柴油机后喷对DOC/NSR系统存储和脱除NOx的影响机制研究

The collaboration of DOC and NSR is presently considered as the promising way to reduce NOx emissions from light-duty diesel engine. Aiming at the question that DOC assisted NSR system has relatively low catalytic activity and low NOx removal efficiency under low exhaust temperature，a novel project was present based upon synergetic post-injection of diesel engine and DOC/NSR system. Through optimization matching of in-cylinder purification and after-treatment from diesel engine，the NOx removal peformance under low temperature was improved. Diesel post-injection and DOC/NSR catalysts were taken as the primary research object，and the main study objects include four parts as follows：(1) Design and performance evaluation of micro-nano DOC and NSR catalysts；(2) Effect of in-cylinder exhaust on the Low temperature oxidation behavior of diesel oil；(3) Influence mechanism assessment of micro-nano DOC catalysts on the NO and NO2 storage of NSR catalysts；(4) Mechanism of diesel post-injection on the NOx storage and reduction of micro-nano DOC/NSR system. Quantitative analyses the effect of the post-injection parameters on the reduction components in exhaust emissions through precise control of diesel post-injcetion.The influence of exhaust components under diesel post-injection on NO/NO2 and DOC-out temperature control of DOC catalysts was explored. Mechanism of NOx storage and reduction of NSR catalysts under different reducing composition was revealed, and the evolutions of by-product exhausts were also evaluated to avoid the secondary pollution, which was helpful for further providing theoretical basis for NOx removal with diesel post-injection technology.

采用DOC和NSR协同作用是降低轻型柴油机NOx排放的一种有效措施。针对DOC/NSR技术在低温环境下催化活性和NOx脱除效率较低的问题，申请人提出柴油机后喷技术和DOC/NSR系统相结合的新思路，通过机内和机外措施的合理匹配，提高对NOx的低温脱除性能。本项目拟以柴油机后喷和DOC/NSR为研究对象，重点研究： (1) 微纳DOC与NSR催化剂设计及性能评价；(2) 缸内废气环境对后喷柴油低温氧化行为的影响；(3) 微纳DOC对LNT吸附NO和NO2的影响机制评价；(4) 后喷对微纳DOC/NSR系统吸附和脱除NOx的作用机制。从精确控制柴油机后喷参数入手，定量分析后喷参数对排气还原组分的影响，探寻后喷排气组分对DOC调节NO/NO2比率和DOC出口温度的影响规律，揭示不同还原组分下NSR存储和还原NOx的作用机理，评价副产物生成机制，为利用柴油机后喷技术脱除NOx排放研究提供理论基础。

本项目对柴油机后喷对DOC/NSR系统存储和脱除NOx的影响机制进行了深入研究。利用改进的溶胶凝胶法结合浸渍法制备了一系列不同活性组分的DOC和NSR催化剂，并利用X射线衍射（XRD）、比表面积（BET）和扫描电子显微镜（SEM/EDS）透射电子显微镜（TEM）、X射线光电子能谱（XPS）等表征方式对DOC和NSR催化剂催化剂的理化性能进行表征；通过原位红外漫反射（In-suit DRIFTs）和程序升温脱附（NOx-TPD）试验评价了催化剂的存储还原反应活性。基于模拟气实验平台，研究了不同的温度、Mn负载量、O2浓度和NO浓度对催化剂存储性能的影响；以周期性存储还原试验，研究了不同存储时间对催化剂存储性能的影响差异。开展了NSR及DOC+NSR催化剂的性能试验，并分别在不同温度、O2浓度及空速条件下，进一步分析了DOC对NSR催化剂脱除NOx性能的影响。分析DOC出口端的温度变化规律及DOC调节NO/NO2比率的影响机制。开展周期性循环试验。在NO/O2和NO/O2/H2氛围下探究C3H6和H2对NO2生成量及DOC氧化性能的影响。利用柴油机台架实验，研究了不同后喷参数和工况下柴油机燃烧特性和排放特性的变化规律，采用多组分傅里叶红外气体分析仪（FTIR）对不同后喷策略下非常规排放污染物分布，探究后喷策略与高活性的轻质HCs含量及分布的对应关系。通过本基金研究，揭示了不同还原组分下NSR存储和还原NOx的作用机理，评价了副产物生成机制，为利用柴油机后喷技术脱除NOx排放研究提供理论基础。