CN116085098A - Method for reducing crystallization of SCR (selective catalytic reduction) double-spraying system and vehicle - Google Patents

Method for reducing crystallization of SCR (selective catalytic reduction) double-spraying system and vehicle Download PDF

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CN116085098A
CN116085098A CN202310363381.9A CN202310363381A CN116085098A CN 116085098 A CN116085098 A CN 116085098A CN 202310363381 A CN202310363381 A CN 202310363381A CN 116085098 A CN116085098 A CN 116085098A
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urea
scr
heat
mass flow
engine
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CN116085098B (en
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耿磊
杨海龙
吕志华
贾德民
袁志玲
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Weichai Power Co Ltd
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Weichai Power Co Ltd
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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
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • 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
    • 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]
    • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
    • 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
    • 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
    • Y02T10/12—Improving ICE efficiencies

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)

Abstract

The invention belongs to the technical field of vehicles, and discloses a method for reducing crystallization of an SCR double-spray system and a vehicle, wherein the method for reducing crystallization of the SCR double-spray system comprises the following steps: s1: judging whether the engine meets the crystallization risk detection condition or not; if yes, S2 is carried out; s2: detecting crystallization risk, and judging whether the SCR double-spraying system has crystallization risk or not; if yes, S3 is carried out; if not, returning to the step S1; s3: the urea injection quantity of the rear-stage SCR is reduced by a first urea injection quantity; the urea injection amount of the pre-SCR increases by a second urea injection amount. The method for reducing the crystallization of the SCR double-spray system can reduce the risk of the crystallization of the rear-stage SCR without increasing the crystallization of the front-stage SCR, thereby reducing the crystallization of the SCR double-spray system.

Description

Method for reducing crystallization of SCR (selective catalytic reduction) double-spraying system and vehicle
Technical Field
The invention relates to the technical field of vehicles, in particular to a method for reducing crystallization of an SCR double-spray system and a vehicle.
Background
Diesel engine exhaust aftertreatmentThe system is provided with SCR (Selective Catalytic Reduction, selective catalytic reduction technology) which aims at the tail gas emission of diesel vehicles
Figure SMS_1
The SCR injection system comprises a urea nozzle and a mixer, wherein the urea nozzle injects urea into the mixer, the urea is mixed with tail gas in the mixer, and hydrolysis and pyrolysis reactions of the urea occur at high temperature to generate +.>
Figure SMS_2
Use of +.>
Figure SMS_3
Reduction->
Figure SMS_4
The tail gas is +.>
Figure SMS_5
Is reduced to->
Figure SMS_6
And->
Figure SMS_7
. Urea is sprayed into the mixer to easily form crystals, and excessive crystallization can lead to poor conversion efficiency of nitrogen oxides and easy escape of part of ammonia, thereby affecting the overall performance of the catalyst. In the prior art, crystallization is generally reduced by optimizing the structure of the mixer, however, structural design and experimental verification are required for optimizing the structure of the mixer, the period is long, the effect is general, and the mixing uniformity and the crystallization amount are difficult to control.
Disclosure of Invention
The invention aims to provide a method for reducing crystallization of an SCR double-spray system and a vehicle, which are used for solving the problems that crystallization is reduced by optimizing the structure of a mixer, the period is long, the effect is general, and the mixing uniformity and the crystallization amount are difficult to control in the prior art.
To achieve the purpose, the invention adopts the following technical scheme:
a method of reducing crystallization in an SCR dual spray system, comprising:
s1: judging whether the engine meets the crystallization risk detection condition or not;
if yes, S2 is carried out;
s2: detecting crystallization risk, and judging whether the SCR double-spraying system has crystallization risk or not;
if yes, S3 is carried out;
if not, returning to the step S1;
s3: the urea injection quantity of the rear-stage SCR is reduced by a first urea injection quantity; the urea injection amount of the pre-SCR increases by a second urea injection amount.
As a preferable mode of the method for reducing crystallization of the SCR dual-injection system, determining whether the engine meets the crystallization risk detection condition includes:
judging whether the engine is electrified or not, and judging whether the water temperature of the engine is greater than or equal to the set water temperature or not;
if yes, meeting crystallization risk detection conditions;
if not, the crystallization risk detection condition is not satisfied.
As a preferable scheme of the method for reducing crystallization of the SCR dual spray system, performing crystallization risk detection, determining whether the SCR dual spray system has crystallization risk includes:
s21: judging whether the duration time of the absolute value of the ratio of the difference value of the current engine speed and the previous engine speed to the previous engine speed is larger than or equal to the set time or not;
if yes, S22 is carried out;
if not, returning to the step S1;
s22: according to engine exhaust temperature
Figure SMS_8
Urea aqueous solution temperature->
Figure SMS_9
Engine exhaust gas mass flow->
Figure SMS_10
And urea solution mass flow->
Figure SMS_11
Calculating to obtain a heat ratio Q, wherein the heat ratio Q is the ratio of the heat in the exhaust gas of the engine to the heat required by urea decomposition; based on the current engine speed and the current engine torque, a caloric ratio limit value is obtained>
Figure SMS_12
；
S23: judging whether the heat quantity ratio Q is smaller than the heat quantity ratio limit value
Figure SMS_13
；
If yes, the crystallization risk exists in the SCR double-spraying system;
if not, the SCR double-spray system has no crystallization risk.
As a preferable scheme of the method for reducing the crystallization of the SCR double-injection system, the heat ratio limit value is obtained according to the current engine speed and the current engine torque
Figure SMS_14
Comprising the following steps:
obtaining a heat ratio limit value according to the current engine speed and the current engine torque through an engine speed-engine torque-heat ratio limit value relation table
Figure SMS_15
。
As a preferable scheme of the method for reducing the crystallization of the SCR double-injection system, the method is based on the exhaust temperature of the engine
Figure SMS_16
Urea aqueous solution temperature->
Figure SMS_17
Engine exhaust gas mass flow>
Figure SMS_18
And urea solution mass flow->
Figure SMS_19
The calculation of the heat quantity ratio Q includes:
by the formula:
Figure SMS_20
wherein Q is a heat ratio;
Figure SMS_24
Exhaust heat for the engine;
Figure SMS_26
Absorbing heat for liquid water;
Figure SMS_21
Absorbing heat for liquid water phase change;
Figure SMS_23
Absorbing heat for the gaseous water;
Figure SMS_25
Absorbing heat for urea solids;
Figure SMS_27
absorbing heat for urea melting;
Figure SMS_22
Absorbing heat for urea phase change;
Figure SMS_28
wherein->
Figure SMS_29
Is the exhaust gas mass flow;
Figure SMS_30
Is hair-growingSpecific heat of engine exhaust;
Figure SMS_31
Engine exhaust temperature;
Figure SMS_32
Is urea melting temperature;
Figure SMS_33
wherein->
Figure SMS_34
Is liquid water mass flow;
Figure SMS_35
Specific heat for liquid water;
Figure SMS_36
Is the boiling point of water;
Figure SMS_37
Is the temperature of the urea aqueous solution;
Figure SMS_38
wherein->
Figure SMS_39
Is the latent heat of vaporization of water;
Figure SMS_40
wherein->
Figure SMS_41
，
Figure SMS_42
Is the gaseous water mass flow;
Figure SMS_43
Specific heat for gaseous water;
Figure SMS_44
wherein->
Figure SMS_45
Is urea mass flow;
Figure SMS_46
Specific heat for solid urea;
Figure SMS_47
wherein->
Figure SMS_48
Is urea fusion heat;
Figure SMS_49
The molecular mass of urea;
Figure SMS_50
wherein->
Figure SMS_51
Is the vaporization latent heat of urea;
Figure SMS_52
wherein->
Figure SMS_53
Is the mass flow of urea solution; a is a constant;
the method comprises the steps of,
Figure SMS_54
wherein B is a constant; and calculating to obtain the heat quantity ratio Q.
As a preferable mode of the method for reducing the crystallization of the SCR double-spray system, the method is characterized by comprising the following steps of
Figure SMS_55
Obtaining the mass flow limit value of the urea solution>
Figure SMS_56
The method comprises the steps of carrying out a first treatment on the surface of the According to the mass flow rate m of urea solution 5 And urea solution mass flow limit->
Figure SMS_57
And obtaining a first urea injection quantity and a second urea injection quantity.
As a preferable scheme of the method for reducing the crystallization of the SCR double-spray system, the method is based on the mass flow rate m of urea solution 5 And urea solution mass flow limit
Figure SMS_58
Obtaining the first urea injection quantity includes:
the mass flow rate m of the urea solution 5 And the urea solution mass flow limit
Figure SMS_59
Is equal to the first urea injection quantity.
As a preferable scheme of the method for reducing the crystallization of the SCR double-spray system, the method is based on the mass flow rate m of urea solution 5 And urea solution mass flow limit
Figure SMS_60
Obtaining the second urea injection quantity includes:
obtaining a correction coefficient according to the exhaust temperature of the engine;
the mass flow rate of the urea solution
Figure SMS_61
And said urea solution mass flow limit +.>
Figure SMS_62
And multiplying the difference value of (2) by the correction coefficient to obtain a second urea injection quantity.
As a preferable mode of the method for reducing crystallization of the SCR dual injection system, obtaining the correction coefficient according to the exhaust temperature of the engine includes:
the correction factor is obtained from the engine exhaust temperature by means of an engine exhaust temperature-correction factor relationship table.
The vehicle comprises an engine and a post-treatment system, wherein the post-treatment system comprises an SCR double-spraying system, a DOC and a DPF, the SCR double-spraying system comprises a front-stage SCR and a rear-stage SCR, and waste gas discharged by the engine sequentially passes through the front-stage SCR, DOC, DPF and the rear-stage SCR.
The invention has the beneficial effects that:
the invention provides a method for reducing crystallization of an SCR double-spray system and a vehicle, wherein in the method for reducing crystallization of the SCR double-spray system, when judging that the crystallization risk exists in the SCR double-spray system, the urea injection quantity of a rear-stage SCR is reduced by a first urea injection quantity, and the urea injection quantity of a front-stage SCR is increased by a second urea injection quantity. Since the more the urea injection quantity is, the easier the crystallization is, when the crystallization risk exists, reducing the urea injection quantity of the post-stage SCR can reduce the risk of the post-stage SCR crystallization. In order to make the total amount of nitrogen oxides in the exhaust gas treated by the SCR double-injection system unchanged, namely, not reducing the amount of nitrogen oxides treated by the SCR double-injection system, the urea injection amount of the former-stage SCR is increased by the second urea injection amount, so that the amount of nitrogen oxides which can be treated by the first urea injection amount reduced by the latter-stage SCR is approximately equal to the amount of nitrogen oxides which can be treated by the second urea injection amount increased by the former-stage SCR. Because the front-stage SCR is closer to the engine, the temperature of the engine exhaust passing through the front-stage SCR is higher, the front-stage SCR is less prone to crystallization, and the original urea injection amount of the front-stage SCR is smaller, so that the crystallization of the front-stage SCR cannot be increased after the urea injection amount of the front-stage SCR is increased by the second urea injection amount. Therefore, the crystallization effect of the SCR double-spraying system can be reduced.
Drawings
FIG. 1 is a flow chart of a method for reducing crystallization of an SCR dual spray system according to an embodiment of the present invention;
FIG. 2 is a flowchart of S2 in a method for reducing crystallization in an SCR dual spray system according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.
In the description of the present invention, unless explicitly stated and limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
In the present invention, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.
In the description of the present embodiment, the terms "upper", "lower", "right", and the like are based on the orientation or positional relationship shown in the drawings, and are merely for convenience of description and simplicity of operation, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the invention. Furthermore, the terms "first," "second," and the like, are used merely for distinguishing between descriptions and not for distinguishing between them.
The invention provides a method for reducing crystallization of an SCR double-spray system, which is shown in fig. 1 and comprises the following steps:
s1: judging whether the engine meets the crystallization risk detection condition or not; if yes, S2 is performed.
Specifically, judging whether the engine is electrified or not, and judging whether the water temperature of the engine is greater than or equal to a set water temperature or not; if yes, meeting crystallization risk detection conditions; if not, the crystallization risk detection condition is not satisfied. In this example, the water temperature was set at 70 ℃.
S2: detecting crystallization risk, and judging whether the SCR double-spraying system has crystallization risk or not; if yes, S3 is carried out; if not, returning to S1.
Specifically, as shown in fig. 2, S21: judging whether the duration time of the absolute value of the ratio of the difference value of the current engine speed and the previous engine speed to the previous engine speed is larger than or equal to the set time or not; if yes, S22 is carried out; if not, returning to S1. I.e. judge to satisfy
Figure SMS_63
Is smaller than or equal to the first set ratio and +.>
Figure SMS_64
Whether the duration time is more than or equal to the set time under the two conditions of being less than or equal to the second set ratio; if yes, S22 is carried out; if not, returning to S1. Wherein n is the current engine speed;
Figure SMS_65
Engine speed is the previous time;
Figure SMS_66
Is the current engine torque;
Figure SMS_67
The engine torque is the previous time. In this embodiment, the first set ratio is 1%, and the second set ratio is 1%. In this embodiment, the set time is 120s.
S22: according to engine exhaust temperature
Figure SMS_68
Urea aqueous solution temperature->
Figure SMS_69
Engine exhaust gas mass flow->
Figure SMS_70
And urea solution mass flow->
Figure SMS_71
Calculating to obtain a heat ratio Q, wherein the heat ratio Q is the ratio of the heat in the exhaust gas of the engine to the heat required by urea decomposition; based on the current engine speed and the current engine torque, a caloric ratio limit value is obtained>
Figure SMS_72
。
Specifically, according to the current engine speed and the current engine torque, a heat ratio limit value is obtained through an engine speed-engine torque-heat ratio limit value relation table
Figure SMS_73
. The engine speed-engine torque-heat ratio limit relation table is obtained by performing an engine bench test in the earlier stage.
Specifically, according to engine exhaust temperature
Figure SMS_74
Urea aqueous solution temperature->
Figure SMS_75
Engine exhaust gas mass flow>
Figure SMS_76
And urea solution mass->
Figure SMS_77
The heat quantity ratio Q is calculated by the following formula. />
Figure SMS_80
Wherein Q is a heat ratio;
Figure SMS_82
Heat J is exhausted by the engine;
Figure SMS_84
Absorbing heat for liquid water, J;
Figure SMS_78
Heat is absorbed for the liquid water phase change, J;
Figure SMS_81
Absorbing heat for gaseous water, J;
Figure SMS_83
Absorbing heat for urea solids, J;
Figure SMS_85
Absorbing heat for urea melting, J;
Figure SMS_79
Absorbs heat for urea phase transition, J.
Figure SMS_86
Wherein->
Figure SMS_87
Is the exhaust gas mass flow rate, kg/h;
Figure SMS_88
Specific heat of exhaust of the engine, J/kg ℃;
Figure SMS_89
Engine exhaust temperature, DEG C;
Figure SMS_90
Is urea melting temperature, DEG C.
Wherein the exhaust gas mass flow rate
Figure SMS_91
The ECU calculates the exhaust gas mass flow according to the engine intake mass flow and the fuel injection amount>
Figure SMS_92
The method comprises the steps of carrying out a first treatment on the surface of the Engine exhaust temperature->
Figure SMS_93
Detecting by a first temperature sensor; specific heat of exhaust gas of engine>
Figure SMS_94
And urea melting temperature->
Figure SMS_95
Are constant.
Figure SMS_97
Wherein->
Figure SMS_101
，
Figure SMS_104
Is liquid water mass flow rate, kg/h;
Figure SMS_99
Specific heat of liquid water, J/kg ℃;
Figure SMS_102
Is the boiling point of water, DEG C;
Figure SMS_105
Is the temperature of the urea aqueous solution, DEG C;
Figure SMS_107
The mass flow rate of the urea solution is kg/h; a is a constant, a=0.675±0.03. Wherein the urea aqueous solution temperature->
Figure SMS_96
And detecting by a second temperature sensor. Urea solution mass flow->
Figure SMS_100
The mass flow of urea solution is calculated by the ECU according to the volume flow of nitrogen oxides in the exhaust gas of the engine>
Figure SMS_103
. Specific heat of liquid water>
Figure SMS_106
And boiling point of water>
Figure SMS_98
Are constant.
Figure SMS_108
Wherein->
Figure SMS_109
Is the vaporization latent heat of water, kJ/kg. Latent heat of vaporization of water>
Figure SMS_110
Is constant.
Figure SMS_111
Wherein->
Figure SMS_112
，
Figure SMS_113
The mass flow rate of urea is kg/h;
Figure SMS_114
Specific heat of solid urea, J/kg ℃; b is a constant, b=0.325±0.03. Solid urea specific heat->
Figure SMS_115
Is constant.
Figure SMS_116
Wherein->
Figure SMS_117
，
Figure SMS_118
Is the mass flow rate of the gaseous water, kg/h;
Figure SMS_119
Specific heat for gaseous water, J/kg ℃. Wherein the gaseous water has a specific heat->
Figure SMS_120
Is constant.
Figure SMS_121
Wherein->
Figure SMS_122
Is urea fusion heat, kJ/mol;
Figure SMS_123
The molecular weight of the urea is kg/mol. Urea heat of fusion>
Figure SMS_124
And urea molecular mass->
Figure SMS_125
Are all constant.
Figure SMS_126
Wherein->
Figure SMS_127
Is the vaporization latent heat of urea, kJ/kg. Latent heat of vaporization of urea>
Figure SMS_128
Is constant.
S23: judging whether the heat quantity ratio Q is smaller than the heat quantity ratio limit value
Figure SMS_129
The method comprises the steps of carrying out a first treatment on the surface of the If yes, the crystallization risk exists in the SCR double-spraying system; if not, the SCR double-spray system has no crystallization risk.
S3: the urea injection quantity of the rear-stage SCR is reduced by a first urea injection quantity; the urea injection amount of the pre-SCR increases by a second urea injection amount.
Wherein, according to the heat ratio limit value
Figure SMS_130
Obtaining the mass flow limit value of the urea solution>
Figure SMS_131
The method comprises the steps of carrying out a first treatment on the surface of the According to the mass flow of urea solution>
Figure SMS_132
And urea solution mass flow limit->
Figure SMS_133
And obtaining a first urea injection quantity and a second urea injection quantity.
Specifically, according to the heat ratio limit
Figure SMS_134
The urea solution mass flow limit is obtained by the following formula>
Figure SMS_135
。
Figure SMS_137
Wherein->
Figure SMS_141
Is a heat ratio limit;
Figure SMS_143
Heat J is exhausted by the engine;
Figure SMS_138
absorbing a heat limit value J for liquid water;
Figure SMS_139
A limit value J of heat of absorption for the liquid water phase change;
Figure SMS_142
Absorbing a heat limit, J, for gaseous water;
Figure SMS_144
A limit of the heat of absorption for urea solids, J;
Figure SMS_136
Heat of absorption limit, J, for urea melt;
Figure SMS_140
And (3) absorbing the heat limit value for urea phase change, J.
Figure SMS_145
Wherein->
Figure SMS_146
Is the exhaust gas mass flow rate, kg/h;
Figure SMS_147
Specific heat of exhaust of the engine, J/kg ℃;
Figure SMS_148
Engine exhaust temperature, DEG C;
Figure SMS_149
Is urea melting temperature, DEG C.
Wherein the exhaust gas mass flow rate
Figure SMS_150
The ECU calculates the exhaust gas mass flow according to the engine intake mass flow and the fuel injection amount>
Figure SMS_151
The method comprises the steps of carrying out a first treatment on the surface of the Engine exhaust temperature->
Figure SMS_152
Detecting by a first temperature sensor; specific heat of exhaust gas of engine>
Figure SMS_153
And urea melting temperature->
Figure SMS_154
Are constant.
Figure SMS_157
Wherein->
Figure SMS_159
，
Figure SMS_162
Is liquid water mass flow limit value, kg/h;
Figure SMS_156
Specific heat of liquid water, J/kg ℃;
Figure SMS_160
Is the boiling point of water, DEG C;
Figure SMS_163
Is the temperature of the urea aqueous solution, DEG C;
Figure SMS_164
Is the mass flow limit value of urea solution, kg/h; a is a constant, a=0.675±0.03. Wherein the urea aqueous solution temperature->
Figure SMS_155
And detecting by a second temperature sensor. Specific heat of liquid water>
Figure SMS_158
And boiling point of water>
Figure SMS_161
Are constant.
Figure SMS_165
Wherein->
Figure SMS_166
Is the vaporization latent heat of water, kJ/kg.
Figure SMS_167
Wherein->
Figure SMS_168
，
Figure SMS_169
Is urea mass flow limit value, kg/h;
Figure SMS_170
Specific heat of solid urea, J/kg ℃; b is a constant, b=0.325±0.03. Solid urea specific heat->
Figure SMS_171
Is constant.
Figure SMS_172
Wherein->
Figure SMS_173
Is the limit value of the mass flow rate of the gaseous water, kg/h;
Figure SMS_174
Specific heat for gaseous water, J/kg ℃. Wherein (1)>
Figure SMS_175
Specific heat of gaseous water>
Figure SMS_176
Is constant.
Figure SMS_177
Wherein->
Figure SMS_178
Is urea fusion heat, kJ/mol;
Figure SMS_179
The molecular weight of the urea is kg/mol. Urea heat of fusion>
Figure SMS_180
And urea molecular mass->
Figure SMS_181
Are all constant.
Figure SMS_182
Wherein->
Figure SMS_183
Is the vaporization latent heat of urea, kJ/kg. Latent heat of vaporization of urea>
Figure SMS_184
Is constant.
In particular, the urea solution mass flow
Figure SMS_185
And urea solution mass flow limit->
Figure SMS_186
Is equal to the first urea injection quantity.
Specifically, according to the exhaust temperature of the engine, a correction coefficient is obtained; mass flow rate of urea solution
Figure SMS_187
And urea solution mass flow limit->
Figure SMS_188
And (3) multiplying the difference value of the second urea injection quantity by a correction coefficient to obtain the second urea injection quantity. Correction coefficient for transferred urea injection quantityf, correcting can make up the difference of the efficiency characteristics of the front-stage SCR and the rear-stage SCR catalysts.
Wherein, according to the engine exhaust temperature, the correction coefficient is obtained through an engine exhaust temperature-correction coefficient relation table. The engine exhaust temperature-correction coefficient relation table is obtained by a preliminary test.
The heat ratio Q represents the ratio of the heat in the exhaust gas of the engine to the heat required for urea decomposition, and the larger the heat ratio Q is, the more sufficient the heat required for urea decomposition is, and the less easy crystallization is caused; conversely, the smaller the heat ratio Q, the easier it is to crystallize. When the heat ratio Q is judged to be smaller than the heat ratio limit value
Figure SMS_189
In this case, it is indicated that there is a risk of crystallization, and the post-SCR urea injection is decreased by the first urea injection and the pre-SCR urea injection is increased by the second injection. Since the more the urea injection quantity is, the easier the crystallization is, when the crystallization risk exists, reducing the urea injection quantity of the post-stage SCR can reduce the risk of the post-stage SCR crystallization. In order to make the total amount of nitrogen oxides in the exhaust gas treated by the SCR double-injection system unchanged, namely, not reducing the amount of nitrogen oxides treated by the SCR double-injection system, the urea injection amount of the former-stage SCR is increased by the second urea injection amount, so that the amount of nitrogen oxides which can be treated by the first urea injection amount reduced by the latter-stage SCR is approximately equal to the amount of nitrogen oxides which can be treated by the second urea injection amount increased by the former-stage SCR. Because the front-stage SCR is closer to the engine, the temperature of the engine exhaust passing through the front-stage SCR is higher, the front-stage SCR is less prone to crystallization, and the original urea injection amount of the front-stage SCR is smaller, so that the crystallization of the front-stage SCR cannot be increased after the urea injection amount of the front-stage SCR is increased by the second urea injection amount. />
The invention also provides a vehicle, which adopts the method for reducing the crystallization of the SCR double-spray system; the vehicle comprises an engine and a post-treatment system, wherein the post-treatment system comprises an SCR double-spraying system, a DOC and a DPF, the SCR double-spraying system comprises a front-stage SCR and a rear-stage SCR, and waste gas discharged by the engine sequentially passes through the front-stage SCR, DOC, DPF and the rear-stage SCR.
It is to be understood that the above examples of the present invention are provided for clarity of illustration only and are not limiting of the embodiments of the present invention. Various obvious changes, rearrangements and substitutions can be made by those skilled in the art without departing from the scope of the invention. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.

Claims (10)

1. A method for reducing crystallization in an SCR dual spray system, comprising:
s1: judging whether the engine meets the crystallization risk detection condition or not;
if yes, S2 is carried out;
s2: detecting crystallization risk, and judging whether the SCR double-spraying system has crystallization risk or not;
if yes, S3 is carried out;
if not, returning to the step S1;
s3: the urea injection quantity of the rear-stage SCR is reduced by a first urea injection quantity; the urea injection amount of the pre-SCR increases by a second urea injection amount.
2. The method of reducing crystallization in an SCR dual injection system according to claim 1, wherein determining whether the engine satisfies a crystallization risk detection condition comprises:
judging whether the engine is electrified or not, and judging whether the water temperature of the engine is greater than or equal to the set water temperature or not;
if yes, meeting crystallization risk detection conditions;
if not, the crystallization risk detection condition is not satisfied.
3. The method for reducing crystallization in an SCR dual spray system according to claim 1, wherein performing a crystallization risk detection to determine whether the SCR dual spray system has a crystallization risk comprises:
s21: judging whether the duration time of the absolute value of the ratio of the difference value of the current engine speed and the previous engine speed to the previous engine speed is larger than or equal to the set time or not;
if yes, S22 is carried out;
if not, returning to the step S1;
s22: according to the exhaust temperature t of the engine 0 Temperature t of aqueous urea solution 3 Mass flow of engine exhaust gas m 0 And urea solution mass flow m 5 Calculating to obtain a heat ratio Q, wherein the heat ratio Q is the ratio of the heat in the exhaust gas of the engine to the heat required by urea decomposition; obtaining a heat ratio limit value according to the current engine speed and the current engine torque
Figure QLYQS_1
；
S23: judging whether the heat quantity ratio Q is smaller than the heat quantity ratio limit value
Figure QLYQS_2
；
If yes, the crystallization risk exists in the SCR double-spraying system;
if not, the SCR double-spray system has no crystallization risk.
4. A method of reducing crystallization in an SCR dual injection system according to claim 3, wherein the heat ratio limit is derived based on a current engine speed and a current engine torque
Figure QLYQS_3
Comprising the following steps:
obtaining a heat ratio limit value according to the current engine speed and the current engine torque through an engine speed-engine torque-heat ratio limit value relation table
Figure QLYQS_4
。
5. A method of reducing crystallization in an SCR dual injection system according to claim 3, wherein the temperature t of the exhaust gas of the engine 0 Urea aqueous solution temperature t 3 Engine exhaust mass flow m 0 And urea solution mass flow m 5 The calculation of the heat quantity ratio Q includes:
by the formula:
Figure QLYQS_5
wherein Q is a heat ratio; q (Q) 0 Exhaust heat for the engine; q (Q) 1 Absorbing heat for liquid water; q (Q) 2 Absorbing heat for liquid water phase change; q (Q) 3 Absorbing heat for the gaseous water; q (Q) 4 Absorbing heat for urea solids; q (Q) 5 Absorbing heat for urea melting; q (Q) 6 Absorbing heat for urea phase change;
Figure QLYQS_6
wherein m is 0 Is the exhaust gas mass flow; c 0 Specific heat for engine exhaust; t is t 0 Engine exhaust temperature; t is t 2 Is urea melting temperature;
Figure QLYQS_7
wherein m is 1 Is liquid water mass flow; c 1 Specific heat for liquid water; t is t 1 Is the boiling point of water; t is t 3 Is the temperature of the urea aqueous solution;
Figure QLYQS_8
wherein h is 0 Is the latent heat of vaporization of water;
Figure QLYQS_9
wherein->
Figure QLYQS_10
，m 2 Is the gaseous water mass flow; c 2 Specific heat for gaseous water;
Figure QLYQS_11
wherein m is 3 Is urea mass flow; c 3 Specific heat for solid urea;
Figure QLYQS_12
wherein Q is 7 Is urea fusion heat; m is m 4 The molecular mass of urea;
Figure QLYQS_13
wherein h is 1 Is the vaporization latent heat of urea;
Figure QLYQS_14
wherein m is 5 Is the mass flow of urea solution; a is a constant;
the method comprises the steps of,
Figure QLYQS_15
wherein B is a constant; and calculating to obtain the heat quantity ratio Q.
6. A method of reducing crystallization in an SCR dual spray system according to claim 3, wherein based on said heat ratio limit
Figure QLYQS_16
Obtaining the mass flow limit value of the urea solution>
Figure QLYQS_17
The method comprises the steps of carrying out a first treatment on the surface of the According to the mass flow rate m of urea solution 5 And urea solution mass flow limit->
Figure QLYQS_18
Obtaining a first urea injectionAn amount and a second urea injection amount.
7. The method for reducing crystallization in an SCR dual spray system according to claim 6, wherein the flow rate m is based on the mass flow of urea solution 5 And urea solution mass flow limit
Figure QLYQS_19
Obtaining the first urea injection quantity includes:
the mass flow rate m of the urea solution 5 And the urea solution mass flow limit
Figure QLYQS_20
Is equal to the first urea injection quantity.
8. The method for reducing crystallization in an SCR dual spray system according to claim 6, wherein the flow rate m is based on the mass flow of urea solution 5 And urea solution mass flow limit
Figure QLYQS_21
Obtaining the second urea injection quantity includes:
obtaining a correction coefficient according to the exhaust temperature of the engine;
the mass flow rate m of the urea solution 5 And the urea solution mass flow limit
Figure QLYQS_22
And multiplying the difference value of (2) by the correction coefficient to obtain a second urea injection quantity.
9. The method of reducing crystallization in an SCR dual injection system according to claim 8, wherein obtaining a correction factor based on engine exhaust temperature comprises:
the correction factor is obtained from the engine exhaust temperature by means of an engine exhaust temperature-correction factor relationship table.
10. A vehicle comprising an engine and an aftertreatment system, the aftertreatment system comprising an SCR dual spray system, a DOC and a DPF, the SCR dual spray system comprising a pre-SCR and a post-SCR, exhaust gas from the engine passing through the pre-SCR, DOC, DPF and post-SCR in sequence, characterized in that a method of reducing crystallization of the SCR dual spray system according to any one of claims 1-9 is employed.
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CN109415962A (en) * 2016-07-14 2019-03-01 斯堪尼亚商用车有限公司 System and method for diagnosing the performance of two NOx sensors in the gas exhaust treatment construction including two SCR units
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CN113153501A (en) * 2021-05-07 2021-07-23 潍柴动力股份有限公司 Urea injection amount control method and related equipment
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