Kihyung Lee - Academia.edu (original) (raw)

Papers by Kihyung Lee

PCCI engines can reduce NOx and PM emissions simultaneously without sacrificing thermal efficienc... more PCCI engines can reduce NOx and PM emissions simultaneously without sacrificing thermal efficiency, but a low combustion temperature resulting from early fuel injection, and ignition occurring prior to TDC, can cause higher THC and CO emissions and fuel consumption. In conclusion, it was found that the PCCI combustion achieved by the 2-stage injection strategy with optimized calibration factors (e.g. EGR rate, injection pressure, swirl ratio, intake pressure, injection timing) can reduce NOx and PM emissions simultaneously. This research works are expected to provide valuable information conducive to a development of an innovative combustion engine that can fulfill upcoming stringent emission standards.

for a secondary fuel injection nozzle using a digital image processing method

: Recently, the internal combustion engines have focused on reducing the CO 2 gas in order to cop... more : Recently, the internal combustion engines have focused on reducing the CO 2 gas in order to cope with severe regulations for fuel economy. Therefore, various new technologies have been developed. Among them, cooling system is spotlighted because it has great effect on fuel economy. In this study, we measured the friction losses of engine parts according to engine speed and oil temperature. We also obtained optimized oil temperature which has the minimum friction losses. Then, we selected optimized oil temperature range and gave informations of friction losses for each engine parts. In addition, we analyzed relationship between coolant temperature and oil temperature by using engine performance test system. From this experiment, we obtained the database for relationship between coolant temperature and oil temperature. Then, we found the optimal temperature about engine oil. We analyzed BSFC and exhaust emissions by controlling the high coolant temperture. If we controlled coolant t...

Currently, due to the serious world-wide air pollution by substances emitted from vehicles, emiss... more Currently, due to the serious world-wide air pollution by substances emitted from vehicles, emission control is enforced more firmly and it is expected that the regulation requirements for emission will become more severe. A new concept combustion technology that can reduce the NOx and PM in relation to combustion is urgently required. This study used a split injection method at a 4 cylinder common-rail direct injection diesel engine in order to apply the partially premixed charge compression ignition combustion method without significantly altering engine specifications And it is investigated that the effects of the injection ratio and SCV(swirl control valve) to emission characteristics. From these tests, soot(g) and NOx(g) emission could be reduced to 40% and 92% compared to base engine performance at specified engine driving conditions(6 points with weight factors) according to application of split injection and SCV(swirl control valve).

Processes, 2020

The reduction of the weight of the engine of a vessel or an automobile can result in improved eng... more The reduction of the weight of the engine of a vessel or an automobile can result in improved engine efficiency and lower CO2 emissions. Therefore, this study was conducted to improve the mechanical properties of the AC4CH alloy, an alternative to cast iron for engine fabrication, through the addition of Si and Mg to aluminum. The mechanical properties of the alloy were improved through refinement of the Si structure, grain refinement, and heat treatment. In addition, the applicability of a cylinder block fabricated with the modified AC4CH alloy to a diesel engine was validated through a 300 h durability test.

Energies, 2020

Higher speeds, faster acceleration and longer duration need a more realistic driving cycle. As a ... more Higher speeds, faster acceleration and longer duration need a more realistic driving cycle. As a result, a new test procedure that reflects real-world driving conditions has been applied since 2017, and the previous development environment optimized for NEDC has also changed. In this study, several factors and technologies relating to fuel consumption, such as vehicle weight, tire rolling resistance, drag of aerodynamic, stop–start, and 48 V mild hybrid system, are evaluated as per the new worldwide harmonized light vehicles test procedure (WLTP) and compared with that of the previous European driving cycle (NEDC). The impact of the vehicle weight is increased in case of the WLTP due to faster acceleration compared to that under NEDC. The influence of aerodynamic force is very important as the average and maximum speed are increased. Meanwhile, the impact of idle stop–start technology is lower compared to that under NEDC due to the reduction in idle operation time. The 48-V mild hyb...

Transactions of the Japan Society of Mechanical Engineers Series B, 1990

The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines, 2008

Cycle-resolved fiame characteristics measurement with soot in a HSDI diesel engine using micro-Ca... more Cycle-resolved fiame characteristics measurement with soot in a HSDI diesel engine using micro-Cassegrain system

Journal of ILASS-Korea, 2015

Recently, the engine calibration technique has been much more complicated than that of the past e... more Recently, the engine calibration technique has been much more complicated than that of the past engine case in order to satisfy the strict emission regulations. The current calibration method for the diesel engine which has an increasing market is both costly and time-consuming. New engine calibration method is required to develop for high-quality diesel engines with low cost and release it at the appropriate time. This study provides the optimal calibrating technique for complex engine systems using statistical modeling and numerical optimization. Firstly, it design a test plan based on Design of Experiments, a V-optimality methodology which is suitable looking for set-points, and determine the shape of test engine response. Secondly, it uses functions to make linear regression model for data analysis and optimization to fit the models of engines behavior. Finally, it generates the optimal calibrations obtained directly from empirical engine models using Grey Relational Analysis and compares the calibrations with data. This method can develop a process for systematically identifying the optimal balance of engine emissions.

Thermal Science, 2015

The use of diesel engines for vehicle has been increasing recently due to its higher thermal effi... more The use of diesel engines for vehicle has been increasing recently due to its higher thermal efficiency and lower CO2 emission level. However, in the case of diesel engine, NOx increases in a high temperature combustion region and particulate matter is generated in a fuel rich region. Therefore, the technique of PCCI (premixed charge compression ignition) is often studied to get the peak combustion temperature down and to make a better air-fuel mixing. However it also has got a limited operating range and lower engine power produced by the wall wetting and the difficulty of the ignition timing control. In this research, the effect of injection strategies on the injected fuel behavior, combustion and emission characteristics in a PCCI engine were investigated to find out the optimal conditions for fuel injection, and then ethanol blended diesel fuel was used to control the ignition timing. As a result, the combustion pressures and ROHR (rate of heat release) of the blended fuel becam...

Diesel engine has many advantages such as high thermal efficiency, low fuel consumption and low e... more Diesel engine has many advantages such as high thermal efficiency, low fuel consumption and low emission of CO2. However, the diesel engine faced with strengthened emission regulation about NOx and PM. To suppress NOx emission, after-treatment systems such as Lean NOx Trap (LNT), Selective Catalytic Reduction (SCR) are considered as a more practical strategy. This paper investigated the performance of Lean NOx trap of the 4 stroke diesel engine which had a LNT catalyst. Characteristic of exhaust emission at NEDC mode was analyzed. From this result, the effect of nozzle attaching degree, injection quantity and gas flow change on NOx conversion performance was clarified.

Lecture notes in electrical engineering, 2013

Owing to increasing oil price caused by risk of oil depletion, many researchers have focused to d... more Owing to increasing oil price caused by risk of oil depletion, many researchers have focused to develop various alternative energies. Biodiesel is one of those energies, which has been a hot-issue recently in automotive industries. Because biodiesel has similar characteristics as diesel, it is possible to use present gas stations, facilities and engine without any modification. It has also an advantage that the emission of biodiesel is lower than conventional diesel engine because it contains oxygen in the fuel. However biodiesel has some problems such as corrosiveness and high viscosity. Therefore, in this study, an experiment was conducted to use biodiesel fuel to solve these problems, and the characteristics of combustion and emission were evaluated according to the use of biodiesel blended with diesel fuel and it was compared with diesel fuel. As a result, we found that biodiesel has benefits of reduction in CO 2 and PM emissions compared to diesel fuel.

Journal of Thermal Science and Technology, 2013

As oil prices increase and regulations on emissions are tightened, demands for improved engine pe... more As oil prices increase and regulations on emissions are tightened, demands for improved engine performance such as fuel economy and exhaust emission have increased accordingly. Therefore, various new technologies have been developed to meet such demands. Among them, cooling system is spotlighted because it has great effect on fuel economy, but there has been little work on cooling systems. In this study, we measured friction losses of engine parts according to engine oil temperature (using the strip-down method) and also obtained optimized oil temperature which has the minimum friction losses. In additions, we analyzed the correlation between engine oil temperature and coolant temperature. Based on these results, we determine the optimal range of engine oil temperature and investigate the effect of engine speed and indicated mean effective pressure on fuel consumption and exhaust emission characteristics. Finally, we found that although the fuel consumption was improved in the selected oil temperature range, the characteristics of exhaust emission were not improved under the conditions.

Journal of ILASS-Korea, 2013

Transactions of the Korean Society of Mechanical Engineers B, 2011

NOx (Nitrogen Oxide) reduction system periodically needs a rich or stoichiometric operating condi... more NOx (Nitrogen Oxide) reduction system periodically needs a rich or stoichiometric operating condition to reduce NOx. A new method that optimizes the control of external HC injection into a diesel exhaust pipe for HC-type LNT (Lean NOx Trap) catalyst system has been developed. In this paper, these catalysts are called HC-LNT catalysts. The concentration and amount of HC can be controlled by controlling the external injection. In this study, we investigated the relationship between the spray behavior of hydrocarbons injected into the transparent exhaust pipe and NOx reduction characteristics. From the results of this experiment, we obtained useful information about the optimum injection and position of HC injector to the exhaust pipe. Further, we obtained useful information about the optimal injection condition for an HC-LNT catalyst system with a gasoline PFI (port fuel injection) typeinjector.

Journal of Thermal Science, 2014

This paper investigates the effect of intake port configuration on the swirl that is generated wi... more This paper investigates the effect of intake port configuration on the swirl that is generated within a direct injection (D.I.) diesel engine. The in-cylinder flow characteristics are known to have significant effects on fuel-air mixing, combustion, and emissions. To clarify how to intensify the swirl flow, a swirl control valve (SCV) and a bypass were selected as design parameters for enhancing the swirl flow. The optimal intake port shape was also chosen as a parameter needed to efficiently generate a high swirl ratio. The results revealed that a key factor in generating a high swirl ratio was to control the intake airflow direction passing through the intake valve seat. Further, the swirl intensity was influenced by changing the distance between the helical and tangential ports, and the swirl flow was changed by the presence of a bypass near the intake valve seat. Additionally, the effect of intake port geometry on the in-cylinder flow field was investigated by using a laser sheet visualization method. The experimental results showed a correlation of swirl ratio and mass flow rate. In addition, we found that employing the bypass was an effective method to increase swirl ratio without sacrificing mass flow rate.

Journal of Thermal Science and Technology, 2008

NOx catalytic converter systems periodically require rich or stoichiometric operating conditions ... more NOx catalytic converter systems periodically require rich or stoichiometric operating conditions to reduce NOx. The HC (hydrocarbon) concentration in a diesel engine is typically so low that the HC is not sufficient for NOx conversion. It was proposed that a rich air fuel ratio in a diesel engine could be realized via post fuel injection or supplemental fuel injection into the exhaust gas. A new method that optimizes the control of an external HC injection to diesel exhaust pipes for HC type LNT (Lean NOx Trap) catalyst systems has been developed. The external injection has other benefits: it can be controlled independently without disturbing engine control, it can be adapted to various layouts for exhaust systems, it has no oil dilution problems, among other benefits. In this study, the concentration and amount of HC can be controlled via control of the external injection. This research investigated the spray behavior of hydrocarbons injected into the transparent exhaust pipe. From this experiment, we obtained useful information about the optimal injection conditions for the HC-LNT catalyst system with an MPI injector.

Measurement Science and Technology, 2007

There are many ways to reduce diesel engine exhaust emissions. However, NO x emission is difficul... more There are many ways to reduce diesel engine exhaust emissions. However, NO x emission is difficult to reduce because the hydrocarbon (HC) concentration in a diesel engine is not sufficient for NO x conversion. Therefore, in order to create stoichiometric conditions in the De-NO x catalyst, a secondary injection system is designed to inject liquid HC into the exhaust pipe. The atomization and distribution characteristics of the HC injected from a secondary injector are key technologies to obtain a high NO x conversion because inhomogeneous droplets of injected HC cause not only high fuel consumption but also deterioration of NO x emission. This paper describes the spray characteristics of a secondary injector including the spray angle, penetration length and breakup behaviour of the spray to optimize the reduction rate of the NO x catalyst. In this study, various optical diagnostics were applied to investigate these spray characteristics, the atomization mechanism and spray developing process. The visualization and image processing method for the spray pulsation were developed by high speed photography. The influence of the fuel supply pressure on the spray behaviour and a more detailed spray developing process have been analysed experimentally using image processing. Finally, the experimental results were used to correlate the spray structure to the injection system performance and to provide a design guide for a secondary injector nozzle.

JSME International Journal Series B, 2005

Journal of Mechanical Science and Technology, 2009

Recently, the electrically controlled fuel injection type motorcycle has been emphasized in order... more Recently, the electrically controlled fuel injection type motorcycle has been emphasized in order to meet regulations for exhaust emissions. However, there are many difficulties in selecting the control parameters because the pulsation phenomenon occurs in the intake port due to the higher speed operating range and the smaller layout than for a passenger car. Therefore, we investigated the injector spray characteristics which are applied to a 4-valve motorcycle gasoline engine. The spray characteristics were visualized by using a CCD camera synchronized with the stroboscope at 6000 rpm. Furthermore, we compared the simulation results using the VECTIS code with experimental results. The results showed that the trajectory of the spray was directed towards the lower wall of the intake port when the fuel was injected at closed valve timing. On the other hand, when the fuel was injected at open valve timing, a large portion of the fuel was lifted towards the upper half of the port. In addition, open valve injection makes fuel evaporation time short; this resulted in better mixture formation than a closed valve injection. From this result, we found that injection timing has a great effect on the mixture formation within a motorcycle cylinder.