CN115506874A - Post-processing device for two-stage active and passive SCR coupled hydrogen fuel internal combustion engine and control method thereof - Google Patents

Abstract

The invention relates to a post-processing device for a two-stage active and passive SCR coupled hydrogen fuel internal combustion engine and a control method thereof. The device comprises a plurality of H-shaped connecting pipes connected in sequence ₂ A selective hydrogen catalytic reduction catalyst (2) as a reducing agent and NH ₃ A selective ammonia catalytic reduction catalyst (4) being a reducing agent; a connecting pipeline is arranged between the selective hydrogen catalytic reduction catalyst (2) and the selective ammonia catalytic reduction catalyst (4), and the connecting pipeline is connected with a urea supply source (13); and one end of the selective hydrogen catalytic reduction catalyst (2) far away from the connecting pipeline is provided with an air inlet pipeline for hydrogen combustion engine tail gas to enter, and the air inlet pipeline is connected with a hydrogen supply source. Compared with the prior art, the hair conditionerInventive Simultaneous introduction of H in an aftertreatment System ₂ The nozzle and the urea nozzle supplement the reducing agent H in real time according to the feedback information of the sensor in the electric control unit ₂ Or NH ₃ Coupling active and passive SCR to H ₂ NH generated by SCR devices ₃ The reducing agent is fully utilized to realize low-cost NO _x High-efficiency emission reduction.

Description

A dual-stage-active-passive SCR coupling hydrogen fuel internal combustion engine post-processing device and its Control Method

technical field

The invention relates to the field of automobile engines, in particular to a dual-stage-active-passive SCR coupling hydrogen fuel internal combustion engine post-processing device and a control method thereof.

Background technique

Among the emissions from hydrogen fueled internal combustion engines, nitrogen oxides are the only harmful emissions. The increased combustion rate of the rich mixture leads to higher cylinder pressure and temperature, which ultimately leads to increased NOx emissions. Therefore, in order to obtain the lowest NO _x emissions, the hydrogen engine needs to operate at an equivalence ratio between 0.5 and 0.6. Lean combustion can avoid backfiring in hydrogen-fueled internal combustion engines, but a leaner mixture will cause insufficient engine torque. Although the reduction of NO _x emissions can be achieved by adjusting the injection timing and intake phase, the introduction of aftertreatment devices will enable hydrogen fueled internal combustion engines to achieve low NO _x emissions while maintaining power.

Selective catalytic reduction technology is currently the mainstream technology for NO _x treatment in diesel engine aftertreatment systems. This technology can be subdivided into NH ₃ -SCR and H ₂ -SCR according to the reducing agent used. NH ₃ -SCR uses urea aqueous solution or ammonia water to reduce NO _x to N ₂ and H ₂ O under a certain temperature window and catalytic conditions, because NH ₃ as a reducing agent reacts preferentially with NO _x under the action of a catalyst, rather than with _O2 reaction, showing high selectivity. NH ₃ -SCR usually uses copper or iron or copper-iron composite molecular sieve as catalyst. However, H ₂ -SCR uses H ₂ as a reducing agent, and usually uses Pd-based and Pt-based materials as catalysts.

Patent CN108678864B discloses a control method for hydrogen engine start-up emission reduction and hydrogen consumption rate. The method adopts a rich-burn start strategy and cooperates with a three-way catalytic converter to achieve ultra-low emission of hydrogen engine start-up NO _x ; by dividing the engine The temperature range of the catalytic converter carrier before starting, combined with the influence mechanism of the concentration of hydrogen-air mixture on the formation of _NOx and the influence mechanism of temperature on the catalytic efficiency of the three-way catalytic converter, corresponding control methods are implemented for different temperature ranges to reduce the starting process. Hydrogen consumption rate. This patent not only has complex control strategies, but also requires high sensor accuracy and control accuracy, and is not friendly to engine economy.

Patent 201810924790.0 discloses a combined aftertreatment device suitable for hydrogen fuel internal combustion engines. The control of NO _x emissions is realized through the combined TWC+SCR device, but TWC can only achieve efficient emission reduction under the stoichiometric ratio (λ=1), and the stoichiometric hydrogen internal combustion engine has poor power. The power performance of the hydrogen internal combustion engine is good under the condition of lean combustion (λ>1), but the _O2 content in the exhaust gas is high, which greatly reduces the conversion efficiency of TWC to _NOx , so the TWC+SCR device provided by this invention is only suitable for stoichiometric Compared with the hydrogen internal combustion engine, it cannot meet the _NOx emission requirements of the high-power lean-burn hydrogen internal combustion engine, and its practicability is low.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects in the prior art and provide a method capable of realizing continuous and efficient emission reduction of _NOx in the tail gas of a hydrogen-fueled internal combustion engine with a wide exhaust temperature window, and solving the problem of high _NOx emissions of hydrogen internal combustion engines A dual-stage-active-passive SCR coupled post-processing device for a hydrogen fuel internal combustion engine and a control method thereof.

The purpose of the present invention can be achieved through the following technical solutions:

The invention provides a dual-stage-active-passive SCR coupling hydrogen fuel internal combustion engine post-processing device. The hydrogen fuel internal combustion engine post-processing device provided by the present invention includes two post-processing devices, H ₂ -SCR and NH ₃ -SCR, and also includes an H ₂ nozzle and a urea nozzle. By combining H ₂ -SCR with good activity at low temperature and NH ₃ -SCR with good activity at medium and high temperature, efficient conversion of NO _x can be achieved within a wide exhaust temperature window. At the same time, install H ₂ nozzles upstream of H ₂ -SCR, install urea nozzles upstream of NH ₃ -SCR, replenish reducing agent H ₂ or NH ₃ in real time according to the sensor feedback information in the electronic control unit, couple active and passive SCRs, and make full use of the system's spontaneous Generated reducing agent NH ₃ . This patent is not only applicable to hydrogen-fueled internal combustion engines with a wide range of operating conditions, but also reduces the number of urea injections to achieve low-cost and efficient reduction of _NOx emissions. The specific scheme is as follows:

A dual-stage-active-passive SCR coupling hydrogen fuel internal combustion engine after-treatment device, the device includes sequentially connected selective hydrogen catalytic reduction catalyst with H ₂ as the reducing agent, referred to as H ₂ -SCR, and NH ₃ as the Selective ammonia catalytic reduction catalyst for reducing agent, referred to as NH ₃ -SCR;

A connecting pipe is arranged between the selective hydrogen catalytic reduction catalyst and the selective ammonia catalytic reduction catalytic converter, and the connecting pipe is connected with a urea supply source;

The end of the selective hydrogen catalytic reduction catalyst away from the connecting pipe is provided with an intake pipe for hydrogen internal combustion engine exhaust gas to enter, and the intake pipe is connected with a hydrogen supply source.

Further, the intake pipe is provided with a hydrogen nozzle connected to a hydrogen supply source, and a front gas sensor for detecting the composition and/or temperature of the intake air.

Further, the front gas sensor includes a front temperature sensor, a front _NOx sensor and a H ₂ sensor.

Further, the connecting pipeline is provided with a urea nozzle connected to the urea supply source, and a medium gas sensor for detecting the composition and/or temperature of the reaction gas.

Further, the medium gas sensor includes a medium temperature sensor, a medium NO _x sensor and a NH ₃ sensor. Further, the side of the selective ammonia catalytic reduction catalyst away from the connecting pipe is provided with an outlet pipe; the outlet pipe is provided with a rear _NOx sensor for detecting the _NOx content in the exhaust gas.

Further, the device also includes an electronic control unit for receiving and feeding back signals, and the electronic control unit is signally connected with the hydrogen nozzle, the urea nozzle, the front gas sensor, the middle gas sensor and the rear _NOx sensor.

A method for controlling an aftertreatment device for a hydrogen fuel internal combustion engine with dual-stage-active-passive SCR coupling as described above, the control method comprising the following steps:

St.1 Obtain the working condition information on the intake pipe, and judge whether the exhaust temperature is lower than 300°C;

St.2 uses the selective hydrogen catalytic reduction catalyst and the selective ammonia catalytic reduction catalyst to treat the exhaust gas of the hydrogen internal combustion engine;

St.3 When the current temperature sensor detects that the exhaust gas temperature is lower than 300°C, start the hydrogen injection control step; when the exhaust gas temperature is not lower than 300°C, start the urea injection control step.

Further, the hydrogen injection control step is: start the _NOx conversion MAP based on the selective hydrogen catalytic reduction catalyst to judge the minimum threshold value C _min1 of H ₂ , and monitor whether the concentration of H ₂ is lower than the minimum threshold value C by collecting H ₂ sensors in real time _min1 , when the H ₂ concentration is less than C _min1 , open the hydrogen nozzle and inject hydrogen; when the H ₂ concentration is not less than C _min1 , return to St.2.

Further, the urea injection control step is: starting the NOx conversion MAP based on the selective hydrogen catalytic reduction catalyst, the NOx conversion MAP of the selective ammonia catalytic reduction catalyst and the NH3 absorption and desorption model to judge the minimum NH3 threshold C _min2 , By collecting the signals of _H2 sensor, temperature sensor, medium _NOx sensor and _NH3 sensor in real time, the conversion efficiency of _NOx is monitored, and it is judged in real time whether the concentration of _NH3 is lower than the minimum threshold C _min2 . When the concentration of _NH3 is lower than C _min2 , the urea is turned on Nozzle, spray urea; when the NH ₃ concentration is not less than C _min2 , return to St.2.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention provides a dual-stage-active-passive SCR coupled hydrogen fuel internal combustion engine post-processing device, including two post-processing devices, H ₂ -SCR with good low-temperature activity and NH ₃ -SCR with good mid-high temperature activity. Realize efficient conversion of _NOx within a wide exhaust temperature window, suitable for hydrogen-fueled internal combustion engines with a wide range of operating conditions;

(2) The present invention installs _H2 nozzles and urea nozzles in the post-processing device, supplements the reducing agent _H2 or _NH3 in real time according to the feedback information of the sensor in the electronic control unit, and couples active and passive SCRs to generate _H2 -SCR devices. The NH ₃ reducing agent is fully utilized to achieve low-cost and high-efficiency NO _x emission reduction;

(3) The present invention also provides an injection control strategy applicable to a dual-stage-active-passive SCR coupled post-processing device. Based on real-time monitored temperature and gas concentration signals, it is judged whether the reducing agent concentration is lower than the minimum threshold. When it is judged to be low At that time, reducer injection is started.

Description of drawings

Fig. 1 is the schematic diagram of aftertreatment device in the embodiment;

Fig. 2 is the schematic diagram of injection strategy in the embodiment;

The numbers in the figure show: hydrogen nozzle 1, selective hydrogen catalytic reduction catalyst 2, urea nozzle 3, selective ammonia catalytic reduction catalytic converter 4, front temperature sensor 5, front NO _x sensor 6, H ₂ sensor 7, medium temperature Sensor 8, middle _NOx sensor 9, NH ₃ sensor 10, rear _NOx sensor 11, electronic control unit 12, urea supply source 13.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and the detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

Example

A dual-stage-active-passive SCR coupling hydrogen fuel internal combustion engine post-processing device and its control method, as shown in Figure 1, including a hydrogen nozzle 1, a selective hydrogen hydrogen nozzle with _H2 as a reducing agent arranged behind the hydrogen nozzle 1 Catalytic reduction catalyst 2, the urea nozzle 3 arranged behind the selective hydrogen catalytic reduction catalyst 2, the selective ammonia catalytic reduction catalyst 4 with _NH3 as the reducing agent arranged behind the urea nozzle 3, the airflow flows through the aftertreatment in sequence Install H ₂ -SCR and NH ₃ -SCR, and finally discharge into the atmosphere.

It also includes front temperature sensor 5, front _NOx sensor 6 and _H2 sensor ₇ installed in front of _{H2 -} SCR, middle temperature sensor 8, middle _NOx sensor 9 and NH ₃ sensor 10, rear NO _x sensor 11 installed behind NH ₃ -SCR, electronic control unit 12 and urea injection control unit 13 for receiving and feeding back signals.

In the hydrogen-fueled internal combustion engine aftertreatment device, the exhaust gas first flows through the aftertreatment device H ₂ -SCR, and the chemical reaction process of NO _x in the exhaust gas in the H ₂ -SCR includes chemical formula (1) and chemical formula (2):

Chemical formula (1)NI+2.5H ₂ →NH ₃ +H ₂ O

Chemical formula (2) NO ₂ +3.5H ₂ →NH ₃ +2H ₂ O

Then the gas flow flows through NH ₃ -SCR, and the NH ₃ generated by chemical formula (1) and chemical formula (2) is adsorbed by NH ₃ -SCR, which can be further used as a reducing agent to react with NO _x . The chemical reaction process is as shown in chemical formula (3) Shown in chemical formula (5):

Chemical formula (3) 4NO+4NH ₃ +O ₂ →4N ₂ +6H ₂ O

Chemical formula (4) 8NH ₃ +6NO ₂ →7N ₂ +12H ₂ O

Chemical formula (5) NO+2NH ₃ +NO ₂ →2N ₂ +3H ₂ O

At low exhaust gas temperature, the H ₂ -SCR aftertreatment device with good low temperature activity will convert NO _x into NH ₃ and H ₂ O through chemical formula (1) and chemical formula (2), and the product NH in H ₂ -SCR ₃ enters the NH ₃ -SCR and is adsorbed.

At medium and high exhaust gas temperatures, NH ₃ -SCR with good medium and high temperature activity converts NH ₃ and NO _x into harmless N ₂ and H ₂ O through chemical formula (3), chemical formula (4) and chemical formula (5), and finally realizes High-efficiency NO _x emission reduction for hydrogen-fueled internal combustion engines under wide operating conditions.

When the electronic control unit 12 detects that the reducing agent _H2 or NH needs to be replenished through the feedback information from the front temperature sensor 5, the front _NOx sensor 6, the _H2 sensor 7, the middle temperature sensor 8, the middle _NOx sensor 9, and the _NH3 sensor 10 ₃ , hydrogen nozzle 1 and urea nozzle 3 can inject _H2 and urea producing _NH3 into the system respectively. Finally, the efficient emission reduction effect of NO _x is monitored by the rear NO _x sensor 11 to further realize the efficient emission reduction of NO _x .

When NH ₃ -SCR only relies on NH ₃ , the product of H ₂ -SCR, to achieve efficient NO _x conversion, it is called passive NH ₃ -SCR. When NH ₃ -SCR cannot completely convert _NOx by relying only on the product NH ₃ of H ₂ -SCR, it is necessary to control the urea injection control unit 13 to inject urea supplementary reducing agent NH ₃ into the system through the urea injection control unit 13, which is called active SCR .

As shown in Figure 2, the embodiment adopts the following injection control strategy. By collecting the signals of the front temperature sensor 5 and the front _NOx sensor 6 in real time, it is judged in real time whether the exhaust gas temperature is lower than 300°C. When the H ₂ -SCR-based NO _x conversion MAP is started to determine the minimum H ₂ threshold C _min1 , the H 2 concentration is monitored by real-time acquisition of the H ₂ sensor 7 to see if the H ₂ concentration is lower than the minimum threshold C _min1 . .

When it is judged that the exhaust gas temperature is higher than 300°C, the NO _x conversion MAP based on H ₂ -SCR, the NO _x conversion MAP of NH ₃ -SCR and the NH ₃ adsorption-desorption model are started to determine the minimum threshold value C _min2 of NH ₃ , and the real-time acquisition _H2 sensor 7, medium temperature sensor 8, medium _NOx sensor 9 and _NH3 sensor 10 signal, monitor _NOx conversion efficiency, judge in real time whether the _NH3 concentration is lower than the minimum threshold C _min2 , when less than, open the urea nozzle, spray urea.

In summary, at present, with the clarification of China's dual-carbon goals, hydrogen internal combustion engines have received widespread attention as a zero-carbon emission power plant, but the contradiction between its power performance and NO _x emissions has not yet been resolved. This post-treatment device innovatively combines H ₂ -SCR with high activity at low temperature and NH ₃ -SCR with high activity at medium and high temperature to achieve efficient conversion of NO _x in a wide exhaust temperature window and is suitable for hydrogen in a wide range of operating conditions fuel internal combustion engine. The invention innovatively introduces the H ₂ nozzle and the urea nozzle into the post-treatment system at the same time, supplements the reducing agent H ₂ or NH ₃ in real time according to the feedback information of the sensor in the electronic control unit, couples the active and passive SCR, and treats the NH produced by the H ₂ -SCR device ₃ The reducing agent is fully utilized to achieve low-cost and high-efficiency emission reduction of NO _x , which has broad application prospects.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention to other forms. Any skilled person who is familiar with this profession may use the technical content disclosed above to change or modify the equivalent of equivalent changes. Example. However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims (10)

1. A dual-stage-active-passive SCR coupled hydrogen fuel internal combustion engine aftertreatment device is characterized in that the device comprises sequentially connected _H2 as a selective hydrogen catalytic reduction catalyst (2) and NH ₃ is the selective ammonia catalytic reduction catalyst (4) of reducing agent; A connecting pipeline is arranged between the selective hydrogen catalytic reduction catalyst (2) and the selective ammonia catalytic reduction catalyst (4), and the connecting pipeline is connected with the urea supply source (13); The end of the selective hydrogen catalytic reduction catalyst (2) away from the connection pipe is provided with an intake pipe for hydrogen internal combustion engine exhaust to enter, and the intake pipe is connected with a hydrogen supply source. 2. A kind of dual-stage-active-passive SCR coupled hydrogen fuel internal combustion engine post-processing device according to claim 1, characterized in that, said intake pipe is provided with a hydrogen nozzle (1) connected to a hydrogen supply source ), and front gas sensors to detect intake air composition and/or temperature. 3. a kind of dual-stage-active-passive SCR coupled hydrogen fuel internal combustion engine aftertreatment device according to claim 2, is characterized in that, described front gas sensor comprises front temperature sensor (5), front _NOx sensor ( 6) and _H2 sensor (7). 4. A dual-stage-active-passive SCR coupling hydrogen fuel internal combustion engine post-processing device according to claim 1, characterized in that, the connecting pipeline is provided with a urea nozzle connected to the urea supply source (13) (3), and a medium gas sensor for detecting reagent gas composition and/or temperature. 5. A kind of double-stage-active-passive SCR coupled hydrogen fuel internal combustion engine aftertreatment device according to claim 4, is characterized in that, described middle gas sensor comprises middle temperature sensor (8), middle _NOx sensor ( 9) and NH ₃ sensor (10). 6. A dual-stage-active-passive SCR coupled hydrogen fuel internal combustion engine post-processing device according to claim 1, characterized in that the side of the selective ammonia catalytic reduction catalyst (4) away from the connecting pipeline An outlet pipe is provided; the outlet pipe is provided with a rear _NOx sensor (11) for detecting the _NOx content in the exhaust gas. 7. A dual-stage-active-passive SCR coupling hydrogen fuel internal combustion engine after-treatment device according to any one of claims 1-6, characterized in that the device also includes an electronic control unit for receiving and feeding back signals (12), the electronic control unit (12) is signal-connected with the hydrogen nozzle (1), the urea nozzle (3), the front gas sensor, the middle gas sensor and the rear _NOx sensor (11). 8. A method for controlling the post-processing device for a hydrogen fuel internal combustion engine with dual-stage-active-passive SCR coupling as claimed in any one of claims 1-7, characterized in that the control method comprises the following steps: St.1 Obtain the working condition information on the intake pipe, and judge whether the exhaust temperature is lower than 300°C; St.2 uses the selective hydrogen catalytic reduction catalyst (2) and the selective ammonia catalytic reduction catalyst (4) to treat the exhaust gas of the hydrogen internal combustion engine; St.3 When the current temperature sensor (5) detects that the exhaust gas temperature is lower than 300°C, the hydrogen injection control step is started; when the exhaust gas temperature is not lower than 300°C, the urea injection control step is started. 9. A method for controlling a dual-stage-active-passive SCR-coupled hydrogen fuel internal combustion engine post-processing device according to claim 1, wherein the hydrogen injection control step is: start the selective hydrogen catalytic reduction based The NO _x conversion MAP of the catalytic converter (2) judges the minimum threshold value C min1 of H _{2 , monitors whether the H 2 concentration} is lower than the minimum threshold value C _min1 by collecting the H 2 sensor (7) in _real time, and turns on the hydrogen nozzle when the H ₂ concentration is lower than C _min1 (1), inject hydrogen; when the concentration of H ₂ is not less than C _min1 , return to St.2. 10. A control method for a dual-stage-active-passive SCR coupled hydrogen fuel internal combustion engine post-processing device according to claim 1, characterized in that the urea injection control step is: start the selective hydrogen catalytic reduction based The NOx conversion MAP of the catalytic converter (2), the NOx conversion MAP of the selective ammonia catalytic reduction catalytic converter (4), and the NH3 adsorption and desorption model determine the minimum threshold C _min2 of NH3, and the real-time acquisition of the H2 sensor (7), temperature sensor (8 ), middle NO _x sensor (9) and NH ₃ sensor (10) signals, monitor NO _x conversion efficiency, judge in real time whether the NH ₃ concentration is lower than the minimum threshold C _min2 , when the NH ₃ concentration is less than C _min2 , open the urea nozzle ( 3), inject urea; when the concentration of NH ₃ is not less than C _min2 , return to St.2.

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