a study on backfire control and performance improvement by changing the valve timings in a hydrogen-fueled engine with external injection

A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection Huynh Thanh Cong The Graduate School Sungkyunkwan University Department of Mechanical Engineering A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection Huynh Thanh Cong A Dissertation Submitted to Department of Mechanical Engineering and the Graduate School of Sungkyunkwan University in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Mechanical Engineering) January 2009 Approved by Professor Lee, Jong Tai Major Advisor This certifies that the Dissertation for the degree of Doctor of Philosophy in Engineering of Huynh Thanh Cong is approved Prof Kim, Chul Ju : Thesis Committee Chairman #1 Prof Sung, Nak Won : Thesis Committee Member #2 Prof Ryou, Hong Sun : Thesis Committee Member #3 Prof Choi, Kyu Hoon : Thesis Committee Member #4 Prof Lee, Jong Tai : Thesis Supervisor The Graduate School Sungkyunkwan University December 2008 박사학위 청구논문 지도교수 이 종 태 흡기관분사식 수소기관에서 밸브 타이밍 변화에 의한 역화억제와 성능개선에 연구 성균관대학교 대학원 기계공학과 동력공학전공 현 탄 콩 박사학위 청구논문 지도교수 이 종 태 흡기관분사식 수소기관에서 밸브 타이밍 변화에 의한 역화억제와 성능개선에 연구 A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection 성균관대학교 대학원 기계공학과 동력공학전공 현 탄 콩 박사학위 청구논문 지도교수 이 종 태 흡기관분사식 수소기관에서 밸브 타이밍 변화에 의한 역화억제와 성능개선에 연구 A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection 이 논문을 공학박사학위 청구논문으로 제출합니다 2008 년 10 월 일 성균관대학교 대학원 기계공학과 동력공학전공 현 탄 콩 ACKNOWLEDGEMENTS I express my gratitude to my advisor, Professor Jong Tai Lee, for his guidance, support, and encouragement during the period of this research at the Department of Mechanical Engineering, Sungkyunkwan University I am thankful to Professors Chul Ju Kim (thesis committee chairman), Nak Won Sung, Hong Sun Ryou, and Kyu Hoon Choi for their advice and participation on the dissertation committee I would like also to thank Dr Ki Chol Noh, Joon Kyoung Kang, and Kwang Ju Lee (Ph.D candidate) for their help in the various stages of the investigation I would like to express my heartfelt thanks to the technical staffs, whom are Mr Je Ha Lee and Mr In Seak Park, of Internal Combustion Engine Laboratory, Sungkyunkwan University, for full assistance with experimental apparatus setup and development of H2 research engine I wish also to express my gratitude to my parents and my wife for their unconditional and unwavering support and encouragement during the course of this work Huynh Thanh Cong Sungkyunkwan University Huynh Thanh Cong 0 A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection Ph.D in Engineering CONTENTS List of Tables and Figures i Nomenclature vi Chapter Introduction 1.1 Research background 1.1.1 Why backfire control in H2 engine? 1.1.2 Combustive properties of hydrogen related to backfire occurrence 1.2 Status of H2 researches on backfire control and enhancement of performance 1.2.1 Previous researches on backfire control in H2 engines 1.2.2 VVT studies for performance improvement and NOx reduction 1.3 Purpopes and objectives of research 10 1.4 Methods and contents of research 11 Chapter Development of H2 research engine with MCVVT system 13 2.1 Introduction 13 2.2 Development of MCVVT system 13 2.2.1 Designing concept .13 2.2.2 Mechanical structure of MCVVT system .15 2.2.3 Characteristics of MCVVT system .18 2.3 H2 research engine with MCVVT system 19 2.4 Experimental setup .30 2.5 Experimental method 31 Chapter Possibility of backfire control by changing valve overlap period 35 3.1 Introduction 35 3.2 Backfire occurrence with the change of valve overlap period 35 3.3 Backfire prevention due to the decrease of backflow period 43 3.4 Main prevention factor of backfire by the VOP 48 3.4.1 BFL equivalence ratios with change of the VOP center 48 3.4.2 IVO timing as the main prevention factor of backfire 54 Chapter Method of obtaining both high power and high efficiency without backfire .59 4.1 Introduction 59 4.2 Engine performance with the change of valve overlap period 60 4.2.1 Valve timings for optimizing engine power and efficiency 60 4.2.2 Difference of engine performance with the change of valve timing for H2 and gasoline engines .72 4.3 Realization of high performance by using lean mixture and supercharging 77 4.3.1 Concept to obtain both high power and high efficiency 77 4.3.2 Optimization of engine performance in cases of supercharging and lean mixture 81 Chapter Conclusions 86 Appendix A 89 List of publications 96 Bibliography 98 Abstract 104 List of Publications (in chronologic order, journals included in the science citation index are shown in bold) 2006 J K Kang, T C Huynh, K C Noh, Jong T Lee, J H Lee, A Development and Basic Characteristics of MCVVT Research Hydrogen Engine for Practical Use of External Mixture Type Hydrogen-fueled Engine, Journal of Transaction of Korean Hydrogen and New Energy Society (KHNES), Vol 17, No 3, pp 255-262, September 2006 J K Kang, T C Huynh, K C Noh, Jong T Lee, J H Lee, A Basic Characteristics of SingleCylinder Hydrogen-fueled Engine with External Mixture using MCVVT system, Journal of Transaction of KHNES, pp 84-89, Korea, June 2006 T C Huynh, J K Kang, K C Noh, Jong T Lee, J H Lee, Effect of Valve Overlap Period on Backfire Suppression in Hydrogen-fueled Engine with External Mixture, in Proceedings of KHNES Annual Autumn Meeting, pp 37-45, Korea, 2006 2007 K J Lee, J K Kang, T C Huynh, K C Noh, Jong T Lee, Characteristics of Performance and Backfire for External Mixture type Hydrogen-fueled Engine without Valve Overlap Period, in Transactions of KHNES (ISSN 1738-7264), Vol 18, No 4, pp 374-381, Korea, December 2007 J K Kang, T C Huynh, K C Noh, Jong T Lee, An Investigation of Backfire Control with Valve Overlap Period Change in the Same Supply Energy, Journal of Transactions of KHNES, Vol 18, No 3, pp 348-355, Korea, September 2007 T C Huynh, J K Kang, K C Noh, Jong T Lee, Feasibility of Backfire Control and Engine Performance with Different Valve Overlap Period of Hydrogen-fueled Engine with External Mixture, Journal of Transaction of KHNES, Vol 18, No 1, pp 67-74, Korea, March 2007 J K Kang, K J Lee, T C Huynh, K C Noh, Jong T Lee, Backfire Occurrence with Valve Timing in a External Mixture Hydrogen-fueled Engine, in 2007 Fall Conference Proceedings of the Korean Society of Automotive Engineers (KSAE), Vol 1, pp 452-457, Korea, November 2007 K J Lee, J K Kang, T C Huynh, K C Noh, Jong T Lee, Backfire Characteristics of External Mixture type Hydrogen-fueled Engine without Valve Overlap Period, in Proceedings of KHNES Annual Autumn, pp 87-92, Korea, November 2007 T C Huynh, J K Kang, K C Noh, Jong T Lee, J A Caton, Controlling backfire using Changes of Valve Overlap Period in a Hydrogen-fueled Engine using External Mixture, in Proceedings of the 2007 Fall Technical Conference of the ASME International Combustion Engine Division, Charleston City, South Carolina, USA, October 14-17, 2007 - 96 - T C Huynh, J K Kang, K C Noh, Jong T Lee, A Study on Performance and Combustion Characteristics for Valve Overlap Period Variation in a Hydrogen-fueled Engine with External Mixture, in 2007 Spring Conference Proceedings of KSAE, International Section, Vol 4, pp 1936-1941, Korea, June 2007 Y K Kang, T C Huynh, K C Noh, Jong T Lee, A Study of Backfire Control in a Hydrogenfueled Engine with External Mixture using Changes of Valve Overlap Period, in 2007 Fall Conference Proceedings of the Korean Society of Mechanical Engineers (KSME), Vol 1, pp 3311-3316, Korea, May 2007 2008 T.C Huynh, K J Lee, Jong T Lee, Performance Enhancement and NOx Reduction in a Hydrogen-Fueled Engine with External Injection by Using VVT, Journal of Transaction of the KHNES, December 2008, Vol 19, No 6, pp 474-481 T C Huynh, J K Kang, K C Noh, Jong T Lee, J A Caton, Controlling Backfire for a Hydrogen engine using External Mixture Injection, ASME Transaction -? Journal of Engineering for Gas Turbine and Power, 20 November 2008, 2008 (IF ¡07  0.355) T.C Huynh, K J Lee, Jong T Lee, Reduction of NOx emission in a Hydrogen-Fueled Engine with External Injection by Using Variable Valve Timing, in Proceeding of 2008 KHNES Society Autumn Meeting 2008, pp 42-48, Deajeon, Korea, November 2008 K J Lee, T C Huynh, Jong T Lee, The Effect of Performance Improvement in a HydrogenFueled Engine with External Mixture by Using Valve Overlap Period, in 2008 Spring Conference Proceedings of KSAE, KSAE08-A0147, Korea, November 2008 K J Lee, T C Huynh, J K Kang, Jong T Lee, Comparison of Performance of Hydrogen and Gasoline Engines with Valve Overlap Period, in Proceeding of 2008 KHNES Spring Meeting 2008, Deajeon, Korea, May 2008 K J Lee, T C Huynh, Jong T Lee, Backfire Control of a Hydrogen-Fueled Engine with External Mixture by Using Intake Valve Opening Timing, in 2008 Spring Conference Proceedings of KSAE, Korea, March 2008 - 97 - BIBLIOGRAPHY [1] J T Lee, "Current Status and Characteristics of Hydrogen Fueled Engine," Transaction of KSAE, Vol 18, pp 29-52, 1996 [2] Jong T Lee et al., "The Development of a Dual-Injection Hydrogen-Fueled Engine with High Power and High Efficiency," J of Eng for Gas Turbine and Power, Vol 128, pp 203-212, 2006 [3] J.M Kim et al., "Performance Characteristics of Hydrogen-Fueled Engine with the Direct Injection and Spark Ignition System," SAE 952498 4) L M Das, "Hydrogen Engines: a View of the Past and a Look into the Future," Int J of Hydrogen Energy, Vol 15, pp 425-443, 1990 [5] L M Das, "Hydrogen Engine: Research and Development (R&D) Programs in Indian Institute of Technology," Int J of H2 Energy, Vol 27, pp 953 - 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Journal of Engineering for Gas Turbine and Power, 20 November 2008, 2008 (IF 07 - 0.355) [82] T.C Huynh, K J Lee, Jong T Lee, "Reduction of NOx emission in a HydrogenFueled Engine with External Injection by Using Variable Valve Timing," in Proceeding of 2008 Korean Hydrogen and New Energy Society Autumn Meeting 2008, pp 42-48, Deajeon, Korea, November 2008 [83] T.C Huynh, K J Lee, Jong T Lee, "Performance Enhancement and NOx Reduction in a Hydrogen-Fueled Engine with External Injection by Using VVT, " in Journal of Transaction of the KHNES, December 2008, Vol 19, No 6, pp 474-481 - 103 - 흡기관 분사식 수소기관에서 밸브타이밍 변화에 의한 역화억제와 성능개선에 대한 연구 현 탄 콩 (Huynh Thanh Cong) 성균관대학교 대학원 기계공학과 동력공학전공 흡기관분사식 수소기관은 혼합기간의 증가에 의한 혼합기의 균질도 증가로 인해 직접분사식 수소기관에 비해 높은 열효율을 얻을 수 있다 또한 구조가 간단하여 단기간 내 실용화 시킬 수 있는 수소기관이지만 고부하 시의 역화 발생이 큰 문제로 대두되고 있다 이로 인해 고효율 및 고출력을 갖는 흡기관분사식 수소기관을 실현시키기 위해서는 역화 억제법의 확립이 무엇보다 중요한 관건이다 역화는 모종의 점화원에 의해 조기착화된 빠른 수소화염이 밸브 오버랩기간 중 흡기관 내로 역류하는데 기인한다 상기 역화 발생인자를 고려하면, 밸브 오버랩기간을 짧게 하여 고부하 시 조기점화된 화염이 흡기관으로 역류할 수 있는 기간을 주지 않으면 역화는 발생하기 어렵다 따라서 밸브 오버랩기간의 감소로 역화 발생을 억제할 가능성이 있으나, 오버랩기간의 이에 변화로 대한 역화를 것은 아직 명확하지 않다 특히 억제시키고 고효율을 달성하는 밸브 고희박 혼합기를 과급하여 고효율 및 고출력을 동시에 달성시키는 개념에 대한 검토는 아직 보고된 바 없다 - 104 - 본 연구에서는 흡기관분사식 수소기관에서 역화를 억제하고 고출력과 고효율을 달성시킬 수 있는 가능성을 파악하기 위하여 밸브 오버랩기간 변화에 따른 역화 발생과 제반 기관성능을 해석하였다 상기 목적을 달성하기 위한 주요내용은 다음과 같다 첫째로, 밸브 오버랩기간의 변화에 의한 역화 억제의 가능성을 파악하기 위해, 발화운전 중 밸브타이밍을 기계적으로 변화시키는 기계적 연속 가변 밸브 타이밍 (MCVVT)시스템을 장착한 단기통 연구용 수소기관을 개발하고, 그 유용성을 파악하는 것이다 두번째로, 밸브 오버랩기간 변화에 대하여 역화 억제의 가능성을 평가하고, 역화 억제에 관여하는 주요한 인자가 무엇인가 밝히는 것이다 세번째로, 밸브 오버랩기간 변화에 대한 수소기관의 제반 성능을 파악하는 것이다 마지막으로, 수소기관에서 과급과 흡기밸브 열림시기를 TDC 에 고정시키고 고효율을 발생하는 희박혼합기를 과급하는 방법으로 역화없이 고출력과 고효율을 얻을 수 있는 개념의 실현가능성을 확인하는 것이다 흡기 및 배기 밸브에 장착한 MCVVT 시스템은 동일한 구조이며, 이를 각각 조절하면 흡입 및 배기 밸브의 열림시기와 닫힘시기가 동시에 변경되어 발화 운전 중 원하는 밸브 오버랩기간으로 변화시킬 수 있다 MCVVT 를 장착한 경우의 기계손실은 장착하지 않은 경우보다 크지만 밸브 오버랩기간 및 밸브 타이밍 변화에 의한 역화 억제 가능성을 해석하는데는 그리 큰 문제가 되지 않는다 밸브 오버랩기간 변화에 따른 역화 억제의 가능성을 해석하는 경우, 밸브 오버랩기간은 0CA 에서 50CA 까지 흡기밸브 열림시기는 10aTDC 부터 40bTDC 까지 변화시켰다 밸브 오버랩기간이 감소할수록 - 105 - 역화한계 당량비는 증가하였고 밸브 오버랩기간이 0CA 부근에서 연료공기 당량비는 1.0 보다 농후한 혼합비에서도 역화가 발생하지 않았다 밸브 오버랩기간 감소에 의한 역화 억제는 공급열량 감소의 영향일 수도 있으므로 밸브 오버랩기간이 변화할 때도 동일한 공급열량을 공급하여 역화한계 당량비를 파악한 결과, 상기와 동일한 결과가 보여졌다 이로서 밸브 오버랩기간 감소에 의한 역화 억제는 공급열량 감소에 의한 영향보다 밸브 오버랩기간 변화에 따른 역류기간의 감소 영향이 더 큰데 의한 것으로 밝혀졌다 밸브 오버랩기간 변화에 의한 역화 억제의 주요한 인자를 해석하기 위하여, 밸브 오버랩기간 중심점(밸브 오버랩기간은 고정시키고 흡기밸브 열림시기와 배기밸브 닫힘시기가 동시에 변화되는 것)과 흡기밸브 열림시기를 변화시킨 결과, 밸브 오버랩기간 중심점이 TDC 보다 지각되면 밸브 오버랩기간에 상관없이 역화한계 당량비가 증가되는 것이 보여졌다 이 결과는 밸브 오버랩기간 감소에 의한 역화 억제의 주요한 인자가 흡기밸브 열림시기 변화라는 것을 의미하며, 흡기밸브 열림시기가 TDC 또는 이보다 지각될 경우, 조기점화된 빠른 화염이 연소실에서 흡기관으로 역류할 수 없기 때문에 역화가 발생하지 않는다는 것을 확인하는 것이다 배기밸브 닫힘시기 10aTDC 에서 흡기밸브 열림 시기(20aTDC 부터 TDC 까지)를 진각시킬경우, 공급열량 증가와 냉각손실 감소에 의해 출력 및 열효율이 증가한다 최고 출력은 당량비 1.0 에서, 최고 열효율은 당량비 0.5 에서 나타난다 최대 열효율이 보여지는 당량비 부근에서 NOx 발생은 현저히 감소되며, 이보다 낮은 영역에서는 거의 무공해 수준으로 볼 수 있다 - 106 - 수소기관에서 고효율이 발생되는 과급과 당량비 흡기밸브 0.5 열림시기를 의 TDC 희박혼합기를 에 과급한 고정시키고 결과, 역화 발생없이 당량비 0.5 부근의 고효율을 달성시키고, 당량비 1.0 부근보다 약 1.9 배의 고출력을 실현시킬 수 있었다 이것은 밸브 오버랩기간 변화에 의해서 역화 발생없이 고효율과 고출력을 동시에 달성할 수 있다는 가능성을 입증하는 것이다 그러나 상기 결과는 한정된 운전 조건하의 결과이므로 보다 다양한 운전 조건에 대한 상세한 연구가 필요하다 또한 고과급시 공급열량에 의한 실린더 내 가스 온도의 증가로 NOx 가 증가되므로 과급에 의한 고출력 실현시의 다양한 NOx 감소법의 강구도 검토되어야 할 것으로 생각된다 주체어: 흡기관분사식 수소기관, 기계식 연속 가변 밸브 타이밍 시스템, 역화 억제, 성능 개선, 밸브 오버랩기간, 밸브 오버랩기간의 중심점, 흡기밸브 열림 시기 - 107 - Abstract A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection Huynh Thanh Cong Department of Mechanical Engineering Graduate School of Sungkyunkwan University Hydrogen-fueled engines with external mixture formation have potentially high thermal efficiency because of a more homogeneous inlet mixture In addition, the structure of such engines is relatively simple The practical use of hydrogen can be visible in the short term The occurrence of backfire at high engine load conditions, however, is an important problem Because of this, the method of attaining both high efficiency and high power without backfire in a hydrogen-fueled engine is the most important key The backfire phenomena of hydrogen-air mixtures in the intake system are often a result of backflow of a pre-ignited fast flame from combustion chamber during the valve overlap period When the valve overlap period is short enough, backfire may not occur even under high load operating conditions due to the fact that the pre-ignited flame cannot flow backward into the inlet system The reduction of the valve overlap period, therefore, is used to prevent the occurrence of backfire, but this has not been clearly demonstrated yet In addition, the change of the valve overlap period to control backfire and to realize the concept of obtaining both high efficiency and high power (by supercharging) in a hydrogen-fueled engine has not been reported yet In this research, the change of the valve timings is used to study the feasibility of preventing backfire occurrence and to realize the concept of attaining both high power and higher efficiency without backfire in a hydrogen-fueled engine with external injection - 108 - Key information to achieve the above objectives is as follows Firstly, due to the change of the VOP is used to determine the possibility of backfire control, a Mechanical Continuous Variable Valve Timing (MCVVT) system (to change the timings of mechanical valves) equipped with a hydrogen-fueled engine with external injection are researched and developed Secondly, the change of the valve overlap period is to evaluate the possibility of preventing backfire and to imply the main prevention factor of backfire control Thirdly, the change of the valve overlap period is used to quantify overall engine performances Finally, the feasibility of the concept of obtaining high power and high efficiency without backfire is determined by supercharging at lean mixture ratio of around 0.5 (where the maximum thermal efficiency occurs) and the intake valve opening timing is located at TDC for avoiding backfire Intake and exhaust valves MCVVT system is equipped with the same structure Each system can adjust the intake and exhaust valve opening/closing timings in each period to vary the values of the valve overlap period (VOP) Hydrogen-fueled research engine equipped with MCVVT system has larger mechanical loss than that without MCVVT system when the engine speed increases This loss, however, is interpreted to have not affected of backfire control by changing the valve timings The possibility of controlling backfire is studied by changing the VOP in a wide range from 50CA to zero (where the exhaust valve closing timing is located at 10aTDC) When the VOP reduces from 50CA to 10CA, the backfire limit (BFL) equivalence ratio increases continuously When the VOP is reduced lower VOP 10CA, the BFL equivalence ratio is expanded from 0.3 to over 1.0 without backfire This means that the BFL equivalence ratio is significantly increased with reduction of the VOP The reason here may be caused by the decrease of supplied energy when the valve overlap period reduces Thus, the variation of the BFL equivalence ratio is examined in the cases of equal supplied energy It shows the same results This implies that when the VOP reduces, the increase of BFL equivalence ratio is affected by rather from the reduction of backflow period than the decrease of supplied energy The feasibility of backfire prevention is verified by changing the VOP center (the fixed VOP of the intake valve opening timing and the exhaust valve closing timing to be changing at - 109 - the same time) and the intake valve opening timing When the VOP center is retarded after TDC, the BFL equivalence ratio is observed to be increased In cases of changing the intake valve opening timing with arbitrary VOP, backfire does not occur when the intake valve opening timing is located at TDC or later The results indicate that the IVO timing is the main prevention factor for method of controlling backfire by change of valve overlap period The variation of overall engine performances is quantified by the change of the VOP (the intake valve opening timing changes from 20aTDC to TDC by 10CA increment and the exhaust valve closing timing is located at 10aTDC) for a wide range of fuel-air equivalence ratio For every location of the intake valve opening timing, the best power is observed at around 1.0 because of increased supplied energy Due to the reduction of cooling loss increases, the maximum thermal efficiency occurs at about 0.5 where NOx emissions are reduced significantly The concept of enhancing both power and efficiency without backfire is realized by supercharging at 0.5 (where the maximum thermal efficiency occurs) and the IVO timing at TDC Compared with naturally aspirated cases at the IVO timing at TDC, the brake torque for cases of supercharging is about 1.9 times and 1.45 times higher than that at 0.5 and 1.0, respectively, while thermal efficiency of both cases at 0.5 is almost same (around 32%) Therefore, the possibility of obtaining both high power and high efficiency without backfire by changing the VOP is proved However, the above results are studied in a limiting condition of 0.5 and necessary to research in detail for other various conditions to confirm this concept Accompanying the increase of engine power by supercharging, in addition, the in-cylinder temperature and NOx emissions are increased due to higher supplied energy So, the reduction of NOx emissions is needed to investigate at leaner mixtures Keyword: H2 engine with external injection, MCVVT system, Backfire control, Performance improvement, Valve overlap period, Valve overlap period center, Intake valve opening timing - 110 - .. .A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection Huynh Thanh Cong A Dissertation Submitted to Department... Thanh Cong Sungkyunkwan University Huynh Thanh Cong 0 A Study on Backfire Control and Performance Improvement by Changing the Valve Timings in a Hydrogen-Fueled Engine with External Injection. .. allows changing intake and exhausting valve lift, timing, and duration based on varied engine working condition Therefore, it is used in the un-throttled load control and can realize the variable