運用CFD數值方法於SDI引擎稀油極限提升之研究

本研究為運用計算流體力學商用軟體ANSYS CFD/FLUENT進行運算分析，探討半直接噴射(semi-direct injection, SDI)引擎之缸內流場及油氣分佈情形，藉此找出提升引擎稀油極限的方法。SDI系統概念為進氣門開啟時將燃料噴入汽缸內，類似缸內直接噴射(gasoline direct injection, GDI)的效果。而在本研究中採用液化石油氣(liquefied petroleum gas, LPG)作為燃料，目的是為了改善原汽油燃料系統噴嘴霧化不良的問題。新設計進氣道內加入渦流檔片並搭配SDI系統，可讓傳統氣道燃油噴射(port fuel injection, PFI)引擎產生層狀燃燒的效果，渦流檔片的設計則可使引擎切換成不同的進氣模式，包含均質(homogeneous mode)及層狀模式(stratified mode)。本研究利用所建立的引擎數值模型，分別進行穩態、暫態流場及缸內油氣分佈模擬，其中穩態流場模擬結果與目標引擎之汽缸頭於流量測試平台進行純空氣流場試驗的結果相當接近；暫態流場模擬則是用以觀察SDI引擎的缸內氣流行為，以便了解整體流場的特性；最後於暫態模擬中加入LPG燃料噴射進行缸內油氣計算分析。本研究根據CFD運算分析結果，找出影響油氣分佈情形的關鍵因素並提出改善方案，並在最後進行SDI引擎稀薄燃燒測試，證明所提出之方案可有效提升SDI引擎的稀油極限。

關鍵字

計算流體力學；半直接噴射；稀油極限；液化石油氣；渦流；數值模型

並列摘要

The main objective of this study is to propose the method of improving lean-limit on semi-direct injection (SDI) engine from the viewpoint of in-cylinder flow field and fuel distribution, where the computational fluid dynamics software ANSYS CFD/FLUENT is utilized. The fuel goes into cylinder directly through intake valve near the end of intake stroke, which is called semi-direct injection. This technology is similar to gasoline direct injection system. In our research, the application of liquefied petroleum gas is used to improve in fuel atomization. The new intake port and swirl plate of target engine are designed which can switch to homogeneous and stratified mode. To combine the intake swirl and SDI system, the port fuel injection engine can achieve stratification combustion inside cylinder. In this text, the steady flow, transient flow and fuel distribution simulation are performed via the established CFD engine numerical model. Results show that the coincidence between steady simulation and flow test which is tested for air field experiment on flow bench. Transient simulation can be used to observe swirl characteristic of SDI engine for understanding the air-flow behavior. The gaseous liquefied petroleum gas (LPG) injection is established in transient flow simulation, so that can investigate the fuel distribution inside cylinder. According to above results, a key-point which affects fuel distribution would be concluded, we try to propose a solution. Eventually, the method is demonstrated that it’s effective to improve lean-limit through the lean burn test on SDI engine.

並列關鍵字

Computational fluid dynamics ； Semi-direct injection ； Lean limit ； Liquefied petroleum gas ； Swirl ； Numerical model

參考文獻

[27] 楊清潭，運用CFD數值方法於SDI引擎層狀進氣之研究，碩士論文，國立臺北科技大學車輛工程系，台北，2011。

[39] 廖俊性，運用CFD數值方法於引擎進氣渦流設計，碩士論文，國立臺北科技大學車輛工程系，台北，2008。

[57] Anh Trung Tran，運用液化石油氣於半直接噴射火花點火引擎之設計與控制，博士論文，國立臺北科技大學車輛工程系，台北，2012。

[3] F. Zhao, M. C. Lai, and D. L. Harrington, “Automotive Spark-Ignited Direct-Injection Gasoline Engines,” Progress in Energy and Combustion Science, vol. 25, no.5, 1999, pp. 437-562.

[4] R. Stone, Introduction to Internal Combustion Engines, MACMILLAN Press Ltd, 1999, pp. 162-164.

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運用CFD數值方法於SDI引擎稀油極限提升之研究

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