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목차

Nomenclatures 6

Greek Letters 7

I. 서론 13

1. 연구 배경 13

2. 연구 동향 17

1) 국내 천연가스 연구동향 17

2) 국외 천연가스 연구동향 19

3. 연구 목적 22

II. 이론적 고찰 23

1. 천연가스 연료의 특성 23

1) 발열량과 옥탄가 23

2) 공연비 24

3) 연소한계 24

4) 연소속도 25

5) 인화점 및 착화점 25

2. 기관의 유해배출물 생성원리 26

1) 일산화탄소(CO) 26

2) 탄화수소(THC) 26

3) 질소산화물(NOx) 27

3. 연소과정 이론적 고찰 32

III. 실험 장치 및 방법 36

1. CNG 인젝터 유량특성 평가 36

2. CNG 인젝터 분무가시화 평가 40

3. CNG 연료계 적용 엔진 성능시험 42

1) 엔진 및 부속장치 42

2) CNG 고압 인젝터 시스템 46

2) 엔진 시험장비 및 측정장비 49

4. 시험 방법 및 조건 54

IV. 실험 결과 및 고찰 57

1. 고압 CNG 0.8㎫ 인젝터 적용을 위한 성능평가 57

1) CNG 인젝터 유량 특성 57

2) CNG 인젝터 분무가시화 특성 59

2. CNG 연료계 분사시기 변경에 따른 엔진 최적화 특성 67

1) 분사시기 변경에 따른 출력 특성 67

2) 분사시기 변경에 따른 배출가스 특성 71

3) 분사시기 변경에 따른 연소실 압력 특성 75

3. CNG 0.8㎫ PFI 적용시 MBT 제어 전략 78

1) 점화시기 변경에 따른 출력 특성 78

2) 점화시기 변경에 따른 연소 특성 93

3) 점화시기 변경에 따른 배기배출물 특성 127

4. CNG 0.8㎫ PFI 적용시 공연비 변화에 대한 특성 139

1) 공연비 변경에 따른 출력 특성 139

2) 공연비 변경에 따른 배기배출물 특성 149

3) 공연비 변경에 따른 촉매 변환 효율 158

V. 결론 164

참고문헌 167

ABSTRACT 173

표목차

Table. 1-1. Vehicle registration status of CNG 17

Table. 2-1. Heating value of gases and liquid fuels 23

Table. 2-2. Explosion limit of various gases and gasoline 24

Table. 2-3. Flame speed of various gases and liquid fuel 25

Table. 3-1. Specification of CNG Injector 37

Table. 3-2. Condition of experiment 39

Table. 3-3. Condition of experiment 41

Table. 3-4. Specification of test engine 43

Table. 3-5. Specifications of engine dynamometer 45

Table. 3-6. Specifications of CNG regulator 46

Table. 3-7. Specifications of coriols flow meter 47

Table. 3-8. Specifications control modules 48

Table. 3-9. Specification of combustion analyzer 51

Table. 3-10. Specification of exhaust analyzer 52

Table. 3-11. Specification of lambda sensor 53

Table. 3-12. Engine experimental driving condition 54

Table. 3-13. Experimental driving condition and Valve timing 56

Table. 4-1. Static flow rate characteristic at injector (duration 10㎳) 57

Table. 4-2. Dynamic flow rate characteristic at injector (duration 3.5㎳) 58

Table. 4-3. Opening time and Injection volume according to battery voltage 58

Table. 4-4. Injection volume according to injector supply pressure 59

Table. 4-5. Jet speed at injector nozzle tip 63

그림목차

Fig. 1-1. CNG FIE system schematic diagram of BENZ 21

Fig. 2-1. IMEPH and IMEPL information 34

Fig. 3-1. Schematic diagram of experiment 36

Fig. 3-2. Injector injection waveform of voltage control method 37

Fig. 3-3. Injector needle valve open / close timing and solenoid operating current measurement 38

Fig. 3-4. Schematic diagram of experiment 41

Fig. 3-5. EWGA turbocharger system 42

Fig. 3-6. Schematic diagram of engine test bench 44

Fig. 3-7. MEIDEN EC Dynamometer 45

Fig. 3-8. Photograph of the experimental set-up 49

Fig. 3-9. KISTLER KiBOX Cockpit Program 50

Fig. 3-10. KISTLER KiBOX Cockpit and Pressure sensor 50

Fig. 3-11. Exhaust system and exhaust gas analyzer 52

Fig. 3-12. Photograph of lambda meter 53

Fig. 4-1. Penetration length and spray angle at fuel supply pressure 0.8 ㎫ 60

Fig. 4-2. Gas of spray evolution according at fuel supply pressure 0.8 ㎫ 62

Fig. 4-3. Penetration length and Spray angle at Chamber pressure 0.2 ㎫ 65

Fig. 4-4. Gas of spray evolution according at fuel supply pressure 0.3 ㎫ chamber pressure 0.2 ㎫ 66

Fig. 4-5. Torque and BSFC according to injection timing 70

Fig. 4-6. THC and NOx according to injection timing 74

Fig. 4-7. Cylinder Pressure according to injection timing 77

Fig. 4-8. Torque & exhaust temperature and thermal efficiency according to ignition timing 85

Fig. 4-9. IMEPN and IMEPH according to ignition timing 92

Fig. 4-10. Cylinder pressure according to ignition timing 100

Fig. 4-11. Rate of heat release according to ignition timing 108

Fig. 4-12. MFB 5%, 50%, 90% in Cylinder pressure diagram at Ignition timing BTDC 20℃A 115

Fig. 4-13. MFB and Ignition delay and Combustion duration according to Ignition timing at 1,600rpm MAP50㎪ 119

Fig. 4-14. MFB and Ignition delay and Combustion duration according to Ignition timing at 1,600rpm MAP98.7㎪ 120

Fig. 4-15. MFB and Ignition delay and Combustion duration according to Ignition timing at 2,067rpm MAP64.4kP 121

Fig. 4-16. MFB and Ignition delay and Combustion duration according to Ignition timing at 2,067rpm MAP122.2㎪ 122

Fig. 4-17. MFB and Ignition delay and Combustion duration according to Ignition timing at 2,533rpm MAP50㎪ 123

Fig. 4-18. MFB and Ignition delay and Combustion duration according to Ignition timing at 2,533rpm MAP136.7㎪ 124

Fig. 4-19. MFB and Ignition delay and Combustion duration according to Ignition timing at 3,000rpm MAP64.4㎪ 125

Fig. 4-20. MFB and Ignition delay and Combustion duration according to Ignition timing at 3,000rpm MAP93.3㎪ 126

Fig. 4-21. Exhaust emissions according to ignition timing at 1,600rpm MAP 50㎪ 131

Fig. 4-22. Exhaust emissions according to ignition timing at 1,600rpm MAP 98.7㎪ 132

Fig. 4-23. Exhaust emissions according to ignition timing at 2,067rpm MAP 64.4㎪ 133

Fig. 4-24. Exhaust emissions according to ignition timing at 2,067rpm MAP 122.2㎪ 134

Fig. 4-25. Exhaust emissions according to ignition timing at 2,533rpm MAP 50㎪ 135

Fig. 4-26. Exhaust emissions according to ignition timing at 2,533rpm MAP 136.7㎪ 136

Fig. 4-27. Exhaust emissions according to ignition timing at 3,000rpm MAP 64.4㎪ 137

Fig. 4-28. Exhaust emissions according to ignition timing at 3,000rpm MAP 93.3㎪ 138

Fig. 4-29. Output characteristics according to Lambda at 1,600rpm MAP 50㎪ 143

Fig. 4-30. Output characteristics according to Lambda at 1.600rpm MAP 98.7㎪ 144

Fig. 4-31. Output characteristics according to Lambda at 2,067rpm MAP 64.4㎪ 145

Fig. 4-32. Output characteristics according to Lambda at 2,533rpm MAP 50㎪ 146

Fig. 4-33. Output characteristics according to Lambda at 3.000rpm MAP 64.4㎪ 147

Fig. 4-34. Output characteristics according to Lambda at 3,000rpm MAP 93.3㎪ 148

Fig. 4-35. Exhaust emission according to Lambda at 1,600rpm MAP 50㎪ 152

Fig. 4-36. Exhaust emission according to Lambda at 1,600rpm MAP 98.7㎪ 153

Fig. 4-37. Exhaust emission according to Lambda at 2,067rpm MAP 64.4㎪ 154

Fig. 4-38. Exhaust emission according to Lambda at 2,533rpm MAP 50㎪ 155

Fig. 4-39. Exhaust emission according to Lambda at 3,000rpm MAP 64.4㎪ 156

Fig. 4-40. Exhaust emission according to Lambda at 3,000rpm MAP 93.3㎪ 157

Fig. 4-41. Catalyst Conversion efficiency after changing Lambda 163

초록보기

 This study investigated the method to apply the high-pressure compressed natural gas (CNG) fuel system to the Turbo Gasoline Direct Injection (T-GDI) engine by Port Fuel Injection (PFI) method. The global natural gas vehicle (NGV) automobile industry is flourishing, while domestic NGV automobile technology is not competitive in the global market. For this reason, this study conducted an optimization experiment of the bi-fuel system in which CNG fuel is injected to a gasoline engine by applying the PFI method,. The existing technology is based on the use of low-pressure CNG fuel and gasoline system, leading to poor control and reduced power; thus, the optimization study of the high-pressure fuel system of 0.8MPa applied by the PFI method in the CNG fuel engine was conducted. The characteristics of natural gas, a wide flammability limit and a slow flame speed should be considered when it is applied to the engine. The injectors used in the experiment were BOSHC NGI2 model, of which flow characteristics and spray visualization characteristic assessments were evaluated to check the compatibility with the turbo engine. The 1.4L A T-GDI engine (Kappa Engine) equipped with an electronic waste gate actuator and a dual CVVT system was used. After supplying CNG fuel from 220bar CNG tank to the injectors after depressurization in a two-stage pressure regulator mounted on an AUDI G-TRON vehicle, the characteristics of the engine were verified with Eddy Current Dynamometer from MEIDEN. The combustion stability was monitored in real-time using KISTLER's KiBOX Cockpit Program and pressure sensor, and the exhaust emissions were analyzed using the exhaust gas analyzers, HORIBA's MEXA-9100DEGR and ETAS's LSU4.9 lambda sensor. Drawing on the design of experiments (DoE) methodology by ETAS ASCMO, the experiment was conducted in 304 conditions; eight conditions that showed the maximum power were selected for the current study. Under the eight selected conditions, the optimization point of the engine was studied by changing the fuel injection time, ignition time, and air-fuel ratio (Lambda). The flow characteristics, such as static, dynamic, voltage, and injection pressure, of CNG injector NGI2 model showed no choking phenomenon, and spray visualization characteristic experiments showed the potential applicability of high-pressure fuel to the turbo engine. By changing the injection and Ignition timing during CNG fuel injection at 0.8MPa pressure using PFI method, it was found that there were no significant change of the characteristics of the engine according to the injection timing; the Ignition timing showed that MBT, which shows the maximum power of each operating condition, was BTDC 15 ~ 20°CA. At the MBT condition for each interval, the maximum combustion pressure was at Crank angle ATDC 12~18°CA, and the heat release analysis was best at ATDC 3~9°CA. MFB 5%, mass fraction burned, started near TDC, and MFB 50% formed near ATDC 10°CA. Advancing Ignition timing to BTDC 35°CA increased THC emissions in the form of unburned hydrocarbons and thermal NOx due to high heat and pressure and excess oxygen in the combustion chamber. The engine characteristics, according to the change of Lambda, showed that a lean mixture results in reduced torque and BSFC but improved thermal efficiency. As Lambda became lean, the oxygen concentration increased, leading to a significant reduction of THC and an increase of Thermal NOx due to high heat temperature and rich oxygen in the combustion chamber. The exhaust gas, after CNG combustion, was measured from downstream and upstream of the pure catalyst, which showed the change ratio of the pure catalyst between the two measures, was maximum at Lambda 0.98. As such, to find the way to apply the natural gas bi-fuel method to the T-GDI engine, this study verified the optimum control conditions of PFI with the high-pressure of 0.8MPa

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