CN114233440B

CN114233440B - Urea double-injection aftertreatment system, control method thereof and vehicle

Info

Publication number: CN114233440B
Application number: CN202111551599.4A
Authority: CN
Inventors: 褚召丰; 吕志华; 方乐; 董婷; 张邦财
Original assignee: Weichai Power Co Ltd
Current assignee: Weichai Power Co Ltd
Priority date: 2021-12-17
Filing date: 2021-12-17
Publication date: 2022-11-29
Anticipated expiration: 2041-12-17
Also published as: CN114233440A

Abstract

The invention relates to the technical field of urea injection, and discloses a urea double-injection post-treatment system, a control method thereof and a vehicle, wherein the urea double-injection post-treatment system comprises: the first selective catalytic reduction component and the second selective catalytic reduction component are sequentially connected in series, the first selective catalytic reduction component is a close coupling selective catalytic reduction component, and the second selective catalytic reduction component is positioned at the downstream of the first selective catalytic reduction component; the first selective catalytic reduction component is also connected with a bypass branch in parallel, and a three-way valve is arranged at the upstream junction of the bypass branch and the branch where the first selective catalytic reduction component is positioned; a first-stage urea injection device is arranged at the upstream of the first selective catalytic reduction component, and a second-stage urea injection device is arranged at the upstream of the second selective catalytic reduction component; an electric heating device is further coupled to the upstream of the first selective catalytic reduction assembly to heat the first selective catalytic reduction assembly so as to enable the first selective catalytic reduction assembly to quickly start spraying.

Description

Urea double-injection aftertreatment system, control method thereof and vehicle

Technical Field

The invention relates to the technical field of urea injection, in particular to a urea double-injection aftertreatment system, a control method thereof and a vehicle.

Background

In order to meet the next generation emission regulation, a close-coupled SCR is added before the six post-treatments of the existing DOC (diesel oxidation type catalytic converter) + DPF (particulate trap) + SCR (selective catalytic reduction component)/ASC (ammonia slip catalyst), so that the NOx during low-temperature cold start is reduced, the specific emission of the NOx is greatly reduced, and the emission limit value is met. In addition, there is a technique to bypass the close-coupled SCR, which can have NOx conversion efficiency of substantially 90% or more when the temperature of the downstream SCR is high, and at this time, the close-coupled SCR (ccSCR) can be bypassed, which reduces the complexity of control and the risk of sulfur poisoning of the close-coupled SCR.

At present, the technology of tightly coupling SCR bypass has some defects, when the engine is started again after idling is reduced, the temperature of a carrier is reduced due to the fact that the tightly coupling SCR is bypassed for a long time and cannot be ignited quickly, and the purpose of reducing emission cannot be achieved when the tightly coupling SCR is started again after the engine is idling reduced for a long time.

Disclosure of Invention

The invention discloses a urea dual-injection aftertreatment system, a control method thereof and a vehicle, which are used for enabling a close-coupled selective catalytic reduction component to quickly ignite when an engine is restarted.

In order to achieve the purpose, the invention provides the following technical scheme:

in a first aspect, a dual urea injection aftertreatment system is provided, comprising: the system comprises a first selective catalytic reduction assembly and a second selective catalytic reduction assembly which are sequentially connected in series, wherein the first selective catalytic reduction assembly is a close-coupled selective catalytic reduction assembly, and the second selective catalytic reduction assembly is positioned at the downstream of the first selective catalytic reduction assembly; the first selective catalytic reduction component is also connected with a bypass branch in parallel, and a three-way valve is arranged at the upstream junction of the bypass branch and the branch where the first selective catalytic reduction component is positioned; a first-stage urea injection device is arranged at the upstream of the first selective catalytic reduction assembly, and a second-stage urea injection device is arranged at the upstream of the second selective catalytic reduction assembly; an electric heating device is also coupled to the upstream of the first selective catalytic reduction assembly.

In the urea double-injection after-treatment system, when the engine needs to be started, if the temperature of the second selective catalytic reduction assembly is lower than the ignition temperature, the three-way valve is controlled to close the bypass branch so as to remove the bypass of the first selective catalytic reduction assembly, the electric heating device is started, the first selective catalytic reduction assembly is heated to be ignited quickly, the problem that the temperature of a carrier is reduced and the first-stage urea injection device cannot be ignited quickly due to the fact that the first selective catalytic reduction assembly is bypassed for too long time is avoided, and the first-stage urea injection device is controlled to inject; and if the temperature of the second selective catalytic reduction assembly is greater than or equal to the ignition temperature, controlling the three-way valve to open the bypass branch so as to bypass the first selective catalytic reduction assembly and enable the second-stage urea injection device to inject.

Optionally, the support of the first selective catalytic reduction assembly is a metal support or a ceramic support.

Optionally, the surface of the metal support is coated with a selective catalytic reduction catalyst.

Optionally, a first diesel oxidation catalytic converter is arranged between the electric heating device and the first selective catalytic reduction assembly, and the first diesel oxidation catalytic converter is a close-coupled diesel oxidation catalytic converter.

Optionally, the carrier of the first diesel oxidation catalytic converter is a metal carrier or a ceramic carrier.

Optionally, a second diesel oxidation type catalytic converter and a particulate trap are sequentially connected in series between the first selective catalytic reduction assembly and the second stage urea injection device along the gas flow direction; and an ammonia slip catalyst is coupled downstream of the second selective catalytic reduction assembly.

In a second aspect, a control method of a urea dual injection after-treatment system according to the above technical solution is provided, which includes: when the engine needs to be started, if the temperature of the second selective catalytic reduction assembly is lower than the ignition temperature, the three-way valve is controlled to close the bypass branch so as to remove the bypass of the first selective catalytic reduction assembly, the electric heating device is started, and the first-stage urea injection device is controlled to inject; if the temperature of the second selective catalytic reduction assembly is greater than or equal to the ignition temperature, controlling the three-way valve to open the bypass branch so as to bypass the first selective catalytic reduction assembly and enable the second-stage urea injection device to inject; when the temperature of the second selective catalytic reduction assembly is greater than or equal to a first set temperature threshold value, controlling the three-way valve to open the bypass branch so as to bypass the first selective catalytic reduction assembly and enable the second-stage urea injection device to inject; and when the temperature of the second selective catalytic reduction assembly is smaller than a first set temperature threshold value, controlling the three-way valve to close the bypass branch so as to remove the bypass of the first selective catalytic reduction assembly and open the first-stage urea injection device and the second-stage urea injection device.

Optionally, when a first diesel oxidation catalytic converter is arranged between the electric heating device and the first selective catalytic reduction assembly and the engine needs to be started, and the electric heating device is started, the first diesel oxidation catalytic converter is controlled to inject hydrocarbons.

Alternatively, the first stage urea injection device is caused to decrease the injection amount when the temperature of the second selective catalytic reduction assembly is greater than a second set temperature threshold and less than a first set temperature threshold.

Alternatively, when the temperature of the second selective catalytic reduction assembly is greater than a second set temperature threshold and less than a first set temperature threshold, the injection amount of the first stage urea injection device is gradually reduced as the temperature of the second selective catalytic reduction assembly increases.

The control method has the same advantages of the urea dual injection after-treatment system compared with the prior art, and is not described in detail herein.

In a third aspect, a vehicle is provided, which comprises the urea double-injection after-treatment system in the technical scheme.

The vehicle and the urea dual injection aftertreatment system have the same advantages compared with the prior art, and the advantages are not described in detail.

Drawings

FIG. 1 is a schematic illustration of a dual urea injection aftertreatment system provided by an embodiment of the application;

FIG. 2 illustrates a variation of the urea dual injection aftertreatment system of FIG. 1;

FIG. 3 is a schematic illustration of a three-way valve in the dual urea injection aftertreatment system of FIG. 1 in a non-bypass state;

FIG. 4 is a graphical representation of the coefficient k as a function of temperature for a second selective catalytic reduction assembly;

FIG. 5 shows a logic diagram of a control method for a dual urea injection aftertreatment system.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

With reference to fig. 1 to 4, an embodiment of the present application provides a dual urea injection aftertreatment system, which includes: a first selective catalytic reduction assembly 72 and a second selective catalytic reduction assembly 75 connected in series, the first selective catalytic reduction assembly 72 being a close-coupled selective catalytic reduction assembly (ccSCR), the second selective catalytic reduction assembly 75 being a conventional SCR (referred to as downstream SCR in fig. 5), the second selective catalytic reduction assembly 75 being located downstream of the first selective catalytic reduction assembly 72; the first selective catalytic reduction assembly 72 is also connected with a bypass branch 21 in parallel, and a three-way valve 1 is arranged at the upstream junction of the bypass branch 21 and the branch 22 where the first selective catalytic reduction assembly 72 is located; a first-stage urea injection device 51 is arranged upstream of the first selective catalytic reduction assembly 72, and a second-stage urea injection device 52 is arranged upstream of the second selective catalytic reduction assembly 75; an electrical heating device 71 is also coupled upstream of the first selective catalytic reduction assembly 72.

In the urea double-injection after-treatment system, when the engine needs to be started, if the temperature of the second selective catalytic reduction assembly 75 is lower than the ignition temperature T2, the three-way valve 1 is controlled to close the bypass branch 21 to release the bypass of the first selective catalytic reduction assembly 72, the electric heating device 71 is started, the first selective catalytic reduction assembly 72 is rapidly heated to the ignition temperature T1 by using high-temperature exhaust and the electric heating device 71, so that the first-stage urea injection device 51 injects urea, and the problem that the first selective catalytic reduction assembly 72 cannot be rapidly ignited due to the reduction of the carrier temperature caused by the overlong bypass time is solved, so that the NOx is effectively reduced, and the purpose of reducing the emission is achieved; if the temperature of the second selective catalytic reduction assembly 75 is greater than or equal to the light-off temperature T2, the three-way valve 1 is controlled to open the bypass branch 21 to bypass the first selective catalytic reduction assembly 72 and cause the second-stage urea injection device 52 to inject. When the first selective catalytic reduction assembly 72 is cooled to the light-off temperature T1 or below due to the long period of time when the engine is in the idle-down condition, the first selective catalytic reduction assembly can be quickly brought to the light-off temperature T1 by the electric heating device 71.

In one embodiment, the carrier of the first selective catalytic reduction assembly 72 is a metal carrier or a ceramic carrier, which can reach the light-off temperature T2 quickly when heated by the electric heating device 71, and the temperature is lowered slowly to prevent quick cooling. In one particular embodiment, the surface of the metallic support is coated with a selective catalytic reduction catalyst to accelerate the catalytic reduction reaction.

In one specific embodiment, a first diesel oxidation catalytic converter 77 is disposed between the electric heating device 71 and the first selective catalytic reduction assembly 72, and the first diesel oxidation catalytic converter 77 is a close-coupled diesel oxidation catalytic converter to facilitate heating the first selective catalytic reduction assembly 72 for rapid light-off and hydrocarbon emission.

In a specific embodiment, the carrier of the first diesel oxidation catalytic converter 77 is a metal carrier or a ceramic carrier. When heated by the electric heater 71, the fuel can reach the ignition temperature quickly, and the temperature is lowered slowly to prevent quick cooling.

In a specific embodiment, a second diesel oxidation catalytic converter (DOC) 73 and a particulate trap (DPF) 74 are sequentially connected in series between the first selective catalytic reduction assembly 72 and the second stage urea injection device 52 along the gas flow direction, and the second diesel oxidation catalytic converter (DOC) 73 and the particulate trap (DPF) 74 have a heat storage function and can provide heat for the second selective catalytic reduction assembly 75 to prevent the second selective catalytic reduction assembly from being rapidly cooled; and an Ammonia Slip Catalyst (ASC) 76 is coupled downstream of the second selective catalytic reduction assembly 75.

Further, the

temperature sensors

41, 42, 43, 44, 45 and 46 are positioned as shown in fig. 1 and 2, respectively, to detect the temperatures of the respective positions and feed them back to the control module, and the nitrogen

oxide NOx sensors

31, 32 and 33 are positioned as shown to detect whether the NOx concentrations of the respective positions meet the requirements and feed them back to the control module.

Based on the same inventive concept, referring to fig. 5, an embodiment of the present application further provides a control method of the above urea dual injection after-treatment system, where the control method includes: when the engine needs to be started, if the temperature of the second selective catalytic reduction assembly 75 is lower than the ignition temperature T2, controlling the three-way valve 1 to close the bypass branch 21, so as to release the bypass of the first selective catalytic reduction assembly 72, starting the electric heating device 71, and controlling the first-stage urea injection device 51 to inject; if the temperature of the second selective catalytic reduction assembly 75 is greater than or equal to the light-off temperature T2, since the second diesel oxidation catalytic converter (DOC) 73 and the particulate filter (DPF) 74 in front of the second selective catalytic reduction assembly 75 have the functions of heat preservation and heat storage, and the SCR temperature will not decrease rapidly, the three-way valve 1 is controlled to open the bypass branch 21 to bypass the first selective catalytic reduction assembly 72 (fig. 3), and the second-stage urea injection device 52 injects the urea; when the temperature of the second selective catalytic reduction assembly 75 is greater than or equal to the first set temperature threshold TH, the conversion efficiency of the second selective catalytic reduction assembly 75 is high at this time, and the emission requirement can be met, the three-way valve 1 is controlled to open the bypass branch 21 to bypass the first selective catalytic reduction assembly 72, the first-stage urea injection device 51 stops injecting urea, and the exhaust gas after the vortex is injected by the second-stage urea injection device 52 only through the main flow passage of the second diesel oxidation catalytic converter (DOC) 73+ the particulate trap (DPF) 74+ the second selective catalytic reduction assembly (SCR) 75/the Ammonia Slip Catalyst (ASC) 76; when the temperature of the second selective catalytic reduction assembly 75 is less than the first set temperature threshold TH, the three-way valve 1 is controlled to close the bypass branch 21 to release the bypass of the first selective catalytic reduction assembly 72, and the first-stage urea injection device 51 and the second-stage urea injection device 52 are controlled to be opened.

In a specific embodiment, when the first diesel oxidation catalytic converter 77 is provided between the electric heating device 71 and the first selective catalytic reduction assembly 72 and it is required to start the engine, and the electric heating device 71 is started, the first diesel oxidation catalytic converter 77 is controlled to inject hydrocarbons.

In one specific embodiment, when the temperature of the second selective catalytic reduction assembly 75 is greater than the second set temperature threshold TL and less than the first set temperature threshold TH, the first stage urea injection device 51 is controlled to reduce the injection amount to shift the task of injecting urea to the second stage urea injection device 52, so as to maintain the total injection amount substantially constant and avoid urea waste.

In one particular embodiment, when the temperature of the second selective catalytic reduction assembly 75 is greater than the second set temperature threshold TL and less than the first set temperature threshold TH, the injection amount of the first stage urea injection device 51 is gradually decreased as the temperature of the second selective catalytic reduction assembly 75 increases. As shown in fig. 4, the abscissa is the temperature of the second selective catalytic reduction assembly 75, the ordinate is the value of the coefficient k, the actual injection amount of the first stage urea injection device 51 decreases by multiplying the maximum injection amount by the coefficient k, and k in fig. 4 gradually and uniformly decreases with the temperature of the second selective catalytic reduction assembly 75, so as to avoid the sudden change of the urea injection amount, which causes the instability of the system due to too much or too little urea injection. T2 in fig. 4 represents the light-off temperature of the second selective catalytic reduction assembly 75.

Based on the same inventive concept, the embodiment of the application also provides a vehicle which comprises the urea double-injection after-treatment system of the previous embodiment, and the effect is referred to the urea double-injection after-treatment system.

It will be apparent to those skilled in the art that various changes and modifications may be made in the embodiments of the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A control method of a urea dual injection aftertreatment system, the system comprising: the system comprises a first selective catalytic reduction assembly and a second selective catalytic reduction assembly which are sequentially connected in series, wherein the first selective catalytic reduction assembly is a close-coupled selective catalytic reduction assembly, and the second selective catalytic reduction assembly is positioned at the downstream of the first selective catalytic reduction assembly; the first selective catalytic reduction component is also connected with a bypass branch in parallel, and a three-way valve is arranged at the upstream junction of the bypass branch and the branch where the first selective catalytic reduction component is positioned; a first-stage urea injection device is arranged at the upstream of the first selective catalytic reduction assembly, and a second-stage urea injection device is arranged at the upstream of the second selective catalytic reduction assembly; an electric heating device is coupled to the upstream of the first selective catalytic reduction component;

the control method comprises the following steps:

when the engine needs to be started, if the temperature of the second selective catalytic reduction assembly is lower than the ignition temperature, controlling the three-way valve to close the bypass branch so as to remove the bypass of the first selective catalytic reduction assembly, starting the electric heating device and controlling the first-stage urea injection device to inject; if the temperature of the second selective catalytic reduction assembly is greater than or equal to the ignition temperature, controlling the three-way valve to open the bypass branch so as to bypass the first selective catalytic reduction assembly and enable the second-stage urea injection device to inject;

when the engine is started and the temperature of the second selective catalytic reduction assembly is larger than or equal to a first set temperature threshold value, controlling the three-way valve to open the bypass branch so as to bypass the first selective catalytic reduction assembly and enable the second-stage urea injection device to inject, and controlling the three-way valve to close the bypass branch so as to remove the bypass of the first selective catalytic reduction assembly and enable the first-stage urea injection device and the second-stage urea injection device to be opened when the temperature of the second selective catalytic reduction assembly is smaller than the first set temperature threshold value.

2. The control method according to claim 1, wherein the support of the first selective catalytic reduction assembly is a metal support or a ceramic support.

3. The control method of claim 2, wherein the surface of the metal support is coated with a selective catalytic reduction catalyst.

4. The control method of claim 1, wherein a first diesel oxidation catalytic converter is disposed between the electrical heating device and the first selective catalytic reduction assembly, and the first diesel oxidation catalytic converter is a close-coupled diesel oxidation catalytic converter.

5. The control method according to claim 4, characterized in that the carrier of the first diesel oxidation catalytic converter is a metal carrier or a ceramic carrier.

6. The control method according to claim 1, characterized in that a second diesel oxidation catalytic converter and a particulate trap are connected in series in the gas flow direction between the first selective catalytic reduction assembly and the second stage urea injection device in sequence;

and an ammonia slip catalyst is coupled downstream of the second selective catalytic reduction assembly.

7. The control method according to any one of claims 1 to 6, characterized in that when a first diesel oxidation catalytic converter is provided between the electric heating device and the first selective catalytic reduction assembly and it is necessary to start the engine and start the electric heating device, the first diesel oxidation catalytic converter is controlled to inject hydrocarbons.

8. The control method according to any one of claims 1 to 6, characterized in that the first stage urea injection device is caused to reduce the injection amount when the temperature of the second selective catalytic reduction assembly is greater than a second set temperature threshold and less than a first set temperature threshold.

9. The control method according to claim 8, characterized in that when the temperature of the second selective catalytic reduction assembly is greater than a second set temperature threshold and less than a first set temperature threshold, the injection amount of the first stage urea injection device is gradually reduced as the temperature of the second selective catalytic reduction assembly increases.