【作者】 张德满；

【导师】 李舜酩；

【作者基本信息】 南京航空航天大学 ， 车辆工程， 2011， 博士

【摘要】 颗粒物是柴油机尾气排放中主要污染物之一。目前用于减少柴油机颗粒物排放最有效的后处理装置是壁流式颗粒物捕集器,但是由于其再生技术还不是很成熟,严重制约了其广泛使用。因此,深入全面的研究出一种比较适用的颗粒物捕集器的再生技术具有非常重要的意义。本文在总结现有各种再生方法优缺点的基础上,提出了在DOC前喷入柴油,提升发动机尾气温度,实现颗粒物捕集器再生的方法,并对该再生方法进行了全面深入的研究。本文研究的主要内容归纳如下:(1)提出了一种用于壁流式颗粒物捕集器再生的方法。针对目前国内外学者提出的各种柴油机颗粒物捕集器再生方法的优缺点,结合国内柴油机技术及燃油质量,提出一种叫做DOC辅助DPF再生的再生方法。该再生系统结构较简单,控制过程简便,可适用于国内市场上绝大部分柴油机汽车;该再生方法对柴油质量要求不苛刻,对燃油经济性恶化幅度小,对发动机使用寿命损害幅度小。(2)根据DOC辅助DPF再生方法的一个特例,提出怠速再生方法。该方法需要在发动机较高负荷时先喷入少量柴油提升尾气温度,再让发动机回到怠速状态,依靠发动机尾气流量降低,进一步提升尾气温度,实现满载的DPF再生。该再生方法的燃油经济性更好,控制过程更简单。(3)对再生方法的二次污染排放进行研究。研究发现DOC辅助DPF再生方法的二次污染为HC和CO。分析二次污染中HC和CO的来源,发现HC主要是由喷入的柴油在DOC中未完全氧化而产生,CO主要是由再生过程中DPF中的颗粒物未彻底燃烧而生成。对再生过程中HC和CO排放的影响因素进行分析,发现影响二次污染中CO排放的因素主要包括再生时DPF中的颗粒物量、再生时DOC后的尾气温度、再生时的排气流量、和再生时发动机尾气中的氧气浓度;影响二次污染中HC排放的因素主要包括喷油流量、DOC前尾气温度和空速。(4)研究再生方法对DOC和DPF的老化程度。对两种再生方法分别进行4万公里老化试验,研究表明两种再生方法都会对DOC和DPF的性能造成老化,且老化幅度相仿。DOC性能老化主要体现在对CO起燃温度变高,对HC及颗粒物的催化效率降低和再生过程的能量利用率降低;DPF性能老化主要体现在空载时捕集效率降低。不可燃物对DPF背压的影响可以忽略不计。综上所述,本文系统地研究了DOC辅助DPF再生方法及其怠速再生方法。全面分析了再生方法的经济性及二次污染,深入地研究了再生方法对DOC和DPF的老化情况。研究结果对于推广壁流式颗粒物捕集器在柴油车上的广泛应用,减少柴油机颗粒物对环境的污染等方面具有重要的理论意义和工程应用价值。更多还原

【Abstract】 Particulate matter is one main pollutant of the Diesel exhaust. Currently wall-flow diesel particulate filter is the most effective post-processing device used to reduce diesel particulate emissions, but its recycling technology is not very mature, seriously hampered it be widespread used. Therefore, thorough study on a more applicable regeneration method of diesel particulate filters has great significance.Summarized the advantages and disadvantages of various existing regeneration methods, propounded a new regeneration technology. In this technology, diesel is injected into diesel engine exhaust prior to the DOC, and then the temperature of diesel engine exhaust is increased to achieve diesel particulate filters regeneration, and this regeneration technology was comprehensively studied. The main contents of this paper are summarized as follows:(1) A regeneration method for wall-flow diesel particulate filters is proposed. According to the advantages and disadvantages of a variety of diesel particulate filters regeneration methods proposed by the domestic and foreign scholars, combined with the domestic diesel engine technology and fuel quality, a regeneration method called DOC assisted DPF regeneration method is proposed. The structure of this regeneration system and it’s control process is quite simple. This regeneration method suitable for most diesel cars on the domestic markets; The regeneration method is not demanding quality requirements for diesel, the fuel economy deterioration rate is small, no damage to the engine life.(2) According to a special case of DOC assisted DPF regeneration method, idling regeneration method is proposed. In this method, a small amount of diesel is sprayed into diesel exhaust to increase the temperature of engine exhaust when the load of engine is higher, then let the engine return to idle state, relying on the decrease of engine exhaust flow to further enhance the exhaust temperature, to achieve regeneration of DPF. The fuel economy of this regeneration method is better than DOC assisted DPF regeneration method, and it’s control process is easier than DOC assisted DPF regeneration method.(3) The secondary pollution of the regeneration method is investigated. HC and CO is found to be the secondary pollution of DOC assisted DPF regeneration method. The sources of HC and CO are analysised, the HC is mainly produced by the diesel which is not completely oxidized in the DOC. CO is mainly produced by the particulate matter which is not completely combustted in the DPF regeneration process. The factors of HC and CO emission on the regeneration were analyzed. The factors impact CO emission including the the amount of particulate matter in DPF when beginning regeneration、the exhaust gas temperature after DOC during regeneration、the exhaust flow during regeneration、and the oxygen concentration of the engine exhaust gas during regeneration; The factors impact HC emission including the amount of fuel injection, the exhaust gas temperature before DOC and space velocity.(4) The aging of DOC and DPF is investigated. Two methods of regeneration are carried out 40,000km aging test,Studies show that the two regeneration methods all will result in the performance of aging on the DOC and DPF, and the aging magnitude are similar. The degradation of DOC is mainly reflected on the ignition temperature of CO becomes higher, and the catalytic efficiency of HC and particulate matter are become lower;The degradation of DPF is mainly reflected on the trapping efficiency of empty DPF becomes lower. The impact of nonflammable particulate matter on the back pressure of DPF is negligible.In conclusion, the tow regeneration method of diesel particulate filters, DOC assisted DPF regeneration method and the idling regeneration method, are systematically studied in this paper. The fuel economy and the secondary pollution of regeneration methods were comprehensive analysised, the aging of regeneration method to DOC and DPF were in-depth studyed. The results has an important theoretical significance and engineering applications for expanding the applied scope of wall-flow diesel particulate filters in vehicle, reducing diesel particulate matter pollution on the environment.更多还原