GDI稀燃汽油机EGR-LNT协同降低NOx排放基础理论及影响因素机理研究

Lean-burn GDI engine can improve BSFC and emission. But the conventional TWC cannot purify CO, HC and NOx emissions simultaneously because of the oxygen suppression phenomenon under the lean AFR. Based on the previous researches, the applicant has found that the EGR-LNT synergetic control system can optimize both BSFC and emission. But there is a best synergetic control relationship betwee upstream EGR and downstream LNT in the EGR-LNT synergetic control system. More orless upstream EGR could deteriorate NOx control effect of EGR-LNT synergetic control system. This research are proposing to use both theoretical and experimental method and considering mechanism of NOx adsorption, desorption,reaction route of nitrate and nitrite, and reduction reaction in LNT with CHEMKIN software, then it can achieve an integrity mechanism analysis for inlet gaseschange caused by upstream EGR variation and NOx purification process of LNT. This research will finally propose a NOx control mechanism in the EGR-LNT synergetic control system based on the actual synergetic control effect between upstream EGR and downstream LNT, which will also reduce NOX emissions for lean AFR gasoline engine, improve ecological environment and save energy.

直喷稀燃汽油机可以大幅改善其经济性和排放，但由于其在大于化学当量比的条件下燃烧，氧阻抑现象使得传统的三效催化器TWC不能高效地同时净化CO、HC及NOx。申请者研究发现：稀燃汽油机可通过EGR-LNT协同技术实现经济性和排放性二者的优化。EGR-LNT协同控制系统中前端EGR率与后端LNT之间存在最佳协同控制关系。前端EGR率过小或过大都会降低整体的NOx排放控制效果。本研究拟采用理论与试验相结合的研究方法，通过CHEMKIN软件从LNT内部NOx吸附、脱附、硝酸盐和亚硝酸盐路径及其还原过程的机理入手，对前端EGR率变化所引起的后端LNT入口边界条件变化进而对LNT内部NOx催化净化过程的影响进行各反应物机理性探究。依据EGR与LNT的协同控制效果，揭示EGR-LNT协同作用降低稀燃汽油机NOx排放机理，为降低稀燃汽油机NOx排放、改善大气生态环境和节约能源提供坚实的理论基础和科技支撑。

稀薄燃烧的汽油机可以大幅改善其燃油经济性和降低CO、HC及CO2排放，但同时因其偏离当量比燃烧使得汽油机常规三效催化转化器（TWC）失效而造成NOx排放控制变难。通过本课题组研究发现，稀燃汽油机可以通过机内EGR并协同催化后处理器LNT的技术路线来有效控制NOx从而实现经济性和排放性二者的同时优化，并且EGR-LNT协同控制系统中前端EGR率与后端LNT催化器物理、化学特性参数存在最佳协同控制关系。前端EGR率过小或过大都会对EGR-LNT协同控制系统整体的NOx排放控制效果产生一定程度的恶化影响。本研究通过化学反应动力学模拟和实验相结合的方法，从前端EGR与后端LNT两者协同制约的角度，分析并阐明应用EGR-LNT协同系统降低NOx排放问题时所存在的关键科学及协同优化控制问题。本研究对克服稀燃汽油机实际应用的瓶颈技术，即降低稀燃汽油机NOx排放、节能减排构建和谐绿色生态环境社会具有重要意义。