Control method for rapidly reducing cold start nox emissions from a diesel engine

Abstract

The application provides a control method for quickly reducing NOx emission of a diesel engine during cold start, comprising a first control method and a second control method; the first control method and the second control method are simultaneously performed; when the engine is in a cold start state, the first control method is used for controlling an electric heater arranged upstream of a DOC / DPF in an exhaust pipeline to heat, and the second control method is used for controlling an electric heating liquid inlet pipe, a urea pump, an electric heating injection pipe and an electric heating nozzle to heat. The application can make an SCR aftertreatment device in an exhaust aftertreatment system enter a working state as soon as possible, so as to reduce NOx emission in diesel engine exhaust during cold start.

Description

Technical Field

[0001] This invention relates to a control method, and more particularly to a control method for rapidly reducing NOx emissions during cold starts of diesel engines. Background Technology

[0002] With increasingly stringent emission regulations, the China VII emission standard is expected to further reduce the emission limits for NOx, PM, and PN pollutants compared to the China VI standard. Currently, the China VI emission standard for heavy-duty vehicles uses the WHSC and WHTC cycles for bench emissions testing, with NOx emission limits of 0.4 g / kWh and 0.46 g / kWh, respectively. The WHTC cycle is divided into a cold cycle and a hot cycle, with weights of 14% and 86%, respectively. It is anticipated that the NOx emission limit in the China VII standard will be further tightened to 0.20 g / kWh, a reduction of approximately 50% compared to the China VI emission standard.

[0003] NOx emissions from cold-start WHTC cycle engines are the most difficult to control. To meet regulatory requirements, it is necessary to reduce NOx emissions during cold starts of diesel engines as quickly as possible. The most effective way to reduce NOx emissions is to get the SCR device into working condition as early as possible.

[0004] Some of the terms used in this application are as follows:

[0005] DOC: Oxidation Catalyst;

[0006] DPF: Particulate Filter;

[0007] SCR: Selective Catalytic Reduction;

[0008] ASC: Ammonia escape catalyst. Summary of the Invention

[0009] To address at least one technical problem in the prior art, embodiments of the present invention provide a control method for rapidly reducing NOx emissions during cold starts of diesel engines. This method enables the SCR aftertreatment device in the exhaust gas aftertreatment system to quickly enter working condition during a cold start, thereby reducing NOx emissions from the diesel engine exhaust. To achieve the above technical objective, the technical solution adopted by embodiments of the present invention is as follows:

[0010] This invention provides a control method for rapidly reducing NOx emissions during cold starts of diesel engines, including a first control method and a second control method; the first control method and the second control method are performed simultaneously; during engine cold starts, the first control method is used to control an electric heater installed upstream of the DOC / DPF on the exhaust pipe to perform heating, and the second control method is used to control the electric heating inlet pipe, urea pump, electric heating injection pipe and electric heating nozzle to perform heating.

[0011] Furthermore, the first control method includes:

[0012] Step S101: Obtain engine coolant temperature and ambient temperature. When engine coolant temperature is less than cold start coolant temperature threshold and ambient temperature is greater than set ambient temperature threshold, determine that the engine is in cold start state.

[0013] Step S102: Check if the battery voltage is within the normal range. If yes, proceed to the next step; otherwise, exit the first control method.

[0014] Step S103: Control the electric heater to heat at 100% drive duty cycle;

[0015] Step S104: Determine whether the exhaust temperature T2 downstream of the electric heater, the exhaust temperature T3 upstream of the SCR, and the exhaust temperature T4 downstream of the SCR are all greater than the first temperature threshold; if so, proceed to the next step; otherwise, return to step S103.

[0016] Step S105: Control the electric heater to heat with the calculated drive duty cycle;

[0017] Step S106: Determine whether the exhaust temperature T2 downstream of the electric heater, the exhaust temperature T3 upstream of the SCR, and the exhaust temperature T4 downstream of the SCR are all greater than the second temperature threshold; if so, control the electric heater to stop heating; otherwise, return to step S105.

[0018] The second temperature threshold is greater than the first temperature threshold.

[0019] Furthermore, the ambient temperature threshold is set to -10℃.

[0020] Furthermore, the first temperature threshold is set to 220°C.

[0021] Furthermore, the second temperature threshold is set to 250°C.

[0022] Further, step S105 includes:

[0023] Step S1051: Calculate the difference between the second temperature threshold and the SCR average temperature; the SCR average temperature is the average of the upstream exhaust temperature T3 and the downstream exhaust temperature T4 of the SCR.

[0024] Step S1052: Multiply the difference by the exhaust specific heat capacity and exhaust mass flow rate to calculate the energy of temperature increase per unit time;

[0025] Step S1053: Divide the energy required for heating per unit time by the maximum power of the electric heater to obtain the required drive duty cycle of the electric heater, and then multiply by the voltage correction coefficient to obtain the calculated drive duty cycle.

[0026] Furthermore, the second control method includes:

[0027] Step S201: Obtain the upstream exhaust temperature T3 of the SCR;

[0028] Step S202: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the urea pump pressure build-up temperature threshold; if so, proceed to the next step; otherwise, return to the previous step.

[0029] Step S203: The urea pump builds up pressure. After the urea pump has built up pressure, proceed to the next step.

[0030] Step S204: Drive the electrically heated liquid inlet pipe, urea pump, electrically heated injection pipe and electrically heated nozzle to perform heating according to the set drive duty cycle;

[0031] Step S205: Determine whether the urea temperature inside the electric heating nozzle has reached the preset urea temperature. If yes, proceed to the next step; otherwise, return to the previous step.

[0032] Step S206: Control the electric heating inlet pipe, urea pump, and electric heating injection pipe to stop heating;

[0033] Step S207: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the urea injection temperature. If so, it means that urea can be injected. Control the electric heating urea pump to inject and proceed to the next step. Otherwise, return to the previous step.

[0034] Step S208: Based on the exhaust mass flow rate and urea injection quantity, consult the MAP table of electric heating nozzle drive duty cycle to determine the drive duty cycle of the electric heating nozzle, and drive the electric heating nozzle to perform heating using the drive duty cycle obtained from the MAP table.

[0035] Step S209: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the target temperature threshold; if so, proceed to the next step; otherwise, return to the previous step.

[0036] Step S210: Control the electric heating nozzle to stop heating.

[0037] Furthermore, the preset urea temperature is set to 93℃~98℃.

[0038] Furthermore, the urea spraying temperature is set between 150℃ and 155℃.

[0039] Furthermore, the target temperature threshold is set between 222℃ and 230℃.

[0040] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows: the present invention enables the SCR aftertreatment device in the exhaust gas aftertreatment system to enter the working state as soon as possible during the cold start of the diesel engine, so as to reduce NOx emissions in the diesel engine exhaust gas during cold start. The present invention simultaneously controls the electric heater to heat the exhaust gas, and controls the electric heating inlet pipe, urea pump, electric heating injection pipe, and electric heating nozzle to heat the urea during the cold start of the diesel engine. Even in the cold start state, urea can be injected in time and decomposed into ammonia gas, effectively reducing NOx emissions. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the exhaust gas aftertreatment system in an embodiment of the present invention.

[0042] Figure 2 This is a flowchart of the first control method in an embodiment of the present invention.

[0043] Figure 3 This is a flowchart of the second control method in an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] In the description of the embodiments of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances.

[0047] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] like Figure 1 As shown, an exhaust gas aftertreatment system includes an electric heater, a DOC / DPF, and an SCR / ASC arranged sequentially along the exhaust pipe; a mixer is installed at the upstream inlet of the SCR; a urea tank is connected to a urea pump via an electrically heated inlet pipe, the urea pump having a heating function, and the urea pump is connected to an electrically heated nozzle via an electrically heated injection pipe; the electrically heated nozzle is connected to the mixer; the electrically heated inlet pipe, the urea pump, the electrically heated injection pipe, and the electrically heated nozzle are all controlled by the aftertreatment control unit; a liquid temperature sensor is installed at the electrically heated nozzle;

[0049] The exhaust gas aftertreatment system also includes a first temperature sensor located upstream of the electric heater, a second temperature sensor located downstream of the electric heater (between the electric heater and the DOC / DPF), a third temperature sensor located upstream of the SCR (between the SCR / ASC and the DOC / DPF), and a fourth temperature sensor located downstream of the SCR (between the SCR / ASC). The first temperature sensor is used to send the exhaust temperature T1 upstream of the electric heater to the aftertreatment control unit, the second temperature sensor is used to send the exhaust temperature T2 downstream of the electric heater to the aftertreatment control unit, the third temperature sensor is used to send the exhaust temperature T3 upstream of the SCR to the aftertreatment control unit, and the fourth temperature sensor is used to send the exhaust temperature T4 downstream of the SCR to the aftertreatment control unit.

[0050] The exhaust aftertreatment system also includes a differential pressure sensor, with its two ends connected to the upstream and downstream ends of the DOC / DPF, respectively. The differential pressure sensor is not closely related to the control method of this application, and its description is omitted.

[0051] This invention proposes a control method for rapidly reducing NOx emissions during cold starts of diesel engines, comprising a first control method and a second control method; the first and second control methods are performed simultaneously; during engine cold starts, the first control method controls an electric heater installed upstream of the DOC / DPF in the exhaust pipe to perform heating, and the second control method controls an electric heating inlet pipe, a urea pump, an electric heating injection pipe, and an electric heating nozzle to perform heating;

[0052] like Figure 2 As shown, the first control method includes:

[0053] Step S101: Obtain engine coolant temperature and ambient temperature. When engine coolant temperature is less than cold start coolant temperature threshold and ambient temperature is greater than set ambient temperature threshold, determine that the engine is in cold start state.

[0054] Since urea solution will freeze at or below -11℃, the ambient temperature threshold is set to -10℃. When the ambient temperature is ≤ the set ambient temperature threshold, the urea tank needs to be thawed before the first control method can be implemented.

[0055] Step S102: Check if the battery voltage is within the normal range. If yes, proceed to the next step; otherwise, exit the first control method.

[0056] Step S103: Control the electric heater to heat at 100% drive duty cycle;

[0057] That is, initially control the electric heater to operate at full power.

[0058] Step S104: Determine whether the exhaust temperature T2 downstream of the electric heater, the exhaust temperature T3 upstream of the SCR, and the exhaust temperature T4 downstream of the SCR are all greater than the first temperature threshold; if so, proceed to the next step; otherwise, return to step S103.

[0059] The first temperature threshold is set to 220℃;

[0060] Step S105: Control the electric heater to heat with the calculated drive duty cycle;

[0061] Step S106: Determine whether the exhaust temperature T2 downstream of the electric heater, the exhaust temperature T3 upstream of the SCR, and the exhaust temperature T4 downstream of the SCR are all greater than the second temperature threshold; if so, control the electric heater to stop heating; otherwise, return to step S105.

[0062] The second temperature threshold is set to 250℃;

[0063] Specifically, step S105 includes:

[0064] Step S1051: Calculate the difference between the second temperature threshold and the SCR average temperature; the SCR average temperature is the average of the upstream exhaust temperature T3 and the downstream exhaust temperature T4 of the SCR.

[0065] Step S1052: Multiply the difference by the exhaust specific heat capacity and exhaust mass flow rate to calculate the energy of temperature increase per unit time;

[0066] Step S1053: Divide the energy required for heating per unit time by the maximum power of the electric heater to obtain the required drive duty cycle of the electric heater, and then multiply by the voltage correction coefficient to obtain the calculated drive duty cycle.

[0067] like Figure 3 As shown, the second control method includes:

[0068] Step S201: Obtain the upstream exhaust temperature T3 of the SCR;

[0069] Step S202: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the urea pump pressure build-up temperature threshold; if so, proceed to the next step; otherwise, return to the previous step.

[0070] The pressure build-up temperature threshold for the urea pump is set between 100℃ and 105℃.

[0071] Step S203: The urea pump builds up pressure. After the urea pump has built up pressure, proceed to the next step.

[0072] Step S204: Drive the electrically heated liquid inlet pipe, urea pump, electrically heated injection pipe and electrically heated nozzle to perform heating according to the set drive duty cycle;

[0073] Step S205: Determine whether the urea temperature inside the electric heating nozzle has reached the preset urea temperature. If yes, proceed to the next step; otherwise, return to the previous step.

[0074] The preset urea temperature is 93℃~98℃;

[0075] Step S206: Control the electric heating inlet pipe, urea pump, and electric heating injection pipe to stop heating;

[0076] Step S207: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the urea injection temperature. If so, it means that urea can be injected. Control the electric heating urea pump to inject and proceed to the next step. Otherwise, return to the previous step.

[0077] The urea spraying temperature is set between 150℃ and 155℃.

[0078] Step S208: Based on the exhaust mass flow rate and urea injection quantity, consult the MAP table of electric heating nozzle drive duty cycle to determine the drive duty cycle of the electric heating nozzle, and drive the electric heating nozzle to perform heating using the drive duty cycle obtained from the MAP table.

[0079] Step S209: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the target temperature threshold; if so, proceed to the next step; otherwise, return to the previous step.

[0080] The target temperature threshold is set between 222℃ and 230℃;

[0081] Step S210: Control the electric heating nozzle to stop heating;

[0082] Once the diesel engine enters the hot cycle, the urea will no longer need to be heated.

[0083] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A control method for rapidly reducing NOx emissions during cold starts of diesel engines, characterized in that, It includes a first control method and a second control method; the first control method and the second control method are performed simultaneously; when the engine is in a cold start state, the first control method is used to control the electric heater installed upstream of DOC / DPF on the exhaust pipe to perform heating, and the second control method is used to control the electric heating inlet pipe, urea pump, electric heating injection pipe and electric heating nozzle to perform heating; The first control method includes: Step S101: Obtain engine coolant temperature and ambient temperature. When engine coolant temperature is less than cold start coolant temperature threshold and ambient temperature is greater than set ambient temperature threshold, determine that the engine is in cold start state. Step S102: Check if the battery voltage is within the normal range. If yes, proceed to the next step; otherwise, exit the first control method. Step S103: Control the electric heater to heat at 100% drive duty cycle; Step S104: Determine whether the exhaust temperature T2 downstream of the electric heater, the exhaust temperature T3 upstream of the SCR, and the exhaust temperature T4 downstream of the SCR are all greater than the first temperature threshold; if so, proceed to the next step; otherwise, return to step S103. Step S105: Control the electric heater to heat at a calculated drive duty cycle; Step S105 includes: Step S1051: Calculate the difference between the second temperature threshold and the SCR average temperature; the SCR average temperature is the average of the upstream exhaust temperature T3 and the downstream exhaust temperature T4 of the SCR. Step S1052: Multiply the difference by the exhaust specific heat capacity and exhaust mass flow rate to calculate the energy required for temperature rise per unit time; Step S1053: Divide the energy required for heating per unit time by the maximum power of the electric heater to obtain the required drive duty cycle of the electric heater, and then multiply by the voltage correction coefficient to obtain the calculated drive duty cycle. Step S106: Determine whether the exhaust temperature T2 downstream of the electric heater, the exhaust temperature T3 upstream of the SCR, and the exhaust temperature T4 downstream of the SCR are all greater than the second temperature threshold; if so, control the electric heater to stop heating; otherwise, return to step S105. The second temperature threshold is greater than the first temperature threshold; The ambient temperature threshold is set to -10℃; The first temperature threshold is set to 220℃; The second temperature threshold is set to 250℃; The second control method includes: Step S201: Obtain the upstream exhaust temperature T3 of the SCR; Step S202: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the urea pump pressure build-up temperature threshold; if so, proceed to the next step; otherwise, return to the previous step. Step S203: The urea pump builds up pressure. After the urea pump has built up pressure, proceed to the next step. Step S204: Drive the electrically heated liquid inlet pipe, urea pump, electrically heated injection pipe and electrically heated nozzle to perform heating according to the set drive duty cycle; Step S205: Determine whether the urea temperature inside the electric heating nozzle has reached the preset urea temperature. If yes, proceed to the next step; otherwise, return to the previous step. Step S206: Control the electric heating inlet pipe, urea pump, and electric heating injection pipe to stop heating; Step S207: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the urea injection temperature. If so, it means that urea can be injected. Control the electric heating urea pump to inject and proceed to the next step. Otherwise, return to the previous step. Step S208: Based on the exhaust mass flow rate and urea injection quantity, consult the MAP table of electric heating nozzle drive duty cycle to determine the drive duty cycle of the electric heating nozzle, and drive the electric heating nozzle to perform heating using the drive duty cycle obtained from the MAP table. Step S209: Determine whether the exhaust temperature T3 upstream of the SCR is greater than the target temperature threshold; if so, proceed to the next step; otherwise, return to the previous step. Step S210: Control the electric heating nozzle to stop heating; The preset urea temperature is 93℃~98℃; The urea spraying temperature is set between 150℃ and 155℃. The target temperature threshold is set between 222℃ and 230℃.

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