNG) engine. In this paper, parametric study is performed by KIVA-3V to investigate fuel-air mixture with respect to injection timing, cycle equivalence ratio and engine speed. With open-valve injection intensive mixing during intake and compression stroke results in relatively homogeneous mixture in the cylinder. Sequential induction of fuel-air mixture and fresh air results in stratification in the cylinder among the test cases at closed-valve injection. There is close similarity in the calculated distributions of the mixture in the cylinder with different cycle equivalence ratios and engine speeds. The results are compared against pressure traces and flame images obtained in a single cylinder engine converted from a 11L six-cylinder heavy duty diesel engine.

• 한국산학기술학회논문지
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• 제18권5호
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• pp.700-707
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• 2017

전 세계적으로 천연가스 시장에서는 천연가스의 저열량화 추세로 뚜렷하게 변화되고 있다. 이러한 추세는 국내의 천연가스 열량기준에 변화를 가져왔으며, 낮은 열량의 천연가스 도입으로 인해 현재 사용되고 있는 가스기기의 성능에도 변화가 있을 것으로 예측된다. 따라서 본 연구에서는 혼소엔진의 연소특성을 파악하기 위해 CNG 혼소율 변화를 이용하여 열효율, 도시평균유효압력 변동계수 및 열방출 특성을 고찰하였다. CNG 혼소율은 투입되는 연료의 총합 대비 공급되는 천연가스연료의 에너지로 계산하여 천연가스연료가 디젤연료를 대체하는 비율로 정의하였다. 엔진 실험조건으로는 공급되는 천연가스의 발열량은 $10,400kcal/Nm^3$이며, $1800rpm/500N{\cdot}m$의 엔진 운전조건에서 디젤연료의 분사시기는 BTDC $16^{\circ}CA$, 분사압력은 85 MPa로 설정하여 엔진의 성능 및 연소 실험을 진행하였다. 엔진 실험결과로 CNG 혼소율이 변화함에 따라 공급되는 디젤 연료량 역시 변화하고, CNG 혼소율이 증가할수록 디젤 연료량이 감소함으로써 점화에너지가 줄어들어 점화지연기간이 길어지는 연소특성을 나타내며, 이로 인해 엔진의 열효율과 출력도 감소하는 경향을 보였다. 그러나 연소안정성은 5% 미만으로 안정적인 엔진의 연소상태를 보여 실험의 신뢰성을 확보할 수 있었다.

• 한국자동차공학회논문집
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• 제24권2호
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• pp.161-168
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• 2016

CNG engine has been used as a transportation because of higher thermal efficiency and lower CO2 and particulate matter. However its out put power is decreased due to cylinder-to-cylinder variation during the supply of air-fuel mixture to the each cylinder. It also causes noise and vibration. So in this study, 1D engine simulation model was validated by comparison with experiment data and 3D CFD simulation was conducted to steady-state flow analysis about each manifold geometry. Then, the effects of various intake manifold geometries on variation were evaluated by using 1D-3D coupling analysis at engine speed of 2100 rpm range in 12 L CNG engine. As a result, variation was improved about 4 % though 3D CFD analysis and there was a variation within 3 % using 1D-3D coupling analysis.

• 한국자동차공학회논문집
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• 제6권4호
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• pp.178-185
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• 1998

To reduce the particulate matter and nitrogen oxides from diesel engine, many studies are proceeding and being accomplished practically. In this situation CNG engine has important meaning both as a clean fuel and an alternative energy. In order to present the direction and application of CNG, we simulated various operating conditions, that is, spark timing, compression ratio and fuel composition etc. Thus we try to understand how those affect performance and exhaust characteristics. The simulation program results found that the optimum combustion start angle was 21$^{\circ}$ at 1800rpm and fuel composition affects performance and emissions, also we could understand the formation of emission as crank angle is changed.