Design and evaluation of an Integrated SCR and exhaust Muffler from marine diesels

Integrated, compact, diesel after treatment system that combines selective catalytic reduction (SCR) for NOX control with a reactive muffler to reduce exhaust noise was designed and evaluated under various conditions. Considering the installation size, noise reduction, performance of SCR, exhaust back pressure and its effects on engine performance, it provides the basis for the design of the Integrated SCR-Muffler. Based on the two-load method and engine model established by AVL/Boost, the source impedance of engine has been found out. The transfer matrix of exhaust system was calculated from three-dimension finite element method which used equivalent fluid to describe the problem of wave propagation in the catalyst. On the basis of computational results, comprehensive analysis of noise reduction was made, the computed insertion loss of original muffler, SCR and Integrated SCR-Muffler was 32.1, 23.5 and 32.8 dB(A), respectively. The CFD simulation results prove that the Integrated SCR-Muffler is capable of increasing homogeneity of NH3 and improving NOX reduction efficiency due to the effect of silencing elements including perforated pipe and perforated plate, even though the pressure loss increased considerably when compared with SCR. Furthermore, the numerical results from simulations are compared with test. For most investigated operating conditions of D2 driving cycle, simulated emission results show a good consistency with experimental data. The Integrated SCR-Muffler shows a better performance than original muffler and SCR as far as IL, NOX reduction efficiency and pressure loss are concerned.