A wide temperature window high-efficiency diesel engine post-processing device and its control method

Abstract

The invention belongs to the technical field of engine tail gas purification, in particular to a high-efficiency diesel engine post-processing device with a wide temperature window and a control method thereof. The invention is a high-efficiency diesel engine post-processing device with a wide temperature window and its control method. The main technical problem to be solved is to make NO X The conversion efficiency temperature window of the system is greatly extended to the low temperature direction, and the temperature window for post-treatment to work is extended to 150°C. This system includes (EH)DOC+DPF+SCR The two-stage reductant injection control is adopted at the appropriate time for the exhaust condition and the exhaust condition, and the quota control of the reductant based on the temperature window is carried out respectively before the (EH)DOC and before the SCR, so as to ensure that the engine has an efficient NO in a wide temperature window. X Conversion efficiency.

Description

technical field [0001] The invention belongs to the technical field of engine tail gas purification, in particular to a high-efficiency diesel engine post-processing device with a wide temperature window and a control method thereof. Background technique [0002] In order to reduce and eliminate harmful emissions from diesel engines and meet the current National VI emission regulations, a combination of technologies such as oxidation catalyst (DOC), selective catalytic reduction agent (SCR), and particle capture DPF are usually used. In recent years, the SCRF technology has been further developed, which directly coats the SCR catalyst on the DPF. The advantages of this technology are the ability to simultaneously treat NOx and filter PM, and significantly reduce the volume of aftertreatment. [0003] In the future, emission regulations will be further strengthened, and the control of pollutant emissions will be more stringent. The most prominent challenge is the insufficien...

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Problems solved by technology

[0008] The scheme described in the patent document CN201611220481.2 is to arrange a nozzle upstream of the SCRF, and arrange a nozzle downstream of the SCRF and upstream of the SCR. The two adopt open and closed-loop control methods respectively, based on the previously calibrated Map and their respective injection positions. Upstream and downstream NO x Sensors and ammonia sensors, although most of the working conditions can achieve precise control, but due to the use of more expensive sensors, especially ammonia sensors, the system cost is relatively high

[0009] Patent document CN201480080214.2 Although the double closed-loop control of reductant feed injection is adopted, more sensors are still used, including 5 exhaust temperature sensors, 5 NO x Sensors, 2 ammonia sensors, the structure is extremely complex, the cost is higher, and the reliability is reduced

In addition, the NO involved in the closed-loop control x Both the NH3 sensor and the NH3 sensor have a start-up process, and effective closed-loop control of emissions cannot be performed during the cold start and warm-up process

[0010] Patent document CN201711442193.6 uses only a single urea injection device in front of the SCRF to inject the reducing agent, which cannot reasonably allocate the reducing agent according to the distribution of active sites on the SCRF and SCR catalysts. Among them, the utilization rate of the activity of the SCR catalyst will be lower than The activity utilization rate on the SCRF, it is difficult to give full play to the catalytic function of the SCR catalyst, resulting in the waste of some functions

[0011] According to the above patent documents, one nozzle is arranged at the inlet of SCRF and before the SCR to form a double injection method. Compared with the single injection method before SCRF, the injection accuracy can be improved, but the NO x The improvement of conversion efficiency is still limited, that is, when the engine is running at cold start, warm-up and low-temperature conditions with low load for a long time, due to the low exhaust temperature, generally below 200°C or even lower, the efficiency of the SCR catalyst is relatively low at this time. Low, generally unable to inject reducing agent, no NO x conversion efficiency

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