臺灣博碩士論文加值系統

自從Mitsubishi Motor 於1995年開始採用缸內燃油噴射(gasoline direct injection, GDI)技術於汽車引擎之後，全世界均廣為認知此項技術的優點，包括節省油耗、降低排氣污染、增加燃燒效率，進而提升整體性能輸出。通常缸內燃油噴射技術必須配合缸內氣流的滾轉與/或旋轉運動以達到所需求的空氣/燃料混合型態(homogeneous或 stratified charge)，才能達成上述之目的。因此，探討缸內流場以及噴霧流場與氣流運動交互作用後的結構與衍化有其必要性。本研究利用商業套裝計算流體動力學(computational fluid dynamics, CFD)軟體STAR-CD，針對一部四行程單缸二閥機車引擎，探討在有、無加入燃油噴射的狀況下，於進氣和壓縮行程期間分析缸內氣流繞著缸徑軸上的滾轉運動和繞著汽缸軸上的旋轉運動以及缸內燃油噴射之噴霧流場與氣流運動交互作用後的結構與衍化，並使用質點影像速度儀(particle image velocimetry, PIV)量測噴油嘴將燃料射出於一大氣壓力下之霧化情形，並藉由循環渦度滾轉比、循環渦度旋轉比、噴霧穿透長度及霧化液滴粒徑，了解缸內氣流及噴霧特性。計算結果顯示，引擎的缸內流場為極佳之滾轉運動，缸內燃油噴射隨時間衍化的軌跡與氣流的交互作用將可作為設計缸內直噴引擎的重要參考。噴霧實驗結果發現，經噴油嘴射出的燃料，在短時間內具有高澎脹、高穿透以及高霧化，並使用粒徑分析儀量測50 bar結果顯示，在不同距離下，霧化的液滴平均直徑約為30~50 μm。

Abstract
The gasoline direct injection (GDI) has been engaged to the combustion system of an automotive engine since 1995 by the Mitsubishi Motor. It has been well recognized that the fuel consumption, exhaust emission, and engine performance can be drastically increased by application of the GDI technology. The GDI technology usually must be combined with the in-cylinder flow motion in order to regulate the mixture concentration distribution in the cylinder to a target pattern. By using this technology, the mixture preparation in the engine cylinder can be homogeneous or stratified charge and therefore the combustion can proceed under control. The GDI technology, however, is not popularly used in the small motorcycle engine. In this study, the feasibility of application of the GDI technology to a single cylinder, two-valve, 249 cm3 displacement motorcycle engine is studied numerically and experimentally. The engine is installed by a fuel injector and is hooked up to a modified engine test bench. The in-cylinder flows with/without fuel injections are calculated by a commercial software package of CFD code, the STAR-CD. The in-cylinder flow shows the evolution process of the tumble motion and strong tumble intensity. Coherent tumbling structure starts to appear after 40o crank angle from the top dead center during the intake stroke. It persists even to the final stage of the compression stroke. Therefore, taking the strategy of injecting the fuel during the intake stroke (about 90o after top dead center) to form the homogeneous charge for the high-load and high-speed operation as well as injecting the fuel during the compression stroke (about 60o before the top dead center) to form the stratified charge for the low-load and low-speed operation becomes possible. The tumble flow motion and its interaction with the atomized fuel droplets are also studied. The position, direction, timing, and pressure of injection are found to be the most important parameters. In order to characterize the injection features, the atomization characteristics of fuel injection in the atmosphere are measured by a particle image velocimetry. The spray penetration and droplet size distribution are presented.

摘要 i
Abstract ii
目錄 iii
符號索引 v
表圖索引 viii
第一章 緒論 1
1.1 研究動機 1
1.2 文獻回顧 3
1.3 研究目的 8
第二章 計算模擬模型與實驗之研究方法 9
2.1 計算模擬模型之方法 9
2.1.1 計算流力軟體的簡介 9
2.1.2 統御方程式 11
2.1.3 數值方法 13
2.1.4 數值模擬 25
2.1.5 物理參數定義 27
2.2 噴霧實驗之研究方法 29
2.2.1 實驗設備 29
2.2.2 實驗儀器 30
第三章 缸內流場計算結果與討論 37
3.1 缸內氣流滾轉運動 37
3.1.1 引擎轉速1500 RPM之流場結構與衍化過程 37
3.1.1.1 計算截面於對稱面上 37
3.1.1.2 計算截面於Z = 1.81 cm 41
3.1.1.3 計算截面於Z = -1.81 cm 44
3.1.2 引擎轉速2500 RPM之流場結構與衍化過程 47
3.1.2.1計算截面於對稱面上 47
3.1.2.2計算截面於Z = 1.81 cm 50
3.1.2.3計算截面於Z = -1.81 cm 53
3.1.3 量化分析 56
3.1.3.1 循環平均滾轉比 57
3.2 缸內氣流旋轉運動 59
3.2.1 引擎轉速1500 RPM之流場結構與衍化過程 60
3.2.1.1 計算截面y = 6 cm 60
3.2.1.2 計算截面y = 5 cm 63
3.2.1.3 計算截面y = 4 cm 64
3.2.1.4 計算截面y = 3 cm 65
3.2.1.5 計算截面y = 2 cm 66
3.2.2 引擎轉速2500 RPM之流場結構與衍化過程 67
3.2.2.1 計算截面y = 6 cm 67
3.2.2.2 計算截面y = 5 cm 70
3.2.2.3 計算截面y = 4 cm 71
3.2.2.4 計算截面y = 3 cm 72
3.2.2.5 計算截面y = 2 cm 73
3.2.3 量化分析 73
3.2.3.1 循環平均旋轉比 74
3.3 比較 75
第四章 噴嘴在一大氣壓下的噴霧特性 76
4.1 側向截面噴霧流場結構與衍化過程 76
4.2 正向截面噴霧流場結構與衍化過程 77
4.3 正向截面噴霧之全域速度場 78
4.4 量化分析 78
4.4.1 燃油液滴速度梯度沿著z軸(rx = 0)之分佈 79
4.4.2 燃油液滴速度梯度沿著rx軸(z/dw = 238)之分佈 79
4.4.3 燃油液滴速度梯度沿著rx軸(z/dw = 380)之分佈 80
4.4.4 噴霧流場之液滴粒徑分析 80
第五章 結論與建議 81
5.1 結論 81
5.2 建議 82
參考文獻 83

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