CN113356988B - Online diagnosis method for Urea crystallization risk of Urea-SCR system - Google Patents
Online diagnosis method for Urea crystallization risk of Urea-SCR system Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M15/00—Testing of engines
- G01M15/04—Testing internal-combustion engines
- G01M15/10—Testing internal-combustion engines by monitoring exhaust gases or combustion flame
- G01M15/102—Testing internal-combustion engines by monitoring exhaust gases or combustion flame by monitoring exhaust gases
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
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Abstract
An online diagnosis method for Urea crystallization risk of a Urea-SCR system comprises the following steps: (1) calculating the urea injection amount, the exhaust mass flow, the SCR inlet temperature and the urea crystallization risk state of all working condition points to obtain a urea crystallization risk factor threshold valueR C (ii) a (2) When actual urea crystallization risk factorR≥R C At the moment, the system has urea crystallization risk, and a urea crystallization risk duration counter starts to calculate the equivalent value of the crystallization risk durationT D (ii) a (3) Actual urea crystallization risk factorR＜80%R C When is not in use, andT C when the temperature is higher than 350 ℃, the system enters a crystallization elimination state, and the equivalent value of the urea crystallization risk duration counter to the crystallization risk elimination time is up toT R Calculating; (4) on-line diagnostic module toT D +T R The real-time accumulated value is used as a judgment basis of the risk level of the system, and when the accumulated value exceeds calibration limit values of different degrees, the system reports the crystallization risk levels of different degrees.
Description
Technical Field
The invention relates to an online diagnosis method for Urea crystallization risks of a Urea-SCR system, belonging to the technical field of motor vehicle emission control.
Background
The exhaust gas of the engine contains harmful substances (NO for short) such as nitrogen oxidesx) The main components of which are NO and NO2。NOxIs N in air sucked into cylinder by engine2And O2Reaction products at elevated temperatures. Emission legislation on NO of enginesxThe amount of emission of (c) is limited and limits of various degrees are specified.
Urea selective catalytic reduction technology (Urea-SCR technology for short) for controlling NO by enginexThe main technology of the discharge is that,the most common forms of this technique are: the ammonia gas is generated by decomposing the urea aqueous solution, and the ammonia gas and NO are reacted under the action of an SCR (selective catalytic reduction) catalystxThe selective catalytic reduction reaction is carried out to generate nitrogen and water which are then discharged into the atmosphere, and different urea amounts are sprayed into the exhaust gas of the diesel engine to carry out NO treatmentxThe discharge amount of the fuel is effectively controlled.
Fig. 1 is a schematic structural diagram of a conventional Urea-SCR system, Urea crystals (also called Urea deposits) are a common problem in the practical application process of the Urea-SCR system, and accumulation of the Urea crystals can cause exhaust back pressure to rise, so that the working efficiency of a catalyst is reduced, the economical efficiency and the emission characteristic of an engine are poor, and in severe cases, an exhaust pipe can even be blocked, so that the engine cannot normally work.
No corresponding sensor or detection device on the current vehicle can detect the occurrence of urea crystallization, the problem of urea crystallization is usually discovered only after the urea crystallization degree seriously affects the dynamic property or emission property of the vehicle, and the engine runs for a long time under the condition of poor economy and emission property.
Disclosure of Invention
The invention aims to monitor the risk of Urea crystallization in the initial stage of Urea crystallization and realize the aim of preventing the risk of Urea crystallization of a Urea-SCR system.
The technical scheme of the invention is as follows, and the method for diagnosing the Urea crystallization risk of the Urea-SCR system on line comprises the following steps:
(1) obtaining a crystallization risk distribution diagram comprising a high risk area, a critical area and a low risk area through a bench urea crystallization risk test of a target engine-aftertreatment system, and obtaining a urea crystallization risk factor threshold value R based on the slope of a critical state curve in the diagramC(ii) a The ratio of urea injection quantity to exhaust mass flow is used as the ordinate axis of the crystallization risk distribution diagram, and the SCR inlet temperature is used as the abscissa axis of the crystallization risk distribution diagram.
(2) And a crystallization risk online diagnosis module arranged in the system acquires information such as engine speed, torque, exhaust mass flow, SCR inlet NOx concentration, SCR inlet temperature, SCR outlet temperature, urea injection amount and the like in the ECU as calculation input of an actual urea crystallization risk factor.
(3) Defining an actual urea crystallization risk factor
Wherein QUIs the urea injection quantity, mfexhExhaust gas mass flow, TCIs the SCR inlet temperature; after confirmation of the crystallization risk profile, C can be obtained1Value, C2The value and the crystallization risk factor in the critical state can be used as the judgment threshold value R of the critical state of the urea crystallizationC。
(4) Under the target working condition, the actual urea crystallization risk factor R is larger than the threshold value R of the urea crystallization risk factorCAnd (4) considering that the Urea-SCR system has Urea crystallization risk at the moment, and starting the Urea crystallization risk duration counter.
(5) When the actual urea crystallization risk factor is larger than the threshold value R of the urea crystallization risk factorCWhen the actual urea crystallization risk factor is larger than the urea crystallization risk factor threshold value R, determining the equivalent coefficient of the crystallization risk duration time based on the SCR inlet temperature, the actual urea crystallization risk factor, the urea crystallization risk factor threshold value and the injection amountCDetermining a crystallization risk duration equivalent coefficient based on the SCR inlet temperature, the actual urea crystallization risk factor, the urea crystallization risk factor threshold and the injection amount when the actual urea crystallization risk factor is greater than the urea crystallization risk factor threshold RCDetermining a crystallization risk duration equivalent coefficient f based on the SCR inlet temperature, the actual urea crystallization risk factor, the urea crystallization risk factor threshold and the injection amountD：
fD＝QU(R-RC)/(TC+C3)；
Wherein C is3The crystallization temperature correction coefficient.
Calculating the crystallization risk duration equivalence by the following formula:
TD＝fD×tD
wherein, tDIs the duration of time at risk of crystallization; t isDThe value will participate as an addend in the integration operation of the risk duration counter.
(6) When the actual urea crystallization risk factor is smaller than the threshold value R of the urea crystallization risk factorCDetermining a crystallization risk elimination time equivalent coefficient f based on the SCR inlet temperature, the actual urea crystallization risk factor, the urea crystallization risk factor threshold and the injection amountR：
fR＝QU(R-RC)*(TC-350)*C4
Wherein, C4To eliminate the temperature correction coefficient.
Calculating the crystallization risk elimination time equivalent T by the following equationR：
TR＝fR×tR；
Wherein, tRFor the time in the crystallization risk eliminated state, R is smaller than R in the crystallization risk eliminated stateCTherefore, T isRThe value is negative and will also participate as an addend in the integration operation of the risk duration counter.
(7) The risk duration counter will continue to calculate the crystallization risk duration equivalent TDAnd crystallization risk elimination time equivalent TRIf the current state of the SCR system is not in the urea crystallization forming state or the urea crystallization eliminating state, the SCR system is considered to be in the crystallization stable state, and the crystallization risk degree integral value is not changed any more.
(8) The value of the risk duration counter is greater than T1, giving a diagnostic result: low risk of urea crystallization, T1 being a low risk duration threshold; the value of the risk duration counter is greater than T2, giving a diagnostic result: moderate risk of urea crystallization, T2 being a medium risk duration threshold; the value of the risk duration counter is greater than T3, giving a diagnostic result: high risk of urea crystallization, T3 is a high risk duration threshold.
The invention has the advantages that the invention provides a method for quantitatively evaluating the Urea crystallization risk state of a target Urea-SCR system, the method comprises the steps of calculating an actual Urea crystallization risk factor on line and comparing the actual Urea crystallization risk factor with a Urea crystallization risk factor threshold value to obtain a duration equivalent value of the Urea-SCR system running in a crystallization risk state and a duration equivalent value of the Urea-SCR system running in a crystallization elimination state, by continuously outputting the Urea crystallization risk state of the Urea-SCR system through the real-time accumulation of the 2 equivalent values, the risk is helped to be discovered at the early stage of the Urea crystallization tendency of the system, and can give out crystallization risk diagnosis results of different grades and degrees, so that a vehicle user can know the urea crystallization risk grade of the aftertreatment system in real time, and corresponding measures can be taken to avoid the Urea crystallization state of the Urea-SCR system for a long time.
The urea crystallization critical state test is carried out by using the engine-aftertreatment system consistent with a target vehicle model, the crystallization risk factor threshold is obtained based on the crystallization risk distribution diagram of the target engine-aftertreatment system obtained by the test, good crystallization risk correlation is achieved, and meanwhile the urea crystallization risk factor threshold obtained based on the test can be used for all vehicle models of the engine-aftertreatment family and has good universality.
Drawings
FIG. 1 is a schematic structural diagram of a prior Urea-SCR system;
FIG. 2 is a method of obtaining a threshold urea crystallization risk factor;
FIG. 3 is a functional flow chart of the on-line diagnosis of the risk of urea crystallization;
FIG. 4 is a diagram of the operating principle of a urea crystallization risk duration integrator;
FIG. 5 is a urea crystallization risk level determination module.
Detailed Description
The functional flow chart of the embodiment for online diagnosis of the risk of Urea crystallization of the Urea-SCR system is shown in FIG. 3.
After the Urea-SCR system starts to work, a crystallization risk online diagnosis module arranged in the system collects Urea injection quantity through ECU data flow,Calculating an actual urea crystallization risk factor R according to signals such as exhaust mass flow, SCR inlet temperature and the like; the actual risk factor R of urea crystallization and the threshold value R of the risk factor of urea crystallizationCBy comparison, if the actual urea crystallization risk factor R is greater than the urea crystallization risk factor threshold RCThen the calculation of the crystallization risk duration equivalence T is startedD(ii) a At the moment, the crystallization risk duration integrator also starts to work and outputs a crystallization risk degree integral value; when the actual urea crystallization risk factor R is larger than the threshold value R of the urea crystallization risk factorCIn this state, the output crystallization risk degree integral value increases.
If the actual urea crystallization risk factor R is smaller than the threshold value R of the urea crystallization risk factorCThen, calculation of the crystallization risk elimination time equivalent T is startedRAt this time, the crystallization risk degree integral value output from the crystallization risk duration integrator will decrease; if the calculation result of the crystallization risk degree integral value is less than 0, the external output is 0, and the condition that the output is a negative value is not allowed to occur; the diagnosis module outputs urea crystallization risk results of different degrees to the outside according to different output crystallization risk degree integral values.
The method for obtaining the threshold value of the risk factor of urea crystallization in the present example is shown in fig. 2.
Building an engine-aftertreatment system rack, and performing a series of urea crystallization critical state confirmation tests of typical working condition points under different urea injection quantities; by completing the test and based on the three urea crystallization risk state definitions provided by the invention, the urea crystallization critical state confirmation test result carried out at each working condition point is visually confirmed, so that each working condition point can be ensured to observe at least three urea crystallization risk states of no risk, low risk and high risk; summarizing working condition parameters and urea crystallization risk state results of all test working condition points, determining the position of a point by taking a temperature value of each working condition point as an abscissa and a ratio (beta value) of urea injection quantity to exhaust mass flow as an ordinate, and coloring the point by taking a color corresponding to a final evaluation result of the test point; after all the test working condition points are colored, the boundary of the state transition region is fitted by a straight line or a curve, and finally the coordinate graph can be divided into a high-risk region (orange-red color region), a critical region (yellow color region) and a low-risk region (green color region), wherein the central line of the critical region is a critical state curve, the intercept of the critical state curve and the X axis is C, and the slope of the critical state curve is a critical crystallization factor.
Fig. 4 shows the principle of operation of the urea crystallization risk duration integrator in this example. The present example will count the formation and elimination states of urea crystals separately to obtain a continuous and dynamic diagnosis result of risk of urea crystals.
Collecting signals such as urea injection quantity, exhaust mass flow and SCR inlet temperature through ECU data flow to calculate actual urea crystallization risk factors; the actual risk factor R of urea crystallization and the threshold value R of the risk factor of urea crystallizationCBy comparison, if the actual urea crystallization risk factor R is greater than the urea crystallization risk factor threshold RCConsidering the system in the state of risk of urea crystallization, immediately starting to calculate the equivalent value T of the duration of the risk of crystallizationDAnd simultaneously, the crystallization risk duration integrator starts to work and outputs a crystallization risk degree integral value.
The crystallization risk duration equivalence factor is determined by the following formula: f. ofD＝QU(R-RC)/(TC+C3)。
Equivalent coefficient f of crystallization risk durationDThe molecular formula is formed by two parts, wherein the molecular formula is that an actual urea crystallization risk factor R subtracts a crystallization risk factor threshold value RCMultiplied by the urea injection quantity QUReflecting the positive correlation promotion effect of the urea injection degree exceeding the crystallization critical state and the absolute injection quantity on the crystallization risk; the denominator is the sum of the SCR inlet temperature and the temperature correction constant, reflecting the objective rule that the risk of urea crystallization decreases with the increase of the SCR system temperature.
Equivalent coefficient f of crystallization risk durationDAfter confirmation, multiplying the duration in the urea crystallization risk state to obtain the crystallization risk duration equivalent value TDI.e. TD＝fD×tD；TDAs input to the crystallization risk duration integrator, an integration operation is performed once per secondCalculating and outputting a result used for diagnosing the urea crystallization risk degree of the SCR system, wherein the result is called a crystallization risk degree integral value;
when the system is not in a state of risk for urea crystallization, the output value of the integrator stops increasing. Judging the system state again, and if the SCR inlet temperature is higher than 350 ℃ and the actual crystallization risk factor is lower than the crystallization risk factor threshold of 80%, determining that the system state enters a urea crystallization elimination state; at the moment, the calculation module also calculates the equivalent coefficient of the crystallization risk elimination time at first, the equivalent coefficient of the crystallization risk elimination time is formed by multiplying 3 factors, the factor 1 is the difference of the actual crystallization risk factor minus the threshold value of the crystallization risk factor and then is multiplied by the actual urea injection amount, and the degree of deviation of the urea injection amount from the crystallization critical state is reflected; the factor 2 is the difference between the SCR inlet temperature and the crystallization elimination starting temperature (350 ℃), and reflects the positive promotion effect of the temperature on the elimination of crystallization; the factor 3 is a crystal elimination equivalent process correction coefficient which is related to temperature and reflects the change rule of the urea crystal elimination rate under different temperature conditions;
in the urea crystallization elimination state, the crystallization risk elimination time equivalent value is used as the input of the crystallization risk duration integrator, and the integration operation is performed once per second, but the output result of the integrator is gradually reduced in the state because the value obtained by subtracting the crystallization risk factor threshold value from the actual crystallization risk factor is negative;
and if the current SCR system state is not in the urea crystal forming state or the urea crystal eliminating state, the current SCR system state is considered to be in the crystal stable state, and the crystallization risk degree integral value is not changed any more.
FIG. 5 shows the working principle of the urea crystallization risk level determination module according to this embodiment;
the system grades the urea crystallization risk grade where the SCR system is located at present according to the crystallization risk degree integral value output by the crystallization risk duration integrator, the operation of the integrator is a continuous process, the output value of the crystallization risk grade is continuous, and under the normal condition, the diagnosis result of the diagnosis system is as follows: and when the system is in a urea crystallization risk state and the crystallization state is continuously upgraded, the diagnostic system sequentially reports three diagnostic results of different levels of low crystallization risk, medium crystallization risk and high crystallization risk according to three risk judgment thresholds T1, T2 and T3, and adopts gradually-upgraded warning measures to ensure that a driver knows the existence of the crystallization risk.
Claims (6)
1. An online diagnosis method for Urea crystallization risk of a Urea-SCR system is characterized by comprising the following steps:
(1) obtaining a urea crystallization risk distribution diagram through a bench urea crystallization risk test of a target engine-aftertreatment system, and obtaining a urea crystallization risk factor threshold value R from the slope of a critical state curve in the urea crystallization risk distribution diagramC；
(2) The online crystallization risk diagnosis module of the Urea-SCR system needs to acquire information of engine speed, torque, exhaust mass flow, SCR inlet NOx concentration, SCR inlet temperature, SCR outlet temperature and Urea injection amount in an ECU to complete diagnosis and calculate an actual Urea crystallization risk factor R;
(3) when the actual urea crystallization risk factor R is larger than the threshold value R of the urea crystallization risk factorCWhen the Urea crystallization risk exists in the Urea-SCR system, the Urea crystallization risk duration counter starts to work;
(4) after the urea crystallization risk duration counter works, determining a crystallization risk duration equivalent coefficient f based on SCR inlet temperature, actual urea crystallization risk factor, urea crystallization risk factor threshold value and injection quantityDAnd further calculating to obtain the equivalent value T of the crystallization risk durationD；
(5) When the actual urea crystallization risk factor R is smaller than the threshold value R of the urea crystallization risk factorCIf the SCR inlet temperature is higher than 350 ℃ and the actual urea crystallization risk factor is lower than the urea crystallization risk factor threshold value of 80%, the SCR enters a urea crystallization elimination state;
(6) after the Urea-SCR system is detected to be in the crystallization elimination state, the online diagnosis module is used for diagnosing the Urea precipitation rate based on the SCR inlet temperature, the actual Urea crystallization risk factor and the Urea knotCrystallization risk factor threshold value and injection amount determination crystallization risk elimination time equivalent coefficient fRAnd further calculating to obtain a crystallization risk elimination time equivalent value TR；
(7) The risk duration counter will continue to calculate the crystallization risk duration equivalent TDAnd crystallization risk elimination time equivalent TRReal-time cumulative value of; if the current SCR system state is not in a urea crystallization forming state or a urea crystallization eliminating state, the SCR system state is considered to be in a crystallization stable state, and the crystallization risk degree integral value is not changed any more;
(8) when the value of the risk duration counter is greater than T1, a diagnostic result is given: low risk of urea crystallization; when the value of the risk duration counter is greater than T2, a diagnostic result is given: moderate risk of urea crystallization; when the value of the risk duration counter is greater than T3, a diagnostic result is given: high risk of urea crystallization.
2. The method for online diagnosis of Urea crystallization risk in Urea-SCR system according to claim 1, characterized in that the actual Urea crystallization risk factor R is calculated as follows:
wherein QUIs the urea injection quantity; mf (m) ofexhIs the exhaust mass flow rate; t isCIs SCR inlet temperature, C1As a correction factor for urea injection concentration, C2Is an SCR inlet temperature correction factor;
C1value, C2The values are respectively confirmed by the intercept of the critical state curve in the crystallization risk distribution diagram on the ordinate axis and the abscissa axis.
3. The method for online diagnosis of Urea crystallization risk of Urea-SCR system according to claim 1, characterized in that the equivalent coefficient f of crystallization risk durationDThe calculation method of (2) is as follows:
fD＝QU(R-RC)/(TC+C3)；
wherein Q isUIs the urea injection quantity; r is an actual urea crystallization risk factor; rCIs a urea crystallization risk factor threshold; t is a unit ofCIs the SCR inlet temperature; c3The crystallization temperature correction coefficient.
4. The method for online diagnosis of Urea crystallization risk in Urea-SCR system according to claim 1, characterized in that the crystallization risk duration equivalence TDThe calculation method of (2) is as follows:
TD＝fD×tD
wherein t isDIs the duration of time at risk of crystallization; t isDThe value will participate as an addend in the integration operation of the risk duration counter.
5. The method for diagnosing Urea crystallization risk of Urea-SCR system according to claim 1, characterized in that the crystallization risk elimination time equivalence coefficient fRThe calculation method of (2) is as follows:
fR＝QU(R-RC)*(TC-350)*C4
wherein QUIs the urea injection quantity; r is an actual urea crystallization risk factor; rCIs a urea crystallization risk factor threshold; t is a unit ofCIs the SCR inlet temperature; c4To eliminate the temperature correction coefficient.
6. The method for online diagnosis of Urea crystallization risk in Urea-SCR system according to claim 1, characterized in that the crystallization risk elimination time equivalence TRThe calculation method of (2) is as follows:
TR＝fR×tR；
wherein t isRFor the time in the crystallization risk eliminated state, R is smaller than R in the crystallization risk eliminated stateCTherefore, T isRA negative value will also be considered as beingThe addend participates in the integration operation of the risk duration counter.
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