Research on Optimization Design of SCR Nozzle for National VI Heavy Duty Diesel Engine

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.

Research on Aftertreatment Inlet_Outlet Insulation for A Nonroad Middle Range Diesel Engine

“…Urea dosing into the mixer through a urea injector may be necessary according to a control strategy to achieve a specific NOx conversion efficiency in certain conditions to meet strict regulation requirements. Figure 3 [19] illustrates a urea pyrolysis mechanism and schematic for droplet evaporation, which explains the complex reactions during heat transfer stages within the The experimental results demonstrate that the aftertreatment emission could meet China StageIV regulation emission requirements with a margin, even using aged catalysts, whether with aftertreatment inlet/outlet insulation or not, which provides a reasonable precondition for aftertreatment skin temperature and radiated impact research.…”

“…Urea dosing into the mixer through a urea injector may be necessary according to a control strategy to achieve a specific NOx conversion efficiency in certain conditions to meet strict regulation requirements. Figure 3 [19] illustrates a urea pyrolysis mechanism and schematic for droplet evaporation, which explains the complex reactions during heat transfer stages within the aftertreatment. The urea droplets begin to evaporate when the temperature rises due to being gradually heated by exhaust gas.…”

“…Figure 3. Urea pyrolysis mechanism [19] In a word, the urea droplets are heated up and water evaporates first, followed by the thermolysis of urea into ammonia and isocyanic acid [20].…”

Aftertreatment DeNOx Systems for Future Light Duty Lean-Burned Emission Regulations

“…Hence, the properties of the urea-water solution spray become particularly critical for enhancing NOx elimination. There are two papers of this special issue devoted to study the injection and mixing of the urea-water solution [2,3]. Kapusta et al [2] have studied the flow characteristics and have determined the global and local spray parameters for the urea-water solution compared to pure water.…”

“…Thus, the importance of precisely determining the spray parameters of urea-water solutions was highlighted for obtaining reliable results by CFD simulations. On the other hand, Qian et al [3] focused their study on the design of the urea-water solution nozzle. Using CFD simulation, they proposed and optimized nozzle design that can increase the uniformity of the NH 3 distribution at the inlet face of the SCR from 0.58 (for the standard design) to 0.92.…”