Low-temperature efficient formaldehyde purification system for methanol engine and control method

Abstract

The invention discloses a low-temperature efficient formaldehyde purification control method for a methanol engine, and relates to post-treatment of the methanol engine, and the method comprises the following steps: collecting the inlet temperature of a methanol oxidation catalyst of the methanol engine; according to the inlet temperature of the methanol oxidation catalyst and a preset characteristic temperature, judging a post-processing working mode of the methanol engine; and if the working mode of the methanol engine after-treatment is a low-temperature mode, starting a heating mode running based on the after-treatment air supply amount to heat a methanol engine after-treatment system so as to enable a methanol oxidation catalyst in the methanol engine after-treatment system to reach a target temperature. The invention further discloses a low-temperature efficient formaldehyde purification system for the methanol engine. According to the scheme, the special catalyst is rapidly activated at the low temperature, and the oxygen-enriched environment is provided, so that emission of formaldehyde and unburned methanol can be greatly reduced, and the methanol engine can meet the requirements of current and future expected ultralow emission regulations.

Description

Technical Field

[0001] This invention relates to methanol engine aftertreatment, and more specifically, to a low-temperature, high-efficiency formaldehyde purification system and control method for methanol engines. Background Technology

[0002] With the deepening global push for "carbon peaking and carbon neutrality," the development and application of low-carbon clean fuels have become crucial for emission reduction in the transportation sector. Methanol, as a widely available and clean-burning low-carbon fuel, exhibits significantly lower carbon emissions throughout its life cycle compared to traditional fossil fuels, demonstrating immense application potential. However, methanol engines still face a severe technical bottleneck in their industrialization: controlling the emission of unconventional pollutant formaldehyde, especially during cold starts. Unlike gasoline or diesel engines, methanol engines have unique exhaust compositions. Due to methanol's high latent heat of vaporization, the cylinder temperature is low during cold starts, resulting in extremely incomplete combustion and the production of large amounts of unburned methanol. This unburned methanol undergoes further incomplete oxidation during exhaust, generating the more toxic formaldehyde. Formaldehyde is classified as a Group 1 carcinogen by the World Health Organization, and its emissions are strictly limited by regulations in various countries, thus becoming a focal point and challenge in methanol engine emission control.

[0003] Currently, aftertreatment solutions for methanol engines largely draw on traditional internal combustion engine technologies, which have significant shortcomings. First, the widely used three-way catalytic converter is designed for gasoline vehicle exhaust, exhibiting poor low-temperature catalytic activity and selectivity for formaldehyde, resulting in unsatisfactory purification efficiency. Second, the efficient operation of all catalysts depends on a specific temperature window (typically an ignition temperature above 250°C). During the initial 1 to 3 minutes of a cold start, the exhaust temperature is far below this threshold, causing the catalyst to be in a "cold" and ineffective state, creating a significant pollutant emission window during which over 80% of formaldehyde is emitted. Furthermore, while enhanced oxidation catalysts or diesel engine SCR technology have shown some effectiveness, the former still fails to address the fundamental issue of low-temperature activity, while the latter is complex, costly, and carries the risk of methanol potentially poisoning the SCR catalyst. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a low-temperature high-efficiency formaldehyde purification system and control method for methanol engines. By rapidly activating a special catalyst at low temperatures and providing an oxygen-rich environment, the system can significantly reduce formaldehyde and unburned methanol emissions, enabling methanol engines to meet current and future ultra-low emission regulations.

[0005] The present invention discloses a low-temperature, high-efficiency formaldehyde purification control method for methanol engines, which involves collecting the inlet temperature of the methanol oxidation catalyst of the methanol engine; determining the working mode of the methanol engine aftertreatment based on the inlet temperature of the methanol oxidation catalyst and a preset characteristic temperature; if the working mode of the methanol engine aftertreatment is a low-temperature mode, then activating a heating mode based on the aftertreatment gas supply to heat the methanol engine aftertreatment system, so that the methanol oxidation catalyst in the methanol engine aftertreatment system reaches the target temperature.

[0006] Preferably, the heating mode based on the post-treatment gas replenishment volume specifically refers to: While starting the electric heater in the methanol engine aftertreatment system, the methanol engine aftertreatment system is replenished with gas.

[0007] Preferably, the heating power of the electric heater is calculated using the following formula: , In the formula, W hot k is the heating power of the electric heater. act q is the catalyst activity coefficient. air To replenish the gas flow rate, q exh For exhaust flow rate, C p η is the specific heat capacity, η is the heating efficiency, T1 is the first characteristic temperature, and T target ΔT represents the inlet temperature of the methanol oxidation catalyst. comp This is a dynamic heat loss compensation item.

[0008] Preferably, the amount of supplemental air in the methanol engine aftertreatment system is calculated using the following formula: , In the formula, λ1 is the target excess air coefficient, λ base To ensure the minimum excess air coefficient for the reaction, λ max The maximum permissible excess air coefficient, n is the exponent for adjusting the shape of the curve, and q mf.i For fuel consumption, q maw.i Engine air intake volume.

[0009] Preferably, after activating the heating mode based on aftertreatment supplementary air volume, the target air-fuel ratio in the methanol engine is collected, and when the target air-fuel ratio is a set air-fuel ratio threshold, methanol is injected into the cylinder after injection to increase the exhaust temperature.

[0010] Preferably, the injection volume of the in-cylinder post-injection methanol is: , In the formula, q Meoh K represents the injection volume of methanol after injection into the cylinder. T.ambK is the ambient temperature correction factor. O2 C is the correction factor for exhaust oxygen concentration. FOC For the heat capacity of the methanol oxidation catalyst, H Meah η is the calorific value of methanol. ox For oxidation efficiency, T1 is the first characteristic temperature, and T target This is the inlet temperature of the methanol oxidation catalyst.

[0011] Preferably, the operating modes of the methanol engine aftertreatment include low temperature mode, transition mode and normal mode; If the inlet temperature of the methanol oxidation catalyst is lower than the first characteristic temperature, it is determined to be in low-temperature mode; If the inlet temperature of the methanol oxidation catalyst is greater than or equal to the first characteristic temperature, but less than the preset second characteristic temperature, it is determined to be in transition mode. If the inlet temperature of the methanol oxidation catalyst is greater than or equal to the second characteristic temperature, it is determined to be in normal mode.

[0012] Preferably, in the transition mode, the electric heater stops working, but continues to provide supplemental air and in-cylinder post-injection of methanol.

[0013] Preferably, in the normal mode, the electric heater stops working, but continues to supply gas.

[0014] A low-temperature, high-efficiency formaldehyde purification system for methanol engines, comprising: The formaldehyde purification unit includes a formaldehyde oxidation catalyst, which is connected to the exhaust pipe. The heating unit includes an electric heater and an in-cylinder methanol injection system; The air replenishment unit includes an air tank, an air replenishment pipe, and a solenoid valve. The air tank is used to store compressed air, and the two ends of the air replenishment pipe are connected to the air tank and the exhaust pipe, respectively. The intelligent control unit includes a temperature sensor and a controller. The temperature sensor is used to collect the inlet temperature of the methanol oxidation catalyst, and the controller controls the heating unit and the gas injection unit based on the inlet temperature of the methanol oxidation catalyst using the low-temperature high-efficiency formaldehyde purification method for methanol engines as described in any one of claims 1-9.

[0015] Beneficial effects The advantages of this invention are: 1. Achieve ultra-low formaldehyde emissions: By rapidly activating a dedicated catalyst at low temperatures and providing an oxygen-rich environment, formaldehyde and unburned methanol emissions, especially during the cold start phase, can be significantly reduced, enabling methanol engines to meet current and future ultra-low emission regulations.

[0016] 2. Achieving rapid ignition and overcoming the cold start challenge: The "electrochemical" dual-mode synergistic heating strategy can significantly shorten the time for the catalyst to reach its effective operating temperature, fundamentally solving the problem of low purification efficiency in the initial stage of cold start in traditional systems.

[0017] 3. Intelligent and reliable: The closed-loop control logic based on temperature feedback is simple and reliable, ensuring that the system can operate automatically and accurately under different operating conditions. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the low-temperature, high-efficiency formaldehyde purification system for methanol engines according to the present invention.

[0019] Among them: 1-Methanol fuel tank, 2-Methanol engine, 3-Exhaust pipe, 4-Formaldehyde oxidation catalyst, 5-Oxidation catalyst, 6-DPF, 7-Temperature sensor, 8-Gas storage tank, 9-Main air pipe, 10-Solenoid valve. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of the claims of the present invention are still within the scope of the claims of the present invention. Example 1 The present invention provides a low-temperature, high-efficiency formaldehyde purification and control method for methanol engines, comprising the following steps: Step 1: Cold start identification and decision-making.

[0021] The inlet temperature T1 of the methanol oxidation catalyst of the methanol engine is collected and compared with the first characteristic temperature T2. If T1 is less than or equal to T2 (e.g., 150°C), the low temperature mode is entered.

[0022] Step 2: Low Temperature Mode.

[0023] Start the electric heater and calculate the heating power based on the target temperature: , In the formula, k act is the catalyst activity coefficient, which changes based on the catalyst's historical operating conditions (such as cumulative high-temperature operating time and cold start count) and the current state's decay factor or health factor. For new catalysts, k... act ≈1.1 provides a slightly excess of heat energy to ensure rapid ignition; as the catalyst ages, the system will appropriately increase k. act This compensates for the decrease in activity and ensures cold-start performance throughout the entire lifecycle. This demonstrates the system's adaptive capability. ΔT compThis is a dynamic heat loss compensation term. It no longer simply assumes an ideal environment, but estimates it in real time through a model; its value is related to the current exhaust flow rate, vehicle speed, and ambient temperature. ΔT comp =f(q exh V vehicle ,T ambient This allows the system to respond more accurately to complex real-world operating conditions and reduces energy waste. air To replenish the gas flow rate, q exh For exhaust flow rate, C p η is the specific heat capacity, and η is the heating efficiency.

[0024] Initiate Qi replenishment. Qi replenishment amount: q air Calculate using the following formula: , In the formula, λ base It is the minimum excess air coefficient that guarantees the reaction, λ max It is the maximum permissible excess air coefficient, and n is the exponent for adjusting the shape of the curve.

[0025] The air supply volume changes dynamically with temperature. During the cold start phase when the temperature is lowest, the system uses the maximum air supply volume (λ). max This provides a strong oxygen supply, ensuring maximum contact with oxygen even when the catalyst activity is low. As the catalyst temperature T1 increases, its activity increases, and the required excess oxygen gradually decreases to λ. base This allows for on-demand oxygen supply, avoiding excessive oxygen supplementation that could lead to heat loss during exhaust. a Target air supply volume, in kg / h; λ1 is the target excess air coefficient, determined by exhaust temperature and flow rate, and ranges from 1.0 to 1.2, based on calibration data; 6.45 is the theoretical air-fuel ratio of methanol; q mf.i Fuel consumption, read from engine information, in kg / h; q maw.i Engine intake air volume, read from engine information, in kg / h.

[0026] In the engine, the target air-fuel ratio is 1.0-1.2, which is an oxygen-rich state. At this point, methanol is injected into the cylinder in small quantities. The methanol oxidizes and releases heat in the methanol oxidation catalyst, accelerating the temperature rise of the aftertreatment process. Methanol injection quantity calculation: , In the formula, K T.amb This is the ambient temperature correction factor, which varies with the ambient temperature T. ambient Changes with, specifically, K T.amb =1+0.005×(25-T ambient For example, when T ambient At -15℃, KT.amb =1.2; T ambient At 35℃, K T.amb =0.9. K O2 The exhaust oxygen concentration correction factor is dynamically adjusted based on the measured O2% value from the oxygen sensor: K O2 =21% / O2%. Where 21% is the standard atmospheric oxygen concentration. C FOC For the heat capacity of the methanol oxidation catalyst, H Meah η is the calorific value of methanol. ox This refers to the oxidation efficiency.

[0027] Step 3: Transition mode for temperature increase and mode switching.

[0028] When the methanol oxidation catalyst inlet temperature T1 is greater than or equal to the first characteristic temperature T2, but less than the second characteristic temperature T3 (e.g., 200°C), electric heating is stopped to save energy, but air injection and necessary in-cylinder post-injection continue to be maintained, using the heat of chemical reaction to maintain the temperature rise.

[0029] Step 4: Normal Mode.

[0030] When the inlet temperature T1 of the methanol oxidation catalyst is greater than or equal to the characteristic temperature T3, the catalyst is considered to have entered the high-efficiency operating window and normal evolution mode. In this mode, the electric heater is turned off, and only the supplementary air provides an oxygen-rich environment, utilizing the exhaust gas's own temperature to achieve efficient methanol purification. In-cylinder post-injection can be initiated or stopped in small amounts as needed (e.g., if formaldehyde concentration exceeds the standard). Under sufficient oxygen conditions, the three-way catalyst TWC catalyzes the following reaction: CH3OH + CO + NOX → N2 + H2O + CO2. Excess methanol, formaldehyde, and carbon monoxide are also absorbed by oxygen and undergo the following reaction: CH3OH + CH2O + CO + O2 → H2O + CO2, reducing pollution emissions at this stage. In-cylinder post-injection methanol can be adjusted based on formaldehyde sensor data to ensure complete formaldehyde oxidation.

[0031] This invention features intelligent mode switching based on multiple temperature thresholds: it presets multiple characteristic temperatures (e.g., T2=150°C, T3=200°C) and automatically and seamlessly switches between low-temperature purification mode, transition mode, and normal purification mode based on real-time acquired catalyst inlet temperature. This dynamic control ensures that the system operates at its optimal state under all conditions, balancing purification efficiency and energy consumption.

[0032] Example 2 See Figure 1 A low-temperature, high-efficiency formaldehyde purification system for methanol engines, which mainly consists of the following components: Formaldehyde purification unit: The core is the formaldehyde oxidation catalytic converter 4, which uses a low-temperature and highly active catalyst (such as Ag-Pd / γ-Al2O3 or Pt-Pd / CeO2) and can be ignited below 150°C. Optionally, a three-way catalytic converter or an oxidizer can be integrated for co-processing carbon monoxide, hydrocarbons, and nitrogen oxides.

[0033] Heating unit: One is heated by an electric heater, which is used to quickly raise the temperature during cold start and is installed between the air supply pipe 9 and the formaldehyde oxidation catalytic converter 4; the other is chemically heated by injecting methanol into the cylinder later. Methanol oxidizes and releases heat on the formaldehyde oxidation catalytic converter. That is, the present invention adopts an "electric-chemical" dual-mode cooperative heating strategy, innovatively combining electric heating with in-cylinder post-injection of methanol chemical heating (using its own fuel and high heat release efficiency) to form a synergistic effect. This strategy can raise the catalyst temperature to the active window with the lowest energy consumption and the fastest speed during cold start, overcoming the deficiencies of a single heating method.

[0034] Air supply unit: It consists of an air storage tank 8, an air supply pipe 9, and a solenoid valve 10 installed in the air supply pipe 9. The air storage tank 8 stores compressed air. The two ends of the air supply pipe 9 are respectively connected to the air storage tank 8 and the exhaust pipe 3, and are used to supply air to create an oxygen-rich environment in the formaldehyde oxidation catalytic converter 4 of the after-treatment system.

[0035] Intelligent control unit: It consists of a temperature sensor 7 and a controller. The temperature sensor 7 is used to collect the inlet temperature of the methanol oxidation catalytic converter. The controller controls the heating unit and the air supply unit based on the inlet temperature of the methanol oxidation catalytic converter by applying the above-mentioned low-temperature and high-efficiency formaldehyde purification method for methanol engines.

[0036] After the engine starts, the controller obtains parameters such as the engine coolant temperature, speed, load, and fuel consumption. The controller collects the inlet temperature of the methanol oxidation catalytic converter measured by the temperature sensor, that is, T1. Subsequently, the controller compares T1 with a preset first characteristic temperature T2 (for example, 150°C). If T1 is less than T2, it is determined that the engine is in a cold start or low-temperature operation state, and the low-temperature purification mode is activated: start the electric heater, open the solenoid valve 10, and at the same time perform in-cylinder post-injection of methanol.

[0037] The controller continuously monitors T1. When T1≥T2 but <T3 (the second characteristic temperature, for example, 200°C), the electric heater is stopped to save electricity, but the air supply and necessary in-cylinder post-injection are continued to maintain the temperature rise using the chemical reaction heat. When T1≥T3, it is determined that the catalytic converter has entered the high-efficiency working window, and the normal purification mode is entered. In this mode, the electric heater is turned off, and only the air supply provides an oxygen-rich environment, and the high-efficiency purification of methanol can be achieved using the exhaust gas temperature itself. The in-cylinder post-injection can be carried out in a small amount or stopped according to actual needs (such as when the formaldehyde concentration is detected to exceed the standard).

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention, and these will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A low-temperature, high-efficiency formaldehyde purification and control method for methanol engines, characterized in that, The inlet temperature of the methanol oxidation catalyst of the methanol engine is collected; the working mode of the methanol engine aftertreatment is determined based on the inlet temperature of the methanol oxidation catalyst and the preset characteristic temperature; if the working mode of the methanol engine aftertreatment is the low temperature mode, the heating mode based on the aftertreatment gas supply is activated to heat the methanol engine aftertreatment system so that the methanol oxidation catalyst in the methanol engine aftertreatment system reaches the target temperature.

2. The low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 1, characterized in that, The heating mode based on post-treatment gas replenishment is specifically as follows: While starting the electric heater in the methanol engine aftertreatment system, the methanol engine aftertreatment system is replenished with gas.

3. The low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 2, characterized in that, The heating power of the electric heater is calculated using the following formula: ， In the formula, W hot k is the heating power of the electric heater. act q is the catalyst activity coefficient. air To replenish the gas flow rate, q exh For exhaust flow rate, C p η is the specific heat capacity, η is the heating efficiency, T1 is the first characteristic temperature, and T target ΔT represents the inlet temperature of the methanol oxidation catalyst. comp This is a dynamic heat loss compensation item.

4. The low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 3, characterized in that, The amount of supplemental air for the methanol engine aftertreatment system is calculated using the following formula: ， In the formula, λ1 is the target excess air coefficient, λ base To ensure the minimum excess air coefficient for the reaction, λ max The maximum permissible excess air coefficient, n is the exponent for adjusting the shape of the curve, and q mf.i For fuel consumption, q maw.i Engine air intake volume.

5. The low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 1, characterized in that, After activating the heating mode based on aftertreatment supplementary air volume, the target air-fuel ratio in the methanol engine is collected, and when the target air-fuel ratio is at the set air-fuel ratio threshold, methanol is injected into the cylinder after injection to increase the exhaust temperature.

6. The low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 5, characterized in that, The injection volume of methanol after in-cylinder injection is: ， In the formula, q Meoh K represents the injection volume of methanol after injection into the cylinder. T.amb K is the ambient temperature correction factor. O2 C is the correction factor for exhaust oxygen concentration. FOC For the heat capacity of the methanol oxidation catalyst, H Meah η is the calorific value of methanol. ox For oxidation efficiency, T1 is the first characteristic temperature, and T target This is the inlet temperature of the methanol oxidation catalyst.

7. The low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 5, characterized in that, The methanol engine aftertreatment operating modes include low temperature mode, transition mode and normal mode; If the inlet temperature of the methanol oxidation catalyst is lower than the first characteristic temperature, it is determined to be in low-temperature mode; If the inlet temperature of the methanol oxidation catalyst is greater than or equal to the first characteristic temperature, but less than the preset second characteristic temperature, it is determined to be in transition mode. If the inlet temperature of the methanol oxidation catalyst is greater than or equal to the second characteristic temperature, it is determined to be in normal mode.

8. A low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 7, characterized in that, In the transition mode, the electric heater stops working, but continues to provide supplemental air and in-cylinder methanol injection.

9. A low-temperature, high-efficiency formaldehyde purification and control method for methanol engines according to claim 7, characterized in that, In the normal mode, the electric heater stops working, but continues to supply gas.

10. A low-temperature, high-efficiency formaldehyde purification system for methanol engines, characterized in that, include: The formaldehyde purification unit is equipped with a formaldehyde oxidation catalyst (4) and is connected to the exhaust pipe (3); The heating unit includes an electric heater and an in-cylinder methanol injection system; The air replenishment unit includes an air storage tank (8), an air replenishment pipe (9), and a solenoid valve (10). The air storage tank (8) is used to store compressed air. The two ends of the air replenishment pipe (9) are connected to the air storage tank (8) and the exhaust pipe (3) respectively. The solenoid valve (10) is installed in the air replenishment pipe (9). The intelligent control unit includes a temperature sensor (7) and a controller. The temperature sensor (7) is used to collect the inlet temperature of the methanol oxidation catalyst. The controller controls the heating unit and the gas supply unit based on the inlet temperature of the methanol oxidation catalyst using the low-temperature high-efficiency formaldehyde purification method for methanol engines as described in any one of claims 1-9.

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