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In previous study, the model for flash-boiling spray of multicomponent fuel was constructed and was implemented into KIVA code. This model considered the detailed physical properties and evaporation process of multicomponent fuel and the bubble nucleation, growth and disruption in a nozzle orifice and injected fuel droplets. These numerical results using this model were compared with experimental data which were obtained in the previous study using a constant volume vessel. The spray characteristics from numerical simulation qualitatively showed good agreement with the experimental results. Especially, it was confirmed from both the numerical and experimental data that flash-boiling effectively accelerated the atomization and vaporization of fuel droplets. However, in this previous study, injection pressure was very low (up to 15 MPa), and the spray characteristics of high pressure injection could not be analyzed.

The purpose of this study is to cool the internal EGR (Exhaust Gas Recirculation) gas and form a uniform mixture by the injection of fuel into internal EGR gas. In previous studies, the internal EGR has a problem that high-temperature and low-density EGR gas flows into the cylinder and these causes the deterioration of fuel economy and exhaust emission performances [1]. In addition, internal EGR gas collides with fresh air tumble from the intake valves and, distribution of the in-cylinder oxygen concentration becomes heterogeneous. Additionally, the poor volatility of diesel fuel makes it difficult to achieve HCCI combustion in CI (Compression Ignition) engines. In order to resolve these problems, Fuel is injected into the internal EGR gas during the intake stroke. This injection cools the internal EGR gas by high latent heat derived from the promotion of fuel evaporation and equalizes the distribution of oxygen concentration in the cylinder.

Because the transportation industry uses fossil fuels as much as 1/4 of the total, CO2 emission from transport sector should be reduced. Therefore, carbon neutral (CN) fuel has been attracted attention. However, hydrogen and ammonia have low energy density and are difficult to be stored and transported. In this study, synfuel produced by Fischer-Tropsch (FT) reaction. This fuel is produced with carbon dioxide absorbed from the direct air capture and electricity derived from renewable energy, so it is possible to achieve CN. However, FT fuel tends to have less aromatics and a higher cetane number than diesel fuel. Therefore, excessive early ignition occurs at low speed and low load in application to diesel engine. The purpose of this study is to suppress early ignition by controlling the amount of air flowing into the cylinder. The numerical results showed that the ignition timing and combustion could be controlled using Miller cycle by late intake valve closing (LIVC).