於2020 年，Euro 5 排放標準要求兩輪車 THC 排放量需減少Euro 4 標準的 73.68%， 如符合該標準觸媒轉化器和發動機調整工作成本增加。首先主要在於減少冷啟動 HC 排放，約佔 HC 總排放量的 80%。為了解決這個問題，本研究提出了兩種技術，即進氣口預熱（IPP）和雙火花塞（TSP），此兩項技術應用於傳統的 125 cc 踏板車發動機。
研究結果顯示，IPP 方法可以成為減少低端踏板車發動機冷啟動階段 HC 排放較高的解決方案。通過 IPP 效應改善混合條件和燃燒進程可將 HC 濃度在開環操作的前 10 秒內降低 49.53%，在前 100 秒內總體降低 29.3%。 此外，在最初的 100 秒運行期間，觀察到一氧化碳 (CO) 濃度降低了 54.4%，並發現與原況發動機相比較，加裝預熱塞的發動機 NOx 濃度在最初的 100 秒內增加了 50%，為了達到這些效果，需要將發動機進氣口墊片材料更換為銅質材料，並使用帶狀加熱器預熱 400 秒。通過使用預熱塞，無需更換進氣口墊片或花費大量精力重新設計發動機，可以將預熱時間大幅縮短至 15 秒，該技術也對 HC 排放的影響也有所降低。總而言之在開環操作的前 10 秒內 HC 濃度降低 20%，在前 100 秒內整體降低 9.81%，發現 CO 濃度在最初的 100 秒內下降了 12.2%，在前 100 秒內 NOx 濃度增加了 9.88%。
另一方面，TSP 方法似乎是一種在穩態點火而非冷啟動階段減少 THC 排放較高的解決方案。 事實上，雖然 TSP 配置似乎有效地提高了冷啟動期間的超稀薄燃燒性能，但對混合氣混和效果的影響並無太大效果，造成 HC (4.05%) 和 CO (6.35%) 排放量略有下降，但在冷啟動階段運行 100 秒期間，NOx 排放量增加了 12.07%。
然而在穩態點火階段，在相對稀薄的條件下發動機的能力為13.6% ，可以明顯減少 HC 排放。 結果顯示如妥協NOx 排放量增加兩倍，可將 HC 減少 29.14%，CO 排放量減少 47.07%。

In 2020, the implementation of the Euro 5 emission standard for two-wheeled vehicles necessitates a 73.68% reduction in total hydrocarbon (THC) emissions in comparison to the Euro 4 standard. Complying with this standard has resulted in an increased cost of catalytic converters and engine tuning efforts. Presently, the main challenge lies in reducing cold-start HC emissions, which constitute approximately 80% of the overall HC emissions. To address this issue, this dissertation presents two techniques, namely intake port preheating (IPP) and twin spark plug (TSP), which have the potential to be applied to a conventional 125 .c.c scooter engine.
The findings suggest that the IPP approach can be a highly effective solution in reducing HC emissions for low-end scooter engines during the cold-start phase. Improvements in mixture condition and combustion progression by IPP effect can result in a 49.53% reduction in HC concentration during the first 10 seconds of open-loop operation, and a 29.3% reduction overall during the first 100 seconds. Additionally, a reduction of 54.4% in carbon monoxide (CO) concentration was observed during the first 100 seconds of operation. However, nitrogen oxides (NOx) concentration of the preheated engine is found to increase higher by 50% during the initial 100 seconds compared to that of a conventional engine. To achieve these effects, the engine port gasket material needs to be replaced by a cooper one to preheat for 400 seconds using a strip heater. This long preheating time could be substantially reduced to 15 seconds by the use of glow plug without changing the port gasket or putting a significant effort on redesign the engine, thereby bringing this method applicable. In a compromise, the effects of this technique on HC emissions are also reduced. Specifically, a 20% reduction in HC concentration during the first 10 seconds of open-loop operation, and a 9.81% reduction overall during the first 100 seconds can be achieved. The CO concentration is found to drop by 12.2% during the initial 100 seconds. NOx concentration, however, is found to be increased higher by 9.88% during the first 100 seconds.
The TSP approach, on the other hand, appears to be more effective solution for THC emissions reduction during steady-state firing rather than cold-start phase. Indeed, although the TSP configuration appears to be more effectively in enhancing the ultra-lean combustion performance during cold start, the impact on mixture preparation is not sufficient. This results in a slight decrease in HC (4.05%) and CO (6.35%) emissions but an increase of 12.07% increase in NOx emissions during 100 seconds operation of the cold-start phase.
However, the capability of operating the engine under relatively leaner conditions by 13.6% during steady-state firing phase allows an obvious reduction in HC emissions. The results reveal that a compromise on two time of NOx emissions increase, can result in a 29.14% reduction in HC and a 47.07% reduction in CO emissions.

Contents
Dissertation Validation Letter i
Acknowledgement ii
摘要 iii
Abstract v
Contents vii
Table of Figures xi
Table of Tables xv
List of Abbreviations xvii
List of Symbols xix
Chapter 1: Introduction 1
1.1 Background and motivation 1
1.2 Sources of engine hydrocarbon emissions 3
1.2.1 Steady-state firing phase 4
1.2.2 Cold-start phase 7
1.3 Approaches to reduce HC emissions 12
1.3.1 First approach: Reducing wall films during the cold-start to enhance mixture conditions. 13
1.3.2 Second approach: Enhance the combustion efficiency for lean burn combustion 17
1.4 Objectives of the dissertation 22
1.5 Structure of the dissertation 23
Chapter 2: Methodology 25
2.1 Experiment setup 27
2.2 Numerical setup 31
2.2.1 Governing equations and mathematical model description of the 3-D CFD simulation 33
2.2.2 Model development and meshing 39
2.2.3 Injection setup 41
2.2.4 Boundary and initial condition setup 42
2.2.5 Chemical kinetic mechanism and fuel surrogate creation 46
2.3 CFD model validation 48
2.4 Summary 53
Chapter 3: Characteristic of the cold-start phase of a scooter engine under different ambient temperatures 54
3.1 Introduction 54
3.2 Study method 54
3.3 Results 56
3.3.1 Mixture preparation analysis 56
3.3.2 Wall film formation analysis 58
3.3.3 Combustion progress analysis 61
3.4 Summary 64
Chapter 4: An investigation into the potential of intake port preheating (IPP) approach to reduce HC emissions during the cold-start phase 66
4.1 The potential of employing the IPP-SH system to reduce HC emissions during the cold-start phase 66
4.1.1 Introduction 66
4.1.2 Study method 68
4.1.3 Results 75
4.2 The potential of employing IPP-GP system to reduce HC emissions during its cold-start phase 87
4.2.1 Introduction 87
4.2.2 Study method 88
4.2.3 Results 95
4.2.4 Summary 111
Chapter 5: An investigation into the potential of twin spark plug configuration to reduce THC emissions 113
5.1 Study effects of twin spark plug configuration on scooter engine during the steady-state firing phase 113
5.1.1 Introduction 113
5.1.2 Study method 114
5.1.3 Results 117
5.2 Study effects of twin spark plug configuration on scooter engine during the cold-start phase 125
5.2.1 Introduction 125
5.2.2 Study method 126
5.2.3 Results 127
5.3 Summary 134
Chapter 6: Conclusions 136
6.1 Conclusion 136
6.2 Future works 139
References 141

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