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Since it is well known that the flow and spray characteristics are critical factors on the performance and emission in a direct-injection diesel engine, this study aims to investigate the interaction between flow and spray characteristics. At first, in-cylinder flow distributions in swirl/tumble adapter for 4-valve cylinder head of DI diesel engine were investigated under steady conditions with different SCV angles mounted on the cylinder head by using 2-D LDV. It was found that swirl flow is more dominant than tumble on spray interaction in the engine. For the analysis, the in-cylinder flow was quantified in terms of non-dimensional rig swirl/tumble, mean flow coefficient, swirl ratio/tumble ratio. It was confirmed that the swirl ratio is controlled between 2.3 and 3.8 by changing SCV angles. Spray characteristics of the intermittent injection also were investigated by using PDA system to measure droplet size and velocity.

To provide an appropriate direction for development of transient control algorithm in a gasoline engine, transient performance analysis and evaluation under rapid accelerating and decelerating driving conditions were implemented by experimental study. In order to evaluate the characteristics of transient performance quantitatively, the concept and method by transient response specifications were introduced. Several performance parameters in terms of engine speed (RPM), mass air flow (MAF), manifold absolute pressure (MAP), fuel injection duration (ΔtInj) and air excess ration (λ) were measured simultaneously during the rapid opening and closing of the throttle valve using the step motor controlled by PC. Transient response specifications and non- dimensional variables in terms of delay time rate, rising time rate and settling time rate characterized the transient performance of a gasoline engine quantitatively.

Intake-generated in-cylinder flow and subsequent combustion characteristics were studied respectively in a 4-valve spark ignition engine. The flow characteristics of four-valve cylinder head were examined under a steady flow condition for intake ports with three different entry angles; θ=15°, 20° and 25°. The velocity and angular momentum distributions in the tumble adaptor were measured with PIV (Particle Image Velocimetry). Subsequent effects of tumble flow generated by various intakes ports on the lean burn characteristics were also investigated. The lean burn performances were examined in a four-valve pentroof engine. The combustion duration under lean mixture conditions was calculated by heat release analysis of the pressure trace. The results show that flow structure is complicated by valve interference at low valve lift.