A methanol and natural gas dual-fuel engine and control method

Abstract

This invention discloses a methanol / natural gas dual-fuel engine and its control method. The engine includes a cylinder block, a natural gas storage tank, a methanol fuel tank, an engine intake pipe, a common rail, nozzles, and a methanol vaporizer for generating methanol vapor. The engine intake pipe is connected to the cylinder block, and the common rail is connected to the engine intake pipe through the nozzles. The natural gas storage tank is connected to the common rail through the intake pipe, and the methanol fuel tank is connected to the methanol vaporizer through a methanol delivery pipe. The methanol vaporizer is connected to the common rail through a methanol vapor delivery pipe and a methanol vapor buffer. The engine uses methanol as the primary fuel and natural gas as an auxiliary fuel. During cold starts at low temperatures, natural gas is used as the fuel. After the engine coolant reaches a certain temperature, the liquid methanol is heated by the waste heat of the exhaust gas through the vaporizer, turning the liquid methanol into methanol vapor. The methanol fuel enters the cylinder as methanol vapor for combustion, making cold starts of the engine easier.

Description

Technical Field

[0001] The present invention relates to the technical field of dual-fuel engines, and in particular to a methanol and natural gas dual-fuel engine and a control method thereof. Background Art

[0002] As an internal combustion engine fuel, natural gas has been widely used in the taxi and commercial vehicle segments. Compared with gasoline and diesel fuels, the operating costs of natural gas vehicles have certain advantages. Natural gas has a high degree of external dependence and its price fluctuates greatly due to changes in the external environment, resulting in uncertainty in the market prospects of commercial vehicles fueled by natural gas. Therefore, the use of methanol to replace natural gas as the next generation of alternative fuel for commercial vehicles has strong practical significance.

[0003] With the global restrictions on greenhouse gas emissions, methanol-fueled engines are being used more and more widely. Methanol, as a clean and efficient fuel, has abundant raw material sources, low cost, and a good industrial foundation in my country, and has been widely used. Methanol, as a fuel for internal combustion engines, has been applied and promoted in passenger cars and commercial vehicles. However, under the existing technical conditions, due to the high ignition temperature, large latent heat of vaporization, and low saturated vapor pressure of methanol, methanol's characteristics make it very difficult to cold start the engine at low temperature. Therefore, the products currently on the market all use gasoline as an auxiliary fuel for cold start and heat engine process at low temperature. This dual-fuel technical solution requires the use of two fuel supply systems, including two fuel pumps and nozzles, and the control system is relatively complex. At the same time, methanol is injected into the cylinder as a liquid fuel. Due to poor methanol atomization, it is easy to wash the friction pair of the cylinder liner, causing increased wear of the cylinder liner, and it is easy to dilute the engine oil and increase the emission of pollutants, which seriously affects the reliability and durability of the engine.

[0004] In order to avoid the inconvenience of adding two fuels to customer application scenarios, the biggest obstacle faced by using a single methanol fuel is to solve the low-temperature cold start performance. The relevant patents propose alcohol hydrogen combustion technology, that is, using a vehicle cracker to crack methanol into carbon monoxide and hydrogen (such as Chinese patents CN208843725U, CN 108915909B and CN208843726U). This technology uses the waste heat of engine exhaust gas and absorbs the heat of exhaust gas. Under high temperature conditions, methanol undergoes a catalytic cracking reaction, and liquid methanol is cracked into hydrogen and carbon monoxide cracking gas, which then enters the cylinder for combustion. However, this methanol catalytic cracking technology has practical engineering problems such as insufficient catalyst structural strength, large catalyst volume, unstable catalyst cracking temperature, and low gas production efficiency. In addition, after a unit mass of methanol is cracked into hydrogen and carbon monoxide, the molar volume of the two gases is large, resulting in a reduction in engine intake and a decrease in the charging coefficient, which seriously affects the engine power. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a dual-fuel engine using methanol as a main fuel and natural gas as an auxiliary fuel and a control method thereof, wherein the engine can be easily cold-started at low temperatures and the thermal efficiency of the engine is effectively improved.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A methanol and natural gas dual-fuel engine comprises a cylinder body, a natural gas storage tank, a methanol fuel tank, and an engine intake pipe, wherein the engine intake pipe is connected to the cylinder body, and further comprises a common rail pipe, a nozzle, and a methanol vaporizer for forming methanol vapor. The common rail pipe is connected to the engine intake pipe through the nozzle, the natural gas storage tank is connected to the common rail pipe through an intake pipeline, the methanol fuel tank is connected to the methanol vaporizer through a methanol delivery pipeline, and the methanol vaporizer is connected to the common rail pipe through a methanol vapor delivery pipeline and a methanol vapor buffer.

[0008] The nozzle is arranged on the engine intake pipe to form a common nozzle structure for methanol steam fuel and natural gas fuel.

[0009] The exhaust port of the cylinder body is connected with an exhaust pipe, and the methanol vaporizer is arranged on the exhaust pipe.

[0010] A heating water jacket is arranged outside the engine air intake pipe for heating and keeping the air intake pipe warm.

[0011] The methanol delivery pipeline is provided with a methanol one-way valve for preventing the methanol vapor generated by the methanol vaporizer from flowing back under abnormal circumstances.

[0012] A pressure reducing valve and a pressure stabilizing valve are arranged in sequence on the air intake pipeline connected to the natural gas storage tank, and the upper part of the methanol fuel tank is connected to the pressure stabilizing valve through a high-pressure pipeline.

[0013] The common rail pipe is a three-way structure with two inlets and one outlet, the two inlet ends are respectively connected to the methanol steam buffer and the natural gas pressure regulating valve, and one outlet end is connected to the nozzle.

[0014] The methanol vaporizer is arranged at the rear end of the engine post-processing three-way catalytic converter, and the high-temperature exhaust gas fully flows through the vaporizer. The methanol vaporizer is equipped with an electric exhaust gas bypass valve, and the bypass valve opening is closed-loop controlled by detecting the methanol vapor temperature feedback.

[0015] The heating water jacket is connected to a small circulation of the engine cooling system.

[0016] A control method for a methanol and natural gas dual-fuel engine is as follows: methanol fuel is used as the main fuel, natural gas fuel is used as the auxiliary fuel, dual fuel is used for fuel supply, natural gas fuel is used for starting and heat engine conditions, and after the heat engine is completed, methanol vapor is used as the main fuel to enter the normal working mode.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. The engine uses methanol fuel as the main fuel and natural gas as the auxiliary fuel. Natural gas is used as the fuel for low-temperature cold start. After the engine coolant reaches a certain temperature, the liquid methanol uses the waste heat of the exhaust gas to heat the carburetor, turning the liquid methanol into methanol vapor. The methanol fuel enters the cylinder in the form of methanol vapor for combustion, making the engine easy to start at low temperature.

[0019] 2. Methanol is injected into the intake pipe in a vapor state and mixed more evenly with fresh air, which is conducive to accelerating the combustion speed, improving the effective thermal efficiency of the engine, and reducing the content of unburned methanol and HC in the emission pollutants; in addition, it can effectively avoid the problem of oil dilution, greatly reduce the wear of cylinder liners and other parts, and improve the reliability and durability of the engine;

[0020] 3. The injection method of methanol vapor uses a set of gas nozzles shared with natural gas, which has a simple structure, is easy to arrange and install, and has a relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following is a brief description of the contents and symbols in the drawings of this specification:

[0022] Figure 1 It is a schematic diagram of the engine of the present invention.

[0023] In the figure:

[0024] 1. Natural gas storage tank; 2. Methanol fuel tank; 3. Methanol vapor buffer; 4. Methanol shut-off valve; 5. Exhaust pipe; 6. Cylinder block; 7. EGR cooler; 8. Turbocharger; 9. Methanol vaporizer; 10. Methanol check valve; 11. Intercooler; 12. EGR valve; 13. Intake pipe; 14. EGR mixer; 15. Nozzle; 16. Common rail pipe; 17. Natural gas shut-off valve; 18. Pressure regulating valve; 19. Pressure reducing valve. DETAILED DESCRIPTION

[0025] The specific implementation modes of the present invention will be further explained in detail below through the description of embodiments with reference to the accompanying drawings.

[0026] like Figure 1 As shown, the methanol and natural gas dual-fuel engine uses methanol fuel as the main fuel and natural gas as the auxiliary fuel. Natural gas is used as fuel during low-temperature cold starting. After the engine coolant reaches a certain temperature, the liquid methanol uses the waste heat of the exhaust gas to be heated through the vaporizer to turn the liquid methanol into methanol vapor. The methanol fuel enters the cylinder in the form of methanol vapor for combustion, making it easy to start the engine at low temperature.

[0027] Methanol is injected into the intake pipe in a vapor state and mixed more evenly with the fresh air, which helps to speed up the combustion rate, improve the effective thermal efficiency of the engine, and reduce the content of unburned methanol and HC in the emission pollutants. In addition, it can effectively avoid the problem of oil dilution, greatly reduce the wear of cylinder liners and other parts, and improve the reliability and durability of the engine.

[0028] The dual-fuel engine comprises a cylinder body 6, a natural gas storage tank 1, a methanol fuel tank 2, an engine intake pipe 13, a common rail pipe 16, a nozzle 15 and a methanol vaporizer 9 for forming methanol vapor; the engine intake pipe is connected to the cylinder body, the common rail pipe is connected to the engine intake pipe through the nozzle, the natural gas storage tank is connected to the common rail pipe through the intake pipeline, the methanol fuel tank is connected to the methanol vaporizer through the methanol delivery pipeline, and the methanol vaporizer is connected to the common rail pipe through the methanol vapor delivery pipeline and the methanol vapor buffer 3.

[0029] The nozzle is arranged on the engine intake pipe to form a common nozzle structure for methanol steam fuel and natural gas fuel; preferably, the common rail pipe is a two-inlet and one-outlet three-way structure, the two intake ends are respectively connected to the methanol steam buffer and the natural gas pressure regulating valve, and one outlet end is connected to the nozzle. Methanol steam and natural gas injection share a common rail pipe and nozzle, and the common rail pipe can stabilize the fuel gas pressure; according to the methanol flow rate, if the flow rate of one nozzle is insufficient, multiple nozzles can be connected in parallel on the common rail pipe.

[0030] The exhaust port of the cylinder body is connected to an exhaust pipe 5, and a methanol vaporizer is arranged on the exhaust pipe. An EGR cooler 7 and a turbocharger 8 are arranged on the exhaust pipe. The EGR cooler is connected to the engine intake pipe through an EGR valve 12, and the turbocharger is connected to the engine intake pipe through an intercooler 11; further, the methanol vaporizer is arranged at the rear end of the engine post-processing three-way catalytic converter, and the high-temperature exhaust gas fully flows through the vaporizer. The methanol vaporizer has an electric exhaust bypass valve built in. By detecting the methanol vapor temperature feedback, the bypass valve opening size is closed-loop controlled, thereby controlling the heated exhaust gas volume to achieve the requirement of stable control of the methanol vapor temperature. After the liquid methanol is vaporized by the methanol vaporizer, a certain amount of methanol vapor is guaranteed to be stored in the methanol buffer tank, which can meet the requirements of transient high-load acceleration of the engine. The steam temperature of methanol after vaporization is controlled at about 70°. Since the boiling point of methanol is 64.7°C, this temperature ensures that methanol enters the cylinder in a gaseous state and burns, avoiding methanol condensation and liquid methanol diluting the engine oil. On the other hand, it heats the intake temperature of the engine under low load, reduces pumping air losses, and improves the thermal efficiency of the engine.

[0031] An interlayer heating water jacket is provided outside the engine intake pipe for heating and insulating the intake pipe; further, the heating water jacket is connected to the engine cooler system small circulation, and the intake pipe is insulated by the engine coolant to ensure that in a low temperature environment, the methanol vapor will not condense into liquid methanol after being injected through the nozzle, thereby preventing the liquid methanol fuel from entering the cylinders and causing poor uniformity, affecting the combustion stability and combustion uniformity of each cylinder.

[0032] A methanol check valve 10 is provided on the methanol delivery pipeline to prevent the methanol vaporizer from generating methanol vapor backflow under abnormal circumstances. A methanol check valve is arranged between the methanol vaporizer and the methanol fuel tank. The purpose of the check valve is mainly to prevent the methanol vaporizer from generating high methanol vapor under abnormal circumstances, causing methanol vapor backflow and resulting in high pressure in the methanol fuel tank. At the same time, due to the presence of the check valve, when the engine is shut down, the pressure-maintaining capacity in the methanol fuel tank decreases, and the methanol in the vaporizer flows back into the methanol fuel tank, causing the vaporizer to dry burn due to the lack of methanol liquid, and ensuring that the vaporizer is always filled with a certain amount of methanol during the engine start-up process, ensuring the pre-production of methanol vapor in the heat engine stage.

[0033] The air intake pipeline connected to the natural gas storage tank 1 is provided with a pressure reducing valve 19 and a pressure stabilizing valve 18 in sequence. The top of the methanol fuel tank is connected to the pressure stabilizing valve through a high-pressure pipeline, and the pressure stabilizing valve forms a natural gas pressure stabilizer. The methanol fuel supply system does not need to be equipped with a methanol electric pump, and the injection pressure of the methanol fuel comes from the natural gas high-pressure tank. The methanol fuel tank is a metal high-pressure resistant fuel tank that can withstand a pressure of more than 1MPa. A high-pressure pipeline is arranged above the methanol fuel tank, and the high-pressure pipeline is connected to the outlet of the natural gas fuel tank pressure stabilizer. The high pressure (0.8-0.9MPa) after the natural gas is decompressed is used to pressurize the methanol fuel in the methanol fuel tank to ensure the pressure required for the methanol fuel to enter the injection.

[0034] The injection method of methanol vapor uses a common set of gas nozzles with natural gas, which has a simple structure, is easy to arrange and install, and has a relatively low cost.

[0035] In the present invention, the engine uses methanol fuel as the main fuel and natural gas engine (CNG) as the auxiliary fuel, and adopts a dual-fuel fuel supply method; natural gas is used as fuel during low-temperature cold start, and after the engine coolant reaches a certain temperature, liquid methanol uses the waste heat of exhaust gas to be heated through a vaporizer to convert liquid methanol into methanol vapor, and the methanol fuel enters the cylinder in the form of methanol vapor for combustion.

[0036] Methanol fuel and natural gas are two fuels with very friendly complementarity. From the molecular formula, both fuels have one carbon atom and four hydrogen atoms, but methanol has one more oxygen atom than natural gas fuel. As internal combustion engine fuel, methanol vapor and natural gas have many similar combustion characteristics. The octane number of the two fuels' anti-knock index reaches 127 and 114 respectively, which is higher than the anti-knock performance of gasoline engines, so the compression ratio of the engine can be increased. Both fuels can be premixed and diffused by spark plug ignition. Since the vaporization temperature of natural gas is -162°C, it is very easy to form a uniform mixture with air even in extremely low winter conditions, and the low-temperature cold start is very good, which can make up for the difficulty of methanol's low-temperature cold start. The boiling point of methanol fuel at normal pressure is 64.7°C, which is relatively easy to heat and vaporize into methanol vapor. After methanol is vaporized, it enters the cylinder in gaseous form for combustion. This method is exactly the same as the combustion of natural gas entering the cylinder. The same natural gas nozzle and electronic control system can be used. Both fuels use equivalent mixture control method, and the exhaust post-treatment uses a three-way catalytic converter, which has a high conversion efficiency of exhaust pollutants. Moreover, this method of injecting methanol vapor avoids the methanol entering the cylinder in liquid form, which would cause increased cylinder liner wear and oil dilution, and reduces the emission of unburned methanol and HC.

[0037] The control method of natural gas and methanol fuels of the present invention has three modes: starting mode, heat engine mode, and normal working mode. In the starting mode, the electric control cut-off valve of the methanol fuel supply system is closed, the electric control cut-off valve of the natural gas is opened, and the engine uses a single natural gas for cold starting. Since the vaporization pressure of natural gas is -162°C, it is easy to form a homogeneous mixed gas with air in a low temperature environment, and the cold starting effect is relatively good. After the start is successful, the engine enters the heat engine mode, and the heat engine process also uses natural gas fuel. The engine ignition angle and injection amount control all use the natural gas characteristic value MAP written by the control system. When the heat engine reaches a certain degree, the engine performs condition judgment according to parameters such as ambient temperature, coolant temperature, methanol vapor temperature and pressure. If the heat engine completion condition is met, it enters the normal working mode. In the normal working mode, the methanol electric control cut-off valve is first opened to ensure that the methanol vapor enters the common rail pipe, and then the natural gas electric control cut-off valve is disconnected. Since a certain amount of natural gas will remain in the common rail pipe, there is a transition condition in which two fuels participate in combustion at the same time. The judgment condition of whether the transition condition is ended can be judged according to the closed-loop feedback of the air-fuel ratio. After completing the transition condition, the engine enters the methanol single fuel operation mode, and the ignition angle and injection quantity control both use the methanol characteristic values ​​that have been written in the control system.

[0038] Preferred embodiments of the present invention are:

[0039] The methanol and natural gas dual-fuel engine of the present invention has two independent fuel tanks, and the natural gas fuel supply system mainly includes natural gas storage tank 1, pressure reducing valve 19, pressure stabilizing valve 18, natural gas cut-off valve 17, methanol natural gas nozzle 15 and other components, and the methanol fuel supply system includes: methanol fuel tank 2, methanol steam buffer tank 3, methanol vaporizer 9, methanol check valve 10, methanol cut-off valve 4, common rail pipe 16 and other components. The natural gas storage tank stores compressed natural gas (CNG), which generally has a pressure of 10-20MPa. The capacity of the natural gas storage tank does not need to be too large, and the general volume is 1 / 10 of the volume of the methanol fuel tank. After the compressed natural gas is reduced by the pressure reducing valve, the pressure is reduced to about 1-2MPa, and then passes through the pressure stabilizing valve, and the pressure is stably controlled at 0.7-0.8MPa.

[0040] The methanol fuel tank is connected to the pressure regulating valve through a high-pressure pipeline, which can stably transfer the pressure of the pressure regulating valve to the methanol fuel tank to provide pressure for methanol injection. The methanol vaporizer is arranged in series on the exhaust pipe, and there is an exhaust gas bypass valve inside. The amount of high-temperature exhaust gas flowing through the vaporizer can be controlled by the valve opening size. Under different working conditions, the requirements for methanol steam production can be met according to the flow demand of methanol. After methanol passes through the vaporizer, the steam generated is temporarily stored in the buffer tank. The volume size of the methanol steam buffer tank is designed according to the engine displacement size to meet the hysteresis effect of methanol vaporizer production of methanol steam under transient working conditions. The common rail pipe is a device that connects natural gas and methanol steam to balance the pressure stability before fuel injection. The nozzle is arranged on the common rail pipe connected to the intake end, and the outlet end is connected to the intake main pipe. A single-point injection method is adopted (depending on the nozzle flow size, if the nozzle flow is not enough, multiple nozzles can be used in parallel between the intake main pipe and the common rail pipe).

[0041] Methanol vapor or natural gas fuel is mixed with EGR exhaust gas and fresh air in the EGR mixer 14. The function of the mixer is to fully mix the methanol vapor (or natural gas) fuel with fresh air and EGR exhaust gas to form a mixed gas with uniform temperature and concentration before entering the intake pipe. The main intake pipe is equipped with a heating water jacket. The heating medium is engine coolant. The coolant is taken from the small cycle of the engine cooling system to ensure that the engine also has a preheating function when warming up, so as to avoid the methanol vapor condensing into liquid methanol in the intake pipe before entering the cylinder, affecting the uniformity of methanol fuel entering each cylinder, and then affecting the combustion stability of the engine. EGR adopts a high-pressure EGR system, and the EGR rate is controlled by the EGR valve. The exhaust gas temperature after EGR intercooling is controlled at 100-120°C.

[0042] According to the different ambient temperature and engine coolant temperature, the engine is divided into three working modes: starting condition, warm-up condition, and normal working condition. In both starting condition and warm-up condition, natural gas fuel is used for injection. When the engine starts, the electronic control system sends instructions to the natural gas cut-off valve 17 and the methanol cut-off valve 4 to open the natural gas cut-off valve and close the methanol cut-off valve 4. After the compressed natural gas is regulated by the pressure reducing valve and the pressure stabilizing valve, a stable injection pressure is formed in the common rail pipe. The general injection pressure is adjusted within the range of 0.7-0.8MPa to meet the natural gas injection requirements. After the engine starts successfully, it enters the warm-up stage and continues to use natural gas fuel injection. At this time, the methanol fuel tank transmits the pressure transmitted by the natural gas regulator, and the methanol in the methanol fuel tank is pressed into the methanol vaporizer. The vaporizer is arranged at a height lower than the methanol fuel tank. Even if the methanol cut-off valve is in a closed state, liquid methanol can be filled in the methanol vaporizer by gravity. In the warm-up stage, the vaporizer controls the exhaust gas bypass valve to close the opening, and the exhaust gas is fully circulated through the vaporizer to accelerate the methanol vaporization speed and quickly produce methanol vapor. When the coolant temperature rises to a certain temperature (generally 65°C), combined with whether the methanol vapor pressure and temperature conditions of the methanol vapor buffer tank are met (the judgment conditions are that the methanol vapor pressure is greater than 0.8MPa and the temperature is higher than 65°C), the engine enters the normal working mode. At this time, the electronic control system sends a command to the methanol cut-off valve, the methanol cut-off valve opens, and then closes the natural gas cut-off valve. There is a time difference between the opening and closing of the two cut-off valves. The specific time difference can be optimized and calibrated through calibration parameters to ensure the stability of the fuel when switching between the two fuels and avoid engine speed fluctuations. After entering the normal working mode, according to the different theoretical air-fuel ratios of methanol and natural gas to air, the flow characteristics of the nozzle adopt the injection pulse width of methanol fuel, and the other control parameters of the ignition angle are also switched to the parameters of the methanol fuel working condition.

[0043] In normal mode, the exhaust temperature is not stable due to the transient working conditions of the engine, and the methanol vapor production has the phenomenon of unstable flow. For example, when accelerating suddenly, the instantaneous demand for methanol vapor injection flow is large, and the exhaust temperature preheating is insufficient at this time. Therefore, the arranged methanol vapor buffer tank can make up for the large flow demand of methanol vapor under transient working conditions. When the engine continues to work under high load, the exhaust temperature is high, and the methanol vaporizer produces more methanol vapor, causing the pressure and temperature of the methanol buffer tank to rise. At this time, the electronic control system can control the exhaust gas bypass valve inside the methanol vaporizer, adjust the flow of high-temperature exhaust gas flowing through the vaporizer, and play a role in controlling the flow of methanol production from the vaporizer. In addition, a methanol check valve is arranged at the fuel inlet of the methanol vaporizer. The check valve can prevent the steam pressure in the methanol vaporizer from exceeding the pressure in the methanol fuel tank, resulting in methanol vapor reflux. This arrangement structure ensures the normal supply of methanol vapor under various working conditions of the engine and controls the temperature and pressure of methanol vapor within a certain range.

[0044] The above is only an explanation of the preferred embodiments of the present invention, and the above technical features can be arbitrarily combined to form multiple embodiments of the present invention.

[0045] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A control method for a methanol and natural gas dual-fuel engine, characterized in that: The methanol and natural gas dual-fuel engine comprises a cylinder body, a natural gas storage tank, a methanol fuel tank, and an engine intake pipe, wherein the engine intake pipe is connected to the cylinder body, and is characterized in that it also comprises a common rail pipe, a nozzle, and a methanol vaporizer for forming methanol vapor, wherein the common rail pipe is connected to the engine intake pipe through the nozzle, the natural gas storage tank is connected to the common rail pipe through an intake pipeline, the methanol fuel tank is connected to the methanol vaporizer through a methanol delivery pipeline, and the methanol vaporizer is connected to the common rail pipe through a methanol vapor delivery pipeline and a methanol vapor buffer; The nozzle is arranged on the engine intake pipe to form a common nozzle structure for methanol steam fuel and natural gas fuel; the exhaust port of the cylinder body is connected to the exhaust pipe, and the methanol vaporizer is arranged on the exhaust pipe; the engine intake pipe is provided with a heating water jacket for heating and heat preservation of the intake pipe; the methanol delivery pipeline is provided with a methanol check valve for preventing the methanol vaporizer from generating methanol vapor backflow under abnormal conditions; the intake pipeline connected to the natural gas storage tank is provided with a pressure reducing valve and a pressure regulating valve in sequence, and the upper part of the methanol fuel tank is connected to the pressure regulating valve through a high-pressure pipeline; the common rail pipe is a two-in-one-out three-way structure, the two intake ends are respectively connected to the methanol steam buffer and the natural gas pressure regulating valve, and one outlet end is connected to the nozzle; the methanol vaporizer is arranged at the rear end of the engine post-processing three-way catalytic converter, and the high-temperature exhaust gas flows through the vaporizer. The methanol vaporizer has an electric exhaust bypass valve built in, and the bypass valve opening size is closed-loop controlled by detecting the methanol vapor temperature feedback; the heating water jacket is connected to the engine cooling system small cycle; The control method is as follows: methanol fuel is used as the main fuel, natural gas fuel is used as the auxiliary fuel, dual fuel is used for fuel supply, natural gas fuel is used for starting and heat engine operation, and after the heat engine is completed, methanol steam is used as the main fuel to enter the normal working mode; According to the different external environment temperature and engine coolant temperature, the engine is divided into three working modes: starting condition, warm-up condition and normal working condition; both starting condition and warm-up condition use natural gas fuel for injection; when the engine starts, the electronic control system sends instructions to the natural gas cut-off valve and the methanol cut-off valve to open the natural gas cut-off valve and close the methanol cut-off valve. After the compressed natural gas is regulated by the pressure reducing valve and the pressure stabilizing valve, a stable injection pressure is formed in the common rail pipe to meet the natural gas injection requirements; after the engine starts successfully, it enters the warm-up stage and continues to use natural gas fuel injection. At this time, the methanol fuel tank transmits the pressure transmitted by the natural gas regulator to press the methanol in the methanol fuel tank into the methanol vaporizer. The vaporizer is arranged at a height lower than the methanol fuel tank. Even if the methanol cut-off valve is in a closed state, liquid methanol can be filled in the methanol vaporizer by gravity; in the warm-up stage, the vaporizer controls the exhaust gas bypass valve to close the opening, and the exhaust gas fully flows through the vaporizer to accelerate the methanol vaporization speed and quickly produce methanol vapor; When the coolant temperature rises to a certain temperature, the methanol vapor pressure and temperature conditions of the methanol vapor buffer tank are combined to see whether the methanol vapor pressure is greater than 0.8MPa and the temperature is higher than 65℃. If the conditions are met, the engine enters the normal working mode. At this time, the electronic control system sends a command to the methanol cut-off valve, the methanol cut-off valve opens, and then the natural gas cut-off valve is closed. The two cut-off valves are opened and closed, and there is a time difference in the switch. The specific time difference is optimized and calibrated through calibration parameters to ensure the stability of the fuel provided when switching between the two fuels to avoid engine speed fluctuations; after entering the normal working mode, according to the different theoretical air-fuel ratios of methanol and natural gas to air, the flow characteristics of the nozzle adopt the injection pulse width of methanol fuel.

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