Control method for urea injection of engine postprocessor

Abstract

The invention relates to a control method for urea injection of an engine postprocessor. The control method comprises the following steps that gas concentration data in a postprocessor sample rack test and temperature data of an engine rack are collected respectively; the collected temperature data are input into an SCR temperature model to calculate temperature field distribution of different axial positions in the SCR postprocessor; the collected gas concentration data and temperature field distribution are input into an SCR chemical dynamics model to be calculated and input into a gas concentration equation together with the quantity, collected by the engine rack, of each kind of gas component flowing into a catalytic device, and calculated SCR carrier ammonia storage is obtained; and then the calculated SCR carrier ammonia storage and an SCR carrier ammonia storage preset value are judged so as to realize urea injection control. According to the method, the ammonia storage amount in an SCR carrier is calculated forward, and closed-loop control over urea injection is realized, so that the conversion rate of tail gas NOx reaches more than 96%, and emission finally meets emissionregulation requirements of national VI standards or above.

Description

technical field [0001] The invention relates to the field of automobiles, in particular to a method for controlling urea injection of an engine post-processor. Background technique [0002] At present, with the upgrade of engine emission regulations, the National VI regulations NO x (nitrogen oxides) requirements are more stringent. In order to meet the requirements of China VI emission regulations, SCR (Selective catalytic reduction: Selective catalytic reduction) post-processor is generally used to reduce NO x . Among them, urea injection control is the key. On the one hand, urea must reach a certain amount of injection to ensure high-efficiency NO x Transformation, so that the emission meets the requirements of the National VI emission regulations. On the other hand, from the perspective of economy and urea crystallization, the amount of urea injection should not be too much. Therefore, precise control of urea injection is the core technology. [0003] CN109411027A d...

AI Technical Summary

Problems solved by technology

However, it is based on the traditional bench calibration, which has the following defects: (1) The calibration period is long, and the test method needs to conduct single-point tests on more than hundreds of operating points for universal characteristics, and the workload is huge

(2) There are many calibration parameters, including SCR maximum ammonia storage capacity, NO x Conversion efficiency, ammonia adsorption time constant map and ammonia release time constant map and other parameter calibration, the calibration is complicated, and the boundary conditions are difficult to control, prone to experimental errors; (3) Calibration of ammonia adsorption time constant map and ammonia release time constant Map, request SCR exit NH 3 The concentration reaches 10ppm, but in the actual bench calibration test, because the SCR itself has a strong ammonia storage capacity, and there is an ASC on the post-processor that specifically absorbs ammonia leakage, so to achieve this condition, each working point needs to spend 0.5- The time varies from 1 hour, the calibration method is complicated, the cycle is long, and the cost is high

[0005] In order to accurately control the injection amount of urea in the SCR post-processor, it is necessary to finely calibrate the complex chemical reactions that occur in the SCR post-processor. The traditional calibration method is mainly based on the engine bench calibration, which requires more than hundreds of universal characteristics. A single-point test is carried out at each working point, and then verified by the standard WHTC (transient cycle: World harmonized transient cycle) and WHSC (steady-state cycle: World harmonized steady state cycle). This method has a long calibration period, high cost, and consumes A large amount of manpower and material resources, and requires high professional level and experience of calibration personnel and other disadvantages

In addition, the urea injection method is basically open-loop control, which is only suitable for stable engine conditions. When the whole vehicle is actually running, it works under transient conditions, so the urea injection controlled by the traditional calibration method will exist. large error

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