本文旨在以三維暫態計算流體力學數值模擬，針對入口邊界條件及活塞頂曲面設計對於缸內直噴引擎燃燒室流場動態之影響進行分析。研究中探討了暫態壓力、暫態質量流率及定壓力三種入口邊界與曲面活塞、平活塞及凸面活塞三種活塞面於2000 rpm部分負載及5500 rpm全負載兩種轉速條件下之冷流場特性。除對模擬所得之缸內流場結構及渦度分佈變化進行定性之比較外，研究中也以漩流比、滾流比及紊流動能等整體流場參數進行量化分析。歸納模擬結果可知，入口邊界對於流場有相當程度之影響，且考慮計算之可靠性，採用暫態質量流率做為入口邊界較為適當。但在無法獲得暫態流量邊界進行模擬時，採入口邊界之平均壓力之定壓力邊界亦可得合理之結果。三種活塞頂部曲面在5500 rpm下，以平面活塞設計最有助於缸內紊流之產生，但凸頂活塞之燃燒室則可產生較強之滾流。在2000 rpm下，於進氣行程區間以凸面活塞有較強之側向滾流，而碗狀活塞則是提供較佳之漩流比與紊流動能。研究並於碗狀活塞模擬案例中加入了噴霧模型，針對具有缸內燃料噴霧下之流場動態進行初步分析，發現燃料噴霧僅對側向滾流造成較大影響，對缸內正向滾流、漩流及紊流動能動態影響不大。

The objectives of the present reaserch is to numerically investigate effects of inlet boundary conditions and contours of piston top on the in-cylinder flow dynamics of gasoline direct injection engines. Three-dimensional transient computation fluid dynamics simulations were carried out in this study for engines operating at 2000 rpm part load and 5500 rpm full load conditions. The flow field evolutions in the cylinder were qualitatively studied; moreover, quantitative comparisons were performed on global flow parameters including swirl ratio, tumble ratio, and turbulent kinetic energy. Transient inlet mass flow rate and transient inlet pressure obtained from one-dimensional full-cycle engine gas dynamic simulation as well as the average inlet pressure were utilized as the inlet boundary condition at the intake manifold for the simulations. The results show that although the inlet boundary condition does affect the in-cylinder flow characteristics, the flow evoluations were qualitatively identical for the three inlet conditions investigated. Average inlet pressure can thus be utilized to obtain qualitative flow field evolutions when the transient mass flow rate is not available. In the case of 5500 rpm, turbulent kinetic energy was found to be the largest in the combustion chamber with flat piston, while dome type piston was able to induce stronger flow tumble. At 2000 rpm, higher sideway tumble ratio was found in the chamber with dome-shaped piston and chambers with bowl type piston were able to generated higher swirl ratio and turbulent kinetic energy. Numerical simulations that include fuel spray model were also performed for the case with bowl type piston, the results showed that the sideway tumble was affected by the liquid fuel spray; however, little influence was observed for the normal tumble ratio, swirl ratio and turbulent kinetic energy.

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