Investigation on the urea deposit formation and thermal decomposition characteristics in the SCR aftertreatment system of a diesel engine.

Selective catalytic reduction is the most efficient and reliable equipment for NOx control in current diesel engines. However, the issue of urea crystallization becomes increasingly serious with the implement of the new emissions standards. In this paper, urea deposit samples collected from engine test bed and tube furnace were characterized by thermogravimetric analysis and Fourier transform-infrared analysis to aid the comprehension of urea deposit formation. Moreover, thermogravimetric tests were conducted to disclose the effects of catalyst on the thermal decomposition processes of urea deposit. The results indicated that less temperature resistant species are formed in the engine test bed than in the tube furnace at conditions with the same temperatures. The main compositions in the World Harmonized Transient Cycle (WHTC) urea deposits are urea, cyanuric acid (CYA) and ammelide, implying that accelerating the decomposition of these species could prevent the accumulation of urea deposit. CuWTi, Cuß and CuZSM catalysts could lead to increased yield of CYA during pure urea thermolysis. Cuß, CuWTi and VWTi catalysts tend to promote the thermolysis of CYA while VWTi has the most significant catalytic effects on the thermal decomposition of ammelide and ammeline.

Micro Lubrication and Heat Transfer in Wedge-Shaped Channel Slider with Convex Surface Texture Based on Lattice Boltzmann Method.

Hydrodynamic lubrication is widely used between two relatively moving objects, and the effect of fluid flow state and temperature distribution on lubrication performance in wedge-shaped gaps is a popular topic to study. In this paper, the incompressible double-distribution lattice Boltzmann method (LBM) is applied to study the effect of micro convex surface texture on micro lubrication and heat transfer in wedge-shaped channels. By comparing this model with the analytical solution of an infinitely wide wedge slider, the maximum pressure calculated by LBM is 0.1081 MPa, and the maximum pressure calculated by the Reynolds equation is 0.1079 MPa. The error of the maximum pressure is 1.11%, and the Reynolds equation result is slightly smaller. The reason is that the Reynolds equation ignores the influence of fluid inertia force on oil film pressure. The results indicate that the application of LBM can be used to study lubrication problems. Compared with the Reynolds equation, LBM can calculate the velocity field and pressure field in the film thickness direction, and can also observe precise flow field details such as vortices. Three micro convex texture shapes were established to study the effects of different convex textures on micro lubrication and oil film temperature distribution, and the velocity distribution, temperature distribution and oil film pressure along the oil film thickness direction were given. Under the same conditions, comparing the oil film pressure with and without surface texture, the results show that the maximum oil film pressure with surface texture 3 is increased by about 4.34% compared with that without surface texture. The slightly convex texture can increase the hydrodynamic lubrication effect and obtain greater load-bearing capacity, helping to reduce the possibility of contact friction. The results show that the convex surface texture can improve the hydrodynamic lubrication performance, increase the load carrying capacity and reduce the possibility of contact friction, and the convex surface texture can influence the temperature distribution of the oil film. At 3.6 mm in the slider length direction and 7.5 µm in the oil film thickness direction, the temperature of surface texture 1 is 402.64 K, the temperature of surface texture 2 is 403.31 K, and the temperature of surface texture 3 is 403.99 K. The presence of vortices is captured at a high convergence ratio.

Numerical Investigation on the Urea Deposit Formation Process in a Selective Catalytic Reduction System of a Diesel Engine Based on a Fluid-Solid Coupling Method.

Currently, selective catalytic reduction (SCR) systems have become an essential part in diesel engines, and urea crystallization is one of the most serious issues in SCR systems. In this paper, the urea deposit formation processes in the SCR system were investigated by numerical simulations based on a fluid-solid coupling method. The results show that the masses of the wall film and solid urea are larger at conditions with lower temperatures and higher injection rates. At higher temperatures, cyanate ions and ammonium ions are the most predominant compositions in the wall film, while at lower temperatures, solid urea is the main composition. It could also be deduced that the location of urea crystallization is more affected by the design of mixer at higher temperatures, whereas at lower temperatures, the location and installation angle of urea-water solution injector play a more important role.

[Effects of CXCR4 silence induced by RNA interference on cell cycle distribution and apoptosis of Jurkat cells].

This study was aimed to investigate the effect of down-regulating the CXCR4 expression on cell cycle and cell apoptosis of human T-ALL Jurkat cells. The CXCR4 specific siRNA plasmid vector was constructed and then transfected into the cultured Jurkat cell line by DMRIE-C. The expression of CXCR4 mRNA was detected by RT-PCR, the cell distribution in cell cycle and cell apoptosis were determined by flow cytometry. The experiments were divided into 3 groups: group A (blank control), group B (non-silencing dsRNA as negative control) and group C (CXCR4 siRNA). The results showed that the expression level of CXCR4 mRNA in Jurkat cells transfected with CXCR4 siRNA (group C) decreased and cell proportion in G(0)/G(1) phase increased as compared with group A (56.9% +/- 1.4% vs 68.3% +/- 2.4% and 35.8% +/- 1.9% vs 18.1% +/- 1.2% respectively) (p < 0.01), cell proportion in G(2)/M and S phase decreased as compared with group A (19.8% +/- 1.7%, 44.4% +/- 2.1% vs 27.2% +/- 1.5%, 54.7% +/- 2.8% respectively) (p < 0.01). The apoptosis rate of Jurkat cells in group C increased as compared with group A (20.9% +/- 2.0% vs 3.13% +/- 0.9% respectively) (p < 0.01), and the comparison between group A and B showed no statistical difference. It is concluded that the CXCR4 specific siRNA can effectively down-regulate the CXCR4 mRNA expression, which induces the cell apoptosis and cell cycle arrest, thereby inhibits the Jurkat cell proliferation.