CN116717354B - Emission treatment system suitable for lean-burn methanol engine and control method - Google Patents

Abstract

The invention provides an emission treatment system and a control method suitable for lean-burn methanol engines. The system consists of a booster pipeline, a booster pipeline control valve, a bypass pipeline, a bypass pipeline control valve, and at least one oxidation catalytic converter. It consists of a device, a selective reduction catalytic converter with methanol as the reducing agent, at least two temperature sensors and two nitrogen and oxygen sensors, and a control execution system. The control execution system carries out intelligent control to complete the exhaust gas emission treatment. The system has a simple structure and low cost. It does not use urea but uses methanol as the reducing agent. Therefore, users do not need to frequently add urea and just add methanol normally. It is easy to use and the methanol supply method adopts in-cylinder post-injection. This There is no need for additional reducing agent storage tanks, injection systems, etc.

Description

Emission treatment system and control method suitable for lean-burn methanol engines

Technical field

The present invention relates to the technical field of lean-burn methanol engines, and more specifically, to an emission treatment system and a control method suitable for lean-burn methanol engines.

Background technique

The existing post-treatment system of lean-burn methanol engines often follows the DOC+DPF+urea-SCR+ASC technical route of diesel engines. DOC removes unburned or incompletely burned hydrocarbons or hydrocarbons emitted by the engine through catalytic oxidation; DPF removes particles emitted by the engine through its particle capture function; urea-SCR uses urea as a reducing agent, by injecting urea, First, urea is decomposed at a higher temperature to produce ammonia, and then the ammonia reacts with the nitrogen oxides produced by the engine to remove the nitrogen oxides (in order to ensure that nitrogen oxides are effectively removed, these ammonia must be in excess ); Finally, ASC removes excess ammonia in urea-SCR through oxidation reaction.

Its technical shortcomings include many parts, complex systems, and high costs. In particular, urea requires special storage tanks, injection pumps, nozzles and other parts. Also, engine users need to frequently add urea in addition to fuel. In addition, industrial research has found that methanol and ammonia may react under certain conditions to form highly toxic hydrocyanic acid, which poses a safety risk.

Contents of the invention

In view of this, in order to solve the above problems, the present invention provides an emission treatment system and a control method suitable for lean-burn methanol engines. The technical solution is as follows:

An emission treatment system suitable for lean-burn methanol engines, the system includes: a supercharger bypass system and an aftertreatment system;

The supercharger bypass system includes a boost pipeline, a boost pipeline control valve, a bypass pipeline, a bypass pipeline control valve and a first oxidation catalytic converter located on the bypass pipeline;

The post-treatment system includes a catalytic converter system and a measurement and control execution system. The catalytic converter system includes a selective reduction catalyst with methanol as a reducing agent and a second oxidation catalytic converter. The measurement and control execution system includes a measurement system and a control execution system. The measurement system includes a first temperature sensor, a second temperature sensor and a first nitrogen and oxygen sensor; wherein,

The first temperature sensor and the first nitrogen oxygen sensor are located upstream of the selective reduction catalyst, and the second temperature sensor is located between the selective reduction catalyst and the second oxidation catalyst;

The control execution system is used to collect the first temperature value measured by the first temperature sensor and compare it with a preset characteristic value; if the first temperature value is greater than or equal to the characteristic value, control the The supercharging pipeline control valve is in an open state, and the bypass pipeline control valve is in a closed state, so that the exhaust gas discharged by the lean-burn methanol engine passes through the supercharging pipeline and allows the supercharger to The exhaust gas in the pressurization pipeline is pressurized; the second temperature value measured by the second temperature sensor and the first nitrogen oxygen concentration value measured by the first nitrogen oxygen sensor are collected, and the A temperature value, the second temperature value and the first nitrogen and oxygen concentration value are used to calculate the first methanol injection amount; if the first temperature value is less than the characteristic value, the booster pipeline control valve is controlled to be closed state, the bypass line control valve is in an open state, so that the exhaust gas discharged from the lean-burn methanol engine passes through the bypass line, and the first oxidation catalytic converter is connected to the bypass line. The exhaust gas in the engine is catalytically oxidized; the second methanol injection amount is calculated based on the first temperature value and the preset heating requirement; and the fuel injection system of the lean-burn methanol engine is controlled according to the first methanol injection amount/the third The dimethanol injection amount is used for in-cylinder post-injection, so that the selective reduction catalytic converter uses methanol to catalytically reduce the nitrogen oxides in the exhaust gas discharged from the supercharger/the first oxidation catalytic converter, and also allows the The second oxidation catalyst catalytically oxidizes the exhaust gas discharged from the selective reduction catalyst.

Preferably, in the above emission treatment system, the measurement system further includes a second nitrogen oxygen sensor, the second nitrogen oxygen sensor is located between the selective reduction catalytic converter and the second oxidation catalytic converter;

The control execution system is also used to:

If the first temperature value is greater than or equal to the characteristic value, the first nitrogen oxygen concentration value and the second nitrogen oxygen concentration value measured by the second nitrogen oxygen sensor are collected again after a preset first running time. concentration value, and calculate the nitrogen-oxygen conversion efficiency of the selective reduction catalytic converter; adjust the first methanol injection amount according to the nitrogen-oxygen conversion efficiency.

Preferably, in the above emission treatment system, the control execution system is also used for:

Compare the nitrogen-to-oxygen conversion efficiency with a preset conversion efficiency limit; if the nitrogen-to-oxygen conversion efficiency is less than the conversion efficiency limit, rear injection of the lean-burn methanol engine is prohibited and the speed and torque are limited.

Preferably, the control execution system is also used for:

If the first temperature value is less than the characteristic value, the first temperature value is re-collected after the preset second running time, and compared with the characteristic value again; if the first temperature value is re-compared, If it is less than the characteristic value, the lean-burn methanol engine will be prohibited from rear injection, and the speed and torque will be limited.

Preferably, the measurement system includes a third temperature sensor located downstream of the second oxidation catalyst;

The control execution system is also used to:

If the first temperature value is less than the characteristic value, the second temperature value and the third temperature value measured by the third temperature sensor are collected again after a preset third running time, and the temperature difference is calculated. value; if the temperature difference is greater than the preset temperature difference threshold, the lean-burn methanol engine is prohibited from rear injection and the speed and torque are limited.

Preferably, in the above emission treatment system, the control execution system is also used for:

Perform fault monitoring on the first temperature sensor, the second temperature sensor, the third temperature sensor, the first nitrogen oxygen sensor and the second nitrogen oxygen sensor; if the first temperature sensor, the If any sensor among the second temperature sensor, the third temperature sensor, the first nitrogen oxygen sensor and the second nitrogen oxygen sensor fails, the lean-burn methanol engine will be prohibited from rear injection and the speed limit will be limited. Twist.

This application also provides a control method, which is applied to a control execution system in an emission treatment system suitable for lean-burn methanol engines. The method includes:

Collect the first temperature value measured by the first temperature sensor and compare it with a preset characteristic value;

If the first temperature value is greater than or equal to the characteristic value, control the booster pipeline control valve to be in an open state and the bypass pipeline control valve to be in a closed state, so that the exhaust gas discharged from the lean-burn methanol engine passes through the booster pipeline control valve. pressurize the pipeline and allow the supercharger to supercharge the exhaust gas in the supercharged pipeline;

Collect the second temperature value measured by the second temperature sensor and the first nitrogen oxygen concentration value measured by the first nitrogen oxygen sensor, and use the first temperature value, the second temperature value and the first nitrogen oxygen concentration value to The concentration value calculates the first methanol injection amount;

If the first temperature value is less than the characteristic value, the boost line control valve is controlled to be in a closed state and the bypass line control valve is in an open state, so that the exhaust gas emitted by the lean-burn methanol engine Pass the bypass line and use the first oxidation catalytic converter to catalytically oxidize the exhaust gas in the bypass line;

Calculate the second methanol injection amount based on the first temperature value and the preset heating requirement;

The fuel injection system of the lean-burn methanol engine is controlled to perform in-cylinder post-injection according to the first methanol injection amount/the second methanol injection amount, so that the selective reduction catalyst uses methanol to inject the supercharger/the The nitrogen oxides in the exhaust gas discharged from the first oxidation catalytic converter are catalytically reduced, and the second oxidation catalytic converter is also allowed to catalytically oxidize the exhaust gas discharged from the selective reduction catalytic converter.

Preferably, in the above control method, the method further includes:

If the first temperature value is greater than or equal to the characteristic value, the first nitrogen oxygen concentration value and the second nitrogen oxygen concentration value measured by the second nitrogen oxygen sensor are collected again after a preset first operating time. , and calculate the nitrogen-oxygen conversion efficiency of the selective reduction catalytic converter;

The first methanol injection amount is adjusted according to the nitrogen-oxygen conversion efficiency.

Preferably, in the above control method, the method further includes:

Compare the nitrogen-to-oxygen conversion efficiency with a preset conversion efficiency limit; if the nitrogen-to-oxygen conversion efficiency is less than the conversion efficiency limit, rear injection of the lean-burn methanol engine is prohibited and the speed and torque are limited.

Preferably, in the above control method, the method further includes:

If the first temperature value is less than the characteristic value, re-acquire the first temperature value after a preset second running time, and compare it with the characteristic value again;

If the first temperature value is smaller than the characteristic value after re-comparison, the lean-burn methanol engine is prohibited from post-injection and the speed and torque are limited.

Compared with the existing technology, the beneficial effects achieved by the present invention are:

The invention provides an emission treatment system and a control method suitable for lean-burn methanol engines. The control execution system collects the first temperature value measured by the first temperature sensor and compares it with the preset characteristic value; if the first temperature value Greater than or equal to the characteristic value, the control valve of the supercharging pipeline is opened and the control valve of the bypass pipeline is closed. The exhaust gas emitted by the lean-burn methanol engine increases the exhaust gas in the supercharging pipeline through the supercharging pipeline and the supercharger. pressure processing; collecting the second temperature value measured by the second temperature sensor, the first nitrogen oxygen concentration value measured by the first nitrogen oxygen sensor, and the second nitrogen oxygen concentration value measured by the second nitrogen oxygen sensor, and calculating the first Methanol injection amount; if the first temperature value is less than the characteristic value, the control valve of the booster pipeline is closed and the control valve of the bypass pipeline is opened. The exhaust gas discharged from the lean-burn methanol engine passes through the bypass pipeline and the first oxidation catalytic converter. The exhaust gas in the bypass line is catalytically oxidized; the second methanol injection amount is calculated based on the first temperature value and the preset temperature rise demand; and the fuel injection system of the lean-burn methanol engine is controlled according to the first methanol injection amount/the second methanol injection amount. In-cylinder post-injection is performed, the selective reduction catalytic converter uses methanol to catalytically reduce the nitrogen oxides in the exhaust gas discharged from the supercharger/first oxidation catalytic converter, and the second oxidation catalytic converter catalytically reduces the exhaust gas discharged from the selective reduction catalytic converter. Oxidation.

In the present invention, the entire emission treatment system consists of a booster pipeline, a booster pipeline control valve, a bypass pipeline, a bypass pipeline control valve, at least one oxidation catalyst, and a selective reduction catalytic converter with methanol as the reducing agent. It consists of a sensor, at least two temperature sensors, two nitrogen and oxygen sensors and a control execution system. The control execution system carries out intelligent control to complete the exhaust gas emission treatment. The control execution system can be integrated into the engine control unit. The system has a simple structure and low cost. It does not use urea but uses methanol as the reducing agent. Therefore, users do not need to frequently add urea and can just add methanol normally. It is easy to use and the methanol supply method adopts post-injection in the cylinder. This There is no need for additional reducing agent storage tanks, injection systems, etc.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the provided drawings without exerting creative efforts.

Figure 1 is a schematic structural diagram of an emission treatment system suitable for lean-burn methanol engines provided by an embodiment of the present invention;

Figure 2 is a layout structure of a lean-burn methanol engine matching the emission treatment system shown in Figure 1 provided by an embodiment of the present invention;

Figure 3 is a method flow chart of a control method provided by an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

In order to facilitate understanding of the present invention, the relevant concepts involved in the present invention are first described below:

(1) Lean-burn methanol engine: It can also be called a lean-burn methanol engine. That is, an internal combustion engine that uses methanol as fuel and the ratio of air to fuel is higher than the stoichiometric ratio. Due to the physical and chemical properties and combustion characteristics of methanol, lean-burn methanol engines have some unique properties that are different from diesel engines (which are also lean-burn):

1) Exhaust temperature characteristics: Methanol is more volatile than diesel and mixes more fully with air. Therefore, the exhaust temperature of methanol engines is higher than that of diesel engines under common operating conditions. But on the other hand, due to the low calorific value of methanol, cold start and slow temperature rise, the combustion state in the cylinder is poor at this time, and a large amount of unburned methanol, as well as incomplete combustion products such as formaldehyde will be emitted.

2) Emission characteristics:

A. Methanol engine emissions contain relatively high concentrations of methanol and formaldehyde (more so during cold starts) and other carbon, hydrogen and oxygen compounds, which are mostly harmful to the human body. At present, the national environmental protection department has put forward control requirements for methanol and formaldehyde emission levels of methanol engines used on roads.

B. Methanol is easier to vaporize than diesel, mixes more evenly with air than diesel droplets, and burns more completely, so the level of particulate matter emissions is lower.

C. Due to the lean combustion, there is an excess of oxygen in the engine. Under high temperature and oxygen-rich conditions, nitrogen and oxygen in the engine combine to generate a large amount of nitrogen oxides, mainly nitric oxide and less nitrogen dioxide.

D. There are other pollutants such as carbon monoxide and hydrocarbons that are similar to diesel engines.

(2) Post-treatment catalytic unit: Through the catalyst, the pollutants, oxygen and external reactants (optional) in the engine exhaust react with each other, and are eventually converted into harmless water, nitrogen, carbon dioxide and other substances. The catalytic efficiency of specific catalysts for specific reactions is different from each other, but they are all greatly affected by temperature. Generally, there is a certain temperature range in which they can exert higher activity; if it is lower than the activity range, the conversion efficiency of the catalyst is insufficient; if it is higher than the activity interval, not only is the conversion efficiency insufficient, but long-term use may also lead to a permanent decline in catalyst performance. In addition, as emission regulations become increasingly stringent, the after-treatment system of modern engines is usually a multi-stage combination and system integration control of multiple catalytic units.

The following is a brief introduction to several post-treatment catalytic units commonly used in diesel and natural gas engines, and their feasibility of application in lean-burn methanol engines:

1) Three-Way Catalyst (TWC, Three-Way Catalyst) can promote the three-way catalytic reaction through the precious metals inside it, converting harmful carbon monoxide, carbon hydroxides, nitrogen oxides, etc. in the exhaust into harmless water, nitrogen and carbon dioxide. The three-way catalytic converter also has good processing capabilities for methanol and formaldehyde, and has application prospects in equivalent combustion methanol engines. However, the ratio of exhaust pollutants of lean-burn methanol engines is different from that of equivalent-burning methanol engines. The nitrogen oxide content is higher, and TWC is not applicable to it.

2) Oxidation Catalyst (OC, Oxidation Catalyst), such as DOC (Diesel Oxidation Catalyst) used for diesel engine after-treatment. The principle is that the oxidation precious metal catalyst can convert carbon monoxide, hydrocarbons, and carbon hydroxide compounds in the exhaust gas. etc. are oxidized by oxygen into harmless water and carbon dioxide. The oxidation catalyst has a purifying effect on methanol and formaldehyde and can be used in lean-burn methanol engines. However, lean-burn methanol engines have more unburned methanol and incomplete combustion products under low-temperature conditions. Direct use of DOC treatment will dissipate the heat released by the oxidation of these emissions, resulting in greater energy loss.

3) Selected Catalyst Reduction (SCR) and Ammonia Slip Catalyst (ASC). The principle of SCR is to use a catalyst to allow the reducing agent (which can come from the fuel or be additionally injected) to react with the nitrogen oxides in the exhaust, eventually converting it into harmless water and nitrogen (and possibly carbon dioxide). . SCR can flexibly control the degree of reaction by controlling the amount of reductant introduced, so it is also suitable for lean-burn methanol engines with high nitrogen and oxygen emissions. SCR can be distinguished according to different reducing agents, such as H ₂ -SCR (hydrogen is used as the reducing agent), NH ₃ -SCR (ammonia is used as the reducing agent), Urea-SCR (urea is used as the reducing agent, which is first thermally decomposed to generate ammonia, and then Reacts with nitrogen oxides), HC-SCR (engine hydrocarbon fuels such as gasoline, diesel, natural gas, etc. directly serve as reducing agents), etc. Ammonia slip catalyst (ASC, Ammonia Slip Catalyst) is only used to match NH ₃ -SCR and Urea-SCR. Since this type of SCR generally uses an excess of reducing agent, it converts the excess ammonia remaining in the SCR through precious metal catalytic oxidation. For harmless water and nitrogen. At present, the most widely used diesel engine in this regard is Urea-SCR+ASC.

However, there are some disadvantages to using Urea-SCR+ASC in lean-burn methanol engines. The first is that urea injection requires a separate urea storage tank, injection system, etc. When using it, in addition to going to a methanol station to refill methanol fuel, users also have to go to a gas station or Urea is added at service stations, which is costly and inconvenient to use. In addition, under certain conditions, unburned methanol, formaldehyde, etc. in the exhaust may decompose with urea to produce ammonia gas, which may undergo an ammonia oxidation reaction to generate highly toxic hydrocyanic acid, which is harmful to human health.

Methanol can also be directly used as the reducing agent for the SCR reaction. Even if MeOH-SCR is used, the activity temperature window of this catalytic method is narrower than that of Urea-SCR. For engine operation conditions with large temperature changes, the post-processing system needs to be systematically modified. Optimization, the present invention takes this as the core to carry out systematic design and optimization.

4) Particle trap (Particulate Filter), typically such as the particle trap (DPF, Diesel Particulate Filter) used in diesel engines. For methanol engines, due to sufficient combustion and low particulate matter emissions, particulate traps are not yet required according to current regulatory limits.

(3) Post-injection in the fuel cylinder: refers to one or more injections after the main fuel injection (used for normal combustion and power output) during an engine operating cycle. At this time, because the engine is not in the combustion stroke, a small proportion of the post-injected fuel is burned in the cylinder, and most of it is discharged directly from the engine. This method is to meet certain special needs, such as rapid heating of the aftertreatment, or allowing fuel to directly enter the aftertreatment to participate in certain chemical reactions without adding a nozzle. Both cases are covered by the present invention.

During the invention creation process of this application, the inventor discovered through research:

The existing after-treatment systems of lean-burn methanol engines often copy the DOC+DPF+urea-SCR+ASC technical route of diesel engines, or only omit the DPF (that is, use the DOC+urea-SCR+ASC technical route). This type of technical route has the following technical flaws:

1) Under low-temperature conditions, unburned methanol is directly catalytically oxidized by DOC, resulting in large heat loss; 2) SCR requires the introduction of urea as a reactant, so the product needs to be equipped with storage tanks, injection systems, etc., which is costly and inconvenient to use; 3) When applied to methanol engines, SCR and ASC may also generate highly toxic hydrocyanic acid and other substances; 4) Although some technologies use methanol-SCR to avoid the above-mentioned problems, additional methanol delivery pipes need to be arranged Road and methanol nozzle, there is no detailed explanation on how to deal with the excess methanol injected to remove nitrogen and oxygen, and the problem of insufficient methanol-SCR activity at low temperatures is still not solved.

It can be seen that the shortcomings of current technology include large heat loss, many required parts, high cost, risk of highly toxic emissions, or lack of systematicness and comprehensiveness.

Based on this, in the embodiment of the present invention, an emission treatment system suitable for lean-burn methanol engines is proposed, which can effectively purify nitrogen oxides, carbon monoxide, methanol, formaldehyde, etc. in the exhaust of methanol engines at different exhaust temperatures. It eliminates pollutants without introducing new toxic substances, and uses methanol fuel directly as the reactant. It has high heat utilization rate and does not require additional reactants such as urea, which can save space and cost.

In order to make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

The emission treatment system suitable for lean-burn methanol engines provided by the embodiment of the present invention includes a supercharger bypass system and a post-processing system. The post-processing system includes a catalytic converter system and a measurement and control execution system. The measurement and control execution system includes a measurement system and a control execution system. .

Referring to Figure 1, Figure 1 is a schematic structural diagram of an emission treatment system suitable for lean-burn methanol engines provided by an embodiment of the present invention. The supercharger bypass system in the emission treatment system includes a supercharger pipeline 1, a supercharger pipe path control valve 2, bypass line 3, bypass line control valve 4 and the first oxidation catalytic converter 5 located on the bypass line 3 (that is, the OC located on the bypass line 3 in Figure 1), the catalytic The system includes a selective reduction catalyst 6 with methanol as the reducing agent (i.e., MeOH-SCR in Figure 1) and a second oxidation catalyst 7 (i.e., OC located downstream of MeOH-SCR in Figure 1). The measurement system includes a selective reduction catalyst located at The first temperature sensor 8 upstream of the selective reduction catalytic converter 6, the second temperature sensor 9 located between the selective reduction catalytic converter 6 and the second oxidation catalytic converter 7, the third temperature sensor 10 located downstream of the second oxidation catalytic converter 7, The first nitrogen oxygen sensor 11 is located upstream of the selective reduction catalyst 6 and the second nitrogen oxygen sensor 12 is located between the selective reduction catalyst 6 and the second oxidation catalyst 7 .

As shown in Figure 1, the emission treatment system suitable for lean-burn methanol engines also includes a control execution system 13, methanol fuel tank A, lean-burn methanol engine B, port injection C, in-cylinder direct injection D, and exhaust gas recirculation system (Exhaust GasRecirculation, EGR) E. Engine control unit (ECU) F. It should be noted that 3 to 13 in Figure 1 are new hardware structures of the present invention, while 1 to 2 and A to F can form a conventional methanol engine without post-processing. In addition, in Figure 1 The exhaust gas recirculation system E shown in dotted lines is an optional structure. Referring to Figure 2, Figure 2 is an arrangement structure of a lean-burn methanol engine matching the emission treatment system shown in Figure 1 provided by an embodiment of the present invention. The methanol power system includes an emission treatment system and other contents. The emission treatment system includes an additional Pressure bypass system and after-treatment system, the supercharger bypass system includes booster pipeline 1, booster pipeline control valve 2, bypass pipeline 3, bypass pipeline control valve 4 and the first oxidation catalytic converter 5. The post-treatment system includes a catalytic converter system and a measurement and control execution system. The catalytic converter system includes a selective reduction catalytic converter 6 and a second oxidation catalytic converter 7. The measurement and control execution system includes a measurement system and a control execution system 13. The measurement system includes the first temperature Sensor 8, second temperature sensor 9, third temperature sensor 10, first nitrogen oxygen sensor 11 and second nitrogen oxygen sensor 12. Other contents include methanol fuel tank A, lean methanol engine B, port injection C, cylinder Internal direct injection D, exhaust gas recirculation system E, engine control unit F, the control execution system 13 may be included in the engine control unit F (that is, the control execution system 13 may be integrated into the engine control unit F).

Based on the structure of the present invention shown in Figure 1, air enters the lean-burn methanol engine B through the intake pipe, and the methanol fuel is input into the lean-burn engine from the methanol fuel tank A through the fuel delivery pipe in the form of intake port injection C or in-cylinder direct injection D. In methanol engine B, it burns and performs external work; then the exhaust gas produced by the combustion of lean-burn methanol engine B flows out. The exhaust gas recirculation system E can be used to return part of the exhaust gas into the intake pipe, or it can not be used; finally, the exhaust gas passes next to the supercharger The purification system and after-treatment system are purified and finally discharged into the atmosphere.

Specifically, the control execution system 13 executes the following process:

Collect the first temperature value measured by the first temperature sensor 8 and compare it with the preset characteristic value;

If the first temperature value is greater than or equal to the characteristic value, control the booster pipeline control valve 2 to be in an open state and the bypass pipeline control valve 4 to be in a closed state, so that the exhaust gas discharged by the lean-burn methanol engine B passes through the booster pipeline. 1. Let the supercharger supercharge the exhaust gas in the supercharging pipeline 1; collect the second temperature value measured by the second temperature sensor 9 and the first nitrogen oxygen concentration value measured by the first nitrogen oxygen sensor 11 , and calculate the first methanol injection amount according to the first temperature value, the second temperature value and the first nitrogen oxygen concentration value;

If the first temperature value is less than the characteristic value, control the boost line control valve 2 to be in a closed state and the bypass line control valve 4 to be in an open state, so that the exhaust gas discharged by the lean-burn methanol engine B passes through the bypass line 3, And make the first oxidation catalytic converter 5 catalytically oxidize the exhaust gas in the bypass line 3; calculate the second methanol injection amount based on the first temperature value and the preset temperature rise demand;

The fuel injection system of the lean-burn methanol engine B is controlled to perform in-cylinder post-injection according to the first methanol injection amount/the second methanol injection amount, so that the selective reduction catalyst 6 uses methanol to inject the supercharger/first oxidation catalyst 5 The nitrogen oxides in the exhaust gas are catalytically reduced, and the second oxidation catalyst 7 is also allowed to catalytically oxidize the exhaust gas exhausted from the selective reduction catalyst 6 .

That is to say, a characteristic value T can be set for the temperature measured by the first temperature sensor 8 upstream of the selective reduction catalytic converter 6 (i.e., the first temperature value) (which can be specifically set according to different engine uses, catalyst performance, etc.), The control execution system 13 compares the first temperature value with the characteristic value T. It should be noted that this characteristic value T is the catalytic activity limit.

When the first temperature value is greater than or equal to the characteristic value T, it is considered that the lean-burn methanol engine B is running at a higher load. At this time, the exhaust temperature is high enough and each catalytic converter can work at a high efficiency. The control execution system 13 controls the booster pipeline control valve 2 to remain open and the bypass pipeline control valve 4 to remain closed, so that the exhaust gas discharged from the lean-burn methanol engine B passes through the booster pipeline 1 instead of the bypass pipeline 3 , at this time, the supercharger can work normally and ensure the supercharging performance of the engine.

The exhaust gas continues to pass into the selective reduction catalytic converter 6. According to the values measured by the upstream and downstream temperature sensors of the selective reduction catalytic converter 6 and the upstream nitrogen and oxygen concentration sensor (i.e., the first temperature value, the second temperature value measured by the second temperature sensor 9 temperature value, the first nitrogen oxygen concentration value measured by the first nitrogen oxygen sensor 11) to calculate the amount of methanol reducing agent required at this time (i.e., the first methanol injection amount), and control the fuel injection system of the lean-burn methanol engine B ( Port injection C or in-cylinder direct injection D) provides a corresponding amount of methanol through in-cylinder post-injection, thereby achieving the catalytic reduction of nitrogen oxides by methanol and generating harmless water, carbon dioxide and nitrogen. It should be noted that the process of calculating the first methanol injection amount based on the values measured by the upstream and downstream temperature sensors and the upstream nitrogen and oxygen concentration sensor of the selective reduction catalytic converter 6 is a mature implementation solution in the industry and will not be described in detail here. For example, Say, the first methanol injection amount = the first nitrogen and oxygen concentration value × engine exhaust flow × methanol molecular weight × methanol/nitrogen oxide theoretical molecular ratio / (air molecular weight × conversion efficiency), where engine exhaust flow = engine intake air Flow + engine fuel consumption, engine air intake flow and engine fuel consumption are real-time monitoring values, methanol molecular weight, methanol/nitrogen oxide theoretical molecular ratio, air molecular weight are fixed values, conversion efficiency is a preset value, and is consistent with the first The temperature value corresponds to the average value of the second temperature value.

Then, the exhaust gas flows through the second oxidation catalytic converter 7, and excess methanol, formaldehyde, carbon monoxide, etc. contained in the exhaust gas are catalytically oxidized into harmless water and carbon dioxide. At this point, efficient purification of methanol engine exhaust gas is achieved.

In practical applications, the value measured by nitrogen and oxygen concentration sensors upstream and downstream of the selective reduction catalytic converter 6 can also be supplemented to monitor and close the loop on the effect of the selective reduction catalytic converter 6 on removing nitrogen oxides. Specifically, the first nitrogen and oxygen concentration value is re-collected after the preset first operating time, and the second nitrogen and oxygen concentration value measured by the second nitrogen and oxygen sensor 12 is collected, and the nitrogen of the selective reduction catalytic converter 6 is calculated based on this. Oxygen conversion efficiency, nitrogen-oxygen conversion efficiency = (first nitrogen-oxygen concentration value - second nitrogen-oxygen concentration value) / first nitrogen-oxygen concentration value; the first methanol injection amount is adjusted according to the nitrogen-oxygen conversion efficiency. It should be noted that the method of adjusting the first methanol injection amount according to the nitrogen-oxygen conversion efficiency is a mature technology in the industry and will not be described again here.

On this basis, the control execution system 13 can also monitor system faults through nitrogen-oxygen conversion efficiency. Specifically, compare the nitrogen-to-oxygen conversion efficiency with the preset conversion efficiency limit; if the nitrogen-to-oxygen conversion efficiency is less than the conversion efficiency limit, it is considered that the conversion efficiency is low, possibly due to an incorrect injection amount or catalyst failure, and lean methanol is prohibited at this time. The engine sprays after the engine and limits the speed and torque to prevent accidents, and issues a warning to remind the user that the engine or aftertreatment is faulty and requires repair. Of course, if the nitrogen-oxygen conversion efficiency is greater than or equal to the conversion efficiency limit, continue monitoring.

When the first temperature value is less than the characteristic value T, it is considered that the exhaust temperature of the lean-burn methanol engine B is not sufficient for each catalytic converter to effectively activate, and the after-treatment should be rapidly heated at this time. On the one hand, the control execution system 13 controls the supercharging pipeline control valve 2 to remain closed and the bypass pipeline control valve 4 to remain open, so that the exhaust gas discharged from the lean-burn methanol engine B passes through the bypass pipeline 3 and the first oxidation catalytic converter. 5. Do not pass through the booster pipeline 1. This is because the supercharger will cause the exhaust temperature to drop at this time. If the exhaust temperature needs to be increased, it should be avoided to lower the exhaust temperature again. On the other hand, this is also The post-injection in the fuel cylinder should be turned on, and with the help of the first oxidation catalytic converter 5 in the bypass line 3, the post-injected methanol that is not burned in the cylinder can be quickly oxidized and exothermic on the first oxidation catalytic converter 5 to improve aftertreatment. temperature. Of course, during this process, if the current first temperature value is equal to or greater than the characteristic value T, the process ends, and the control execution system 13 executes the control plan under the above condition of "the first temperature value is greater than or equal to the characteristic value".

The exhaust gas continues to flow into the selective reduction catalyst 6, and the control execution system 13 calculates the amount of methanol reducing agent required at this time (i.e., based on the first temperature value and the preset temperature rising demand (i.e., the target temperature value as the temperature rising target)). second methanol injection amount), and controls the fuel injection system (port injection C or in-cylinder direct injection D) of lean-burn methanol engine B to provide a corresponding amount of methanol through in-cylinder post-injection, thereby achieving the reduction of nitrogen oxides by methanol. Catalytic reduction produces harmless water, carbon dioxide and nitrogen. It should be noted that the process of calculating the second methanol injection amount based on the first temperature and the target temperature is a mature implementation solution in the industry, and will not be repeated here. For example, the second methanol injection amount = selective reduction catalyst 6 heat capacity Obtained through simple and proven experiments.

Then, the exhaust gas flows through the second oxidation catalytic converter 7, and excess methanol, formaldehyde, carbon monoxide, etc. contained in the exhaust gas are catalytically oxidized into harmless water and carbon dioxide. At this point, efficient purification of methanol engine exhaust gas is achieved.

On this basis, the control execution system 13 can also monitor system faults through the first temperature value. Specifically, the first temperature value is re-collected after the preset second running time, and compared with the characteristic value again; if the first temperature value is smaller than the characteristic value after re-comparison, it is considered that the post-processing temperature rise efficiency is low, which may be If the injection amount is wrong or the catalyst fails, the lean-burn methanol engine will be prohibited from post-injection and limited speed and torque to prevent accidents. A warning will be issued to remind the user that the engine or after-treatment is faulty and requires repair. Of course, if the first temperature value is greater than or equal to the characteristic value after re-comparison, monitoring will continue.

In addition, the control execution system 13 can also monitor system faults through the second temperature value and the third temperature value measured by the third temperature sensor 10 . Specifically, the second temperature value is re-collected after the preset third running time, and the third temperature value measured by the third temperature sensor 10 is collected, and the temperature difference is calculated (temperature difference=second temperature value-th three temperature values); if the temperature difference is greater than the preset temperature difference threshold, it is considered that there is a fault in the second oxidation catalytic converter 7 and the pipeline in which it is located (generally, there may be air leakage in the pipeline, or the catalytic function is severely reduced), and this During this period, rear injection of lean-burn methanol engines is prohibited, and speed and torque limits are imposed. Of course, if the temperature difference is less than or equal to the temperature difference, continue monitoring.

In addition, in practical applications, the control execution system 13 can also judge the credibility of the sensor to monitor system faults. Specifically, fault monitoring is performed on the first temperature sensor 8, the second temperature sensor 9, the third temperature sensor 10, the first nitrogen oxygen sensor 11 and the second nitrogen oxygen sensor 12, that is to say, the first temperature value, The second temperature value, the first nitrogen oxygen concentration value and the second nitrogen oxygen concentration value are respectively compared with their corresponding safe and trusted upper limits and safe and trusted upper limits. Taking the first temperature sensor 8 as an example, if the first collected If the temperature value is greater than its corresponding safe and trusted upper limit, or less than its corresponding safe and trusted upper limit, the first temperature sensor 8 is considered to be faulty; if the first temperature sensor 8, the second temperature sensor 9, the third temperature sensor 10, and the If any sensor in the first nitrogen oxygen sensor 11 and the second nitrogen oxygen sensor 12 fails, the rear injection of the lean-burn methanol engine will be prohibited and the speed and torque will be limited to prevent accidents, and a warning will be issued to remind the user of the engine or aftertreatment. It is faulty and needs to be repaired.

It can be seen that the present invention is based on SCR using methanol as the reducing agent, and controls the nitrogen oxides emitted by the engine through post-injection in the lean-burn methanol engine cylinder, and then processes excess methanol, formaldehyde, carbon monoxide and other substances through oxidation catalysis. pollutants, achieving high-efficiency and low-cost emission control of methanol engines; through the supercharger pipeline bypass combined with the oxidation catalytic converter, the post-processing temperature of the lean-burn methanol engine is quickly heated when the engine is operating at low temperature, so that the temperature reaches the Catalysts have an active window with high conversion efficiency. Therefore, the present invention has the following advantages:

1) The present invention proposes a selective catalytic reduction method using in-cylinder post-injection methanol as the reducing agent to replace the traditional urea SCR to purify nitrogen oxides, and then cooperate with an oxidation catalytic converter to treat excess methanol, formaldehyde, carbon monoxide and other pollutants, while avoiding It eliminates the possibility of ammonia oxidation of methanol to generate highly toxic hydrocyanic acid, thereby achieving efficient treatment of pollutants emitted by lean-burn methanol engines. And compared with the traditional technical route, there is no need to introduce additional reactants, which reduces system complexity, saves parts, and reduces costs.

2) In order to solve the problem of methanol engines emitting a lot of pollutants and slowing down the temperature rise at low temperatures, the present invention proposes the method of post-injection of methanol in the cylinder + supercharger pipeline bypass + pre-catalytic oxidizer, so that the methanol can be emitted in the oxidation catalyst. Rapid oxidation releases heat under the action, thereby achieving rapid temperature rise of the post-processing, which is conducive to bringing the system temperature into the activity window of the catalyst as soon as possible, solving the problem of difficult emission control when the methanol engine operates at low temperature in the existing solution.

3) The present invention also provides a control strategy for the above hardware system, which not only achieves rapid temperature rise and efficient catalysis through switching of valves and post-injection modes, but also integrates identification and alarm functions for possible failure modes of the system.

In summary, the emission treatment system proposed by the present invention and suitable for lean-burn methanol engines has the advantages of space saving, cost saving, wide applicability, efficient purification, and perfect control strategy.

Optionally, based on the emission treatment system suitable for lean-burn methanol engines provided in the above embodiments of the present application, another embodiment of the present invention also provides a control method, which is applied to the control execution system therein, Referring to Figure 3, Figure 3 is a method flow chart of a control method provided by an embodiment of the present invention, including the following steps:

S10: Collect the first temperature value measured by the first temperature sensor and compare it with a preset characteristic value.

S20, if the first temperature value is greater than or equal to the characteristic value, control the booster pipeline control valve to be in an open state and the bypass pipeline control valve to be in a closed state, so that the exhaust gas discharged from the lean-burn methanol engine passes through the booster pipeline, And the supercharger is used to supercharge the exhaust gas in the supercharging pipeline.

S30: Collect the second temperature value measured by the second temperature sensor and the first nitrogen oxygen concentration value measured by the first nitrogen oxygen sensor, and calculate the second temperature value based on the first temperature value, the second temperature value and the first nitrogen oxygen concentration value. One methanol injection volume.

S40, if the first temperature value is less than the characteristic value, control the supercharging pipeline control valve to be in a closed state and the bypass pipeline control valve to be in an open state, so that the exhaust gas discharged by the lean-burn methanol engine passes through the bypass pipeline, and the bypass pipeline control valve is opened. The first oxidation catalytic converter catalytically oxidizes the exhaust gas in the bypass line.

S50: Calculate the second methanol injection amount based on the first temperature value and the preset heating requirement.

S60, control the fuel injection system of the lean-burn methanol engine to perform in-cylinder post-injection according to the first methanol injection amount/the second methanol injection amount, so that the selective reduction catalytic converter uses methanol to discharge the gas from the supercharger/first oxidation catalytic converter. The nitrogen oxides in the exhaust gas are catalytically reduced, and the second oxidation catalytic converter is also allowed to catalytically oxidize the exhaust gas discharged from the selective reduction catalytic converter.

Optionally, in another embodiment of the present invention, the above control method further includes the following steps:

If the first temperature value is greater than or equal to the characteristic value, the first nitrogen and oxygen concentration value is re-collected after the preset first running time, and the second nitrogen and oxygen concentration value measured by the second nitrogen and oxygen sensor is collected, and the selective reduction is calculated Nitrogen-oxygen conversion efficiency of the catalytic converter.

The first methanol injection amount is adjusted according to the nitrogen-oxygen conversion efficiency.

Optionally, in another embodiment of the present invention, the above control method further includes the following steps:

Compare the nitrogen-to-oxygen conversion efficiency with the preset conversion efficiency limit; if the nitrogen-to-oxygen conversion efficiency is less than the conversion efficiency limit, the lean-burn methanol engine will be prohibited from rear injection and the speed and torque will be limited.

Optionally, in another embodiment of the present invention, the above control method further includes the following steps:

If the first temperature value is smaller than the characteristic value, the first temperature value is re-collected after a preset second running time, and compared with the characteristic value again.

If the first temperature value is smaller than the characteristic value after re-comparison, the lean-burn methanol engine is prohibited from post-injection and the speed and torque are limited.

Optionally, in another embodiment of the present invention, the above control method further includes the following steps:

If the first temperature value is less than the characteristic value, re-acquire the second temperature value after the preset third running time, collect the third temperature value measured by the third temperature sensor, and calculate the temperature difference;

If the temperature difference is greater than the preset temperature difference threshold, the lean-burn methanol engine is prohibited from rear injection and the speed and torque are limited.

Optionally, in another embodiment of the present invention, the above control method further includes the following steps:

Perform fault monitoring on the first temperature sensor, the second temperature sensor, the third temperature sensor, the first nitrogen oxygen sensor and the second nitrogen oxygen sensor.

If any sensor among the first temperature sensor, the second temperature sensor, the third temperature sensor, the first nitrogen oxygen sensor and the second nitrogen oxygen sensor fails, the rear injection of the lean-burn methanol engine is prohibited and the speed and torque are limited.

It should be noted that the detailed execution process of each step in the embodiment of the present invention can be found in the corresponding description of the above-mentioned emission treatment system suitable for lean-burn methanol engines, and will not be described again here.

The above is a detailed introduction to an emission treatment system and control method suitable for lean-burn methanol engines provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation modes of the present invention. The description of the above embodiments is only It is used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the field, there will be changes in the specific implementation and application scope according to the idea of the present invention. In summary, this The content of the description should not be construed as limiting the invention.

It should be noted that each embodiment in this specification is described in a progressive manner. Each embodiment focuses on its differences from other embodiments. The same and similar parts between the various embodiments are referred to each other. Can. As for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. For relevant details, please refer to the description in the method section.

It should also be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations There is no such actual relationship or sequence between them. Furthermore, the terms "comprises," "comprises," or any other variation thereof are intended to cover a non-exclusive inclusion such that a list of elements inherent in, or otherwise included in, a process, method, article, or apparatus includes , elements inherent in a method, article or device. Without further limitation, an element defined by the statement "comprises a..." does not exclude the presence of additional identical elements in a process, method, article, or apparatus that includes the stated element.

The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be practiced in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. An emission treatment system suitable for use with a lean burn methanol engine, the system comprising: a supercharger bypass system and an aftertreatment system;

the booster bypass system comprises a booster pipeline, a booster pipeline control valve, a bypass pipeline control valve and a first oxidation catalyst positioned on the bypass pipeline;

the aftertreatment system comprises a catalyst system and a measurement and control execution system, wherein the catalyst system comprises a selective reduction catalyst and a second oxidation catalyst which take methanol as a reducing agent, the measurement and control execution system comprises a measurement system and a control execution system, and the measurement system comprises a first temperature sensor, a second temperature sensor and a first nitrogen-oxygen sensor; wherein,

The first temperature sensor and the first nitrogen-oxygen sensor are located upstream of the selective reduction catalyst, and the second temperature sensor is located between the selective reduction catalyst and the second oxidation catalyst;

the control execution system is used for collecting a first temperature value measured by the first temperature sensor and comparing the first temperature value with a preset characteristic value; if the first temperature value is greater than or equal to the characteristic value, controlling the supercharging pipeline control valve to be in an open state and the bypass pipeline control valve to be in a closed state, so that waste gas discharged by the lean-burn methanol engine passes through the supercharging pipeline and the supercharger carries out supercharging treatment on the waste gas in the supercharging pipeline; collecting a second temperature value measured by the second temperature sensor and a first nitrogen-oxygen concentration value measured by the first nitrogen-oxygen sensor, and calculating a first methanol injection amount according to the first temperature value, the second temperature value and the first nitrogen-oxygen concentration value; if the first temperature value is smaller than the characteristic value, controlling the pressurizing pipeline control valve to be in a closed state and the bypass pipeline control valve to be in an open state, so that the exhaust gas discharged by the lean-burn methanol engine passes through the bypass pipeline and the first oxidation catalyst carries out catalytic oxidation on the exhaust gas in the bypass pipeline; calculating a second methanol injection amount based on the first temperature value and a preset heating requirement; and controlling a fuel injection system of the lean-burn methanol engine to perform in-cylinder post injection according to the first methanol injection amount/the second methanol injection amount, so that the selective reduction catalyst performs catalytic reduction on nitrogen oxides in exhaust gas discharged by the supercharger/the first oxidation catalyst by methanol, and further performs catalytic oxidation on the exhaust gas discharged by the selective reduction catalyst by the second oxidation catalyst.

2. The system of claim 1, wherein the measurement system further comprises a second nitrogen-oxygen sensor located between the selective reduction catalyst and the second oxidation catalyst;

the control execution system is further configured to:

if the first temperature value is greater than or equal to the characteristic value, the first nitrogen-oxygen concentration value is acquired again through a preset first operation time period, the second nitrogen-oxygen concentration value measured by the second nitrogen-oxygen sensor is acquired, and the nitrogen-oxygen conversion efficiency of the selective reduction catalyst is calculated; and adjusting the injection quantity of the first methanol according to the nitrogen-oxygen conversion efficiency.

3. The system of claim 2, wherein the control execution system is further configured to:

comparing the nitrogen-oxygen conversion efficiency with a preset conversion efficiency limit value; and if the nitrogen-oxygen conversion efficiency is smaller than the conversion efficiency limit value, prohibiting the lean-burn methanol engine from post-injection, and limiting the speed and the torque.

4. The system of claim 1, wherein the control execution system is further configured to:

if the first temperature value is smaller than the characteristic value, the first temperature value is acquired again through a preset second operation duration, and the first temperature value is compared with the characteristic value again; and if the first temperature value is smaller than the characteristic value after re-comparison, prohibiting the lean-burn methanol engine from post-injection and limiting the speed and the torque.

5. The system of claim 2, wherein the measurement system further comprises a third temperature sensor located downstream of the second oxidation catalyst;

the control execution system is further configured to:

if the first temperature value is smaller than the characteristic value, the second temperature value is acquired again through a preset third operation time period, a third temperature value measured by the third temperature sensor is acquired, and a temperature difference value is calculated; and if the temperature difference is larger than a preset temperature difference threshold, prohibiting the lean-burn methanol engine from post-injection, and limiting the speed and the torque.

6. The system of claim 5, wherein the control execution system is further configured to:

performing fault monitoring on the first temperature sensor, the second temperature sensor, the third temperature sensor, the first nitrogen-oxygen sensor and the second nitrogen-oxygen sensor; and if any one of the first temperature sensor, the second temperature sensor, the third temperature sensor, the first nitrogen-oxygen sensor and the second nitrogen-oxygen sensor fails, the lean-burn methanol engine is forbidden to post-spray and limit the speed and the torque.

7. A control method, characterized in that the control method is applied to a control execution system in an emission treatment system adapted to a lean-burn methanol engine, the method comprising:

collecting a first temperature value measured by a first temperature sensor, and comparing the first temperature value with a preset characteristic value;

if the first temperature value is greater than or equal to the characteristic value, controlling a supercharging pipeline control valve to be in an open state and a bypass pipeline control valve to be in a closed state, so that waste gas discharged by the lean-burn methanol engine passes through a supercharging pipeline and a supercharger carries out supercharging treatment on the waste gas in the supercharging pipeline;

collecting a second temperature value measured by a second temperature sensor and a first nitrogen-oxygen concentration value measured by a first nitrogen-oxygen sensor, and calculating a first methanol injection amount according to the first temperature value, the second temperature value and the first nitrogen-oxygen concentration value;

if the first temperature value is smaller than the characteristic value, controlling the supercharging pipeline control valve to be in a closed state and the bypass pipeline control valve to be in an open state, so that waste gas discharged by the lean-burn methanol engine passes through a bypass pipeline, and enabling a first oxidation catalyst to catalyze and oxidize the waste gas in the bypass pipeline;

Calculating a second methanol injection amount based on the first temperature value and a preset heating requirement;

and controlling a fuel injection system of the lean-burn methanol engine to perform in-cylinder post injection according to the first methanol injection amount/the second methanol injection amount, so that the selective reduction catalyst performs catalytic reduction on nitrogen oxides in exhaust gas discharged by the supercharger/the first oxidation catalyst by methanol, and further performs catalytic oxidation on the exhaust gas discharged by the selective reduction catalyst by the second oxidation catalyst.

8. The method of claim 7, wherein the method further comprises:

if the first temperature value is greater than or equal to the characteristic value, the first nitrogen-oxygen concentration value is acquired again through a preset first operation time period, the second nitrogen-oxygen concentration value measured by a second nitrogen-oxygen sensor is acquired, and the nitrogen-oxygen conversion efficiency of the selective reduction catalyst is calculated;

and adjusting the injection quantity of the first methanol according to the nitrogen-oxygen conversion efficiency.

9. The method of claim 8, wherein the method further comprises:

comparing the nitrogen-oxygen conversion efficiency with a preset conversion efficiency limit value; and if the nitrogen-oxygen conversion efficiency is smaller than the conversion efficiency limit value, prohibiting the lean-burn methanol engine from post-injection, and limiting the speed and the torque.

10. The method of claim 7, wherein the method further comprises:

if the first temperature value is smaller than the characteristic value, the first temperature value is acquired again through a preset second operation duration, and the first temperature value is compared with the characteristic value again;

and if the first temperature value is smaller than the characteristic value after re-comparison, prohibiting the lean-burn methanol engine from post-injection and limiting the speed and the torque.