Ammonia fuel engine aftertreatment system and control method

Abstract

The invention discloses an ammonia fuel engine post-processing system and a control method, and relates to the field of ammonia fuel engines, in the system, an air branch is fully mixed with ammonia fuel injected from an ammonia fuel nozzle at an intake manifold through a first mixer; after mixed gas participates in combustion in a cylinder, waste gas is exhausted after acting through a turbine; waste gas sequentially passes through the first-stage SCR, the second mixer, the second-stage SCR and the ammonia leakage catalyst; the ammonia reducing agent nozzle is arranged at an inlet of the second mixer; the sensor modules are respectively arranged at a position between the first-stage SCR and the second-stage SCR and a position behind the ammonia leakage catalyst; and the ammonia reducing agent nozzle takes measurement data of the sensor module as an input boundary, and performs active and passive ammonia injection control through logical judgment. The problem that NOx is contained in exhaust gas of an existing ammonia engine and unburned ammonia is discharged can be solved.

Description

Technical Field

[0001] The present application relates to the field of ammonia fuel engines, and in particular to an ammonia fuel engine after-treatment system and a control method. Background Art

[0002] With the current development needs, the research and development of new low-carbon and zero-carbon alternative fuels and their engine technologies is imminent. The development of ammonia fuel engines is currently an ideal route. At present, the emission requirements for both automotive and marine engines are becoming more and more stringent, and the emission limits for NOx (nitrogen oxides) and ammonia are tightened. However, ammonia engines have high NOx emissions and produce a large amount of unburned ammonia. The existing ammonia fuel engine after-treatment system only has a dual SCR route for marine after-treatment, and does not involve the control of the after-treatment system.

[0003] Based on the above problems, there is an urgent need to provide an ammonia fuel engine after-treatment system and control method that can solve the problem of NOx and unburned ammonia in the exhaust of existing ammonia fuel engines, thereby meeting the emission requirements of automotive ammonia fuel engines and marine ammonia fuel engines. Summary of the invention

[0004] The purpose of the present application is to provide an ammonia fuel engine after-treatment system and control method, which can solve the problem of NOx and unburned ammonia in the exhaust gas of existing ammonia fuel engines.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides an ammonia fuel engine aftertreatment system, the ammonia fuel engine aftertreatment system comprising: an air branch, a first mixer, an ammonia fuel nozzle, a cylinder, a turbine, a first stage SCR, an ammonia reductant nozzle, a second mixer, a second stage SCR, an ammonia slip catalyst, and a sensor module;

[0007] The air branch is fully mixed with the ammonia fuel injected from the ammonia fuel nozzle at the intake manifold through the first mixer; after the mixed gas is burned in the cylinder, the exhaust gas is discharged after the turbine works; the exhaust gas passes through the first-stage SCR, the second mixer, the second-stage SCR and the ammonia leakage catalyst in sequence; the ammonia reductant nozzle is arranged at the inlet of the second mixer; the sensor modules are respectively arranged at the position between the first-stage SCR and the second-stage SCR and the position after the ammonia leakage catalyst;

[0008] The ammonia reducing agent nozzle uses the measurement data of the sensor module as an input boundary and performs active and passive ammonia reducing agent injection control through logical judgment.

[0009] Optionally, the air branch includes an air filter, a compressor, an intercooler and a throttle valve connected in sequence.

[0010] Optionally, the sensor module includes: a first nitrogen oxide sensor, an ammonia sensor, a first temperature sensor, a second nitrogen oxide sensor, and a second temperature sensor;

[0011] The first nitrogen oxide sensor and the ammonia sensor are arranged on the pipeline between the first-stage SCR and the second mixer; the first temperature sensor is arranged on the pipeline between the second mixer and the second-stage SCR; the second nitrogen oxide sensor and the second temperature sensor are arranged on the pipeline at the outlet of the ammonia slip catalyst.

[0012] Optionally, the direct injection combustion aid in the cylinder includes: diesel, hydrogen and dimethyl ether.

[0013] In a second aspect, the present application provides a control method for an ammonia fuel engine aftertreatment system, which is applied to the ammonia fuel engine aftertreatment system. The control method for the ammonia engine aftertreatment system includes:

[0014] Check whether the reading of the ammonia sensor is 0;

[0015] If the reading of the ammonia sensor is 0, the reading of the first nitrogen oxide sensor is not 0, and the ammonia reducing agent nozzle is not working, it is determined whether the absolute value of the difference between the measurement value NOx1 of the first nitrogen oxide sensor and the measurement value NOx2 of the second nitrogen oxide sensor is less than or equal to the first threshold value. If so, the NOx in the first-stage SCR is not completely converted, and the ammonia reducing agent nozzle is controlled to start spraying, and ammonia gas is sprayed by ammonia reserve closed-loop injection or open-loop ammonia nitrogen ratio;

[0016] If the reading of the ammonia sensor is not 0, the reading of the first nitrogen oxide sensor is not 0, and the difference between the ammonia sensor and the first nitrogen oxide sensor is less than or equal to the second threshold, the ammonia scorer starts to work and determines the ammonia mass flow rate by using the ammonia concentration value measured by the ammonia sensor;

[0017] When the maximum ammonia adsorption amount in the ammonia slip catalyst is greater than or equal to the adsorption amount threshold, the ammonia fuel nozzle is controlled to reduce the injection amount of the ammonia fuel;

[0018] If the absolute value of the difference between the ammonia sensor and the first nitrogen oxide sensor is greater than the second threshold, the catalyst active sites in the first-stage SCR are saturated, and NOx and NH3 are not completely converted in the first-stage SCR. The correction factor of the ammonia fuel equivalent NOx is determined by the average temperature of the first-stage SCR and the second-stage SCR. The indication of the first nitrogen oxide sensor is corrected according to the correction factor, and the corrected indication is used as the input of the second-stage SCR, and ammonia injection is performed according to the ammonia storage closed loop or open loop.

[0019] Optionally, the ammonia fuel mass flow rate specifically includes the following formula:

[0020] Ammonia mass flow rate (mg / s) = ammonia concentration × exhaust flow rate × 277.78 × 17 / 10^3 / 29.

[0021] Optionally, the process of determining the adsorption amount threshold is:

[0022] Determine the average temperature of the first-stage SCR and the second-stage SCR according to the readings of the first temperature sensor and the second temperature sensor;

[0023] The adsorption amount threshold is determined according to the average temperature of the first-stage SCR and the second-stage SCR and the ammonia adsorption amount of the ASC varying with temperature MAP.

[0024] Optionally, the corrected indication NOx3 is determined using the formula NOx3=NOx1-NH3 concentration×β; wherein β is the correction factor.

[0025] Optionally, the process of ammonia injection in a closed loop of ammonia storage is:

[0026] Obtain the ammonia storage set value and the actual ammonia storage value in the first-stage SCR and the second-stage SCR;

[0027] The dynamic ammonia demand is obtained by adjusting the deviation between the ammonia storage set value and the actual ammonia storage value through PI control;

[0028] The steady-state ammonia demand is obtained based on the difference between the actual ammonia injection amount and the ammonia storage change amount;

[0029] The closed-loop ammonia demand is obtained by adding the steady-state ammonia demand and the dynamic ammonia demand.

[0030] Optionally, the process of open loop ammonia injection is:

[0031] Determine the ring-opening ammonia demand based on the air velocity and the average temperature of the first-stage SCR and the second-stage SCR;

[0032] Ammonia open and closed loop injection is performed according to the open loop ammonia demand.

[0033] According to the specific embodiments provided in this application, this application has the following technical effects:

[0034] The present application provides an ammonia engine aftertreatment system and a control method, which uses ammonia injection based on ammonia fuel engine technology and installs a mixer at the intake manifold position to fully premix ammonia and air, thereby improving the combustion efficiency in the cylinder; the dual SCR aftertreatment provided by the present application adopts active and passive ammonia injection control, that is, the first-stage SCR does not spray NH3, and uses the unburned ammonia in the engine exhaust to convert NOx, greatly improving the utilization rate of the unburned ammonia in the engine exhaust, saving costs, and the ammonia reductant nozzle uses the original ammonia supply system of the system, and does not require the urea injection device commonly used in the current aftertreatment, avoiding the risk of crystallization caused by urea injection. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 This is a schematic diagram of the structure of an ammonia engine after-treatment system in one embodiment of the present application;

[0037] Figure 2 This is a flow chart of a control method for an ammonia engine after-treatment system in one embodiment of the present application;

[0038] Figure 3 Schematic diagram of the ammonia injection principle. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0040] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0041] In an exemplary embodiment, Figure 1 As shown, an ammonia fuel engine after-treatment system is provided, which includes: an air branch, a first mixer, an ammonia fuel nozzle, a cylinder, a turbine, a first-stage SCR, an ammonia reductant nozzle, a second mixer, a second-stage SCR, an ammonia leak catalyst and a sensor module; the direct injection combustion aid in the cylinder includes but is not limited to: highly reactive fuels such as diesel, hydrogen and dimethyl ether.

[0042] The air branch is fully mixed with the ammonia injected from the ammonia fuel nozzle at the intake manifold through the first mixer; after the mixed gas participates in combustion in the cylinder, the exhaust gas is discharged after passing through the turbine; the exhaust gas passes through the first-stage SCR, the second mixer, the second-stage SCR and the ammonia leakage catalyst in sequence; the ammonia reductant nozzle is arranged at the inlet of the second mixer; the sensor modules are respectively arranged at the position between the first-stage SCR and the second-stage SCR and at the position after the ammonia leakage catalyst; that is, in the present application, no reductant injection device is arranged before the first-stage SCR, and only unburned ammonia in the exhaust gas is used to convert NOx, thereby further improving the utilization rate of unburned NH3 in the engine exhaust and saving costs.

[0043] The ammonia reducing agent nozzle uses the measurement data of the sensor module as an input boundary and performs active and passive ammonia injection control through logical judgment.

[0044] The specific logical judgment is:

[0045] There is no NH3 gas injector before the first-stage SCR. It only relies on the unburned ammonia in the exhaust of the ammonia engine to convert NOx in the SCR, and detects the readings of the first nitrogen oxide sensor and the ammonia sensor. In the actual process, there are two situations in the detection of NOx and NH3 in the exhaust after the first-stage SCR. The first is that the NOx concentration and NH3 concentration are both 0, indicating that the NOx and unburned ammonia in the exhaust are completely reacted in the first-stage SCR. The other situation is that the NH3 concentration measured by the ammonia sensor and the NOx concentration measured by the first nitrogen oxide sensor are not both 0. This result is divided into the following three situations: NOx is not completely converted (situation 1), NH3 leakage occurs (situation 2), and the catalyst active site adsorption is saturated, and NOx and NH3 are both leaked (situation 3).

[0046] The air branch circuit includes an air filter, a compressor, an intercooler and a throttle valve which are connected in sequence.

[0047] The sensor module includes: a first nitrogen oxide sensor, an ammonia sensor, a first temperature sensor, a second nitrogen oxide sensor, and a second temperature sensor;

[0048] The first nitrogen oxide sensor and the ammonia sensor are arranged on the pipeline between the first-stage SCR and the second mixer; the first temperature sensor is arranged on the pipeline between the second mixer and the second-stage SCR; the second nitrogen oxide sensor and the second temperature sensor are arranged on the pipeline at the outlet of the ammonia slip catalyst.

[0049] Based on the same inventive concept, the embodiment of the present application also provides a control method for implementing the above-mentioned ammonia fuel engine aftertreatment system. The implementation scheme for solving the problem provided by the control method is similar to the implementation scheme recorded in the above-mentioned method, so the specific limitations in the control method embodiments of one or more ammonia fuel engine aftertreatment systems provided below can refer to the above-mentioned limitations on ammonia fuel engine aftertreatment systems, and will not be repeated here.

[0050] In an exemplary embodiment, Figure 2 As shown, a control method for an ammonia fuel engine aftertreatment system is provided, comprising:

[0051] S1, check whether the reading of the ammonia sensor is 0;

[0052] S2, if the ammonia sensor indicates 0, the nitrogen oxide sensor indicates not 0, and the ammonia reducing agent nozzle is not working, determine whether the absolute value of the difference between the first nitrogen oxide sensor measurement value NOx1 and the second nitrogen oxide sensor measurement value NOx2 is less than or equal to the first threshold, that is, |NOx1-NOx2|≤the first threshold (threshold 1). If it is established, it is represented as situation 1, and the NOx in the first stage SCR is not completely converted. The second ammonia nozzle is controlled to start spraying, and ammonia is sprayed by ammonia reserve closed-loop injection or open-loop ammonia nitrogen ratio;

[0053] S3, if the reading of the ammonia sensor is not 0, and the reading of the first nitrogen oxide sensor is not 0, the nitrogen oxide sensor has cross sensitivity, that is, NH3 leakage is mistakenly detected as NOx. And the absolute value of the difference between the ammonia sensor and the first nitrogen oxide sensor is less than or equal to the second threshold, that is, |NOx1-NH3|≤the second threshold (threshold 2), indicating that both the ammonia sensor and the nitrogen oxide sensor measure NH3 leakage, and the ammonia scorer starts to work, and the NH3 concentration value measured by the ammonia sensor is used to determine the ammonia mass flow rate;

[0054] The ammonia mass flow rate specifically includes the following formula:

[0055] NH3 mass flow rate (mg / s) = NH3 concentration × exhaust flow rate × 277.78 × 17 / 10^3 / 29.

[0056] S4, when the maximum ammonia adsorption amount in the ammonia leakage catalyst is greater than or equal to the adsorption amount threshold, the first ammonia nozzle is controlled to reduce the injection amount of NH3 to prevent the tail exhaust NH3 leakage from exceeding the standard;

[0057] The process of determining the adsorption threshold is as follows:

[0058] Determine the average temperature of the first-stage SCR and the second-stage SCR according to the readings of the first temperature sensor and the second temperature sensor;

[0059] The adsorption amount threshold is determined according to the average temperature of the first-stage SCR and the second-stage SCR ((T1+T2) / 2) and the ammonia adsorption amount of the ASC varying with temperature MAP.

[0060] S5, if the absolute value of the difference between the ammonia sensor and the first nitrogen oxide sensor is greater than the second threshold, that is, |NOx1-NH3|>threshold 2, then it belongs to situation 3, the catalyst active site in the first-stage SCR is saturated, NOx and NH3 are not completely converted in the first-stage SCR, the NOx concentration measured by the first nitrogen oxide sensor is much greater than the NH3 concentration measured by the ammonia sensor, and because NH3 will have cross-sensitivity interference on the NOx sensor measurement, it is necessary to correct the measurement value of the first nitrogen oxide sensor, that is, determine the correction factor of NH3 equivalent to NOx through the average temperature of the first-stage SCR and the second-stage SCR; correct the reading of the first nitrogen oxide sensor according to the correction factor, and the corrected reading is used as the input of the second-stage SCR, and ammonia injection is performed according to the ammonia storage closed loop or open loop.

[0061] The corrected indication NOx3 is determined using the formula NOx3=NOx1-NH3 concentration×β, where β is the correction factor.

[0062] like Figure 3 As shown, the process of ammonia injection in the ammonia storage closed loop is:

[0063] Obtain the ammonia storage setting value and actual ammonia storage value in the first-stage SCR and the second-stage SCR; the SCR ammonia storage setting value can be checked according to the average temperature and air velocity of the first-stage SCR and the second-stage SCR. The control unit calculates the actual ammonia storage of the SCR through the chemical reaction kinetic model according to the upstream NOx concentration, exhaust flow and NH3 injection

[0064] The dynamic ammonia demand is obtained by adjusting the deviation between the ammonia storage set value and the actual ammonia storage value through PI control;

[0065] The steady-state ammonia demand is obtained based on the difference between the actual ammonia injection amount and the ammonia storage change amount;

[0066] The closed-loop ammonia demand is obtained by adding the steady-state ammonia demand and the dynamic ammonia demand.

[0067] like Figure 3 As shown, the process of open-loop ammonia injection is:

[0068] Determine the open-loop NH3 demand based on the airspeed and the average temperature of the first-stage SCR and the second-stage SCR;

[0069] NH3 open and closed loop injection is performed according to the open loop NH3 demand.

[0070] This application installs an ammonia sensor, two nitrogen oxide sensors, and two temperature sensors in the post-treatment system. When the front-stage SCR passively converts NOx, it makes logical judgments on three situations: NH3 leakage, incomplete NOx conversion, and incomplete conversion of both NOx and NH3. It controls the second-stage ammonia nozzle to inject NH3, thereby avoiding the risk of tail NH3 leakage and NOx exceeding the limit caused by NH3 overspray. The second-stage SCR adopts an active injection strategy, and NH3 injection considers open-closed loop control, which greatly improves the feasibility of engineering implementation.

[0071] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. An ammonia fuel engine aftertreatment system, characterized in that: The ammonia fuel engine aftertreatment system comprises: an air branch, a first mixer, an ammonia fuel nozzle, a cylinder, a turbine, a first stage SCR, an ammonia reductant nozzle, a second mixer, a second stage SCR, an ammonia slip catalyst and a sensor module; The air branch is fully mixed with the ammonia fuel injected from the ammonia fuel nozzle at the intake manifold through the first mixer; after the mixed gas is burned in the cylinder, the exhaust gas is discharged after the turbine works; the exhaust gas passes through the first-stage SCR, the second mixer, the second-stage SCR and the ammonia leakage catalyst in sequence; the ammonia reductant nozzle is arranged at the inlet of the second mixer; the sensor modules are respectively arranged at the position between the first-stage SCR and the second-stage SCR and the position after the ammonia leakage catalyst; The ammonia reducing agent nozzle uses the measurement data of the sensor module as an input boundary and performs active and passive ammonia reducing agent injection control through logical judgment.

2. The ammonia fuel engine aftertreatment system according to claim 1, characterized in that: The air branch circuit includes an air filter, a compressor, an intercooler and a throttle valve which are connected in sequence.

3. The ammonia fuel engine aftertreatment system according to claim 1, characterized in that: The sensor module includes: a first nitrogen oxide sensor, an ammonia sensor, a first temperature sensor, a second nitrogen oxide sensor, and a second temperature sensor; The first nitrogen oxide sensor and the ammonia sensor are arranged on the pipeline between the first-stage SCR and the second mixer; the first temperature sensor is arranged on the pipeline between the second mixer and the second-stage SCR; the second nitrogen oxide sensor and the second temperature sensor are arranged on the pipeline at the outlet of the ammonia slip catalyst.

4. The ammonia fuel engine aftertreatment system according to claim 1, characterized in that: The direct injection combustion aids in the cylinder include: diesel, hydrogen and dimethyl ether.

5. A control method for an ammonia fuel engine after-treatment system, applied to the ammonia fuel engine after-treatment system according to any one of claims 1 to 4, characterized in that: The control method of the ammonia engine aftertreatment system includes: Check whether the reading of the ammonia sensor is 0; If the reading of the ammonia sensor is 0, the reading of the first nitrogen oxide sensor is not 0, and the ammonia reducing agent nozzle is not working, it is determined whether the absolute value of the difference between the measurement value NOx1 of the first nitrogen oxide sensor and the measurement value NOx2 of the second nitrogen oxide sensor is less than or equal to the first threshold value. If so, the NOx in the first-stage SCR is not completely converted, and the ammonia reducing agent nozzle is controlled to start spraying, and ammonia gas is sprayed by ammonia reserve closed-loop injection or open-loop ammonia nitrogen ratio; If the reading of the ammonia sensor is not 0, the reading of the first nitrogen oxide sensor is not 0, and the difference between the ammonia sensor and the first nitrogen oxide sensor is less than or equal to the second threshold, the ammonia scorer starts to work and determines the ammonia mass flow rate by using the ammonia concentration value measured by the ammonia sensor; When the maximum ammonia adsorption amount in the ammonia slip catalyst is greater than or equal to the adsorption amount threshold, the ammonia fuel nozzle is controlled to reduce the injection amount of the ammonia fuel; If the absolute value of the difference between the ammonia sensor and the first nitrogen oxide sensor is greater than the second threshold, the catalyst active sites in the first-stage SCR are saturated, and NOx and NH3 are not completely converted in the first-stage SCR. The correction factor of the ammonia fuel equivalent NOx is determined by the average temperature of the first-stage SCR and the second-stage SCR. The indication of the first nitrogen oxide sensor is corrected according to the correction factor, and the corrected indication is used as the input of the second-stage SCR, and ammonia injection is performed according to the ammonia storage closed loop or open loop.

6. The control method of the ammonia fuel engine after-treatment system according to claim 5, characterized in that: The ammonia fuel mass flow rate specifically includes the following formula: Ammonia mass flow rate (mg / s) = ammonia concentration × exhaust flow rate × 277.78 × 17 / 10^3 / 29.

7. The control method of the ammonia engine after-treatment system according to claim 5, characterized in that: The process of determining the adsorption threshold is as follows: Determine the average temperature of the first-stage SCR and the second-stage SCR according to the readings of the first temperature sensor and the second temperature sensor; The adsorption amount threshold is determined according to the average temperature of the first-stage SCR and the second-stage SCR and the ammonia adsorption amount of the ASC varying with temperature MAP.

8. The control method of the ammonia fuel engine after-treatment system according to claim 5, characterized in that: The corrected indication NOx3 is determined using the formula NOx3=NOx1-NH3 concentration×β, where β is the correction factor.

9. The control method of the ammonia fuel engine after-treatment system according to claim 5, characterized in that: The process of ammonia injection in a closed loop of ammonia storage is as follows: Obtain the ammonia storage set value and the actual ammonia storage value in the first-stage SCR and the second-stage SCR; The dynamic ammonia demand is obtained by adjusting the deviation between the ammonia storage set value and the actual ammonia storage value through PI control; The steady-state ammonia demand is obtained based on the difference between the actual ammonia injection amount and the ammonia storage change amount; The closed-loop ammonia demand is obtained by adding the steady-state ammonia demand and the dynamic ammonia demand.

10. The control method of the ammonia fuel engine after-treatment system according to claim 5, characterized in that: The process of open loop ammonia injection is: Determine the ring-opening ammonia demand based on the air velocity and the average temperature of the first-stage SCR and the second-stage SCR; Ammonia open and closed loop injection is performed according to the open loop ammonia demand.

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