• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.221-228
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• 2013

An experimental study was carried out to investigate the effects of the injection timing on the spray and combustion characteristics in a spray-guided direct-injection spark-ignition (DISI) engine under lean stratified operation. An in-cylinder pressure analysis, exhaust emissions measurement, and visualization of the spray and combustion were employed in this study. The combustion in a stratified DISI engine was found to have both lean premixed and diffusion controlled flame combustion characteristics. The injection timing condition corresponding to the stratified mixture characteristics was verified to be a dominant factor for these flame characteristics. For the early injection timing, a non-luminous blue flame and low combustion efficiency were observed as a result of the lean homogeneous mixture formation. On the other hand, a luminous sooting flame was shown at the late injection timing because of an under-mixed mixture formation. In addition, the smoke emission and incomplete combustion products were increased at the late injection timing as a result of the increased locally rich area. On the other hand, the NOx emissions decreased and IMEP increased as the injection timing retarded. The combustion phasing produced by the injection timing was verified as the reason for this observation.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.2
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• pp.103-108
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• 2012

A MILD (Moderate and Intense Low oxygen Dilution) combustor decreases NOx formation effectively during the combustion process and NOx formation is affected significantly by the exhaust gas entrainment rate toward fuel and air. The present study focused on the new MILD combustor, which has coaxial cylindrical tube. The outside tube of the new MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. The connection pipe is set between the outer side and the inner side tubes and coaxial air nozzle is inserted at the center of the connection pipe. A numerical analysis is accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of air nozzle exit velocity, nozzle diameter, nozzle exit position and exhaust gas side pressure. The entrainment rate is proportional to the square root of air nozzle exit velocity and negatively proportional to the pressure difference between the exhaust gas side and furnace side pressures. The effect of air nozzle exit position is not considerable on the exhaust gas entrainment.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.6
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• pp.73-82
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• 2012

The main and side reactions of the three selective catalytic reduction (SCR) reactions with ammonia over a vanadium-based catalyst have been investigated using synthetic gas mixtures in the temperature range of $170{\sim}590^{\circ}C$. The three SCR reactions are standard SCR with pure NO, fast SCR with an equimolar mixture of NO and $NO_2$, and $NO_2$ SCR with pure $NO_2$. Vanadium based catalyst has no significant activity in NO oxidation to $NO_2$, while it has high activity for $NO_2$ decomposition at high temperatures. The selective catalytic oxidation of ammonia and the formation of nitrous oxide compete with the SCR reactions at the high temperatures. Water strongly inhibits the selective catalytic oxidation of ammonia and the formation of nitrous oxide, thus increasing the selectivity of the SCR reactions. However, the presence of water inhibits the SCR activity, most pronounced at low temperatures. In this study, the experimental results are analyzed by means of a dynamic one-dimensional isothermal heterogeneous plug-flow reactor (PFR) model according to the Eley-Rideal mechanism.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.742-749
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• 2002

Numerical Study with detailed chemistry has been conducted to investigate the flame structure and NOx formation characteristics in oxygen -enhanced(CH$_4$/O$_2$-$N_2$) and oxygen-enhanced-EGR(CH$_4$/O$_2$-$CO_2$) counter diffusion flame with various strain rates. A small amount of $N_2$is included in oxygen-enhanced-EGR combustion, in order to consider the inevitable $N_2$contamination by $O_2$production process or air infiltration. The results are as follows : In CH$_4$/O$_2$-$CO_2$flame it is very important to adopt a radiation effect precisely because the effect of radiation changes flame structure significantly. In CH$_4$/O$_2$-$N_2$flame special strategy to minimize NO emission is needed because it is very sensitive to a small amount of $N_2$. Special attention is needed on CO emission by flame quenching, because of increased CO concentration. Spatial NO production rate of oxygen-enhanced combustion is different from that of air and oxygen-enhanced-EGR combustion in that thermal mechanism plays a role of destruction as well as production. In case CH$_4$/O$_2$-$CO_2$flame contains more than 40% $CO_2$it is possible to maintain the same EINO as that of CH$_4$/Air flame with accomplishing higher temperature than that of CH$_4$/Air flame. EINO decreases with increasing strain rate, and those effects are augmented in CH$_4$/O$_2$flame.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.185-190
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• 2001

Numerical Study with detailed chemistry has been conducted to investigate the flame structure and NOx formation characteristics in oxygen-enhanced$(CH_4/O_2-N_2)$ and oxygen-enhanced-EGR$(CH_4/O_2-CO_2)$ counter diffusion flame with various strain rates. A small amount of $N_2$ is included in oxygen-enhanced-EGR combustion, in order to consider the inevitable $N_2$ contamination by $O_2$ production process or air infiltration. The results are as follows : In $CH_4/O_2-CO_2$ flame it is very important to adopt a radiation effect precisely because the effect of radiation changes flame structure significantly. In $CH_4/O_2-N_2$ flame special strategy to minimize NO emission is needed because it is very sensitive to a small amount of $N_2$. Special attention is needed on CO emission by flame quenching, because of increased CO concentration. Spatial NO production rate of oxygen-enhanced combustion is different from that of air and oxygen-enhanced-EGR combustion in that thermal mechanism plays a role of destruction as well as production. In case $CH_4/O_2-CO_2$ flame contains more than 40% $CO_2$ it is possible to maintain the same EINO as that of $CH_4/Air$ flame with accomplishing higher temperature than that of $CH_4/Air$ flame. EINO decreases with increasing strain rate, and those effects are augmented in $CH_4/O_2$ flame. Complementary study is needed with extending the range of strain rate variation.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.2
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• pp.267-271
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• 2009

The Marine Environment Protection Committee(MEPC) which is the IMO's specialized committee on marine pollution related matters deals with GHG related issues to discuss and compile possible approaches on technical, operational and market based measures to address GHG emissions from ships. The nitrous oxide($N_2O$) which remains generally in the atmosphere for around 114 years is one of the green house gases. The global warming potential of $N_2O$ is 310 times than $CO_2$ in the given period 100 years. It seems that the $N_2O$ formation is influenced by the nitrogen compound contained in the fuel which is named as "Fuel N" during the combustion process or the NOx, SOx and $H_2O$ through the emission gases before exhausted into the atmosphere. This paper has carried out an experimental study of the $N_2O$ concentration profiles by the change of $NH_3$ flows in the planner premixed combustion with using $C_3H_8$ and air.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.5
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• pp.61-66
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• 2009

An experimental investigation was conducted to analyze the effects of biodiesel-ethanol and biodiesel-diesel blended fuels on the characteristics of combustion and exhaust emissions, and size distributions of particulate matter in a single cylinder diesel engine. The three types of test fuel were biodiesel and two blended fuels which were added ethanol and diesel by 20 % volume based fraction into biodiesel, respectively. In this study, the injection rate, combustion pressure, exhaust emissions and size distributions of particulate matter were measured under various injection timings and injection pressures. The experimental results show that biodiesel-ethanol blended fuel has lengthened ignition delay and low combustion pressure in comparison with those of biodiesel and biodiesel-diesel blended fuel even if all fuels indicated similar trends of injection rate under equal injection pressures. In addition, the ethanol blended fuel significantly reduced nitrogen oxidies (NOx) and soot emissions. And then the size distribution of particulate matters shows that blended fuels restrain the formation of particles which were beyond the range of 150nm comparison with biodiesel fuel.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.51-59
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• 2002

In this study, cycle simulation was performed to investigate the effect of EGR on combustion characteristics and emissions including NO and soot using a two-zone model in a DI diesel engine. The NO formation was well predicted for different EGR rate and temperature using a two-zone model. The oxygen in the inlet charge was replaced by CO$_2$ and H$_2$O with EGR. The reduction in the inlet charge oxygen resulted in very large reduction in NO level at the same inlet charge temperature. The effect of EGR was to reduce the burned gas temperature. When EGR was increased from 0% to 15%, the peak flame temperature was decreased by 50$\^{C}$ and it caused about 57% NO reduction. EGR caused increase of the overall inlet charge temperature which offset some of benefit of lower flame temperature resulting from O$_2$ displacement. Cooling the EGR was confirmed to provide additional benefits by lowering NO emission. It also reduced soot emission.

• Journal of Power System Engineering
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• v.13 no.3
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• pp.20-26
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• 2009

디젤기관에서 배출되는 유해배출성분인 NOx(Nitrogen oxides)와 PM(Particulate matter)은 기관 실린더내의 혼합기 분포에 의해 그 생성이 지배된다. 이 때문에 그 유해배출물들을 저감하기 위해서는 연소의 전단계인 혼합기 분포 및 그 생성과정의 해석은 매우 중요하다. 디젤기관에서 노즐로부터 분사된 연료는 주위기체와 혼합기를 형성하는 과정에서 액체에서 기체로 상변화를 동반한다. 따라서 분무의 혼합기형성과정을 해석하기 위해서는 액상과 기상을 동시에 분리하여 계측하는 것이 필요하다. 그러므로 본 연구에서는 디젤분무를 대상으로 Melton 등이 제안한 엑시플렉스(Exciplex) 형광법을 이용하여, 분무의 액상과 기상을 동시에 2차원분리해서 가시화촬영을 행하였다. 그 엑시플렉스 형광법을 이용하여 획득한 이미지에 화상 응용해석을 실시하여 비정상증발디젤분무의 혼합기형성과정에 대한 정보를 얻고자 하였다. 엑시플렉스 형광법을 이용해서 증발분무의 거동측성을 해석한 결과 프랙틸해석을 이용한 분무 흐트러짐(Disturbance)의 평가에서 플랙틸차원은 분사압력의 변화에 관계없이 하나의 값, 약 1.1로 정리 할 수 있고, 그 결과 각 분사압력에 대한 분무 기상외곽곡선(외주)은 거의 동일한 정도의 요철형상을 갖는다.

• International Journal of Automotive Technology
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• v.7 no.6
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• pp.675-680
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• 2006

In the direct injected gasoline engine, atomized spray is desired to achieve efficient mixture formation needed to good engine performance because the injection process leaves little time for the evaporation of fuels. Therefore, substantial understanding of global spray structure and quantitative characteristics of spray are decisive technology to optimize combustion system of a GDI engine. The combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition(SCCI) engine according to intake temperature and compression ratio was examined. The fuel was injected directly to the cylinder under the high temperature condition resulting from heating the intake port. With this injection strategy, the SCCI combustion region was expanded dramatically without any increase in NOx emissions, which were seen in the case of compression stroke injection. Injection timing during the intake temperature was found to be an important parameter that affects the SCCI region width. The mixture stratification and the fuel reformation can be utilized to reduce the required intake temperature for suitable SCCI combustion under each set of engine speed and compression ratio conditions.