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Optimization study is performed for the scavenging process as the first step for the development of a poppet-valve type automotive two-stroke diesel engine. The scavenging flow pattern is varied by the RSSV (rotatable shrouded scavenging valve) system, which was designed for application of a shroud valve to an actual engine. The scavenging flow is analyzed by flow visualization and numerical calculations under a steady condition. Water is used as the working fluid, instead of air for effective visualization of the flow pattern in the flow visualization study. More details in the scavenging characteristics are observed by a dye experiment, in which the dye path indicates the flow streamline in the cylinder. In the numerical study, three-dimensional flows are calculated by a modified version of KIVA-2 code, with a special technique to consider the valve and shroud shapes.

Numerical analysis of the flow field and fuel spray in a gasoline direct-injection (GDI) engine is performed by a modified version of the KIVA code. A simple valve treatment technique is employed to handle multiple moving valves without difficulties in generation of a body-fitted grid. The swirl motion of a hollow-cone spray is simulated by injecting droplets with initial angular momentum around the nozzle periphery. The model for spray-wall impingement is based on single droplet experiments with the droplet behaviors after impingement determined by experimental correlations. Different behaviors of an impinging droplet depend on the wall temperature and the critical temperature of fuel with the fuel film taken into account. The test engine is a 4-stroke 4-valve gasoline engine with a pent-roof head and vertical ports to form a reverse tumble flow during the intake stroke. A hollow-cone spray by a high-pressure swirl injector is employed to enhance mixture preparation and mixing.

Three-dimensional computation of the flow field and fuel spray in a DISC engine is performed using a modified version of KIVA-II. A special valve treatment technique is employed to simulate multiple moving valves without excessive efforts for body-fitted grid generation. The test engine is a 4-valve 4-stroke gasoline engine with a pent-roof head and a hollow-cone spray by a high-pressure swirl injector. The injection strategy is divided into two categories, ‘early’ and ‘late’ injection to optimize the combustion process. A spray-wall impingement model based on a single droplet experiment is implemented to consider both ‘early’ and ‘late’ injection case. Parametric studies are performed with respect to the load, injection timing, duration and position, spark-plug position, and the combustion chamber geometry. Results show that the current numerical analysis is capable of representing the spray motion and mixture formation in an operating engine qualitatively.

Analysis of flow field and charge distribution in a gasoline direct-injection (GDI) engine is performed by a modified version of the KIVA code. A particle-based spray model is proposed to simulate a swirl-type hollow-cone spray in a GDI engine. Spray droplets are assumed to be fully atomized and introduced at the sheet breakup locations as determined by experimental correlations and energy conservation. The effects of the fuel injection parameters such as spray cone angle and ambient pressure are examined for different injectors and injection conditions. Results show reasonable agreement with the measurements for penetration, dispersion, global shape, droplet velocity and size distribution by Phase Doppler Particle Anemometry(PDPA) in a constant-volume chamber. The test engine is a 4-stroke 4-valve optically accessible single-cylinder engine with a pent-roof head and tumble ports.