Calculation method of scr system closed loop control

Abstract

The invention relates to a computing method, in particular to an SCR system closed-loop control computing method and belongs to the technical field of aftertreatment systems of diesel engines. Through a NOx conversion efficiency computing module, a NOx conversion efficiency measured value is obtained through computing, the NOx conversion efficiency measured value is compared with a NOx conversion efficiency target value, feedback correction is conducted so that a feedback control coefficient can be obtained, and feedback adjustment is conducted on the feedforward urea injection amount through the feedback control coefficient. During feedback adjustment, the computing time of feedback control and the feedback adjustment time are both taken into consideration, accurate control over a system is adjusted in time, delay of the injection system is avoided, the accurate of closed-loop control and the highest efficiency of the system are guaranteed, and safety and reliability are achieved.

Description

technical field [0001] The invention relates to a calculation method, in particular to a closed-loop control calculation method of an SCR system, which belongs to the technical field of diesel engine post-processing systems. Background technique [0002] Nitrogen oxides (NOx) are the main pollutants emitted by diesel engines, and the SCR post-treatment technology is the main technical means to reduce NOx in the exhaust gas of national IV, national V and national six diesel engines. The basic principle is formed by injecting urea hydrolysis atomization Ammonia reacts with NOx in the exhaust gas in the catalyst to generate harmless nitrogen. With the gradual tightening of diesel vehicle emission regulations, the NOx emission limit is getting lower and lower. At the National V and National VI stages, the SCR post-processing control system is required to have more precise control capabilities. [0003] At present, there are two control methods of urea injection in SCR system: ...

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Problems solved by technology

[0004] Analyzing the traditional urea injection control method above, there may be the following problems: the NOx emission value of the original engine used in the open-loop control, the concentration value of the urea aqueous solution, the exhaust flow value, the urea injection rate and the NH 3 The storage value will be different due to the change of the use environment (such as: catalyst performance, temperature, etc.), so that the measurement deviation cannot be compensated (that is, the change in the urea injection amount caused by the above difference cannot be fed back to the control system in time), eventually leading to The actual NOx conversion efficiency is quite different from the set target value, and it is easy to generate high NH 3 Leakage, unable to meet the increasingly stringent National V and National VI emission regulations; and the calculation of feedback control and control adjustment time may not be considered in the closed-loop control, which will lead to delays in the injection system and affect the urea injection control accuracy of the system

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