Selective catalytic reduction (SCR) system with external mixing nozzle metering structure

Abstract

The invention discloses a selective catalytic reduction (SCR) system with an external mixing nozzle metering structure. The system comprises a urea tank used for storing reducing agent, a urea pump, a metering valve, a nozzle and an air source. The metering valve is communicated with a urea pump pipeline, the air resource is communicated with a nozzle pipeline, the metering valve is arranged on the nozzle, and air flow in the air source and the reducing agent sprayed by the metering valve are mixed in the nozzle. The nozzle comprises a urea pipe, an air cap and an air flow gap formed between the urea pipe and the air cap. The SCR system with the external mixing nozzle metering structure has the advantages that an integration level is high, the external mixing type nozzle structure is simple, an atomization mixing effect is good, and the whole system is convenient to control.

Description

technical field [0001] The invention relates to a post-treatment and purification system for diesel vehicle exhaust, in particular to an SCR system with an external mixing nozzle metering structure. Background technique [0002] It is known that it is a common technical route to reduce the nitrogen oxides in the exhaust gas of internal combustion engines, especially diesel engines, by selective catalytic reduction technology (SCR), that is, the reducing agent (aqueous urea solution) is atomized and quantitatively injected into the exhaust pipeline, And through the SCR catalyst, the main harmful gas NO in the exhaust gas x It is converted into nitrogen and water and discharged to achieve the purpose of tail gas purification. [0003] In the prior art, the urea aqueous solution metering and injection device is divided into two types: gas and airless. The gas injection system mainly relies on the pump to pump the reducing agent to the inlet of the metering valve, and accuratel...

AI Technical Summary

Problems solved by technology

[0003] In the prior art, the urea aqueous solution metering and injection device is divided into two types: gas and airless. The gas injection system mainly relies on the pump to pump the reducing agent to the inlet of the metering valve, and accurately meter and inject it into the mixing chamber through the metering valve. The injected reducing agent is atomized once and blown to the nozzle. During the injection process of the nozzle, it is atomized again and injected into the exhaust pipe. This system is atomized by the secondary injection, and the atomization effect is good, but this structure It is more complex, requires high pressure control in the pipeline, consumes a lot of power, and is complicated to control; the other is the airless injection system, which is most typical in the industry with BOSCH's DENOXTRONIC2.2 system, that is, the metering valve is directly set in the row On the air pipe, the metering valve is directly metered and sprayed and atomized. Although the structure of this system is simple, the metering valve is easy to be burnt and corroded near the exhaust pipe. At the same time, because it can only be atomized by liquid injection pressure, the atomization effect is poor.

[0004] In order to solve the above problems, the applicant disclosed a Chinese patent (Patent No. 201020276173.3) of a direct-injection metering injection device. This external mixing structure can reduce the back pressure and solve the problem of atomization when used in an air control system. problem, but the structure is more complex

[0005] In addition, the structural simplification of the SCR system is the main body of the current metering injection system. How to simplify the SCR system to achieve a reasonable control method is the main problem faced by domestic and foreign manufacturers.

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