【作者】 陈贵升；

【导师】 尧命发；

【作者基本信息】 天津大学 ， 动力机械及工程， 2013， 博士

【摘要】 能源和环境是社会发展的两大主题，节能与减排（包括CO2）是当今世界各国面临的两大共同目标。面对排放法规不断升级，开发环境友好、节能的现代车用柴油机给内燃机领域研究工作者和发动机生产企业不断提出难题与新挑战。本文对基于EGR技术路线的低排放重型柴油机燃烧技术进行了开发研究，深入研究了燃烧系统参数对柴油机燃烧、性能和排放的影响机理。在此基础上，研究了基于EGR技术满足国4排放法规的燃烧与排放控制策略，研究开发了满足欧6排放法规的商用重型柴油机，并对EGR系统废气循环引入方式和低十六烷值含氧燃料对柴油机燃烧、性能和排放的影响进行了研究，探寻进一步降低柴油机燃烧过程中碳烟生成和提高循环热效率的技术措施。进气增压系统优化研究表明，两级增压较单级增压能明显提升中、低速大负荷时EGR循环能力，改善NOx-燃油消耗率（BSFC）和NOx-碳烟（soot）的折衷（trade-off）关系，同时还使大负荷的排气温度控制在SCR转化效率较高的温度窗口。燃烧室结构优化设计和喷油器优化匹配的研究表明，通过适当降低燃烧室压缩比、优化设计燃烧室结构参数（缩口直径、凹坑深度）并采用带倒锥度喷孔喷油器，能有效改善油气混合历程，提高油气混合和燃烧速率，同时降低soot和BSFC，并将缸内最大燃烧压力降至合理水平。喷油控制策略的研究表明，在NOx排放控制在国4水平（3.5g/kW.h）附近时，soot较低，喷油控制策略对其影响较小。但随EGR率进一步增加，小负荷工况通过单次喷射、降低喷油压力和推迟喷油正时耦合控制可同时获得较低的NOx和soot排放，并有效降低最大压力升高率（MPRR）；中低转速大负荷时，通过降低喷油压力和推迟喷油定时相结合，在实现等NOx排放水平下显著降低soot排放；高转速中高负荷适宜采用主喷+后喷的多次喷射并耦合高喷射压力的控制策略。基于EGR技术路线的不同升功率国4柴油机燃烧技术开发表明，柴油机增压方案和后处理方案的优化选择应根据排放控制目标和发动机的实际升功率而确定。国4的ESC法规测试结果表明，在升功率为29.8kW/L的功率段，两级增压耦合EGR在无后处理下使各项排放指标均满足国4限值要求，加权BSFC相对基于SCR技术的国4柴油机仅增加3%左右。对于低升功率柴油机，相对于单级增压，两级增压并没有明显的优势。基于该燃烧技术，通过喷油控制策略和后处理技术耦合，成功开发了满足欧6ESC稳态测试循环的商用重型柴油机。结果表明，采用串联的两级增压和中等强度EGR（低于40%），将NOx原始加权比排放控制在欧5水平，通过缸内燃烧优化，柴油机PM加权值和加权BSFC仍处于较好水平。在依次加装DOC、DPF和SCR后处理系统，通过缸内燃烧与后处理匹配技术，DPF的过滤效率达到90%，SCR转化效率达到85%，ESC稳态测试循环的各项排放指标均满足欧6限值要求，而尿素喷射总量降至原机（SCR机型）的1/4～1/5。相比高压EGR（HP-EGR），采用低压EGR（LP-EGR）能有效提高增压系统效率，使柴油机运行在更宽广的EGR率区域，显著降低低速大负荷的soot和BSFC。采用LP-EGR时，通过调节两级增压系统的高、低压涡轮间的废气能量比例能有效降低高转速时的BSFC。针对燃料特性对柴油机影响机理的研究发现，柴油机掺混2,5-二甲基呋喃（DMF）、正丁醇和汽油都能显著降低soot排放，燃料特性改变所导致的滞燃期延长和燃料氧的增加是降低soot的两个主要因素，并且发现着火延迟期延长对降低soot的作用大于燃料中原子氧的作用。石化柴油与低十六烷值含氧燃料混合并耦合中等强度EGR（低于40%），是在简化喷油控制策略和后处理系统条件下实现重型柴油机高效、清洁低温燃烧的有效技术途径。更多还原

【Abstract】 Energy and environment are the two main themes of social development, andenergy saving and emission reduction are two common goals for all countries in thewhole world. With increasingly stringent emission regulations, it is necessary todevelop modern clean diesel engine with high thermal efficiency, which puts forwardnew challenges to internal combustion engine researchers and engine enterprises.In this paper, the combustion technology of a low-emissions heavy-duty (HD)engine with exhaust gas recirculation (EGR) technology, and the effects ofcombustion control parameters on diesel combustion, performance and emissionswere investigated. The combustion and emission control strategies based on EGRtechnology to meet China Stage IV were studied and a HD diesel engine meeting Euro6was successfully developed. In addition, the impacts of EGR introduction way andlow cetane number (CN) oxygenated fuels on diesel combustion, performance andemissions were investigated, the aim of which was to explore the efficiently technicalways to reduce soot and enhance thermal efficiency for diesel engine.The results of boost system optimization show that, compared to single-stageturbocharger, two-stage turbocharger (2TC) can obviously improve EGR recyclabilityand the trade-off of NOx-soot and NOx-BSFC at low speed and high load conditions,meanwhile, the exhaust temperature is much closer to the temperature region whereSCR has high conversion efficiency. The combustion chamber with reducedcompression ratio was designed and the optimization matching of injector wasperformed. The results show that, soot, BSFC and the maximum in-cylinder pressurecan be lowered by properly reducing compression ratio, optimizing structureparameters of combustion chamber (reentrant diameter and bowl depth, etc.) andusing Bosch injector with eight taper holes.The results of fuel injection control strategy show that, with increased EGR rate,NOx, soot and the maximum rate of pressure rise can be efficiently reducedsimultaneously at low loads by reducing injection pressure and postponing injectiontiming with single injection strategy. At low speed and high load conditions, soot andBSFC can also be improved by employing the same control strategy used at low loads.However, it is suitable to employ higher injection pressure and post injection toreduce soot and BSFC at high speed conditions.The experimental study on China Stage IV of diesel engine based on EGR technology was performed under different liter power conditions. The results showthat, the scheme of turbocharger and after-treatment should be optimally selectedaccording to emission control target and practical liter power of diesel engine. ESCcycle test results show that, all emissions can completely meet the limits of ChinaStage IV for the power section of29.8kW/L by using2TC without anyafter-treatment device, and the weighted BSFC is only higher3%compared with thatof the original engine. This means that2TC has the potential to further reduce dieselemissions and meet future more stringent emission regulations.Based on the combustion technology used above, a commercial diesel enginemeeting Euro6was developed successfully. ESC cycle test results of Euro6showthat, NOx weighted emissions can be reduced to the level of Euro5by using2TC andmedium EGR (<40%) with a low level of PM and a good engine performance. Allemissions can completely meet the limits of Euro6by the combined use of DOC,DPF and SCR. At the same time, the average conversion efficiencies of DPF and SCRare as high as90%and85%respectively, and the urea consumption is reduced toabout one fourth to one fifth of the original level through the optimal combinationcontrol of raw NOx emissions and urea/NOx equivalence ratio.Compared to HP-EGR, diesel engine can run over a wider region of EGR rate byusing LP-EGR, which can enhance the efficiency of turbocharging system, and reducesoot and BSFC greatly at low speed and high load conditions. When using LP-EGR,BSFC can be reduced efficiently at high speed by adjusting exhaust energy betweenhigh pressure turbine and low pressure turbine. The study on effects of fuel propertieson engine illustrates that, soot can be reduced dramatically via blending2,5-dimethylfuran (DMF), n-butanol and gasoline into diesel fuel. Extended ignitiondelay and fuel oxygen are two key factors to reduce soot emissions, and ignition delayhas greater effects on soot reduction compared to fuel oxygen. Overall, using low CNoxygenated fuel combined with medium EGR (<40%) is an efficient way for dieselengine to achieve clean diesel low-temperature combustion with high thermalefficiency under the condition of simplified injection strategy and after-treatmentsystem.更多还原