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A diesel engine SCR system control method based on urea decomposition efficiency

An SCR system and urea decomposition technology, which is applied in the field of diesel engine SCR system control based on urea decomposition efficiency, can solve the problems of leakage of injected ammonia gas, difficulty in determining the injection amount of urea aqueous solution, low NOx conversion rate, etc. Achieve the effect of high-efficiency conversion of NOx

Active Publication Date: 2015-11-11
TONGJI UNIV
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Problems solved by technology

[0003] However, there are still certain technical bottlenecks in urea SCR technology, which is mainly reflected in the difficulty in determining the injection volume of urea aqueous solution. Insufficient injection volume will lead to NO x If the conversion rate is too low and the injection volume is too large, ammonia gas will leak and cause secondary pollution

Method used

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  • A diesel engine SCR system control method based on urea decomposition efficiency
  • A diesel engine SCR system control method based on urea decomposition efficiency
  • A diesel engine SCR system control method based on urea decomposition efficiency

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Embodiment 1

[0021] Embodiment 1: Determine the urea decomposition efficiency by parameters such as diesel engine exhaust temperature, space velocity, and urea aqueous solution injection pressure

[0022] The present invention takes a diesel engine with a displacement of 7 liters as an example, uses simulation software to simulate and calculate the internal reaction of the SCR system of the diesel engine, and obtains the change of urea decomposition efficiency with the exhaust temperature under the condition that other influencing factors remain unchanged relationship, such as figure 1 shown.

[0023] Depend on figure 1 It can be seen that the urea decomposition efficiency increases first and then decreases with the exhaust temperature, and when the exhaust temperature is 350 °C, the corresponding urea decomposition efficiency can reach 97.5%.

[0024] Similarly, we can also obtain the relationship between the urea decomposition efficiency and the space velocity and the injection pre...

Embodiment 2

[0025] Example 2: Steady state control method for diesel engine SCR system based on urea decomposition efficiency

[0026] Based on the previous diesel engine SCR system control method, the present invention considers the influence of urea decomposition efficiency on the required urea aqueous solution injection quantity, so as to optimize the control method. Such as image 3 As shown, the specific implementation process of the method is as follows:

[0027] (1): When the diesel engine speed is 700rpm, 1100rpm, 1500rpm, 1900rpm, 2300rpm, and the load percentage is 20%, 40%, 60%, 80% and 100% respectively, the exhaust flow and exhaust gas flow rate of the diesel engine are obtained Static MAP plot of NO concentration. When the diesel engine speed is 1200rpm and the load percentage is 50%, according to the static MAP diagram of the diesel engine, the exhaust flow rate of the diesel engine under this working condition is 120g / s, and the concentration of NO in the exhaust gas i...

Embodiment 3

[0031] Embodiment 3: Correction of injection amount of aqueous urea solution under transient working conditions

[0032] The control methods in the above embodiments are typical steady-state control methods. However, when the engine is in a transient state, this method is difficult to accurately provide the actual required injection amount of urea solution for the engine.

[0033] Therefore, on the basis of the original control method, according to the NO x According to the change law of the conversion rate with the exhaust gas temperature and space velocity, etc., the steady-state injection amount of urea aqueous solution is transiently corrected, and the actual urea aqueous solution injection amount required by the engine under each transient working condition is obtained, as shown in Figure 4 shown.

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Abstract

The invention belongs to the technical field of aftertreatment of diesel engines, and in particular relates to a method for controlling an SCR system of diesel engines based on urea decomposition efficiency. First put forward the concept of urea decomposition efficiency, and give its expression η =f ( t,v,p ). On this basis, a set of diesel engine SCR system control method is formulated: then according to the diesel engine speed and load percentage, the diesel engine exhaust flow and the concentration of NOx in the exhaust gas are obtained through the diesel engine static MAP diagram, and then the basic injection amount of urea aqueous solution is obtained Q 1 Using urea decomposition efficiency vs. Q 1 after correction Q 2, Q 2 is the injection volume of urea aqueous solution under steady state. Considering the transient condition of the diesel engine, it is also possible to Q 2 Perform transient correction to obtain the actual urea aqueous solution injection quantity required by the final diesel engine Q 3. The invention introduces the parameter of urea decomposition efficiency, can accurately provide the injection amount of urea aqueous solution according to different operating conditions of the engine, and effectively reduces the leakage of NH3 while realizing high-efficiency conversion of NOx.

Description

technical field [0001] The invention belongs to the technical field of post-treatment of diesel engine exhaust, and in particular relates to a diesel engine SCR system control method based on urea decomposition efficiency. Background technique [0002] Due to its good power and economy, diesel engines are widely used in various vehicles, construction machinery and agricultural machinery. However, nitrogen oxides (NO x ) emission is one of the main air pollutants, which has caused great harm to the environment and human health. Reducing NOx in Diesel Engines by Purifying Measures in Engine x The emission method has been difficult to meet the increasingly stringent emission regulations, so the current research focus turns to diesel engine aftertreatment technology. And in many lower NO x Among the post-treatment technologies for emissions, ammonia (NH 3 ) as a reducing agent, Selective Catalytic Reduction (SCR) is one of the most promising technologies, and in practical a...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): F01N9/00F01N3/20
CPCY02T10/12Y02T10/40
Inventor 谭丕强杜加振胡志远楼狄明
Owner TONGJI UNIV
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