臺灣博碩士論文加值系統

近年來由於台灣的機車市場快速成長及嚴格的污染法規實施，因此使得在150cc以下的四行程機車引擎研發工作愈趨重要。由於電腦計算速度的加快及價格低廉，大量利用引擎的性能模擬計算來決定最佳化設計參數就成為引擎研發流程的一個重要步驟。以往引擎模擬計算的數學模型都是以汽車引擎為基礎所建立的，其中的燃燒數學模型，對於轉速較高的小排氣量單缸引擎是否適用，有必要進一步討論才能獲得較適合的燃燒數學模型。本文因此強調以實驗建立適合小型四行程引擎的燃燒模型，及以基因演算法來設計最佳性能的引擎參數。在實驗方面，在引擎動力計上量測125cc的四行程引擎油門全開時之汽缸壓力、曲軸角度、空燃比及點火角等參數，以找出適合小型四行程引擎的燃燒模式。在汽缸體積變化及進排氣壓力波傳遞現象的數值模擬方面，使用TVD法以提高計算的準確度。實驗結果顯示以往大排氣量四行程引擎所使用燃燒模型中韋伯(Wiebe)函數的效率參數及形狀因子與小排氣量引擎有所不同，而空燃比、引擎轉速及點火角度的變化對燃燒過程中的燃燒延遲角度並無顯著的影響。雖然改變空燃比對快速燃燒角度並無明顯影響，但引擎轉速增加將使快速燃燒角度明顯的增加。在引擎性能最佳化方面，基因演算法的單點最佳化及多點最佳化不僅能有效搜尋最佳化參數，而且亦能大幅縮短計算時間。在此同時，經基因演算法求得的最佳化進排氣閥門開關角度與實際引擎設計值比較亦能得到一致的結果。

In recent Taiwan''s transportation market, the use of motorcycles and scooters has drastically experienced a rapid growth as convenient vehicles either in urban or rural areas. In order to strive for the market significance, there is a strong need of research and development (R/D) to develop the domestic small engine below 150c.c. in Taiwan. However, it is clear that the existing engine simulation model has been well developed, but is only suitable for larger-sized engine performance analysis and fails to have a well prediction for smaller engines, especially below 150 cc. This dissertation hence makes emphasis on the investigations of developing suitable combustion models for small-size four-stroke engines by experiments and developing an engine performance simulation through genetic algorithm (GA) optimization for small engine design. In the experiment, the 125cc four-stroke engine is used for investigations on a dynamometer test bench to measure such engine parameters as cylinder pressure, crank angle, Air-Fuel (A/F) ratio and ignition timing, etc. In the simulation of the cylinder volume variation and intake/exhaust wave phenomenon, the second-order Total Variation Diminution (TVD) scheme is adopted to enhance the calculation accuracy. Experimental results indicate that the values of the efficiency parameter and the form factor in the Wiebe function, commonly used as the combustion model in engine simulation, have to be modified for the small engine in comparison with the commonly suggested values in the larger-sized engine. In addition, the delay angle of combustion is insensitive to the A/F ratio, engine speed, and spark ignition timing. Although the rapid burning angle is relatively invariant with the A/F ratio, it does show a significant increase with the increase of the engine speed. In the simulation of engine performance optimization, the GA method has ensured that single-point and multi-point optimization can not only effectively seek their optimal parameters, but also the calculation time is reduced drastically. Meanwhile, the simulation results also suggest the appropriate valve timings of intake and exhaust for small engine design, which is also proved by experiments with the engine design data.

COVER
ABSTRACT
ACKNOWLEDGEMENTS
CONTENTS
LIST OF TABLES
LIST OF FIGURES
NOMENCLATURE
I INTRODUCTION
1.1 Background
1.2 Engine Simulation and Mathematical Models
1.3 Combustion Models
1.4 Manifold Models
1.5 Optimization of Engine Design
1.6 Motivations and Objectives
II PHYSICAL PROBLEM AND SIMULATION MODELS
2.1 Four-Stroke Engine Cycle
2.2 Physical Problem
2.3 In Cylinder Models
2.3.1 Cylinder Model
2.3.2 Combustion Model
2.4 Valve Lift and Flow Area Model
2.5 Gas Dynamic Model in the Pipe
2.6 Boundary Conditions
2.6.1 Closed End
2.6.2 Open End
2.6.3 Inflow Into a Pipe
2.6.4 Partially Open End(Nozzle)
2.6.5 Flow Through a Valve
2.7 Summary
III EXPERIMENTAL SETUP AND DATA ANALYSIS
3.1 Experimental Setup and Data Acquistion
3.2 Cylinder Pressure Analysis
3.3 Summary
IV NUMERICAL METHODS AND GENETIC ALGORITHM
4.1 TVD Method
4.2 The Treatment of Boundary Conditions
4.2.1 Boundary Conditions for Closed End
4.2.2 Boundary Conditions for Open End
4.2.3 Boundary Conditions for Inflow Into a Pipe
4.2.4 Boundary Conditions for Partially Open End(Nozzle)
4.2.5 Boundary Conditions for Flow Through a Valve
4.3 Engine Simulation Procedures
4.4 Genetic Algorithm
4.5 Summary
V RESULTS AND DISCUSSIONS
5.1 Validation of the Numerical Method and Boundary Conditions
5.1.1 De Haller Problem
5.1.2 Single-Cylinder Four-Stroke Engine and Single Exhaust Pipe
5.2 Experiment and Combustion Model
5.2.1 Engine Specification
5.2.2 Pressure Measurement and Analysis
5.2.3 Parameters Discussion
5.2.4 Sensitivity Study
5.3 Applied Genetic Algorithm for Optimal Four-Stroke Engine Design
5.3.1 Parameters Coding
5.3.2 Single-Point Optimiztion
5.3.3 Multi-Point Optimization
VI CONCLUSION
REFERENCES
APPENDIX A
APPENDIX B
APPENDIX C
TABLES
FIGURES
VITA

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