scr feedforward control calculation method

Abstract

The invention relates to an SCR feedforward control calculation method. The method comprises the following steps that the SCR efficiency urea jet amount is determined and obtained according to the air speed, the SCR average temperature, the NO2 / NOx ratio, the NOx mass flow and the urea concentration; the ammonia-nitrogen ratio urea jet amount is determined according to the urea concentration, the NO2 / NOx ratio, and the NOx mass flow to be converted; the urea jet amount after ammonia oxidation modification is obtained by multiplying the ammonia-nitrogen ratio urea jet amount by the ammonia oxidation factor; the urea jet amount of a fresh catalyst in the steady state is obtained by comparing the ammonia oxidation modified urea jet amount with the SCR efficiency urea jet mount and selecting the smaller value of the urea jet amount after ammonia oxidation modification and the SCR efficiency urea jet amount; and the feedforward urea jet amount is obtained by multiplying the urea jet amount of the fresh catalyst in the steady state by the transient modifying factor and the aging modifying factor. According to the method, the real-time and accurate control over the feedforward urea jet amount is achieved, and the difficulty of subsequent feedforward control adjustment of the urea jet amount is greatly reduced.

Description

technical field [0001] The invention relates to a calculation method, in particular to an SCR feed-forward control calculation method, which belongs to the technical field of diesel engine post-processing systems. Background technique [0002] At present, SCR post-treatment technology is an important technical means for the reduction of NOx in exhaust gas of National IV, National V and National VI diesel engines. The SCR post-treatment method is mainly to pass a certain amount of urea aqueous solution into the exhaust gas, decompose a certain amount of ammonia gas, and reduce the NOx in the exhaust gas to nitrogen gas which is harmless to the human body. Therefore, accurate calculation of SCR feed-forward control urea injection quantity determines the conversion efficiency of NOx, whether the performance of the catalyst can be fully utilized, and the difficulty of post-feedback control adjustment. [0003] Generally speaking, the method to calculate the feed-forward urea in...

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Problems solved by technology

[0004] 1), NO in exhaust gas is not considered 2 The influence of the proportion of NOx in the catalyst chemical reaction;

[0005] 2) The loss of ammonia due to oxidation under high temperature conditions is not considered;

[0006] 3) The impact of inaccurate concentration of urea aqueous solution is not considered;

[0007] 4) The impact of the diesel engine due to transient changes in working conditions during driving is not considered;

[0008] 5) Changes in urea injection volume due to catalyst aging are not considered

[0009] The method of determining the amount of SCR feed-forward urea injection above may be able to control the exhaust emissions of some diesel engines that require relatively low NOx conversion efficiency, but with the upgrade of emission regulations, for some diesel engines that require relatively high exhaust NOx conversion efficiency , the accuracy of the urea injection volume obtained at present is far from enough

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