Se Hun Min

The objective of this study was to investigate the effect of a premixed ethanol ratio based on the same total heating value in a cylinder on the equivalence ratio distributions and the injected fuel droplet behavior in the cylinder of an RCCI engine. The spray simulation was conducted in two parts. First, we carried out spray validation simulations to determine the spray-influenced factor of the test injector. Next, engine simulations were performed with the spray-influenced factor obtained from the spray validation simulations to investigate the effect of the premixed ethanol ratio based on the same total heating value in a cylinder on the injected fuel atomization and the equivalence ratio distributions. The introduced total heating value was fixed at 595 J based on the lower heating value of diesel, 14 mg. The heating value of the premixed ethanol ratio varied from 0% to 40% based on the same total heating value in the cylinder in steps of 10%. It was revealed that when the premixed ethanol ratio based on the same total heating value in the cylinder was increased, the spray tip penetration value was reduced after 4 deg of diesel was injected because of the short injection duration and the small amount of diesel fuel used. The SMD value was also increased up to 32.58% with an increasing premixed ethanol ratio because of the low kinetic energy of the injected fuel, the short injection duration, the slow evaporation of the injected fuel and the low cylinder temperature.

The objective of this study is to investigate the effect of the premixed ethanol ratio based on the same total heating value in-cylinder on the equivalence ratio distributions and the injected fuel droplet behavior in the cylinder of the RCCI engine. The spray simulation was conducted by dividing two-part. First, the spray validation simulations progressed to find the spray-influenced factor of the test injector. Next, the engine simulations were performed with the spray-influenced factor obtained from spray validation simulations to investigate the effect of the premixed ethanol ratio based on the same total heating value in-cylinder on the injected fuel atomization and the equivalence ratio distributions. The introduced total heating value was fixed at 595J based on the lower heating value of diesel 14mg. The heating value of the premixed ethanol ratio varied from 0% to 40% based on the same total heating value in-cylinder in steps of 10%. It was revealed that when the premixed ethanol ratio based on the same total heating value in-cylinder was increased, the spray tip penetration value was reduced from the time after 4deg of diesel injection start because of the short injection duration by the small amount of diesel fuel. The SMD value was also more enormous up to 32.58% with increasing the premixed ethanol ratio because of the low kinetic energy of the injected fuel by the short injection duration and the slow evaporation of the injected fuel by the low cylinder temperature.

The objective of this study is to investigate the effect of CO₂ mole fraction by simulated‐exhaust gas recirculation (EGR) on the simultaneous reduction of exhaust emission in CI engine, and to find the optimal operating conditions.For the better expression of the actual EGR, the different CO₂ mole fractions from 0% to 20% were applied for the simulated‐EGR. The CO₂ mole fraction by simulated‐EGR was changed in the initial air in steps of 5% from 0% to 20% in the cylinder. The N₂ mole fraction in the initial air was also changed according to the CO₂ mole fraction, and the O₂ mole fraction was fixed by 16.2% due to the same overall equivalence ratio.When the CO₂ mole fraction by simulated‐EGR increased by 5%, the peak cylinder pressure was decreased by about −1.5% and the indicated specific nitrogen oxide value was also reduced from −4.9% to −48.8% because the ignition delay was longer by the higher specific heat of CO₂ than N₂, it induced to suppress the rise of cylinder temperature. In addition, when the start of energizing timing was advanced until BTDC 23 deg, the ISSoot value was decreased because the proportion of premixed combustion was increased.

본 연구는 압축 착화 엔진에서 simulated-EGR의 조성 중 CO₂ 몰 분율에 따른 연소 및 배기 배출물 특성을 비교 분석하는 것을 목적으로 하였다. 벽면과의 충돌 모델은 Mundo Sommerfeld 모델을 사용하였고, 최대 실린더 압력, 착화 지연, IMEP, NO 분포도, soot 분포도 특성의 결과를 비교 분석하였다. CO₂ 몰 분율의 영향을 알아보기 위하여 당량 비를 0.73으로 당량 비를 고정하고, CO₂ 몰 분율을 0%에서 10%로 변경하였다. 연구 결과, CO₂ 몰 분율이 증가할수록 분사된 연료의 증발이 저하되어 착화지연이 길어지고, 최대 실린더 압력도 감소하였다. ISNO의 경우 CO₂의 높은 비열로 인하여 CO₂가 5%씩 증가할 때, ISNO 값이 최대 55%가 감소하였다. 또한, CO₂가 5%씩 증가할 때, soot의 산화가 낮은 온도로 인하여 잘 일어나지 않아 약 10%씩 증가하였다.

The objective of this study is to numerically investigate the effect of cryogenic intake air temperature on the in-cylinder temperature and formation of exhaust emissions in a CI engine. The experimental setup was consisted of a single-cylinder diesel engine. The intake air temperature was varied from 18 °C to 40 °C, which was controlled by cooler and heater. Submodels were applied for the simulations of physical/chemical phenomenon of spray and combustion behaviors. The intake air temperature in numerical condition was varied from −18 °C to 18 °C. The numerical results were validated with experimental results for the reliability of this work. The results of this work were compared in terms of cylinder pressure, rate of heat release (ROHR), indicated specific nitrogen oxide (ISNO), indicated specific carbon monoxide (ISCO), ignition delay, in-cylinder temperature distributions, equivalence ratio distributions, NO mass fraction, and CO mass fraction. When the intake air temperature was decreased in steps of 9 °C, the cylinder temperature and cylinder pressure were decreased in steps of about 14.5 °C and 0.05 MPa, respectively. In all cases, the area where the NO formed in the cylinder was identified with the area of the high equivalence ratio and temperature in the cylinder. The amount of CO generation shows the similar distributions in the cylinder according to the intake air temperature conditions. However, the oxidation rate of formed CO under the low intake air temperature was lower than those of the high intake air temperature.

The objective of this study is to investigate the effect of water injection into intake port on the performance of small CI engine. The ECFM-3Z model was applied for the combustion analysis model, and the amount of injected water were varied 10%, 20% and 30% of injected fuel mass. The results of this work were compared in terms of cylinder pressure, rate of heat release (ROHR), and the ISNO and soot emissions. It was found that the cylinder pressure was decreased from 1.2% to 9.2% when the amount of injected water was increased from 10% to 30%. In the results, NO emission significantly decreased from about 24% to about 85% when the amount of injected water increased due to the specific heat and latent heat of water. Considering the test results, the best conditions for the simultaneous reduction of NO and soot is the BTDC 05deg of injection timing and 30% of water injection mass. It can be expected the best IMEP and ISFC characteristics.