進氣道角度對內燃機引擎汽缸內流場影響之研究

A Study of the Effect of the Angle of Intake Port on the Flow Field in an Internal Combustion Engine

舒小恩(Hsiao-En Shu)

指導教授 ： 鄧治東

中原大學/工學院/機械工程研究所/碩士(2001年)

https://doi.org/10.6840/cycu200100003

摘要

內燃機引擎目前仍是汽、機車動力的主要來源，因此引擎性能係汽、機車設計上所著重的關鍵；而汽缸內的熱流現象對引擎性能的影響至深且鉅。由於汽缸內的燃燒性能主要決定於油氣的混合過程，同時點火前汽缸內的流場結構對於火焰的傳遞及進排氣具重要的影響性；故許多學者致力於研究引擎汽缸內純流場的分析。

研究內燃機流場現象主要可分為實驗與數值模擬兩種方式，實驗雖可量測引擎實際的表現，但多半只能量測到某些特定區間的數據，難以看到完整的流場結構，此外量測實驗設備異常昂貴，加上實驗所需的時間和人力實非一般研究機構所能負擔。隨著近年來電子計算機的快速發展，應用計算流體力學的數值方法可在有限的時間內獲取整體流場現象的模擬，並可針對實際需要以調整引擎操作等相關參數而進行引擎運轉性能的預測。

本研究採用KIVA-3V計算流體力學程式針對一實際引擎以模擬其不同進氣道角度，對產生在汽缸內的流場加以分析、比較；研究中所採用的紊流模式為紊流強度較強之Renormalization Group ( RNG ) 紊流模式。結果顯示，改變進排氣閥的傾斜角度對進氣期間的流場變化有很明顯的影響，其中以垂直閥 (進排氣閥傾斜0度) 所得的 Y軸向(Y方向係垂直於將汽缸對分為二平面的方向)滾流強度、渦漩比、紊流強度、紊流動能等流場強度為最強；若以流體經活塞壓縮後的流場特性進行探討，所得結果顯示壓縮衝程對汽缸內流場的效應是不容忽視的；因此由進氣到壓縮過程結束的整體流場現象，才是影響引擎點火前的油氣混合程度與燃燒品質的關鍵。

關鍵字

內燃機引擎 ； KIVA-3V程式 ； 流場 ； 進氣道角度

並列摘要

Internal combustion (I. C.) engines are still the primary power sources for cars and motor cycles; thus, the performance of those engines is one of the key items studied in their design. It is noted that the thermofluid phenomena play an essential role in the performance of an engine. In addition, the combustion effectiveness inside a cylinder depends on the mixing of the fuel-air mixture. Furthermore, the structure of the fluid flow field immediately before combustion has a major impact on the intake and exhaust of gases and the propagation of flame. As a result, many researchers performed the studies on the flow fields in various engines.

The study of the flow fields in an I. C. engine has two approaches – the experimental technique and the numerical simulation. Even though the former can measure some of the parameters of the engine under study, the measurement can only focus on a specific area of the engine; it can not measure the overall flow field occurring inside the engine. Besides, the experimental apparatus is expensive to set up and the resources needed for time and manpower is tremendous and is prohibitively high for most of the research organizations. In recent years, within a limited amount of time for computation and using computational fluid dynamics (CFD) methodologies for numerical calculations, the high-speed computers have the capabilities to simulate the overall behavior of the flow field in the engine. They can also predict the performance of an engine by adjusting the engine operational parameters.

This study used KIVA-3V CFD methodology to analyze the flow field occurring in an engine – with varying angles of the intake port. The turbulence model used is the Renormalization Group (RNG) k-e turbulence model which provides a relatively higher turbulence than the Standard k-e turbulence model. The results of this study indicate that changing the angle of the intake port has a profound effect on the flow field during the intake stroke of the engine cycle. For the case with the intake-exhaust valves canted at zero degree (the so-called vertical valves), the tumble ratio, swirl ratio, turbulent intensity, and turbulent kinetic energy in the direction perpendicular to the bisecting plane of the cylinder are at their highest levels than those obtained for the other cases. This effect is most pronounced after the compression stroke of the cycle. As a result of this study, it is observed that the behavior of the overall flow field from the intake to the completion of compression stroke has a major impact on the effectiveness of the mixing of fuel-air prior to the ignition of the engine cycle.

並列關鍵字

intake port angles ； internal combustion engine ； flow field ； KIVA -3V code

參考文獻

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