SCR system and engine

An SCR system, comprising a box body, a urea nozzle and a mixer, wherein

• the mixer is arranged inside the box body, and the mixer is of a cylinder shape;
• a first end of the mixer faces the urea nozzle, and a second end of the mixer is configured to discharge a mixed gas;
• the mixer comprises a baffle ring, a swirl tube and a perforated tube that are connected in sequence, and the baffle ring is arranged close to the urea nozzle;
• the baffle ring is provided with a plurality of first through holes, the swirl tube is provided with a plurality of second through holes, and the perforated tube is provided with a plurality of third through holes;
• and
• the mixer comprises an annular baffle, an inner circumference of the annular baffle is connected to an outer wall of the swirl tube and/or an outer wall of the perforated tube, and an outer circumference of the annular baffle is connected to an inner wall of the box body,
• wherein the swirl tube comprises a swirl tube body and a plurality of swirl fins;
• the swirl tube body is of a cylinder shape, and two ends of the swirl tube body are connected to the baffle ring and the perforated tube respectively;
• the plurality of second through holes are provided on the swirl tube body, and the plurality of swirl fins are in one-to-one correspondence to the plurality of second through holes;
• and
• a first end of each of the plurality of swirl fins is connected to the swirl tube body, and a second end of each of the plurality of swirl fins extends outwards along a radial direction of the swirl tube body in an inclined manner.