汽油缸內直接噴射(Gasoline Direct Injection, GDI) 引擎可以在低轉速低負載的操作點下，以層狀燃燒模式(Stratified Mode Operation) 運轉。利用部分富油，整體貧油的方式達到稀薄燃燒(Lean Combustion) 的效果，以獲得低油耗、低排放的表現。本研究針對一搭載可變汽門正時(Variable Valve Timing, VVT) 的GDI 引擎進行實驗研究，透過對汽門正時(Valve Timing) 的調變，可利用內部廢氣再循環(Internal Exhaust Gas Recirculation) 的效果，進一步地改善油耗表現和減少汙染物排放，因此最佳化出GDI 引擎之層狀燃燒模式的性能表現。而本研究分析顯示，在能量耗損方面，排氣閥門開啟(Exhaust Valve Opening, EVO) 的時間與閥門重疊(Valve Overlap) 的程度會影響泵損失(Pumping Loss)；而在能量產出方面，空燃比(Air Fuel Ratio, AFR) 對燃燒熱釋放的特性有很大的影響，而前者受到汽門正時的影響；在排放方面，透過增加閥門重疊角度，使得缸內的殘留氣體(Residual Gas) 增加，導致燃燒溫度較低，因此也使得主要的汙染物NOX 的排放降低。而透過以上對油耗和排放的分析結果也可得出，在層狀燃燒模式下，正閥門重疊(Positive Valve Overlap, PVO) 的效果優於負閥門重疊(Negative Valve Overlap, NVO)。

A Gasoline Direct Injection (GDI) engine can operate under the stratified mode operation at a low speed, low load operating point. By utilizing an overall lean mixture to achieve the stratified operation, we can get the benefit of better fuel consumption and lower emissions as lean combustion. This thesis studies on a GDI engine with the variable valve timing (VVT). With the adjustment of valve timing, internal exhaust gas recirculation (Internal EGR) can be used. The effect of this is to further improve fuel consumption and reduce emissions, thereby optimizing the performance of the stratified mode GDI engine. The analysis of this study shows that in the aspect of energy loss, the exhaust valve opening (EVO) time and the valve overlap degree affect the pumping loss, while in terms of energy output, the air fuel ratio (AFR) has a great influence on the characteristics of the heat release, while the former is affected by the valve timing; On emissions, the residual gas in the cylinder is increased by increasing the valve overlap degree. The increase leads to a lower combustion temperature and therefore lower emissions of the main pollutant, NOX. And from the above analysis of fuel consumption and emissions, it can be concluded that the positive valve overlap (PVO) is superior to the negative valve overlap (NVO) in the stratified mode combustion.

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