随着世界各国对环境保护重视程度的不断增加，从温室气体和污染物两个方面同时对重型柴油机的排放进行控制成为了下一阶段法规的重点发展方向。柴油机既要满足高热效率的要求，也要满足超低排放的要求。到2025年前后，世界主要发达国家和中国要求车用柴油机的有效热效率超过48%，NOx满足近零排放，同时颗粒物数量（PN）和粒径的限值进一步加严。为了满足上述要求，潍柴动力股份有限公司针对下一代柴油机高效和近零排放关键技术开展攻关研究。本论文以此为背景，重点围绕下一代柴油机的活塞顶隔热、超高压喷射、智能高效润滑以及排放后处理等开展机理和关键技术研究，取得了以下研究成果。第一，为减少柴油机活塞顶部热损失，提高活塞表面隔热涂层可靠性，总结了传统高温热障涂层在活塞应用中的不足，通过对热障材料成分的研究分析，在大气等离子喷涂技术基础上改进涂覆工艺，得到比热容、热导率、孔隙率等符合柴油机工作需求的空心氧化钇稳定氧化锆（HOSP YSZ）涂层，并对该涂层进行结合强度、抗冲击性能、热-机械性能、台架整机考核等一系列试验，证明该涂层具有良好的隔热性能和可靠性，可以满足下一阶段高热效率柴油机的要求。第二，研究了柴油机超高喷射压力对于循环油耗的影响规律，结合光学及仿真的手段进一步分析了结论的普适性，同时还研究了超高喷射压力对PN原排的影响、尿素喷射对尾排PN的影响以及颗粒捕集器参数对尾排PN的影响等，为下一代高效低排放柴油机推荐了具有合适喷射压力的燃油系统。第三，针对可变流量机油泵存在的难以精准可靠运行的问题，建立了柴油机全工况精准润滑评价体系，搭建了多因子闭环控制的智能高效润滑系统，保证了机油流量和压力的稳定及精准控制，并通过试验验证了两者的有效性，降低了油耗，提升了柴油机热效率，为可变流量机油系统在长寿命商用柴油车应用奠定了基础。第四，以潍柴动力股份有限公司某高热效率柴油机为基础，研究了高低压废气再循环技术、低温高转化效率后处理技术、热管理技术等对热效率和排放的影响规律，并将所有技术进行系统集成，证明了所选关键技术的组合效果，在实现柴油机有效热效率高达48.45%的同时，NOx排放美国联邦测试循环（FTP）加权值低于0.024 g/(kW?h)，满足了美国加州CARB 2027法规对NOx限值进一步降低90%的要求，达到了预期研究目标。
With the increasing global environmental awareness, the emission control of heavy-duty diesel engines from both greenhouse gases and pollutants has become the key development direction of the next stage regulations. Diesel engines should meet the requirements of high thermal efficiency and ultra-low emission. Around 2025, the effective thermal efficiency of vehicle diesel engines is demanded to exceed 48% with NOx emission being near zero in most of the developed countries and China. Meanwhile, the limit on PN emission will be further tightened. To meet the above re-quirements, the research on the key technologies, including the piston top insulation, ultra-high pressure injection, intelligent and efficient lubrication and after-treatment, of the next generation diesel engine with high efficiency and near-zero emissions was carried out by Weichai Power Co., Ltd. The achievements are summarized as follows.Firstly, to reduce the thermal loss of diesel engine piston top and improve the re-liability of thermal insulation coating on the piston surface, the influence of the com-position of the thermal barrier materials and the coating process based on atmospheric plasma spraying technology was studied to obtain a kind of HOSP YSZ coating whose specific heat capacity, thermal conductivity, and porosity could all meet the working requirements of diesel engines. The obtained coating was subjected to a series of experiments on bond strength, impact resistance, thermal-mechanical properties, and bench-top complete machine assessment. The result showed that the coating had good fuel economy and reliability performances which proved that the coating could meet the requirements of high thermal efficiency diesel engines.Secondly, the effects of high diesel injection pressure on fuel economy were conducted, and the results were further analyzed by optical and simulation methods to prove the general applicability of the result. In addition, the effects of high injection pressure on engine-out PN emission, the effects of urea injection and DPF parameters on final PN emission were investigated. Based on the above research, the optimal pressure of the fuel injection system for the high efficiency and low emission diesel engines was predicted. Thirdly, aiming at the problems existing in the variable flow oil pump, an accurate lubrication evaluation system for diesel engines was established. And an intelligent and efficient lubrication system with multifactor closed-loop control was built to ensure the stable and precise control of oil flow and pressure verified by ex-periments, which reduced the fuel consumption of diesel engines. The results of this part lay a foundation for the application of variable flow systems in long-life commer-cial diesel vehicles.Fourthly, the effects of a double-loop exhaust gas recirculation (EGR) system, high-efficiency after-treatment system and thermal management technology on high efficiency and low emission were studied. At last, all technologies were integrated into a high thermal efficiency diesel engine of Weichai Company. Experiments proved that with the key technical solution combination selected in the subject, this diesel en-gine could achieve a thermal efficiency of 48.45% while the FTP cycle weighting of NOx emission was less than 0.024g/kW.h, which met the NOx emission limit of the CARB 2027 regulation. The expected goal of the research is achieved.
