多缸重型柴油机的预混低温燃烧
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摘要
在一台匹配有两级增压和复合EGR系统的电控高压共轨柴油机上,研究了喷油定时和EGR率对部分负荷预混低温燃烧影响的试验研究.研究结果表明,当采用大比例EGR时,早喷和晚喷情况下均能有效延长滞燃期,获得极低的NOx和碳烟排放,并消除soot-bump区域.早喷比晚喷能够获得更佳的燃烧效率和更低的燃油消耗率,早喷需要高比例EGR率以实现燃烧相位(CA 50)的合理控制,但受到了复合EGR最大循环能力的限制.随着发动机平均有效压力从0.3 MPa提升到0.5 MPa,碳烟排放至少升高了一个数量级,碳烟排放控制成为高效清洁燃烧的主要制约因素,同时还受到压力升高率和氧/燃当量比的限制.在不同负荷下采用适当的早喷定时既能避免燃烧控制对超高EGR率的依赖,又能取得合理的CA 50相位、燃烧效率和氧/燃当量比,具有实现部分负荷超低排放和保持较高热效率的潜力.
In this study,we conducted experiments to investigate the effect of injection timing and the exhaust gas recirculation(EGR) ratio on premixed low-temperature combustion under partial load in an electronically controlled common-rail diesel engine equipped with a two-stage turbocharger and compound EGR system. The results indicate that when a high ratio EGR was applied,both early and later injections were helpful in extending the ignition delay,obtaining low NOx and soot emissions, and eliminating the soot-bump region. Compared to later injection, early injection achieved better combustion efficiency and brake-specific fuel consumption(BSFC). Early injection required a high EGR ratio to effectively control the combustion phase,but the capability of compound EGR introduction was limited. As the engine load varied from 0.3 MPa to 0.5 MPa,the brake-specific soot emission increased by an order of magnitude. Efficient and clean combustion was restricted by soot emission,and was also challenged by the pressure rise rate and oxygen-to-fuel equivalence ratio. The use of appropriate early injection timing under different loads can not only avoid combustion-control dependence on a high ratio EGR,but also obtain reasonable CA50 phase,better combustion efficiency and better oxygen-to-fuel equivalence ratio,which has potential to achieve ultra-low emission at partial load while maintaining high thermal efficiency.
In this study,we conducted experiments to investigate the effect of injection timing and the exhaust gas recirculation(EGR) ratio on premixed low-temperature combustion under partial load in an electronically controlled common-rail diesel engine equipped with a two-stage turbocharger and compound EGR system. The results indicate that when a high ratio EGR was applied,both early and later injections were helpful in extending the ignition delay,obtaining low NOx and soot emissions, and eliminating the soot-bump region. Compared to later injection, early injection achieved better combustion efficiency and brake-specific fuel consumption(BSFC). Early injection required a high EGR ratio to effectively control the combustion phase,but the capability of compound EGR introduction was limited. As the engine load varied from 0.3 MPa to 0.5 MPa,the brake-specific soot emission increased by an order of magnitude. Efficient and clean combustion was restricted by soot emission,and was also challenged by the pressure rise rate and oxygen-to-fuel equivalence ratio. The use of appropriate early injection timing under different loads can not only avoid combustion-control dependence on a high ratio EGR,but also obtain reasonable CA50 phase,better combustion efficiency and better oxygen-to-fuel equivalence ratio,which has potential to achieve ultra-low emission at partial load while maintaining high thermal efficiency.
引文
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[12]付朋飞,尧命发,郑尊清,等.复合EGR对增压柴油机性能和排放影响的试验研究[J].内燃机工程,2016,37(1):8-14.Fu Pengfei,Yao Mingfa,Zheng Zunqing,et al.Experimental study on the influence of compound EGR on performance and emission of turbocharged diesel engine[J].Chinese Internal Combustion Engine Engineering,2016,37(1):8-14(in Chinese).
[2]尧命发,刘海峰.均质压燃与低温燃烧的燃烧技术研究进展与展望[J].汽车工程学报,2012,2(2):79-90.Yao Mingfa,Liu Haifeng.Review and prospect of the combustion technology of homogeneous charge compression ignition and low temperature combustion[J].Chinese Journal of Automotive Engineering,2012,2(2):79-90(in Chinese).
[3]郑尊清,钟小凡,刘海峰,等.生物柴油/DMF混合燃料对柴油机低温燃烧的影响[J].燃烧科学与技术,2017,23(2):104-110.Zheng Zunqing,Zhong Xiaofan,Liu Haifeng,et al.Effect of biodiesel/DMF blended fuel on low temperature combustion in a diesel engine[J].Journal of Combustion Science and Technology,2017,23(2):104-110(in Chinese).
[4]张全长,尧命发,郑尊清,等.进气氧浓度对柴油机低温燃烧影响的试验研究[J].内燃机学报,2009(4):298-305.Zhang Quanchang,Yao Mingfa,Zheng Zunqing,et al.The effect of intake oxygen concentration on the combustion and emission characteristic of the diesel[J].Transactions of CSICE,2009(4):298-305(in Chinese).
[5]黄豪中,谢夏琳,谢正良,等.进气氧浓度和喷油正时对柴油机低温燃烧特性影响的试验研究[J].内燃机工程,2016,37(2):54-58.Huang Haozhong,Xie Xialin,Xie Zhengliang,et al.Experimental study on the effect of intake oxygen concentration and injection timing on low temperature combustion in a diesel engine[J].Chinese Internal Combustion Engine Engineering,2016,37(2):54-58(in Chinese).
[6]Alriksson M,Denbratt I.Low temperature combustion in a heavy duty diesel engine using high levels of EGR[C]//SAE Paper.Detroit,MI,USA,2006-01-0075,2006.
[7]Noehre C,Andersson M,Johansson B,et al.Characterization of partially premixed combustion[C]//SAEPaper.Detroit,MI,USA,2006-01-3412,2006.
[8]于文斌,裴毅强,苏万华.柴油机部分均质预混燃烧模式下混合与化学控制参数对指示热效率的影响[J].内燃机学报,2012(3):193-200.Yu Wenbin,Pei Yiqiang,Su Wanhua.Effects of mixing and chemical parameters on thermal efficiency based on a partially premixed combustion diesel engine[J].Transactions of CSICE,2012(3):193-200(in Chinese).
[9]马帅营.汽油/柴油双燃料高预混合低温燃烧技术应用基础研究[D].天津:天津大学内燃机燃烧学国家重点实验室,2013.Ma Shuaiying.Applied Background Research on Low Temperature Combustion Technology of Highly Premixed Charge Combustion Fueled with Gasoline/diesel Dual-fuel[D].Tianjin:State Key Laboratory of Engines,Tianjin University,2013(in Chinese).
[10]陈贵升,沈颖刚,郑尊清,等.采用EGR的重型柴油机低速高负荷性能与排放特性[J].内燃机学报,2014(2):97-103.Chen Guisheng,Shen Yinggang,Zheng Zunqing,et al.Performance and emission characteristic of HD diesel using EGR under low-speed and high-load conditions[J].Transactions of CSICE,2014(2):97-103(in Chinese).
[11]冯浩,郑尊清,毛斌,等.两级增压系统参数对泵气损失影响的热力学分析[J].内燃机工程,2016,37(5):221-228.Feng Hao,Zheng Zunqing,Mao Bin,et al.Thermodynamic analysis of effect of two-stage turbocharging system parameters on pumping losses[J].Chinese Internal Combustion Engine Engineering,2016,37(5):221-228(in Chinese).
[12]付朋飞,尧命发,郑尊清,等.复合EGR对增压柴油机性能和排放影响的试验研究[J].内燃机工程,2016,37(1):8-14.Fu Pengfei,Yao Mingfa,Zheng Zunqing,et al.Experimental study on the influence of compound EGR on performance and emission of turbocharged diesel engine[J].Chinese Internal Combustion Engine Engineering,2016,37(1):8-14(in Chinese).