• 한국자동차공학회논문집
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• 제22권4호
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• pp.121-130
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• 2014

This paper is the second investigation on the effects of intake flow control methods on the part load performance in a spark ignition engine. In the previous work, two control methods, port throttling and masking, were compared with respect to lean misfire limit, fuel consumption and emissions. In this work, the effects of these two methods on EGR characteristics were studied and simultaneously the differences between EGR and lean combustion as a dilution method were investigated. The results show that EGR limit is expanded up to 23% and 3 ~ 5% improvement in the fuel consumption are achieved around 8 ~ 13% rates by the flow controls comparing with 10% limit and 1.5% reduction around 3% rate of non-control case. The masking method is more effective on the limit expansion than throttling as like as lean misfire limit; however there is no substantial difference in fuel consumptions improvement regardless the control methods except high load condition. Also it is observed that there exist critical EGR rates around which the combustion performance and NOx formation change remarkably and these rates generally coincide with optimum rates for the fuel consumption. In addition, dilution with fresh air is much more advantageous than that of the exhaust gas from the view point of dilution limit and fuel consumption, while utilization of the exhaust gas is more effective on NOx reduction in spite of considerably small dilution compared with the use of fresh air. Finally, the improvement of fuel consumption by massive EGR is highly dependent on the EGR limit at which the engine runs stably, therefore the stratified combustion technique might be a best solution for this purpose.

• 한국자동차공학회논문집
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• 제7권5호
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• pp.22-30
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• 1999

Optimization of in-cylinder flow is regarded as one of the most important factors to realize stable stratified charge combustion in a Spark-ignited Direct Injection(SDI) engine. Therefore, Computational Fluid Dynamic(CFD) simulation technique were used to clarify the characteristics of in-cylinder flow of a SDI engine with top entry intake port. Also, CFD results were compared to experimental results using Laser Doppler Velocimetry(LDV), Particle Image Velocimetry(PIV) and good validations were met. As the results reverse tumble flow generated during intake process was preserved by configuration of curved piston while base and reverse tumbles were diminished at the end of compression stroke in case of flat top piston. In addition, it will be needed to optimize the fuel mixture distribution based on these results.

• 한국가스학회지
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• 제19권4호
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• pp.22-28
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• 2015

LPG가 수송용 연료로서 경쟁력을 유지하기 위해서는 지속적인 기술개발을 통해 휘발유와의 연비격차를 감소시키고 후처리시스템 등에 의한 가격 부담을 낮추어야 한다. 이에 본 연구에서는 안정적인 희박연소 구현을 통한 연비개선을 얻기 위해 실린더 중앙에 점화플러그와 연료분사기가 인접해 있고, 연료가 분사된 후 바로 점화가 이루어지도록 하는 분무유도방식의 LPG 직접분사엔진을 개발의 일환으로 연소제어인자의 변화에 따른 연소 특성을 분석하였다. 안정적인 연소를 위해 국부적으로 농후한 혼합기를 형성하는 성층희박연소의 특성상 일정 수준이상의 질소산화물이 배출되는 문제점을 갖고 있다. 질소산화물 저감을 위해 EGR을 적용한 결과 연료소비율과 THC의 배출은 약간 증가하지만 $NO_x$배출은 약 15% 저감되었다. EGR 적용에 의한 연소속도의 감소는 초기 화염발달 시기에 집중되어 나타났으며 흡입공기의 희석효과에 의해 EGR율이 증가할수록 최대 열방출율 및 열방출율 증가 기울기가 감소하였다.

• 대한기계학회논문집B
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• 제39권1호
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• pp.45-51
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• 2015

최근 강화되는 연료소비율과 배기 규제에 대응하기 위해 자동차용 엔진에 다양한 신기술들이 적용되고 있다. 직접분사식 희박연소 엔진은 안정적인 성층혼합기 연소를 통해 연료소비율 및 배출가스 개선이 가능하지만 과잉공기 조건에서 상대적으로 높은 수준은 질소산화물의 배출은 해결되어야 할 과제이다. 본 연구에서는 직접분사식 희박연소 LPG 엔진에서 가변 밸브 기구를 이용한 흡기 및 배기밸브 시기의 변경이 엔진의 성능 및 배출가스에 미치는 영향을 파악하고자 하였다. 스로틀링을 하지 않은 부분부하 운전 조건에서 흡기밸브 열림 시기의 진각은 공기과잉률의 증가에 의한 질소산화물 배출 증가에 원인으로 작용하였다. 배기밸브 열림 시기를 진각할 경우 팽창일 감소와 펌핑손실 증가에 의해 연료 소비율이 악화되었다.

• 한국수소및신에너지학회논문집
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• 제25권6호
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• pp.643-647
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• 2014

Two types of fuel supply method ar used in CNG vehicles. One is premixed ignition and the other is gas-jet ignition. In premixed ignition, the fuel is introduced with intake air so that homogeneous air-fuel mixture may form. The ignitability of this method depends on the global equivalence ratio. In gas-jet ignition, CNG is introduced directly into the engine combustion chamber. The overall mixture is stratified by retarded fuel injection. In this study, a visualization technique was employed to obtain fundamental properties regarding overall mixture formation of direct injected CNG fuel inside a constant volume chamber. Jet angles, penetrations and projected jet area with respect to ambient pressure are investigated. The penetration decreases apparently and the time reaching the CVC wall was delayed as the chamber pressure increases. This is caused by the higher inertia of the fluid elements that the injected fluid must accelerate and push aside. It is same to liquid fuel such as diesel and gasoline, but this phenomenon is far more prominent for the gaseous fuel.

• 한국자동차공학회논문집
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• 제8권6호
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• pp.51-59
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• 2000

In-cylinder spray flow motion plays an important in the adjustment of mixture preparation with a fundamental spray characteristics and in-cylinder flow field well in direct-injection gasoline engine. In this study, the fundamental spray characteristics such as mean drop size, velocity distribution, spray angle were measured and in-cylinder spray flow motion was visualized in order to optimize intake port, piston top land and combustion chamber shapes in the development stage of mass-produced G야 engine. For these experiments, the PDPA measurements and Mie scattering technique were used for detailed spray characteristics and in-cylinder spray motions were obtained by use of ICCD camera through the single-cylinder optical engine. From the experimental results, the test injector shows a good low-end linearity between the dynamic flow and fuel injection pulse width and the fuel spray of 20mm or less in SMD with good spray symmetry. In addition, the in-cylinder tumble flow has more effect on the homogeneous mixture formation than that of in-cylinder swirl flow at early injection mode and the in-cylinder swirl flow plays a better role of stratified mixture preparation than tumble flow at late injection mode.