Method and system for controlling emitted dose of urea solution by SCR (Selective Catalytic reduction)

Abstract

The invention provides a method and a system for controlling the emitted dose of a urea solution by SCR (Selective Catalytic Reduction) by taking three parameters, namely NH3 storage amount, NOx conversion efficiency and exhaust gas temperature into account. When the working condition of en engine instantaneously changes, the exhaust gas temperature can possibly and suddenly raise to cause increase of exhaust gas flow, and excessive NH3 escape is caused in the prior art; or when the working condition of the engine changes, the emitted dose of the urea solution is lower to cause insufficiency of the NOx conversion efficiency. Under the conditions that the requirements on the catalyst amount and the NH3 escape amount are definite, the maximum NOx conversion efficiency depends on the catalyst reaction temperature and the exhaust gas flow. According to the control method provided by the invention, a target value of the NOx conversion efficiency and the available NOx conversion efficiency based on the NH3 storage amount are added as closed-loop amendments, so that the emitted dose of the urea solution can be accurately controlled, the NOx conversion efficiency is furthest improved and the NH3 escape amount is reduced.

Description

technical field [0001] The invention relates to the technical field of engine emission treatment, in particular to a method and system for controlling the injection amount of a selective catalytic reduction urea solution. Background technique [0002] Selective Catalytic Reduction (SCR, Selective Catalytic Reduction) technology is one of the main post-treatment technologies for eliminating nitrogen oxides in diesel engine exhaust. [0003] According to the function, the SCR system is mainly divided into three parts: the control unit, the urea dosage unit and the catalytic reaction unit. [0004] The control unit of the SCR system is integrated with the engine control unit (ECU), which is mainly used to implement the SCR control strategy, and according to the ambient temperature, exhaust temperature, urea level, urea temperature, urea pressure, nitrogen oxides (NOx) Concentration and other sensor signals control the urea dosage unit, so that the urea dosage unit sprays the u...

AI Technical Summary

Problems solved by technology

Moreover, under the condition that the catalyst and ammonia NH3 slippage requirements are certain, the maximum conversion efficiency of nitrogen oxides only depends on the reaction temperature of the catalyst and the exhaust flow rate.

Therefore, when the working conditions of the engine change instantaneously, if the exhaust temperature rises and the exhaust flow rate increases, it is easy to cause too much ammonia gas to escape, which will cause secondary pollution

Conversely, if the exhaust temperature decreases, the exhaust flow rate decreases, and the injection amount of urea solution is too small, it is easy to cause insufficient nitrogen oxide conversion efficiency

[0016] To sum up, the control method of the injection amount of urea solution in the prior art is not accurate enough, so that the conversion efficiency of nitrogen oxides cannot be maximized, and it is easy to cause environmental pollution

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