A selective catalytic reduction (SCR) system, comprising a box body, a mixer, a baffle and a carrier, the mixer, the baffle and the carrier being sequentially arranged inside the box body in an airflow direction inside the box body, the baffle being provided with a plurality of through holes, and the distribution density of the through holes and/or the hole area of the through holes being negatively correlated with a distribution uniformity index of NH.sub.3 at the baffle. The configuration of the distribution density and the hole area of the through holes can improve the mixing uniformity of ammonia gas, so that a reaction effect of a catalyst and a mixed gas in the carrier is enhanced. The settings of the distribution density and the hole area of the through holes can improve the mixing uniformity of an ammonia gas.

A mixer assembly for mixing, in a mixing tube of an exhaust aftertreatment system, a reductant with an exhaust gas from an internal combustion engine may include a mixer and an electrically heated heating element. The mixer may be positioned in proximity to the reductant injector. The electrically heated heating element may be positioned in proximity to an impingement surface of the mixer. The reductant may directly impinge, after being injected, on the impingement surface causing the reductant to vaporize and mix with the exhaust gas forming a vaporized reductant and exhaust gas mixtures that flows along a flow path defined by the mixing tube. The vaporized reductant and exhaust gas mixture may be heated and further mixed by the electrically heated heating element.

A mixer assembly for mixing, in a mixing tube of an exhaust aftertreatment system, a reductant with an exhaust gas from an internal combustion engine may include a mixer and an electrically heated heating element. The mixer may be positioned in proximity to the reductant injector. The electrically heated heating element may be positioned in proximity to an impingement surface of the mixer. The reductant may directly impinge, after being injected, on the impingement surface causing the reductant to vaporize and mix with the exhaust gas forming a vaporized reductant and exhaust gas mixtures that flows along a flow path defined by the mixing tube. The vaporized reductant and exhaust gas mixture may be heated and further mixed by the electrically heated heating element.