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Technical Paper

The Characteristics of Scavenging Flow in a Poppet-Valve Type 2-Stroke Diesel Engine by Using RSSV System

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.
Technical Paper

Simulation of Fuel/Air Mixture Formation for Heavy Duty Liquid Phase LPG Injection (LPLI) Engines

Submodels are developed for injection, evaporation and wall impingement of a liquid LPG spray. The injection model determines the quality of fuel as two-phase choke flow at the nozzle exit. Wind tunnel experiments show the spray penetration more sensitive to ambient flow velocity than to injection pressure. Most evaporation occurs during choking, while heat transfer from surrounding air has a negligible effect on downstream droplet sizes. Three dimensional simulation shows that the bathtub cavity is better than the dog-dish cavity for stable flame propagation in lean-burn conditions. The injection timing during the IVC period has a negligible effect, while injection during an intake stroke enhances fuel/air mixing to result in more homogeneous cylinder charge.
Technical Paper

Numerical Prediction and Validation of Fuel Spray Behavior in a Gasoline Direct-Injection Engine

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.