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A stoichiometric 2.0L turbocharged DISI engine is developed based upon the Theta 2.0L NA engine. The engine is intended to be installed in a midsize sedan as a downsizing concept, targeting to improve the fuel efficiency of the vehicles installed with the V6 3.3L engines while maintaining the performances. The base 2.0L engine is modified to accommodate the 4∼12MPa direct injection system with the multi-hole injectors and the intake/exhaust variable valve timing (VVT) system. The turbocharger is carefully matched so that the specific power over 85kW/L can be achieved while the maximum torque reached at 2000RPM. The fuel efficiency of the target vehicle was improved significantly due to the reduced friction and pumping losses compared to the vehicle equipped with the V6 3.3L engines. Various advanced gasoline turbocharger technologies for improving the transient performances are evaluated.

The in-cylinder three-dimensional unsteady analysis on the fluid patterns were scrutinized using computational fluid dynamics code. The 3D CAD data were created using the 3D CAD modeling software and the computational meshes were generated considering the movements of intake valves and piston. The calculated results of in-cylinder flow patterns for the pent-roof type combustion chamber were in good agreements with the unsteady water rig experimental results. To investigate the influences of the intake port inclined angle variations on the in-cylinder flow patterns and the resulting in-cylinder tumble ratio, each type of intake port were simulated with the intake port inclined angle variations. The results show that as the intake port inclined angles become smaller, the in-cylinder tumble ratio were strengthened. If the intake port inclined angle was larger than 30 degree, the in-cylinder tumble ratio was saturated.

In this study, the mass of THC is reduced almost 40 percent with spark timing ATDC 7.8CA during 15 seconds from engine start in phase 1 LA4 mode, comparison with TDC 2.8CA (Figure 1, Table 3). One of the reason of HC reduction in vehicle test is reduction of raw THC concentration before CCC (Closed Coupled Catalyst) which is 36% lower level (Figure 3, Table 3). The other reason is that the LOT (Light Off Time) of catalyst is shortened from 34 seconds to below 20 seconds (Figure 7, Table 3). As the spark timing is retarded with same intake air quantity and same RPM, BMEP is reduced (Equation (3), Figure 9). Therefore in order to operate in an idle RPM in vehicle, the mass of intake air should be increased (Figure 5). So a catalyst is heated in shorter period.

A combined experimental and computational study of 3-D unsteady compressible flow in exhaust manifold and CCC system was performed to understand the flow characteristics and to improve the flow distribution of pulsating exhaust gases within monolith. An experimental study was carried out to measure the velocity distribution in production exhaust manifold and CCC under engine operating conditions using LDV (Laser Doppler Velocimetry) system. Velocity characteristics were measured at planes 25 mm away from the front surface of first monolith and between two monolithic bricks. To provide boundary conditions for the computational study, velocity fields according to crank angle were also measured at the entrance of exhaust manifold. The comparisons of exhaust gas flow patterns in the junction and mixing pipe between experimental and computational results were made.

High speed natural light motion picture records synchronized with head gasket ionization probe and in-cylinder pressure data have been made in the transparent engine of different combustion chamber configurations. For knocking cycles, the head gasket ionization current method simultaneously taken with pressure data was able to find the location of knocking occurrence. To investigate the effects of combustion chamber configurations, the flame propagation experiments for pent-roof combustion chamber with center ignition ( Modified Type I engine ) and modified pent-roof ( Type II engine ) combustion chamber were performed with high speed natural light photography technique. The flame propagation of Modified Type I engine represents more uniform patterns than that of Type II engine. The investigation of knocking combustion was also made possible by observing flame propagation with the measuring techniques that use head gasket ionization probe and in-cylinder pressure data.

In this study, single cylinder engines with different tumble ratio were made to show the effects of tumble motion on engine performance and flame propagation. Particle tracking velocimetry technique by using chopper was adopted to examine the in-cylinder flow field for the full understanding of tumble motion. And equivalent angular speed of tumble vortex was obtained from each crank angle and compared with tumble ratio derived from the steady state flow rig test. Flame propagation speed were obtained with the gasket ionization probe and the piston ionization probe. And the combustion pressure in cylinder was measured to analyze the combustion characteristics. In case of high tumble engine, BSFC and BSHC were decreased and BSNOx was increased at part load test, BMEP and combustion peak pressure was increased at full load test. Also, flame propagation characteristics could be understood by use of piston ionization probe.

Four ports which have slightly different shapes have been applied to 3-valve MPI SI engine to develop Axially Stratified Lean Combustion engine. The purpose of port modification test was to investigate the effects of swirl ratio and direction on engine performance and emissions. In the engine test injection characteristics, i.e. timing, flow rate, direction as well as port design significantly effected on the engine combustion. Especially, it was observed that injection timing was the most important factor for combustion stability, but its effect on performance has some differences in accordance with the port designs. To verify the relationship between port shape and injection timing, in-cylinder gas was sampled by high speed gas sampling device varing injection timing through whole intake and compression,. strokes at spark plug position and analyzed by gas chromatography.

The flow characteristics such as flow coefficient and swirl ratio in cylinder were measured at steady-state condition by using a steady-state flow measuring system which consists of an impulse swirl meter and a viscous flow air meter. Effects of the in-cylinder swirl on the emissions (NOx, THC), BSFC, MBT, and lean mixture limit (LML) were investigated by using single cylinder research engine with a helical intake port. The combustion pressure in the cylinder was measured to analyze the combustion duration (such as the initial burn duration and the main burn duration) and COV of IMEP which have an effect on LML. By generating the in-cylinder swirl, the combustion duration is remarkably decreased, while the emissions and BSFC are increased. The lean mixture limit is increased with the in-cylinder swirl ratio. In the case of high swirl ratio (Rs=2.48),the lean mixture limit is increased by 3.3 with optimized fuel inject ion timing.