CN112943418A - Efficient denitration tail gas aftertreatment system of lean burn engine and control method - Google Patents

Efficient denitration tail gas aftertreatment system of lean burn engine and control method Download PDF

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CN112943418A
CN112943418A CN202110108017.9A CN202110108017A CN112943418A CN 112943418 A CN112943418 A CN 112943418A CN 202110108017 A CN202110108017 A CN 202110108017A CN 112943418 A CN112943418 A CN 112943418A
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engine
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CN112943418B (en
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王攀
吴彦
雷利利
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Jiangsu University
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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]
    • 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
    • F01N11/002—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust 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
    • 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
    • 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
    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/14—Nitrogen oxides
    • 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
    • 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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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

The invention relates to the technical field of engine post-treatment and control, in particular to a high-efficiency denitration post-treatment system and a control method for a lean burn engine. The system includes an engine, a fuel injection device, a hydrogen injection device, an LNT system, an SCR system, and an ASC device. The invention utilizes the high-temperature and free radical oxidation effect in the engine cylinder and combines the further oxidation of the LNT system and the high ammonia selectivity of hydrogen, thereby realizing the high-efficiency starting of the rapid SCR reaction and simultaneously avoiding the crystallization problem caused by the injection of a large amount of urea.

Description

Efficient denitration tail gas aftertreatment system of lean burn engine and control method
Technical Field
The invention relates to the technical field of engine post-treatment and control, in particular to a high-efficiency denitration post-treatment system and a control method for a lean burn engine.
Background
The internal combustion engine brings convenience and comfort to life of people, and simultaneously brings certain energy and environmental problems. Among these, the emission restrictions on nitrogen oxides are an important part of the emission legislation of internal combustion engines. Most working condition ranges of passenger cars are concentrated on medium and small loads, and the engine using the lean-burn technology can effectively reduce pumping loss under the operation of the medium and small loads and greatly improve fuel economy. However, the conventional three-way catalyst (TWC) is not effective in controlling nitrogen oxides NO due to engine off equivalence ratio under lean conditionsxAnd (4) discharging.
Lean NOxTrapping (LNT) technology is the emission of NO from lean burn processesxAdsorbing on the catalyst via the carrier and during rich combustion the adsorbed NOxReducing to nontoxic harmless N2The technique of (1). LNT technology due to its higher NO at the exhaust temperature window conditions of a conventional gasoline or diesel enginexThe conversion efficiency is high, and the problem of secondary leakage pollution hardly exists; but during application, especially at high NOxNO emitted during lean burn phase under conditions of concentration and high airspeedxMay not be fully adsorbed for storage. Similarly, Selective Catalytic Reduction (SCR) technology is another, more mature NOxRemoval techniques are also widely used, but the SCR technique uses a reducing agent NH during its application3The need to store in aqueous urea, and the crystallization and leakage problems associated with excessive urea injection, limit its popularity to small vehicles.
It was found that hydrogen has very high (50-70%) NH in certain LNT catalytic systems3Selectivity, and reduction at lower temperatures can further increase NH3And (4) selectivity.
Therefore, by utilizing the effects of heat release and free radical oxidation of the post-injection of the engine and combining the further oxidation of the LNT system and the high ammonia selectivity of hydrogen, the denitration system of the lean-burn engine is improved, the rapid and efficient starting of the SCR reaction can be realized, the crystallization problem caused by the injection of a large amount of urea is avoided, and the size of the urea tank is further reduced.
Disclosure of Invention
In order to achieve the above object, the invention adopts the technical scheme that: the efficient denitration post-treatment system of the lean-burn engine comprises the engine, a fuel injection device, a hydrogen injection device, an LNT system, a urea injection device, an SCR system, an ASC device, a control module, a temperature sensor and gas (NO and NO)xAnd NH3) A concentration sensor; according to the exhaust direction, the LNT system, the SCR system and the ASC device are sequentially arranged in an exhaust pipeline of the engine; the fuel injection device is positioned in the center of the cylinder cover of the engine, performs in-cylinder fuel post-injection, provides a rich combustion environment for an LNT system, and performs NOxAdjusting the content of each component and compensating the exhaust temperature; the hydrogen injection device is positioned at the front end of the LNT system and is close to the LNT system, and is used for injecting hydrogen into the front end of the LNT system and guiding the side reaction to generate more NH3Providing part of reducing agent for the SCR system; the urea injection device is positioned at the front end of the SCR system and is close to the SCR system, and is used for supplying a reducing agent to the SCR system to carry out NOxAnd (4) removing quickly.
Preferably, sensors for detecting the gas temperature and the concentration of the gas components in the exhaust pipe are arranged in the engine and in the exhaust pipe, wherein: the first temperature sensor is positioned in the engine and is close to the center of the cylinder cover; NO sensor and first NOxThe sensor is positioned at the front end of the engine exhaust pipeline and is close to the engine; a second temperature sensor is positioned between the engine and the LNT system and proximate to the LNT system; second NOxSensor and first NH3The sensor is positioned between the LNT system and the SCR system and is close to the LNT system; third NOxSensor and second NH3The sensors are located between the SCR system and the ASC device in sequence according to the exhaust direction.
Preferably, the control module is respectively connected with each injection device and a sensor for detecting the gas temperature and the gas concentration in each position of the engine and the exhaust pipeline, and judges the state of the LNT system and the NH required by the SCR system3Concentration, and reasonably controlling the amount of post-injected fuel, the amount of hydrogen and the amount of urea to optimize NO/NO inside the exhaust pipexThe proportion is improved, the ammonia production of the LNT system in the denitration of the SCR system is promoted, and the NO in the exhaust gas is favorably treatedxQuickly removing, avoiding crystallization caused by excessive urea injection as much as possible, and finally absorbing escaped NH by an ASC device3。
In addition, the invention also provides a control method of the high-efficiency off-sale post-treatment system, which comprises the following steps:
when the engine starts to operate and is in a low-emission condition, and the temperature measured by the second temperature sensor is lower than the optimal temperature of the LNT system by 50K, the fuel injection device implements a near-post-injection strategy to compensate the temperature of exhaust gas, so that the temperature of gas in the exhaust pipe is around the optimal temperature of the corresponding LNT system;
preferably, the near post-injection oil injection is carried out at the average temperature of 1300-1500K (or the main post-injection interval angle is 10-30 ℃ A) in the cylinder, and the oil injection quantity Qp2＝Kp2(Tb-T2)(T1-T0)/QmIn which K isp2Adjusting parameters for near-after-injection, TbTo correspond to the optimum regeneration temperature, T, of the LNT system2Is the temperature, T, measured by the second temperature sensor1Is the temperature, T, measured by the first temperature sensor0Is the temperature, Q, measured by the first temperature sensor at mechanical top dead center of the enginemIs the main fuel injection amount;
preferably, the near-after injection adjustment parameter Kp2The method is selected according to different working conditions and lean-burn engine types, the engine types are sorted according to DI Diesel, RCCI and GDI (HCCI), and corresponding parameters are selected from 1.05-1.25 from high to low.
Second NO when the engine is started and in low emission conditionsxNO measured by sensorxNO for LNT system when concentration reaches a limitxThe memory space is calibrated for the first time;
preferably, the amount of storage is recorded as
Figure BDA0002918242400000031
t0The starting time of the engine or the starting time of the last fuel post-injection of the removal period, teIs a second NOxThe sensor captures the moment of the overrun signal, A2Is a second NOxNO measured by sensorxConcentration, A1Is first NOxNO measured by sensorxAnd (4) concentration.
When the engine is started and in low emission conditions, the second NOxNO measured by sensorxConcentration A2After the limit value is exceeded, the fuel injection device implements a far post-injection strategy to build a rich combustion environment for the LNT system and carry out denitration;
preferably, the far post-injection oil injection is carried out at the average temperature of 800-1000K (or the main post-injection interval angle is 70-90 ℃ A) in the cylinder, and the oil injection quantity Qp1＝Kp1QmWherein Q ismIs the main fuel injection amount, Kp1Adjusting parameters for post-injection, and continuing the post-injection process until the emission is reduced below a limit value; post-spray adjustment parameter Kp1According to different lean-burn engine types and corresponding LNT systems, the higher the catalytic activity of the corresponding LNT system is, the higher the K isp1The smaller and the engine types are ranked according to DI Diesel, RCCI, GDI (HCCI), corresponding Kp1From high to low.
When the engine starts to operate and is in a high emission condition, the fuel injection device performs a middle and rear injection to regulate the exhaust gas components NO/NOxA ratio;
preferably, the middle post-injection oil injection is carried out at the average temperature of 1000-1300K (or the main post-injection interval angle of 30-70 ℃ A) in the engine cylinder, and the oil injection quantity Qp3According to NO/NOxRatio R ═ B1/A1Is adjusted, wherein B1Is the NO concentration measured by the NO sensor, A1Is first NOxNO measured by sensorxAnd (4) concentration.
When the engine is started and in high emission conditions, when the real-time storage amount H is lower than 90% H (mass fraction), and the second NO is usedxNO measured by sensorxAfter the concentration reaches the limit of 75ppm, the urea injection device injects the urea aqueous solution so that the third NO isxNO measured by sensorxConcentrations below a 25ppm emission threshold, where H is the maximum storage capacity calibrated for the LNT system;
preferably, the urea injection amount P decomposes CO (NH) using a urea solution2)+H2O→2NH3+CO2And SCR system internal reduction equation calculation, i.e., -M +0.5K1K2A2M is the real-time ammonia storage capacity of the SCR system, K1For the overcompensation factor, K2An efficiency compensation factor; when P is present<At 0, the urea injection device does not inject, and the ammonia storage amount of the SCR system is calibrated at the moment
Figure BDA0002918242400000032
MNChecking the ammonia storage of the SCR system before urea injection, tau0Is a second NOxNO measured by sensorxAt a time when the concentration is greater than the 75ppm limit, taueIs a third NOxNO measured by sensorxAt a concentration below the 25ppm emission threshold, A3Is a third NOxNO measured by sensorxConcentration, A2Is a second NOxNO measured by sensorxAnd (4) concentration.
When the engine starts to run and is in high emission condition, the NO in the LNT system is addedxThe storage amount is accumulated in real time, when the real-time storage amount H is not less than 90% H (mass fraction), the fuel injection device implements a cooperative remote post-injection strategy, and the hydrogen injection device is opened to build a rich combustion environment for an LNT system, improve the ammonia production amount and carry out NOxWherein H is the maximum storage capacity calibrated for the LNT system;
preferably, the amount of hydrogen injected by the hydrogen injection means is in accordance with the equation
Figure BDA0002918242400000042
Figure BDA0002918242400000043
Calculation, i.e. U ═ M +4K4A2Wherein M is the real-time ammonia storage capacity of the SCR system, K4Taking 1.25-1.8 as a selective compensation coefficient; a. the2Is a second NOxNO measured by sensorxConcentration; when U is turned<When 0, the hydrogen injection device does not inject;
preferably, when the fuel injection device implements a cooperative remote post-injection strategy, the oil injection is carried out at the average temperature of 800-1000K (or the main post-injection interval angle is 70-90 ℃ A) in an engine cylinder, and the oil injection quantity Q isp1Dynamically adjusting according to the injection quantity of the hydrogen injection device.
When the engine starts to run and the hydrogen injection device is started, the ammonia storage amount of the SCR system is accumulated, and the ammonia storage amount is real-time
Figure BDA0002918242400000041
MHChecking the ammonia storage of the SCR system before the hydrogen injection amount, P being the urea injection amount, C1Is first NH3NH measured by sensor3Concentration, A3Is a third NOxNO measured by sensorxConcentration, A2Is a third NOxNO measured by sensorxConcentration, C2Is the second NH3NH measured by sensor3Concentration, T0For the opening time, T, of the hydrogen injection deviceeThe closing timing of the hydrogen injection device.
Total fuel injection quantity Q of post-injection of enginepMust not be greater than main fuel injection quantity QmAnd if the ratio exceeds 80%, selecting the strategy according to the priority of the far post injection, the middle post injection and the near post injection, namely executing the far post injection strategy firstly.
According to the efficient denitration tail gas aftertreatment system and the control method of the lean burn engine, provided by the invention, the in-cylinder post-injection technology, the LNT technology and the SCR technology are combined, so that NO in the tail gas can be rapidly and efficiently removedxOn the basis of pollutants, the use of urea is saved, and the formation of crystals and the volume of a urea tank are further reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a device layout diagram of a high-efficiency denitration tail gas post-treatment system of the present invention.
FIG. 2 is a flow diagram of a low emission part in the control method of the high-efficiency denitration exhaust aftertreatment system.
FIG. 3 is a flow diagram of a high-emission part in the control method of the high-efficiency denitration exhaust aftertreatment system.
Detailed Description
The following detailed description of the embodiments of the present invention will be described in detail with reference to the drawings of the embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, the efficient denitration post-treatment system of the lean burn engine comprises an engine 100, a fuel injection device 101, a first temperature sensor 102, an NO sensor 103, and a first NOxSensor 104, LNT system 200, hydrogen injection device 201, second temperature sensor 202, second NOxSensor 203, first NH3Sensor 204, SCR system 300, urea injection device 301, third NOxSensor 302, second NH3 A sensor 303, an ASC device 400, and a control module 500.
A fuel injection device 101 for in-cylinder fuel post-injection to provide a rich environment for the LNT system 200 and an appropriate NO/NO for the SCR system 300xProportional and exhaust temperature compensation; LNT System 200 for NO in exhaustxIs treated while oxidizing excess NO to NO2(ii) a A hydrogen injection device 201 for injecting hydrogen into the front end of the LNT system 200 to induce side reactions to generate more NH3Providing a part of reducing agent for the SCR system 300 to reduce the injection amount of urea; urea injection system 301 to provide reductant for SCR system 300 for NOxRemoving rapidly; SCR system 300 for slipped NO in LNT system 200xCarrying out high-efficiency treatment; ASC device 400 for NH slip in SCR system 3003Trapping to prevent NH3And leaks into the atmosphere.
The control module 500 is connected to sensors for detecting the gas temperature and the gas concentration in the engine 100 and the exhaust pipe, and determines the state of the LNT system 200 and the NH required by the SCR system 3003Concentration, reasonably controlling the amount of post-injected fuel, the amount of hydrogen and the amount of urea injection through each injection device, and optimizing NO/NO in the exhaust pipelinexRatio and exhaust temperature to favor NO in the exhaustxQuickly removing to avoid the crystallization caused by excessive urea injection, and finally loading by ASCAbsorbing excessive NH by a device 4003。
Referring to FIG. 2, the system is shown at low emissions (first NO)xNO measured by sensor 104xConcentration A1<400ppm), the process is as follows:
in the present embodiment, when engine 100 starts operating, detection a1Whether the value exceeds a limit value (400ppm) or not, and if not, T is judged2<TbIf not more than 50K, the fuel injection device 101 implements a middle post injection strategy for NO/NO in the exhaust gasxAdjustment of the ratio, A1Is first NOxNO measured by sensor 104xConcentration, T2Is the temperature, T, measured by the second temperature sensor 202bCorresponding to the optimal regeneration temperature of the LNT system. Then, if T is satisfied2<TbUnder the condition of-50K, a near-post-injection strategy is implemented to compensate the exhaust temperature; if not, judging A2>If 55ppm is not available, the fuel injection device 101 implements a remote post-injection strategy, and waiting for A2Removal is completed below the emissions threshold (50ppm), otherwise NO for the LNT system 200xThe memory space is calibrated once and recorded as
Figure BDA0002918242400000061
t0The time when the engine 100 starts to start or the time when the last fuel post-injection period starts, teIs a second NOxSensor 203 captures 50 + -5 ppm signal time, A2Is a second NOxNO measured by sensor 203xAnd (4) concentration.
In this embodiment, the near-after injection strategy performs temperature compensation on the exhaust temperature, so that T is2Is kept at TbAnd + -50K. Wherein the near-after injection is at T1When 1400K, the fuel injection quantity Q isp2＝Kp2(Tb-T2)(T1-T0)/Qm，Kp2Adjusting parameters for near-after-injection, TbTo correspond to the optimum regeneration temperature, T, of the LNT system1Is the temperature, T, measured by the first temperature sensor 1020Measured by the first temperature sensor 102 at the mechanical top dead center of the engineObtained temperature, QmIs the main fuel injection amount. Wherein the near-after-spray adjusting parameter Kp2The selection is based on different lean-burn engine types, and the embodiment takes 1.15.
In this embodiment, the middle post injection strategy regulates the exhaust gas composition NO/NOxA ratio; wherein the middle and rear injection is at T1When the pressure is 1150K, the middle and the rear injection quantity Qp3According to NO/NOxRatio R ═ B1/A1Regulating to control R to be 0.35 +/-0.05, namely Qp3＝Kp3QmB1/A1Wherein T is1Is the temperature measured by the first temperature sensor 102, B1Is the NO concentration, K, measured by NO sensor 103p3Adjusting parameters for medium and post-injection, adjusting parameter K for medium and post-injectionp3The present embodiment takes 1.1, chosen for different lean-burn engine types.
In this embodiment, the remote post-injection strategy is to create a rich environment for the LNT system 200 to carry out NOxRemoving; wherein the far post-injection is at T1When 900K, the fuel injection quantity Q isp1＝Kp1QmThe post-spraying process is continued until A2<50ppm of a compound of formula (I) wherein A2Is a second NOxNO measured by sensor 203xConcentration, T1Is the temperature, Q, measured by the first temperature sensor 102mIs the main fuel injection amount, Kp1Adjusting parameters for remote post-injection; remote post-spray adjustment parameter Kp10.25 is taken according to different lean-burn engine types and corresponding LNT system choices.
See fig. 3 for the system at high emissions (first NO)xNO measured by sensor 104xConcentration A1>400ppm), the process is as follows:
in the present embodiment, when engine 100 starts to operate, and A1Detecting NO in the LNT system 200 when the limit (400ppm) is exceededxReal-time memory space H<If 90% H is not present, then A is judged2If the amount exceeds the limit (75ppm), the urea injection device 301 injects the urea aqueous solution after the amount exceeds the limit, and if the amount exceeds the limit, the injection amount is P>0, spraying urea aqueous solution to the SCR system 300, waiting for A3Is lower thanThe removal is completed at the emission threshold (25 ppm); when P is present<0, calibrate the real-time ammonia storage M in the SCR system 300 and continue to determine P<0 or not, constituting a cycle, A1Is first NOxNO measured by sensor 104xConcentration, A2Is a second NOxNO measured by sensor 203xConcentration, A3Is a third NOxNO measured by sensor 302xConcentration, H, the maximum storage capacity calibrated for the LNT system; otherwise, the fuel injection device 101 implements a cooperative post-injection strategy, and simultaneously the hydrogen injection device 201 is opened, the hydrogen injection amount is U, so as to create a rich combustion environment for the LNT system 200 to carry out NOxThe rapid removal of the ammonia is realized, and the ammonia yield is improved.
In the present embodiment, the urea injection amount P is obtained by decomposing CO (NH) with a urea solution2)+H2O→2NH3+CO2And the SCR system 300 internal reduction equation, i.e., -M +0.5K1K2A2M is the real-time ammonia storage capacity, K, of the SCR system 3001For the excess compensation factor, this example takes 1.2; k2For the efficiency compensation factor, this example takes 1.25; a. the2Is a second NOxNO measured by sensor 203xAnd (4) concentration.
In the present embodiment, real-time ammonia storage utilization for SCR system 300
Figure BDA0002918242400000071
Figure BDA0002918242400000072
Calibration by the formula, MNVerifying ammonia storage, τ, of SCR system 300 prior to urea injection0Is a second NOxNO measured by sensor 203xConcentration A2>At time 75ppm,. taueIs a third NOxNO measured by sensor 302xConcentration A3<At time 25ppm, A2Is a second NOxNO measured by sensor 203xConcentration, A3Is a third NOxNO measured by sensor 302xAnd (4) concentration.
In this embodiment, the cooperative post-injection strategy is LNT System 200 operating a Rich Combustion Environment for NOxFast removing; co-operative post-injection of oil at T1When 900K, the fuel injection quantity Q isp1*＝Qp1-K3U＝Kp1Qm-K3U, wherein T1U is the injection quantity of the hydrogen gas injection device 201, Q is the temperature measured by the first temperature sensor 102mIs the main fuel injection amount, Kp1Adjusting parameters for far post-injection, adjusting parameters for far post-injection Kp1The present embodiment takes 0.25, K, depending on the type of lean-burn engine and the corresponding LNT system choice3And (4) selecting the synergistic adjustment coefficient according to the fuel injection quantity and the unit thereof, the hydrogen injection quantity unit and the corresponding LNT system.
In this embodiment, the cumulative real-time ammonia storage of the SCR system 300 is
Figure BDA0002918242400000081
MHChecking the ammonia storage of SCR system 300 for hydrogen injection amount, C1Is first NH3NH measured by sensor 2043Concentration, A3Is a third NOxNO measured by sensor 302xConcentration, A2Is a second NOxNO measured by sensor 203xConcentration, C2Is the second NH3NH measured by sensor 3033Concentration, T0For the opening time, T, of the hydrogen gas injection device 201eThe closing timing of the hydrogen injection device 201.
In the present embodiment, the amount U of hydrogen injected by the hydrogen injection device 201 is according to the equation
Figure BDA0002918242400000082
Calculation, i.e. U ═ M +4K4A2Wherein M is the real-time ammonia storage capacity, K, of the SCR system 3004For selective compensation of the coefficients, this example takes 1.5, A2Is a second NOxNO measured by sensor 203xConcentration; when U is turned<At 0, the hydrogen gas injection device 201 does not inject.
In the present embodiment, the total post-injection quantity Q of the engine 100p＝Qp1(Qp1*)+Qp2+Qp3Must not be greater than main fuel injection quantity QmAnd if the ratio exceeds 80%, selecting the strategy according to the priority of the far post injection, the middle post injection and the near post injection, namely executing the far post injection strategy firstly.
The invention aims to realize the high-efficiency starting of the rapid SCR reaction by utilizing the effects of heat release and free radical oxidation of the post-injection of the engine 100 and combining the further oxidation of the LNT system 200 and the low-temperature high ammonia selectivity of hydrogen, and simultaneously avoid the crystallization problem caused by the injection of a large amount of urea.
The following describes a high-efficiency denitration exhaust gas after-treatment system and a control method of the lean-burn engine with reference to specific embodiments.
In the specific embodiment, a heavy-duty diesel engine which adopts LNT + SCR technology and meets the national six-emission standard is taken as a prototype to evaluate NO of the control strategy of the aftertreatment systemxThe removal effect is compared with the control strategy of the original machine system (no hydrogen injection device and compound post-injection strategy). The engine is arranged on a rack to operate under a steady working condition, the rotating speed of the engine is controlled to be 1400r/min, and the load is controlled to be 25%.
Measuring NO at LNT inlet when original engine aftertreatment system control strategy is adoptedxConcentration of 704ppm, with NO concentration of 639 ppm; after LNT treatment, NO in the exhaust gas at the SCR inlet was measuredxAnd NH3The concentrations were 207ppm and 75ppm, respectively; NO in exhaust after SCR treatmentxThe concentration is 46 ppm; NO of SCR in original systemxThe removal rate was about 77.8%.
When the aftertreatment system strategy of the invention is adopted, after the composite post-injection strategy is started, NO at the inlet of the LNT is measuredxThe concentration is 515ppm, wherein the NO concentration is 304ppm, NO2The occupation ratio is obviously improved; after LNT treatment, NO in the exhaust gas at the SCR inlet was measuredxAnd NH3The concentrations are respectively 101ppm and 239 ppm; NO in exhaust after SCR treatmentxThe concentration is 13 ppm; NO for SCR in a system according to an embodiment of the inventionxThe removal rate was about 87%. NO/NO due to a composite post-injection strategyxHigh NH of turndown and low temperature hydrogen LNT3Alternative, NO of this embodimentxRemoval rateThe urea consumption is greatly reduced while the urea consumption is increased.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. While the foregoing is directed to the preferred embodiment of the present invention, and not intended to limit the invention to the particular form disclosed, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

Claims (12)

1. The efficient denitration tail gas aftertreatment system of the lean burn engine is characterized by comprising an engine, a fuel oil injection device, a hydrogen injection device, an LNT system, a urea injection device, an SCR system, an ASC device, a control module, a temperature sensor and a gas concentration sensor, wherein the LNT system, the SCR system and the ASC device are sequentially arranged in an exhaust pipeline of the engine according to the exhaust direction; the fuel injection device is positioned in the center of the cylinder cover of the engine, performs in-cylinder fuel post-injection, provides a rich combustion environment for an LNT system, and performs NOxAdjusting the content of each component and compensating the exhaust temperature; the hydrogen injection device is positioned at the front end of the LNT system and is close to the LNT system, and is used for injecting hydrogen into the front end of the LNT system and guiding the side reaction to generate more NH3Providing part of reducing agent for the SCR system; the urea injection device is positioned at the front end of the SCR system and is close to the SCR system, and is used for supplying a reducing agent to the SCR system to carry out NOxRemoving rapidly; temperature sensors and gas concentration sensors for detecting the gas temperature and the concentration of each gas component in the exhaust pipeline are arranged in the engine and the exhaust pipeline, wherein: the first temperature sensor is positioned in the engine and is close to the center of the cylinder cover; NO sensor and first NOxThe sensor is positioned at the front end of the engine exhaust pipeline and is close to the engine; a second temperature sensor is positioned between the engine and the LNT system and proximate to the LNT system; second NOxSensor and first NH3The sensor is located between the LNT system and the SCR system and is adjacent to the LNT systemA system; third NOxSensor and second NH3The sensors are sequentially positioned between the SCR system and the ASC device according to the exhaust direction; the control module is respectively connected with each injection device and a sensor for detecting the gas temperature and the gas concentration in each position of the engine and the exhaust pipeline, and judges the state of the LNT system and the NH required by the SCR system3Concentration, and reasonably controlling the amount of post-injected fuel, the amount of hydrogen and the amount of urea to optimize NO/NO inside the exhaust pipexThe proportion is improved, the ammonia production of the LNT system in the denitration of the SCR system is promoted, and the NO in the exhaust gas is favorably treatedxQuickly removing, avoiding crystallization caused by excessive urea injection as much as possible, and finally absorbing escaped NH by an ASC device3。
2. The control method of the high-efficiency denitration exhaust gas after-treatment system of the lean-burn engine as claimed in claim 1, which is divided into at least two stages, namely a low-emission stage and a high-emission stage, and realizes the high-efficiency denitration of the lean-burn engine exhaust gas by controlling the post-injection strategy, monitoring and compensating the exhaust temperature, and adjusting the hydrogen concentration and the ammonia concentration.
3. The method of claim 2, wherein the gas temperature T measured by the second temperature sensor is measured when the engine is initially running and in a low emission condition2<TbAt 50K, the fuel injection device implements a near-post injection strategy, and temperature compensation is carried out on the exhaust temperature so that T2Is kept at TbWithin + -50K, wherein, TbCorresponding to the optimal regeneration temperature of the LNT system.
4. The method of claim 3, wherein the low emission condition is first NOxNO measured by sensorxConcentration A1<400 ppm; the near-rear spraying strategy is that the near-rear spraying is carried out at T11300-1500K or main post-injection interval angle of 10-30 CA, and oil injection quantity Qp2＝Kp2(Tb-T2)(T1-T0)/QmIn which K isp2Adjusting parameters for near-after-injection, TbTo correspond to the optimum regeneration temperature, T, of the LNT system2Is the temperature, T, measured by the second temperature sensor1Is the temperature, T, measured by the first temperature sensor0Is the temperature, Q, measured by the first temperature sensor at mechanical top dead center of the enginemIs the main fuel injection amount.
5. The method for controlling the high-efficiency denitration exhaust gas after-treatment system of the lean-burn engine as claimed in claim 4, wherein the near-post injection adjusting parameter Kp2The method is selected according to different working conditions and lean-burn engine types, the engine types are sorted according to DIDiesel, RCCI and GDI (HCCI), and corresponding parameters are selected from 1.05-1.25 from high to low.
6. The method of claim 2, wherein the second NO is provided when the engine is initially running and in a low emission conditionxNO measured by sensorxConcentration A2NO for LNT system when limit is reachedxThe memory space is calibrated once and recorded as
Figure FDA0002918242390000021
t0The starting time of the engine or the starting time of the last fuel post-injection of the removal period, teIs a second NOxThe moment at which the sensor captures the limit signal, A2Is a second NOxNO measured by sensorxConcentration, A1Is first NOxNO measured by sensorxConcentration; when the engine starts to operate and is in a low emission condition, the second NOxNO measured by sensorxConcentration A2After the limit is exceeded, the fuel injection device implements a remote post-injection strategy to create a rich environment for the LNT system to carry out NOxRemoving; the far back spray strategy is that the far back spray is at T1800-1000K or main post-spraying interval angle 70About 90 CA, and oil injection quantity Qp1＝Kp1QmThe post-spraying process is continued until A2<50ppm of, wherein T1Is the temperature, Q, measured by the first temperature sensormIs the main fuel injection amount, Kp1Adjusting parameters for remote post-injection, A2Is a second NOxNO measured by sensorxAnd (4) concentration.
7. The method for controlling the high-efficiency denitration exhaust gas after-treatment system of the lean-burn engine as set forth in claim 6, wherein the low-emission condition is: first NOxNO measured by sensorxConcentration A1<400 ppm; second NOxNO measured by sensorxConcentration A2When the limit is reached, it means A2When the concentration is 50 plus or minus 5 ppm; overrun finger A2>55 ppm; post-spray adjustment parameter Kp1According to different lean-burn engine types and corresponding LNT systems, the higher the catalytic activity of the corresponding LNT system is, the higher the K isp1The smaller and the engine types in DIDiesel, RCCI, GDI (HCCI) ranking, the corresponding Kp1From high to low, 0.1-0.4 is selected.
8. The method of claim 2, wherein the fuel injection device implements a medium post-injection strategy to adjust the exhaust gas composition NO/NO when the engine is initially running and under high emission conditionsxA ratio; the medium and rear spraying strategy is that medium and rear spraying is carried out at T11000-1300K or main post-spraying with an interval angle of 30-70 CA, and medium post-spraying amount Qp3According to NO/NOxRatio R ═ B1/A1Regulating to control R to be 0.35 +/-0.05, namely Qp3＝Kp3QmB1/A1Wherein T is1Is the temperature measured by the first temperature sensor, B1NO concentration measured for NO sensor, A1Is first NOxNO measured by sensorxConcentration, QmIs the main fuel injection amount, Kp3Parameters were adjusted for medium and late post-injection.
9. The method of claim 8, wherein the high-emission conditions include: first NOxNO measured by sensorxConcentration A1>400 ppm; the middle and rear spray adjusting parameter Kp3The method is selected according to different working conditions and lean-burn engine types, the engine types are sorted according to DIDiesel, RCCI and GDI (HCCI), and corresponding parameters are selected from 1.1-1.5 from high to low.
10. The method of claim 2, wherein the NO in the LNT system is controlled when the engine is running and under high emission conditionsxThe storage capacity is accumulated in real time, and when the real-time storage capacity H is<90% H, and a second NOxNO measured by sensorxConcentration A2Above a limit value, the urea injection device injects the urea aqueous solution so that the third NOxNO measured by sensorxConcentration A3Below an emissions threshold, where H is a maximum storage capacity calibrated for the LNT system; when the engine starts to run and is in high emission condition, the NO in the LNT system is addedxThe storage capacity is accumulated in real time, when the real-time storage capacity H is larger than or equal to 90% H, the fuel injection device implements a cooperative remote post-injection strategy, and the hydrogen injection device is opened to build a rich combustion environment for an LNT system, improve the ammonia production and carry out NOxWherein H is the maximum storage capacity calibrated for the LNT system; when the engine starts to operate and the hydrogen injection device is started, the ammonia storage amount of the SCR system is accumulated, and the real-time storage amount is stored
Figure FDA0002918242390000031
MHChecking the ammonia storage of the SCR system before the hydrogen injection amount, P being the urea injection amount, C1Is first NH3NH measured by sensor3Concentration, A3Is a third NOxNO measured by sensorxConcentration, C2Is the second NH3NH measured by sensor3Concentration, T0For the opening time, T, of the hydrogen injection deviceeThe closing timing of the hydrogen injection device.
11. The method of claim 11, wherein the high-emission conditions are: first NOxNO measured by sensorxConcentration A1>400 ppm; under high emission conditions, the limit is 75ppm and the emission threshold is 25 ppm; decomposing CO (NH) by adopting urea solution for the urea injection quantity P2)+H2O→2NH3+CO2And SCR system internal reduction equation calculation, i.e., -M +0.5K1K2A2M is the real-time ammonia storage amount of the SCR system; k1Taking 1.1-1.3 as an excessive compensation coefficient; k2Selecting 1.1-1.4 according to different SCR systems as an efficiency compensation coefficient; when P is present<At 0, the urea injection device does not inject, and the ammonia storage amount of the SCR system is calibrated at the moment
Figure FDA0002918242390000041
MNChecking the ammonia storage of the SCR system before urea injection, tau0Is a second NOxNO measured by sensorxConcentration A2At a time, τ, greater than a limit of 75ppmeIs a third NOxNO measured by sensorxConcentration A3At a time below the 25ppm emission threshold, A3Is a third NOxNO measured by sensorxConcentration, A2Is a second NOxNO measured by sensorxConcentration; the cooperative remote post-spraying strategy is characterized in that the cooperative remote post-spraying is carried out at T1800-1000K or main post-injection interval angle of 70-90 CA, and oil injection quantity Qp1*＝Kp1Qm-K3U, where U is the injection quantity of the hydrogen injection device, Kp1Adjusting parameters, Q, for remote post-injectionmIs the main fuel injection amount, K3Selecting a synergistic regulation coefficient according to an oil injection quantity unit, a hydrogen injection quantity unit and a corresponding LNT system; the hydrogen quantity of the hydrogen injection device is UAccording to the equation
Figure FDA0002918242390000042
Figure FDA0002918242390000043
Calculation, i.e. U ═ M +4K4A2In which K is4Taking 1.25-1.8 as a selective compensation coefficient, wherein M is the real-time ammonia storage amount of the SCR system, and A2Is a second NOxNO measured by sensorxConcentration; when U is turned<At 0, the hydrogen gas injection device does not inject.
12. The method for controlling the high-efficiency denitration exhaust gas after-treatment system of the lean-burn engine as claimed in claims 2 to 11, wherein the total post-injection quantity Q of the engine isp＝Qp1(Qp1*)+Qp2+Qp3Must not be greater than main fuel injection quantity QmAnd if the ratio exceeds 80%, selecting the strategy according to the priority of the far post injection, the middle post injection and the near post injection, namely executing the far post injection strategy firstly.
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