A new design of a selective catalytic reduction(SCR)mixer called tornado was developed for a heavy-duty diesel engine to solve the urea deposition problem.A combination of CFD simulation and experimental studies was u...A new design of a selective catalytic reduction(SCR)mixer called tornado was developed for a heavy-duty diesel engine to solve the urea deposition problem.A combination of CFD simulation and experimental studies was used to comprehensively evaluate the performance of the tornado mixer.According to the numerical simulations,this mixer can improve the front surface flow uniformity of the SCR carrier by 6.67%and the NH3 distribution uniformity by 3.19%compared to a traditional mixer.Similarly,steady state SCR conversion efficiency test results have shown that the tornado mixer can increase the average SCR conversion efficiency by 1.73%compared to a traditional mixer.Therefore,the tornado mixer outperforms traditional mixers in terms of mixing uniformity,resistance to deposition and impact on NOX emissions.In addition,a dimensionless parameter,the“limiting deviation rate”,is proposed in the present study to improve the mixing uniformity assessment method for SCR mixers(with the explicit intent to evaluate the mixing uniformity more accurately).展开更多
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 n...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, Cu β and CuZSM catalysts could lead to increased yield of CYA during pure urea thermolysis. Cu β, 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.展开更多
文摘A new design of a selective catalytic reduction(SCR)mixer called tornado was developed for a heavy-duty diesel engine to solve the urea deposition problem.A combination of CFD simulation and experimental studies was used to comprehensively evaluate the performance of the tornado mixer.According to the numerical simulations,this mixer can improve the front surface flow uniformity of the SCR carrier by 6.67%and the NH3 distribution uniformity by 3.19%compared to a traditional mixer.Similarly,steady state SCR conversion efficiency test results have shown that the tornado mixer can increase the average SCR conversion efficiency by 1.73%compared to a traditional mixer.Therefore,the tornado mixer outperforms traditional mixers in terms of mixing uniformity,resistance to deposition and impact on NOX emissions.In addition,a dimensionless parameter,the“limiting deviation rate”,is proposed in the present study to improve the mixing uniformity assessment method for SCR mixers(with the explicit intent to evaluate the mixing uniformity more accurately).
基金supported by the National Engineering Laboratory for Mobile Source Emission Control Technology(No.NELMS2018A10)the Science Fund for Young Scholars of Natural Science Fund in Hebei Province(No.E2019202198)+1 种基金the Science and Technology Research Project of Colleges and Universities in Hebei Province(No.QN2019056)the State Key Laboratory of Engines,Tianjin University(No.K2020-15)。
文摘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, Cu β and CuZSM catalysts could lead to increased yield of CYA during pure urea thermolysis. Cu β, 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.
