诱发携带SCR系统柴油机排气管沉积物生成的临界添蓝流量无量纲模型研究

After the studying of deposit formation phenomenon on the exhaust pipe interior wall of the diesel engine with an SCR system, applicants observed that the critical adblue injection rate which result in deposit formation is related to the engine working condition, exhaust pipe wall temperature and structural parameters of SCR system. Without exhaust pipe and SCR system optimized, the critical adblue injection rate is usually too small to meet NOx emission requirement of IMO Tier Ⅲ standard for marine diesel engines. .This project will focus on the following three aspects: the generation and decomposition mechanism of deposit, the dimensionless model to determine the critical adblue injection rate under various boundary conditions, the influence factors and laws of critical adblue injection rate. In the view of the deposit formation on the exhaust pipe interior walls, Ebrahimian’s mechanism model lacked the reaction paths between the molten and the solid matrix state of Biuret; meanwhile, Brack’s model was not consider the hydrolysis reaction path of HNCO. Applicants will improve the reaction paths of the deposit generation and decomposition, and then optimize the reaction rates basing on TGA and HPLC analysis to achieve the applicable deposit reaction mechanism model. Subsequently couple the reaction mechanism model with the exhaust pipe CFD model to develop a model can determine the critical adblue injection rate under various boundary conditions, and then apply the theory of similarity to the key parameters and governing equations of fluid mechanics to establish a universal dimensionless model of critical adblue injection rate. Based on the dimensionless model, simulation analysis will be done to explore the relationship between critical adblue injection rate and the structural parameters of the exhaust pipe and SCR system and it can be used to guide the optimization design of the Urea-SCR system and diesel engine matching.

申请者对携带SCR系统的柴油机排气管内壁面沉积物的生成问题进行了研究：发现诱使沉积物产生的临界添蓝流量与工况、排气管壁温以及SCR结构参数等因素有关，在排气管及SCR结构未经详细优化的情况下，该临界流量低于柴油机NOx排放达到Tier Ⅲ标准所需的添蓝流量。.本课题拟研究沉积物的生成分解机理、临界添蓝流量无量纲模型和影响临界添蓝流量的因素及规律。从柴油机排气管沉积物生成的角度，Ebrahimian机理缺少缩二脲熔融态及固相基质态的反应路径，Brack机理未考虑异氰酸的水解反应，申请者拟完善沉积物生成分解反应路径，基于沉积物热重和液相色谱试验修订反应速率，建立适用的机理模型，并与排气管CFD模型耦合得到临界添蓝流量计算模型；针对计算模型应用相似理论得到普适的临界添蓝流量无量纲模型；基于无量纲模型研究排气管及SCR结构参数影响临界添蓝流量的规律，以期指导SCR系统优化设计及与柴油机匹配。

选择性催化还原系统是柴油机处理NOx排放的主流装置，目前在输出功率超过130kW的柴油机（包括船用柴油机和车用柴油机）上应用越来越广泛，但携带Urea-SCR系统的柴油机排气管内壁面易生成沉积物，导致排气背压增大，严重影响柴油机的动力性、经济性和可靠性。目前携带SCR系统的柴油机排气管内壁面沉积物问题已引起人们的足够重视，但是沉积物反应机理模型的研究与影响因素的研究呈相互独立的局面。在沉积物反应机理模型的研究方面，反应路径有待完善，反应速率仍需优化，尚不足以应用于排气管沉积物的研究；在沉积物影响因素的研究方面，虽然借助试验手段确定了部分因素的影响规律，但研究重点相对分散，且未能从沉积物反应机理的角度进行分析，使得试验结果缺乏理论基础，不具有普遍适用性。.本研究建立了沉积物生成与分解机理模型：从排气管沉积物生成的角度，完善沉积物的反应路径，辨识反应动力学参数，建立适用的沉积物生成与分解机理模型；建立了临界添蓝流量计算模型：耦合沉积物生成与分解机理模型与排气管CFD模型，建立临界添蓝流量计算模型，并结合台架试验，校验了模型精度；对临界添蓝流量计算模型进行无量纲化处理，并设计试验校验了无量纲模型的适用性；基于临界添蓝流量无量纲模型，从柴油机工况、SCR 结构、排气管结构，环境条件的角度对影响临界添蓝流量的因素开展仿真分析与试验研究，确定了关键的影响因素及其规律。