Abstract
For the National VI heavy-duty diesel vehicles, NOx emission regulations are becoming more and more stringent, and the selective catalytic reduction (SCR) system has become a necessary device. The design of the adblue nozzle in the SCR system is especially critical, directly affecting the NOx conversion efficiency and deposit formation. According to the structure of a National VI diesel engine exhaust pipe and SCR system, the nozzle is optimized by computational fluid dynamics (CFD) method to avoid the collision between the urea droplets and the exhaust pipe wall, to ensure that the exhaust gas and the urea droplets are as much as possible in full contact to ensure a sufficient urea pyrolysis. With the optimized nozzle, the NH3 distribution uniformity of the inlet face of the SCR catalyst can increase from 0.58 to 0.92. Additionally, test verifications are implemented based on the spray particle size test and the engine bench tests; the results show that the Sauter mean diameter of the optimized nozzle is more decreased than the initial nozzle and that the NOx conversion efficiency of the World Harmonized Transient Cycle (WHTC) and World Harmonized Stationary Cycle (WHSC) cycle improves by nearly 3%; additionally, it can also avoid deposit formation.
Highlights
With increasingly stringent diesel emission regulations, Selective Catalytic Reduction (SCR)technology is considered one of the most promising technologies for most post-treatment treatments.As the main diesel engine emission control technology in the national VI stage, there are still many problems to be solved in the application of SCR on diesel vehicles
The research shows, for example, that the nozzle structure has a direct impact on the NOx conversion efficiency and deposit formation of the SCR system [1,2]
The critical adblue flow rate at each temperature and space velocity is determined by means of experiments, and it is applied to the adblue injection strategy as the upper limit of the adblue flow rate, which can effectively improve the NOx conversion and avoid the formation of deposits
Summary
With increasingly stringent diesel emission regulations, Selective Catalytic Reduction (SCR). The research shows, for example, that the nozzle structure has a direct impact on the NOx conversion efficiency and deposit formation of the SCR system [1,2]. Fang et al [6] found that the NOx conversion efficiency and amount of deposit formation are related to the decomposition rate of the adblue. The critical adblue flow rate at each temperature and space velocity is determined by means of experiments, and it is applied to the adblue injection strategy as the upper limit of the adblue flow rate, which can effectively improve the NOx conversion and avoid the formation of deposits. The multi-phase flow simulation of the nozzle and SCR flow field is carried out to optimize the nozzle structure, which provides a scientific basis to further improve the NOx conversion and to avoid a deposit
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