內燃機汽缸內的燃燒特性是決定引擎性能與汙染排放的重要參數，為了增進燃燒效率與降低汙染物的排放，進而提升引擎整體性能輸出，本研究於內燃機內除了原有的火星塞(主火星塞)增加一支火星塞(副火星塞)，以達成上述之目的。使用商業套裝計算流體力學 (Computational Fluid Dynamics, CFD) 軟體CONVERGE，對一部二閥單缸四行程124.6 c.c.引擎進行計算分析，找尋雙火星塞引擎的最佳點火位置。在轉速固定5500 RPM時，改變副火星塞與水平之夾角、副火星塞橫向與軸向位置位置，探討汽缸內燃燒狀況。改變副火星塞安裝位置，分析缸內壓力峰值、溫度峰值、輸出指示功、熱效率、平均有效壓力、持續燃燒角度六個性能量化指標與燃燒後產物碳氫化合物質量、氮氧化物質量、一氧化碳質量、二氧化碳質量四個汙染量化指標，探討缸內溫度分布、油氣濃度分布與火焰傳遞速度。比較雙與單火星塞引擎的量化指標，判斷雙火星塞引擎副火星塞的最佳擺放位置。計算分析結果顯示，副火星塞安置的幾何參數重要性的次序為：(1) 軸向偏移，(2) 水平夾角，(3) 橫向偏移。當火星塞與水平之夾角為13°、副火星塞位於參考位置、副火星塞的軸向位置往參考位置向外拉出1 mm時，雙火星塞引擎的缸內壓力峰值、平均缸壓、溫度峰值、輸出指示功、熱效率、平均有效壓力最大、持續燃燒角度最短、氮氧化物排放增加(但仍低於法規標準值，可使用三元觸媒降低)、碳氫化合物排放減少(都遠低於法規標準值)，表示雙火星塞技術有助於提升缸內燃燒效率並改善污染排放。

The combustion characteristics in the cylinder of engines are important parameters that determine engine performance and pollutant emissions. Enhancing the combustion efficiency would increase the engine output and reduce the pollutant emissions and fuel consumption. The present study applied the dual-spark-plug technology to a two-valve, four-stroke, single cylinder reciprocating engine to enhance the combustion efficiency in the engine cylinder. The flow, combustion, fuel distribution, engine performance, and pollutant generation characteristics of the engine were analyzed using a computational fluid dynamics (CFD) program of CONVERGE. The engine speed and the intake efficiency were set at 5500 RPM and 37%, respectively. The typical parameters such as the peak mean pressure, peak mean temperature, indicated work, thermal efficiency, indicated mean effective pressure (IMEP), crank angle at 10%-90% MFB (mass fraction burning), amount of flame remaining before exhaust valve opening, nitrogen oxides (NOx), hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO2) were calculated. The results were compared with those of a corresponding single-spark-plug engine. The secondary spark-plug geometric arrangement (i.e., the angle θ between the secondary spark plug and the horizontal axis, the lateral displacement f of the secondary spark plug, and the axial displacement δ of the secondary spark plug) as well as the fuel-air ratio were focused for analysis. The results showed that the priority sequence of the secondary spark plug geometric arrangement is: the axial displacement δ, the angle θ, then the displacement f. The optimized parameters (δ, θ, f) which would lead to high engine output and low pollutant emission were (-1 mm, 13°, 0). The dual-spark-plug technology could improve the combustion efficiency in the cylinder and improve pollution emissions after optimizing the secondary spark-plug geometric arrangement.

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