• 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.

• 한국자동차공학회논문집
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• 제14권2호
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• pp.166-173
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• 2006

This study investigates a heavy duty diesel engine with swept vol. 12.6L, 4cycle-OHC type to verify the effects of the performance and exhaust gas emission according to the variable specifications of both swirl ratio and flow coefficient in inlet port, combustion bowl and fuel injection system. To meet the high BMEP and stringent exhaust emission standard, a turbocharger with wastegate and an intercooler were installed in the engine. Helical port, major design parameters for combustion chamber and electronic fuel injection pump with 1,000bar were reviewed and applied. Confirmation tests were also performed to meet the target value, $NO_x$ 5.0g/kWh and PM 0.1g/kWh of Euro3 exhaust emission legislation. The results of this study show that not only is it effective to use a relatively bigger bowl size for controlling rapid burning condition due to the decreased in-bowl swirl, but also to use a concave cam with double injection rates to decrease $NO_x$.

• 한국산학기술학회논문지
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• 제20권10호
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• pp.33-39
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• 2019

대형 디젤 엔진에서 NOx, Smoke 등의 배기가스 저감과 연비를 개선하는 것은 주요한 개발 목표이다. 이 목표를 달성하기 위한 다양한 방식 중 연료를 분할하여 분사하는 다단 분사 전략은 주요하게 적용되고 있다. 본 연구에서는 다양한 조건의 다단분사 전략을 적용하여 배기가스, 연비 그리고 연소 소음 관점에서 최적의 성능을 확보할 수 있는 조건을 확인하여 개선정도를 확인하고자 하였다. 1단 파일럿 적용 시, 단일 분사 대비 NOx 저감이 가능한 영역이 있으나, Smoke가 악화되는 문제가 확인되었다. 2단 파일럿 적용 시, 최대 NOx와 Smoke를 각각 73%, 84%까지 저감할 수 있었다. 연소 소음은 최대 압력 상승률 분석을 통해, 또한 연료소비율은 도시 연료 소비율을 계산하여 단일 분사와 비교하여 개선수준을 평가하였다. 이를 통해 15%:15% 2단 파일럿 전략 적용 시, 단일 분사 대비 NOx 32.9%, Smoke 60.4%, 연비 1.95%, 연소소음 19.3%의 개선을 이룰 수 있음을 확인하였다. 향후, 본 연구 결과를 기반으로 운전 영역을 확장하여 각 조건에서의 최적 연료 분사 방식 도출을 통해 전체적인 성능개선을 구현하고자 한다.

• Korean Journal of Chemical Engineering
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• 제35권11호
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• pp.2164-2171
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• 2018

Heavy duty diesel vehicles deteriorate urban air quality by discharging a large volume of air pollutants such as soot and nitrogen oxides. In this study, a newly introduced auxiliary device a fuel activation device (FAD) to improve the combustion efficiency of internal engines by utilizing the cavitation effect was closely investigated by the fluid flow mechanism via a numerical analysis method. As a result, the FAD contributed to fuel atomization from the injection nozzle at lower inlet pressure by reducing the pressure energy. The improved cavitation effect facilitated fuel atomization, and ultimately reduced pollutant emission due to the decrease in fuel consumption. The axial velocity along the flow channel was increased 8.7 times with the aid of FAD, which improved the primary break-up of bubbles. The FAD cavitation effect produced 1.09-times larger turbulent bubbles under the same pressure and fuel injection amount than without FAD.

• 동력기계공학회지
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• 제16권6호
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• pp.11-18
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• 2012

대형 상용 엔진에서 발생하는 유효 도시 마력의 약 4~15%는 마찰 손실을 통해서 사라지며 마찰 손실 중 약 40~55%는 엔진 실린더와 피스톤 사이의 마찰에 의하여 발생하여, 엔진 전체에서 발생하는 마찰 손실 중 가장 많은 부분을 차지하고 있다. 이 연구에서는 엔진 실린더 라이너의 온도 분포 개선을 통해 라이너를 따라 유막을 형성하고 있는 윤활유의 적정 점성을 유지시키는 방법을 제시하고자 한다. 피스톤-라이너에서 발생하는 마찰 특성은 피스톤의 행정 위치에 따라서 접촉 마찰과 유막에 의한 마찰로 구분되며 이에 따라 요구되는 윤활유의 점성 특성 또한 달라진다. 먼저 해석 모델을 통하여 실린더 라이너 내부 온도 분포 특성을 확인한 후 피스톤 마찰 특성을 고려한 적정 온도 분포를 고찰하며 실린더 라이너에 열저항 코팅을 통해서 이를 구현하였다. 또한 실린더-피스톤 간의 마찰/윤활 해석을 통하여 열저항 코팅의 마찰 개선효과를 확인하였다.

• 한국산학기술학회논문지
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• 제7권5호
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• pp.784-787
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• 2006

배기가스 재순환장치는 디젤엔진에서 질소산화물을 저감시키는 기술로서 알려져 있다. 그러나 시스템 적용시 연료소비와 입자상물질을 증가시키기 때문에 기술 적용하는데 있어서 상당히 어려움이 있다. 그래서 실린더내의 연소시스템을 고려한 최적의 배기가스순환 비율을 산정하는 것은 매우 중요하다. 따라서 본 논문은 여러 가지의 EGR율을 변화시키면서 연소와 배기가스에 미치는 영향을 조사했다.

• 청정기술
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• 제22권4호
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• pp.211-224
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• 2016

가솔린 자동차의 내연기관 배기가스 처리를 위한 촉매로 삼원촉매가 널리 사용되고 있다. 반면 디젤 자동차의 배출 오염 물질 처리를 위해서는 다양한 기술들이 연구개발되고 있다. 디젤 자동차의 특징인 희박연소 조건에서 발생하는 질소산화물의 저감과 제거를 위해 티타니아에 담지된 바나듐 촉매가 상용화되어 있다. 바나듐 촉매를 이용한 질소산화물 저감기술은 암모니아를 환원제로 이용함으로써 대형 디젤 차량에 효과적으로 적용할 수 있다. 최근 활발하게 연구개발이 이루어지고 있는 구리가 이온 교환된 제올라이트 촉매는 초고연비 자동차 개발의 필수 기술로 인식되고 있다. 본 총설에서는 디젤 엔진의 배기가스 중 질소산화물을 효과적으로 제거하기 위한 후처리 기술 중 하나인 암모니아를 이용한 선택적 촉매 환원 반응의 촉매로 사용되는 구리가 이온 교환된 제올라이트 촉매와 관련한 최근 연구개발 동향을 소개하고자 한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.801-806
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• 2000

This experimental study is to investigate the intermittent spray characteristics of a multi-hole nozzle in a heavy-duty DI diesel engine. Multi 8 hole$(d_n=0.25mm)$, Multi 3 hole$(d_n=0.42)$ and Sing hole nozzle$(d_n=0.25mm)$ were used in this experiment. By using the 2-D PDPA(phase Doppler particle analyzer), the droplet diameter and the velocity of a diesel spray injected intermittently from the multi and the single-hole nozzle into a still ambient were measured. In order to calculate the mean values such as mean velocity, SMD, AMD etc. and to analyze the intermittent characteristics, the time-window of 0.15ms were applied. In the spray, the small droplet$(D<10{\mu}m)$ was regarded as an air flow, and the correlation between the fuel droplet$(10{\mu}m and the air (low was examined. The normalized axial droplet-air relative velocity of the 8 hole, the 3 hole and the single hole nozzle was evaluated as 0.081, 0.067, 0.06 and in case of the radial droplet-air relative velocity, the normalized. value is 0.014, 0.013 and 0.008 respectively.

• 한국자동차공학회논문집
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• 제9권2호
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• pp.59-66
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• 2001

This experimental study is to investigate the flow characteristics of the multi-hole nozzle used in the fuel injection system of a heavy-duty diesel engine. A multi-hole diesel nozzle with a 2-spring nozzle holder was used in this study and without changing the total orifice exit area, its hole number varied from 3($d_n$=0.42mm) to 8($d_n$=0.25mm). The injection pressure and needle lift were measured and Bosch type injection rates measurement system was used. The discharge flowrates of each orifice in the multi-hole nozzle changed by the flow conditions inside the nozzle sac hole. In case that pump speed and injection quantity were low, the orifice located in the vertex of nozzle tip had a great deal of injection quantity compared with that of others. As the increment of multi-hole number, the injection duration and the mean injection pressure decrease. The mean and peak injection rates, however, increase. Actually, the mean flow coefficient(${C_d}_{(mean)}$) increases, too. The flow coefficient of the multi 8 hole was evaluated as Cd(mean)=0.74 and that is the maximum value among the examined conditions.

• 한국자동차공학회논문집
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• 제16권6호
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• pp.19-25
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• 2008

Selective Catalytic Reduction is effective in the reduction of NOx emission. This research focused to evaluate the performance of a urea-SCR system and was conducted in two procedures. One is SCR reactor test using model gas in order to provide an optimal injection condition itself. In this step, some parametric study on emission temperature, space velocity, aspect ratio and the formation of urea spray were made by using flow visualization and Computation Fluid Dynamics techniques. The basic simulation results contributed in determining the layout for an actual engine test. The other is an engine performance and emission test. The urea injector was placed at the opposite direction of exhaust gases emitted into an exhaust duct and an optimal amount of a reducing agent is estimated accurately under different engine loads and speeds. Furthermore, the variation of NOx emission and applied amount of urea was investigated in terms of modes under the condition of with and without SCR, and other emissions such as PM, CO and NMHC were evaluated quantitatively as well. This research may provide fundamental data for the practical use of urea-SCR in future.