A microwave plasma based ignition device and method for a dual chamber pre-chamber ignition for a methanol engine

Abstract

The application belongs to the technical field of internal combustion engines, and particularly relates to a methanol engine double-cavity pre-chamber ignition device and method based on microwave plasma. The device comprises a microwave generator, a pre-chamber and a methanol engine. The pre-chamber comprises an inner chamber and an outer chamber, the inner chamber is provided with a methanol inlet, the outer chamber is provided with an air inlet, and the inner chamber and the outer chamber are communicated with a cylinder through a same mixed gas inlet. The microwave generator comprises a microwave generating unit and a microwave transmission unit. The microwave transmission unit is connected with the inner chamber and used for conveying the microwave into the inner chamber to generate methanol plasma. The methanol plasma and the air are synchronously introduced into the cylinder from the mixed gas inlet to ignite the mixed gas of the methanol and the air in the cylinder. The application improves the reaction activity of the methanol molecules in the pre-chamber and ignites the methanol directly introduced into the cylinder (from an air inlet) to further improve the combustion efficiency of the methanol engine.

Description

Technical Field

[0001] This invention belongs to the field of internal combustion engine technology, specifically relating to a dual-chamber pre-combustion chamber ignition device and method for a methanol engine based on microwave plasma. Background Technology

[0002] With the continuous growth of energy demand, the extraction of traditional fossil fuels is becoming increasingly difficult, and their use causes serious environmental pollution. Therefore, energy conservation and emission reduction have become a common goal for humanity. With the introduction and implementation of the "dual-carbon" policy, finding clean and renewable alternative fuels has become a focus of the energy industry. Among numerous alternative energy solutions, methanol, as a highly promising new low-carbon fuel, is gradually attracting widespread attention.

[0003] Because methanol's latent heat of vaporization is approximately 1109 kJ / kg, 3.6 times that of gasoline (310 kJ / kg), fuel vaporization at low temperatures absorbs more heat, resulting in a lower mixture temperature. Furthermore, methanol's vapor pressure is highly sensitive to temperature; at room temperature, methanol's evaporation rate is only 1 / 4 that of gasoline, and at 7°C, it's only 1 / 6 that at 20°C. In short, methanol doesn't evaporate sufficiently at low temperatures, making it difficult to achieve the necessary fuel concentration for engine ignition. Moreover, methanol's flash point is approximately 11°C; below this temperature, the reactivity of methanol molecules decreases, further hindering engine ignition. Therefore, traditional methanol internal combustion engines using spark ignition suffer from severe cold-start difficulties in low-temperature environments (especially sub-zero temperatures in northern winters).

[0004] For methanol fuel, considering its high latent heat of vaporization and low electrical conductivity, traditional electric spark ignition would be difficult to develop in the initial flame nucleus during lean combustion, easily leading to ignition failure, unstable combustion, and misfire. Furthermore, this combustion instability could result in incomplete oxidation of methanol, producing emissions such as formaldehyde.

[0005] Therefore, it is necessary to provide a novel pre-combustion chamber plasma ignition method for methanol engines to solve the problems of cold start difficulties and reliable and stable ignition in methanol internal combustion engines. Summary of the Invention

[0006] The purpose of this invention is to provide a dual-chamber pre-combustion chamber ignition device and method for methanol engines based on microwave plasma, which improves the reactivity of methanol molecules and the combustion efficiency of methanol engines.

[0007] To achieve the above objectives, the present invention provides a dual-chamber pre-combustion chamber ignition device for a methanol engine based on microwave plasma, comprising a microwave generator, a pre-combustion chamber, and a methanol engine; the methanol engine includes an intake valve, an exhaust valve, and a cylinder; the intake valve is used to introduce a methanol-air mixture. The pre-combustion chamber includes an inner pre-combustion chamber and an outer pre-combustion chamber, which are used to introduce methanol and air, respectively. The inner and outer pre-combustion chambers are connected to the cylinder through the same mixed gas inlet. The microwave generator includes a microwave generating unit and a microwave transmission unit; the microwave transmission unit is connected to the pre-combustion chamber and is used to transmit microwaves into the pre-combustion chamber to generate methanol plasma; the methanol plasma and the air in the pre-combustion chamber enter the cylinder simultaneously from the mixed gas inlet to ignite the methanol and air mixture in the cylinder.

[0008] Furthermore, the outer pre-combustion chamber is arranged around the periphery of the inner pre-combustion chamber, the mixed gas inlet is located at the bottom of the inner pre-combustion chamber, the two sides of the mixed gas inlet are respectively provided with inlets communicating with the outer pre-combustion chamber, the top is provided with an inlet communicating with the inner pre-combustion chamber, and the bottom is provided with an outlet communicating with the cylinder, so that the air enters the mixed gas inlet from both sides of the outer pre-combustion chamber through convection, mixes with the methanol plasma entering from the top, and then enters the cylinder from the bottom.

[0009] Furthermore, the mixed gas inlet is equipped with a controllable plasma nozzle, and both the methanol inlet and the intake valve are equipped with high-pressure nozzles; and / or, the air introduced into the pre-combustion chamber is hot air, which is preheated by exhaust gas.

[0010] Furthermore, the pre-combustion chamber is an equivalent resonant cavity, and the axial length, radial dimension, or equivalent electrical length of the equivalent resonant cavity satisfies the microwave standing wave formation conditions.

[0011] Furthermore, the end of the microwave transmission unit is provided with an adjustable coupling structure that extends into the pre-combustion chamber, for adjusting the coupling depth, coupling position or microwave output power, thereby adjusting the microwave energy in the pre-combustion chamber.

[0012] Furthermore, the adjustable coupling structure is a retractable coaxial probe or a coupling hole with a rotatable baffle; the adjustable coupling structure is located in the middle of the methanol inlet so that the methanol is sprayed from around the adjustable coupling structure, thereby improving the methanol ionization efficiency; a microwave power sensor and a temperature sensor are provided in the pre-combustion chamber.

[0013] Furthermore, the microwave transmission unit includes a coaxial feed line or a microwave waveguide; The microwave generating unit includes a protective housing and a solid-state microwave source, a microwave power supply, and a control circuit disposed within the protective housing; the solid-state microwave source is connected to the adjustable coupling structure through the microwave transmission unit.

[0014] Furthermore, it also includes an ECU sensing control unit, which is used to calculate the methanol microwave absorption efficiency based on the microwave incident rate, reflectivity, pre-combustion chamber temperature, pre-combustion chamber pressure and methanol injection quantity, and adjust the microwave output power, microwave feed duration and methanol injection quantity according to the methanol microwave absorption efficiency.

[0015] The present invention also provides a method for igniting a dual-chamber pre-combustion chamber of a methanol engine based on microwave plasma, using the dual-chamber pre-combustion chamber ignition device described in any of the above claims, comprising: introducing methanol and air into the inner chamber and the outer chamber of the pre-combustion chamber respectively according to a first preset air-fuel ratio, while simultaneously turning on a microwave generator; methanol plasma is generated under the action of microwaves; The methanol plasma mixes with the incoming air at the mixed gas inlet, undergoing an oxidation-reduction reaction that generates heat. According to the second preset air-fuel ratio, a methanol-air mixture is introduced through the intake valve, and then a flame nucleus is generated under the heat produced by the oxidation-reduction reaction, which is then ignited.

[0016] Furthermore, the first preset air-fuel ratio is (5-6.5):1; the second preset air-fuel ratio is (6-7):1.

[0017] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. The microwave plasma-based dual-chamber pre-combustion chamber ignition method for methanol engines of this invention utilizes microwave energy to ionize methanol molecules into a plasma state, increasing the energy density of methanol molecules and thus reducing the activation energy required for the combustion reaction. The high reactivity of the plasma state causes a vigorous oxidation-reduction reaction with oxygen in the air, releasing a large amount of heat. Finally, the released heat is used to bring more unreacted methanol to the combustion temperature and ignite it, generating positive energy feedback, improving the combustion efficiency and energy utilization of methanol fuel, and minimizing the probability of misfire. This effectively solves the problem of ignition instability caused by the reliance on transient thermal effects in traditional spark plug ignition, and can effectively prevent misfire.

[0018] 2. This invention designs the pre-combustion chamber with a double-walled structure. The inner cavity is used for methanol microwave ionization, while the outer cavity is used for convection flow of hot air. This allows for thorough mixing of air and methanol plasma, which helps improve the redox reaction efficiency and combustion stability of the methanol plasma. Furthermore, it enables the plasma flow to achieve highly stable ignition under the combined effects of thermal effects, free radicals, and turbulence. Simultaneously, the hot air maintains the wall temperature within a suitable range. This heats the injection device, reducing the possibility of thermal quenching after the plasma enters the device. Additionally, the heat generated by the auto-ignition reaction between the hot air and the highly reactive methanol plasma creates a ignition nucleus that enters the main combustion chamber and ignites more methanol fuel.

[0019] 3. The present invention adopts an adjustable coupling structure, which facilitates the real-time adjustment of the microwave energy in the pre-combustion chamber according to different operating conditions. The microwave energy is set in the middle of the methanol inlet so that the methanol is sprayed from around the adjustable coupling structure, thereby improving the methanol ionization efficiency.

[0020] 4. This invention utilizes a high-pressure methanol nozzle to atomize liquid methanol, which can alleviate the problem of unsatisfactory methanol evaporation to some extent. Methanol plasma and hot air are introduced into the inlet of the controllable plasma nozzle respectively. The hot air and highly reactive methanol plasma come into contact and spontaneously combust, generating heat and a ignition nucleus. The methanol plasma entering the main combustion chamber is uniformly mixed with the "combustible mixture" composed of gaseous methanol and air, and ignited by the ignition nucleus. Simultaneously, the heat of reaction rapidly heats the combustible mixture, causing it to reach its ignition point and form a sustained hot flame. 5. The present invention provides a novel ignition method for a methanol engine based on microwave plasma. After the ignition operation is completed, the high-temperature waste heat of the exhaust gas is absorbed by the exhaust gas waste heat recovery system and used to heat the methanol in the pipeline, thereby increasing the temperature and activity of the methanol molecules and improving the energy utilization rate. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a novel ignition method for a methanol engine based on microwave plasma according to the present invention. Figure 2 This is a schematic diagram of a microwave generator. Figure 3 This is the logic diagram of the control system of the present invention.

[0022] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-Microwave generator; 11-Protective housing; 12-Solid-state microwave source; 13-Microwave power supply; 14-Coaxial feeder; 15-Control circuit; 16-Adjustable coupling structure; 2-Pre-combustion chamber; 201-Inner chamber of pre-combustion chamber; 202-Outer chamber of pre-combustion chamber; 3-Methanol engine; 301-Intake valve; 302-Exhaust valve; 303-Cylinder; 304-Piston; 305-Connecting rod; 306-Crankshaft; 307-Cylinder housing; 4-High-pressure nozzle; 5-Controllable plasma nozzle. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] Example 1 Please see Figure 1 This invention provides a dual-chamber pre-combustion chamber ignition device for a methanol engine based on microwave plasma, comprising a microwave generator 1, a pre-combustion chamber 2, and a methanol engine 3; the methanol engine 3 includes an intake valve 301, an exhaust valve 302, a cylinder 303, a piston 304, a connecting rod 305, a crankshaft 306, and a cylinder block housing 307; the intake valve 301 is used to introduce a methanol-air mixture; The pre-combustion chamber 2 includes an inner pre-combustion chamber 201 and an outer pre-combustion chamber 202. The inner pre-combustion chamber 201 is provided with a methanol inlet, and the outer pre-combustion chamber 202 is provided with an air inlet (not shown in the figure, but may be located on the side wall). The inner and outer pre-combustion chambers 201 and 202 are connected by the same mixed gas inlet. Figure 1 The medium- and high-pressure nozzles (4 locations) are connected to the cylinder 303; The microwave generator 1 includes a microwave generating unit and a microwave transmission unit; the microwave transmission unit is connected to the pre-combustion chamber 201 and is used to transmit microwaves into the pre-combustion chamber 201 to generate methanol plasma from the methanol; the methanol plasma and air enter the cylinder 303 simultaneously from the mixed gas inlet to ignite the methanol and air mixture in the cylinder 303.

[0025] This setup converts the electrical energy output from the battery into microwave energy via microwave generator 1. This microwave energy is used to ionize methanol molecules, generating methanol plasma. This plasma spontaneously reacts with oxygen in the air, releasing a large amount of heat. This process converts microwave energy into heat energy, which is used to heat the gaseous methanol in the main combustion chamber to its ignition point (approximately 464°C). The reaction is more complete, the energy release is more concentrated, the reaction rate is higher, the calorific value is higher, and the energy utilization rate is higher. Furthermore, this process does not require spark plug ignition, reducing energy loss to some extent. Under lean combustion technology, methanol, with its high octane number, wide flammability limit, rapid laminar flame speed, and its oxygen-containing properties, holds promise for ultra-lean combustion. Under lean combustion conditions, the air-fuel ratio of methanol can exceed 6.4:1, resulting in higher thermal efficiency, ultra-low carbon monoxide and unburned hydrocarbon emissions, and near-zero nitrogen oxide emissions. Under lean combustion conditions, the microwave plasma ignition described in this invention, through a continuous plasma flow, can not only achieve highly stable ignition under the combined effects of thermal effects, free radicals, and turbulence, but can also increase the air-fuel ratio of the fuel, thus contributing to more efficient ultra-lean combustion.

[0026] Specifically, the outer pre-combustion chamber 202 is arranged around the periphery of the inner pre-combustion chamber 201. The mixed gas inlet is located at the bottom of the inner pre-combustion chamber 201. Inlets communicating with the outer pre-combustion chamber 202 are located on both sides of the mixed gas inlet, with an inlet communicating with the inner pre-combustion chamber 201 at the top and an outlet communicating with the cylinder 303 at the bottom. This arrangement allows air to convect from both sides of the outer pre-combustion chamber 202 into the mixed gas inlet, mix with the methanol plasma entering from the top, and then enter the cylinder 303 from the bottom. This configuration ensures thorough mixing of air and methanol plasma, which helps improve the redox reaction efficiency and combustion stability of the methanol plasma.

[0027] Specifically, the pre-combustion chamber 2 is not merely used as a small cavity for ordinary combustion (or cold flame combustion in multi-stage ignition), but rather as an energy coupling cavity for methanol spray to absorb microwave energy and form methanol plasma. The pre-combustion chamber 2 is designed with a double-walled structure. The inner wall serves as a closed pre-combustion chamber 201, with ceramic sealing feeders at all connections, especially at the microwave inlet. A controllable plasma nozzle 5 is located at the connection to the main combustion chamber (i.e., the gas-mixture inlet). An outer pre-combustion chamber 202 is formed between the outer and inner walls, through which hot air is introduced and connected to the inner wall and the main combustion chamber via the plasma nozzle 5. The geometric dimensions of the pre-combustion chamber 2 are determined based on the microwave operating frequency, the dielectric constant of the gas inside the chamber, the methanol spray concentration, and the engine cylinder head mounting space, enabling the formation of a stable microwave standing wave mode within the pre-combustion chamber. This allows microwave energy to exist stably and continuously within the pre-combustion chamber, facilitating the preferential absorption of microwave energy by atomized methanol molecules, thereby ionizing and generating methanol plasma.

[0028] The material of the pre-combustion chamber 2 should meet the characteristics of low loss, high thermal conductivity and electrical conductivity, effectively reducing the loss during microwave transmission and oscillation; reasonable geometry and size should ensure that the microwave electromagnetic field of the selected frequency is uniformly distributed in the cavity, reducing loss, while avoiding mutual interference between microwave signals of different frequencies, and ensuring that the microwave signal propagates and oscillates in the cavity according to the expected mode.

[0029] Furthermore, the pre-combustion chamber is an equivalent resonant cavity, and the axial length, radial dimension, or equivalent electrical length of the equivalent resonant cavity satisfies the conditions for microwave standing wave formation. The preferred configuration of the standing wave mode is such that the belly of the microwave electric field is located in the methanol high-pressure nozzle spray diffusion region. Thus, methanol droplets or methanol vapor injected into the pre-combustion chamber 201 preferentially pass through the local microwave electric field enhancement region, absorb microwave energy to form methanol plasma or highly reactive methanol molecules, and then enter the main combustion chamber through the controllable plasma nozzle 5, improving the stability of subsequent thermal flame ignition.

[0030] The connection between microwave generator 1 and methanol plasma generation pre-combustion chamber 2 has the following requirements: 1. The connection dimensions must be strictly matched to ensure effective microwave transmission and reduce reflection; 2. The connection should use a coupling element (here, a retractable coaxial probe is selected), such as a coupling ring or coupling hole, to avoid direct coupling; 3. To prevent microwave leakage, the connection should be sealed with sealing gaskets and conductive adhesives to ensure that microwave energy is confined within the waveguide and resonant cavity, reducing electromagnetic interference to the surrounding environment and preventing interference with microwave signals from external electromagnetic fields; 4. The connection structure should have sufficient mechanical strength and stability to withstand various stresses and vibrations during system operation, avoiding loosening and deformation that could affect microwave transmission.

[0031] The common microwave frequency is 2.45 GHz, and the corresponding wavelength in space (medium is air) should be:

[0032] Where c is the speed of electromagnetic waves (equal to the speed of light 3 × 10⁻⁶). 8 m / s The frequency is microwave, i.e., 2.45 GHz.

[0033] Taking a single-cylinder internal combustion engine with a displacement of 0.5 L / cylinder as an example, its pre-combustion chamber length typically does not exceed 15 mm. Therefore, a shortened resonant structure can be used in practice. This shortened microwave resonant structure includes at least one of a center-feed probe, a re-entrant metal boss, a dielectric loading element, or a tuning screw. By changing the equivalent capacitance, equivalent inductance, or equivalent dielectric constant of the pre-combustion chamber, a local standing wave electric field enhancement region can still be formed near the target microwave frequency even under conditions of insufficient space.

[0034] The controllable plasma nozzle 5 uses a single-hole nozzle, and the nozzle diameter should not be too small. The appropriate size should be designed according to the engine operating conditions to prevent the flame core from extinguishing, resulting in poor ignition performance. The injection channel should not be too long to reduce the heat exchange area on the wall and decrease the possibility of quenching. The inner wall material of the injection system should meet the requirements of low heat loss and high temperature resistance; ceramic lining is an option. The injection timing should be chosen as soon as possible; the methanol plasma should enter the nozzle device shortly after generation. If structurally permissible, another microwave field enhancement region can be coupled above the inlet of the plasma nozzle device to prevent plasma loss during transport.

[0035] High-pressure nozzles 4 are installed at both the methanol inlet and the intake valve 301 to inject methanol from the methanol tank into the pre-combustion chamber 201. The high-pressure nozzles 4 are connected to the methanol tank through pipes, and uniformly atomize the liquid methanol in the methanol tank and spray it out. The spray cone angle of the nozzle is matched with the geometry of the pre-combustion chamber 2. Under the premise of matching, the cone angle should be designed to be relatively small. The nozzle is pointed towards the microwave electric field enhancement area. The purpose is to allow the methanol molecules to concentrate and absorb microwave energy to form plasma while avoiding collision with the walls as much as possible, thereby improving the utilization rate of microwave energy.

[0036] Methanol is injected into the pre-combustion chamber 201 and the intake valve 301 through the high-pressure nozzle 4. Due to the compression of the high-pressure nozzle 4 and the friction through the small hole, the injected methanol can be approximated as gaseous and can be uniformly mixed with air.

[0037] Specifically, the air introduced into the pre-combustion chamber 202 is hot air, for example, at 200-500°C. The heat source for the heated air can be exhaust waste heat recovery, or, under cold start conditions, electric heating from the battery. The function of the hot air is to maintain the wall temperature within a suitable range, on the one hand heating the injection device to reduce the possibility of thermal quenching after the plasma enters the injection device, and on the other hand generating heat through the auto-ignition reaction between the hot air and the highly active methanol plasma to generate a ignition nucleus that enters the main combustion chamber to ignite more methanol fuel. In particular, the methanol engine, when used in conjunction with an exhaust waste heat recovery system, such as an alcohol-hydrogen engine, can further improve energy utilization and enhance the cold start performance of the methanol engine.

[0038] Methanol plasma and hot air are introduced into the inlet of the controllable plasma nozzle 5 respectively. The hot air and highly active methanol plasma come into contact and spontaneously combust, generating heat and a ignition nucleus. The methanol plasma entering the main combustion chamber is uniformly mixed with the "combustible mixture" composed of gaseous methanol and air, and ignited by the ignition nucleus. At the same time, the heat of reaction rapidly heats the combustible mixture, causing it to reach the ignition point and form a continuous hot flame.

[0039] Cylinder 303 is the main combustion chamber, which is connected to the pre-combustion chamber 2 via a controllable plasma nozzle 5. Intake valve 301 and exhaust valve 302 are connected to both sides of cylinder 303, and the intake and exhaust processes are controlled by the valves controlled by the control system. In the intake manifold, gaseous methanol is injected by a high-pressure nozzle and mixed evenly with air, then enters the main combustion chamber during the intake stroke. Simultaneously, plasma in the pre-combustion chamber 201 enters the main combustion chamber through the controllable plasma nozzle 5, igniting the methanol-air mixture entering from the intake valve and driving the engine to start.

[0040] Please see Figure 2The end of the microwave transmission unit is provided with an adjustable coupling structure 16 that extends into the pre-combustion chamber 201, which is used to adjust the coupling depth, coupling position or microwave output power, thereby adjusting the microwave energy in the pre-combustion chamber.

[0041] The adjustable coupling structure can be a coupling hole, a coupling ring, a slit coupling port, or a coupling probe. By adjusting the position, opening area, or insertion depth of the coupling structure, the coupling strength of microwave energy entering the pre-combustion chamber can be changed, reducing microwave reflection power and increasing the effective absorption ratio of microwave energy by the methanol spray. Specifically, the adjustable coupling structure is a retractable coaxial probe or a coupling hole with a rotatable baffle; the adjustable coupling structure is located in the middle of the methanol inlet so that the methanol is sprayed from around the adjustable coupling structure, improving the methanol ionization efficiency; a microwave power sensor and a temperature sensor are installed in the pre-combustion chamber. The retractable coaxial probe can adjust its extension length through a control system, thereby adjusting the microwave coupling.

[0042] Specifically, it can also be configured as a retractable coaxial probe array, extending into the pre-combustion chamber 201 through the high-pressure nozzle 4 at intervals. The high-pressure nozzle 4 is provided with through holes at intervals for the retractable coaxial probe to pass through. After assembly, the through holes are sealed to prevent methanol from escaping. The diffusion area into which methanol is injected should match the spatial position of the microwave field enhancement area fed by the retractable coaxial probe array, so as to fully absorb microwave energy and be ionized.

[0043] Furthermore, the microwave transmission unit includes a coaxial feed line 14 or a microwave waveguide; the microwave generation unit includes a protective housing 11 and a solid-state microwave source 12, a microwave power supply 13 and a control circuit disposed within the protective housing 11; the solid-state microwave source 12 is connected to the adjustable coupling structure 16 through the microwave transmission unit.

[0044] The microwave power supply 13 should be an on-board power supply (generally 24 / 12V). If the selected microwave source is a microwave magnetron, it needs to be boosted by an inverter, rectified and filtered by a control circuit, and then modulated into high-voltage DC to drive the microwave magnetron to generate thermionic electrons. The thermionic electrons are controlled and accelerated by electric and magnetic fields and the resonant cavity to generate microwave energy. The microwave signal is input into the pre-combustion chamber 201 through a microwave transmitter (such as a microwave waveguide or coaxial feeder). Optionally, if the selected microwave generating device is a solid-state microwave source, modulation and boosting are not required. Considering the cost and the relatively low uniformity requirement of the microwave field required by the present invention, a magnetron microwave source can be selected.

[0045] The ignition device of this invention also includes an ECU sensing control unit, used to collect microwave incident rate, reflectivity, pre-combustion chamber temperature, pre-combustion chamber pressure, and methanol injection quantity measured by various sensors, calculate the methanol microwave absorption efficiency, and adjust the microwave output power, microwave feed duration, methanol injection quantity, and plasma injection valve opening duration according to the methanol microwave absorption efficiency to ensure stable methanol plasma generation while avoiding energy waste. When the reflection power increases or the methanol absorption efficiency decreases, the control unit adjusts the microwave output power, microwave action time, coupling structure position, or methanol injection quantity to increase microwave energy feed, thereby maintaining the stability of methanol plasma generation. The goal of this control method is to improve the directional absorption efficiency of methanol for microwave energy.

[0046] The methanol microwave absorption efficiency can be determined based on the ratio of effective absorption power to microwave incident power. The effective absorption power is obtained by subtracting the microwave reflection power and the power loss due to waveguide, cavity wall and sealing structure from the microwave incident power.

[0047] When the plasma nozzle 5 is opened, the methanol plasma generated in the pre-combustion chamber 201 will spontaneously produce a violent oxidation-reduction reaction with the hot air between the two walls, releasing a large amount of heat and generating a ignition nucleus. At this time, it is directly released into the cylinder of the methanol engine 3, so that the heat of the reaction released can ignite more "methanol combustible gas" to drive the piston and make the engine run.

[0048] The amount of methanol plasma released in cylinder 303 should take into account the amount of methanol injected into the intake manifold (or cylinder) each time, and release methanol plasma in an appropriate amount to avoid wasting the reaction heat of methanol plasma.

[0049] This invention is not a traditional engine pre-combustion chamber cold flame combustion or jet ignition, but rather a methanol-specific local microwave energy absorption and controllable plasma jet ignition system that can be realized in a small-volume pre-combustion chamber through a local electric field enhancement zone and closed-loop control of methanol microwave absorption.

[0050] Example 2 The present invention also provides a methanol engine ignition method based on microwave plasma, employing a dual-chamber pre-combustion chamber as described above, comprising: according to a first preset air-fuel ratio, introducing methanol and air into the inner chamber and the outer chamber of the pre-combustion chamber respectively, while simultaneously activating a microwave generator; methanol plasma is generated under the action of microwaves; The methanol plasma mixes with the incoming air at the mixed gas inlet, undergoing an oxidation-reduction reaction that generates heat. According to the second preset air-fuel ratio, a methanol-air mixture is introduced through the intake valve and then ignited by the heat generated by the oxidation-reduction reaction.

[0051] Furthermore, the first preset air-fuel ratio is (5-6.5):1; the second preset air-fuel ratio is (6-7):1.

[0052] The ignition principle of this invention is as follows: Methanol injected into the pre-combustion chamber absorbs microwave energy within the chamber, causing a temperature increase and enhanced activity. The ionization energy of methanol molecules is 10.84 eV, and the degree of ionization of low-temperature plasma is generally within... - Theoretically, if there is 1× A mole of methanol molecules, when ionized, can be considered a highly reactive methanol-based low-temperature microwave plasma, capable of spontaneously undergoing a redox reaction with oxygen in the air. Calculations show that...

[0053] It is known that the energy required to generate 1 mol of methanol plasma in an adiabatic system is only 1.0441 J. Considering that air molecules also absorb microwave energy in the actual process, but because methanol molecules are polar molecules, they rotate continuously with the microwave field, resulting in intermolecular friction and collisions, significant temperature changes, and even chemical bond breakage. Therefore, the absorption rate of microwave energy by polar molecules is much higher than that of non-polar molecules. Air is mainly composed of non-polar molecules such as nitrogen and oxygen. Although it also contains polar molecules such as water vapor that can absorb microwave energy, the proportion of polar molecules is too small, and their absorption rate is far lower than that of methanol. Furthermore, the air in this invention does not pass through the pre-combustion chamber 201, making ionization even less likely. Therefore, generating low-temperature microwave plasma does not consume much energy. The methanol plasma spontaneously undergoes a redox reaction with air, and the main reaction equations are as follows:

[0054] In reality, other complex chemical reactions will also occur, such as the oxidation of reactive free radicals in the plasma, such as methyl free radicals. However, since these reactions are relatively minor, they can be ignored here. Calculations show that the heat of reaction for the complete combustion of gaseous methanol is... H = -764 kJ / mol. Since the energy of methanol in plasma state is higher than that of methanol in gaseous state, the heat of reaction in the above equation should also be higher than 764 kJ / mol.

[0055] After the methanol injected into the intake manifold 301 is fully mixed with air, it is injected into the main combustion chamber through a high-pressure nozzle at an air-fuel ratio of 6.4:1 under normal combustion conditions. Simultaneously, plasma-state methanol generated in the pre-combustion chamber is sent into the main combustion chamber. The plasma-state methanol spontaneously undergoes a violent oxidation-reduction reaction with oxygen in the air outside the pre-combustion chamber, releasing a large amount of heat. Based on the above calculations, the heat of reaction generated by the complete oxidation of 1 mol of plasma-state methanol should be higher than 764 kJ / mol; a conservative estimate is given here as 764 kJ / mol. Through calculation:

[0056] Given the average specific heat capacity of methanol C = 2.51 J / (g·℃) and the molar mass of methanol m = 32 g / mol, assuming a cold start condition of -15℃, the methanol is heated to its auto-ignition temperature of approximately 464℃. Given T = 479℃, the energy required to heat 1 mol of methanol from -15℃ to its auto-ignition temperature is 38.47 kJ. Substituting the average specific heat capacity of air, C = 1.01 J / (g·℃), the energy required is similarly... Given T = 479℃ and m = 6.4 × 32 = 204.8 g, the energy required to heat air from -15℃ to its auto-ignition temperature at an air-fuel ratio of 6.4:1 is 99.08 kJ. Heating a mixture containing 1 mol of methanol to its auto-ignition temperature would require 137.55 kJ of energy. Even considering an energy loss of approximately 40%, the heat released from the complete oxidation of 1 mol of methanol in plasma is sufficient to ignite a mixture containing 3 mol of methanol. With the aid of plasma free radicals and turbulence, a "chain reaction" can occur, igniting even more methanol and releasing a large amount of heat, thus driving the piston.

[0057] Based on this calculation ratio, the control unit calculates the methanol microwave absorption efficiency according to the microwave incident power, reflected power, pre-combustion chamber pressure, pre-combustion chamber temperature, and methanol injection quantity. It then adjusts the microwave power, action time, coupling probe position, and methanol injection quantity in the main and pre-combustion chambers to maintain the effective microwave absorption efficiency at around 60%, thus avoiding excessive plasmaification and energy waste.

[0058] Specifically, the concentration of the gas-fuel mixture entering the combustion chamber can make the pre-combustion chamber slightly richer, increasing the methanol molecule density. This is beneficial for improving the absorption of microwave energy by methanol molecules, enhancing the intensity of plasma generation, producing more heat of reaction, ensuring the intensity of the ignition source, and improving the stability and reliability of ignition. The local equivalence ratio can be referenced as follows: pc=1.0–1.3. A leaner main combustion chamber results in more lean air, leading to more complete combustion, a relatively lower combustion temperature, reduced heat transfer loss and knocking tendency, and allowing the engine to operate more stably in the high compression ratio or high efficiency range. This is beneficial for improving combustion thermal efficiency, reducing NOx emissions, minimizing fuel loss, and enhancing fuel economy. Reference range main =0.4–0.7. If it is a cold start condition, the equivalence ratio can be appropriately increased. After the engine stabilizes, it can be gradually switched to lean combustion.

[0059] During the operation of a methanol engine, the exhaust gas mainly consists of carbon dioxide and water. The exhaust gas carries some heat, which should be connected to an exhaust waste heat recovery system after the exhaust manifold to absorb the high-temperature waste heat of the exhaust gas and use it to heat the methanol combustible mixture in the intake manifold. This reduces the energy required to heat the combustible mixture to its auto-ignition temperature, thereby increasing the ignition ratio of the "chain" reaction and further improving energy utilization.

[0060] For some specific implementation methods, please refer to Figure 3 The ignition method includes the following steps: S1. The ECU sensor control unit obtains engine operating parameters to determine whether it is in a cold start condition. S2. If yes, adjust the methanol injection volume and then proceed to step S2; otherwise, proceed directly to step S3. S3. Start the microwave generator to input microwave energy into the pre-combustion chamber cavity; S4. Detect whether the microwave reflection power in the inner cavity is too high using sensors and EDU. If so, adjust the microwave power, action time, or tuning structure, and return to step S3; otherwise, start injecting methanol. S5. Methanol plasma is formed in the local electric field enhancement area of ​​the inner chamber. It comes into contact with the hot air entering from both sides of the plasma nozzle and spontaneously combusts to generate heat and a fire nucleus. Then it is injected into cylinder 303 to ignite the methanol mixture entering from intake valve 301. S6. During the ignition process, monitor whether the engine is working stably. If not, return to step S2. If yes, maintain the current operating parameters (maintain the current stable microwave output and fixed methanol injection quantity) and perform steady-state ignition.

[0061] In summary, this invention utilizes microwave energy to ionize methanol molecules into a plasma state, increasing the energy density of methanol molecules and thus reducing the activation energy required for the combustion reaction. The high reactivity of the plasma state allows it to undergo a vigorous redox reaction with oxygen in the air, releasing a large amount of heat. This released heat is then used to bring more unreacted methanol to its combustion temperature and ignite. The heat generated by one unit of methanol plasma reacting with sufficient oxygen is enough to bring more than two units of gaseous methanol to their ignition point, initiating a chain reaction within the internal combustion engine, generating positive energy feedback, improving the combustion efficiency and energy utilization of methanol fuel, and minimizing the probability of misfire. This invention is expected to solve problems caused by the characteristics of methanol, such as difficulty in low-temperature cold starts, poor ignition intensity under lean combustion conditions, and the difficulty in stable coupling of microwaves in traditional small pre-combustion chambers, as well as the problems of collisions and quenching during methanol droplet atomization.

[0062] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-chamber pre-combustion chamber ignition device for a methanol engine based on microwave plasma, characterized in that, It includes a microwave generator, a pre-combustion chamber, and a methanol engine; the methanol engine includes an intake valve, an exhaust valve, and a cylinder; the intake valve is used to introduce a mixture of methanol and air. The pre-combustion chamber includes an inner pre-combustion chamber and an outer pre-combustion chamber, which are used to introduce methanol and air, respectively. The inner and outer pre-combustion chambers are connected to the cylinder through the same mixed gas inlet. The microwave generator includes a microwave generating unit and a microwave transmission unit; the microwave transmission unit is connected to the pre-combustion chamber and is used to transmit microwaves into the pre-combustion chamber to generate methanol plasma; the methanol plasma and the air in the pre-combustion chamber enter the cylinder simultaneously from the mixed gas inlet to ignite the methanol and air mixture in the cylinder.

2. The microwave plasma-based dual-chamber pre-combustion chamber ignition device for a methanol engine according to claim 1, characterized in that, The outer pre-combustion chamber is arranged around the periphery of the inner pre-combustion chamber. The mixed gas inlet is located at the bottom of the inner pre-combustion chamber. The two sides of the mixed gas inlet are respectively provided with inlets communicating with the outer pre-combustion chamber. The top is provided with an inlet communicating with the inner pre-combustion chamber. The bottom is provided with an outlet communicating with the cylinder. This allows air to enter the mixed gas inlet from both sides of the outer pre-combustion chamber via convection, mix with the methanol plasma entering from the top, and then enter the cylinder from the bottom.

3. The microwave plasma-based dual-chamber pre-combustion chamber ignition device for a methanol engine according to claim 1, characterized in that, The mixed gas inlet is equipped with a controllable plasma nozzle, and both the methanol inlet and the intake valve are equipped with high-pressure nozzles. And / or, the air introduced into the pre-combustion chamber is hot air, which is preheated by exhaust gas.

4. The microwave plasma-based dual-chamber pre-combustion chamber ignition device for a methanol engine according to claim 1, characterized in that, The pre-combustion chamber is an equivalent resonant cavity, and the axial length, radial dimension, or equivalent electrical length of the equivalent resonant cavity satisfies the conditions for microwave standing wave formation.

5. The microwave plasma-based dual-chamber pre-combustion chamber ignition device for a methanol engine according to any one of claims 1-4, characterized in that, The end of the microwave transmission unit is provided with an adjustable coupling structure that extends into the pre-combustion chamber, which is used to adjust the coupling depth, coupling position or microwave output power, thereby adjusting the microwave energy in the pre-combustion chamber.

6. The microwave plasma-based dual-chamber pre-combustion chamber ignition device for a methanol engine according to claim 5, characterized in that, The adjustable coupling structure is a retractable coaxial probe or a coupling hole with a rotatable baffle; the adjustable coupling structure is located in the middle of the methanol inlet so that the methanol is sprayed from around the adjustable coupling structure, thereby improving the methanol ionization efficiency; a microwave power sensor and a temperature sensor are installed in the pre-combustion chamber.

7. The microwave plasma-based dual-chamber pre-combustion chamber ignition device for a methanol engine according to claim 5, characterized in that, The microwave transmission unit includes a coaxial feed line or a microwave waveguide. The microwave generating unit includes a protective housing and a solid-state microwave source, a microwave power supply, and a control circuit disposed within the protective housing; the solid-state microwave source is connected to the adjustable coupling structure through the microwave transmission unit.

8. The microwave plasma-based dual-chamber pre-combustion chamber ignition device for a methanol engine according to claim 1, characterized in that, It also includes an ECU sensing control unit, which is used to calculate the methanol microwave absorption efficiency based on the microwave incident rate, reflectivity, pre-combustion chamber temperature, pre-combustion chamber pressure and methanol injection quantity, and adjust the microwave output power, microwave feed duration and methanol injection quantity according to the methanol microwave absorption efficiency.

9. A method for igniting a dual-chamber pre-combustion chamber of a methanol engine based on microwave plasma, characterized in that, The dual-chamber pre-combustion chamber ignition device according to any one of claims 1-8 includes: according to a first preset air-fuel ratio, introducing methanol and air into the inner chamber of the pre-combustion chamber and the outer chamber of the pre-combustion chamber respectively, and simultaneously turning on a microwave generator; methanol plasma is generated under the action of microwaves. The methanol plasma mixes with the incoming air at the mixed gas inlet, undergoing an oxidation-reduction reaction that generates heat. According to the second preset air-fuel ratio, a methanol-air mixture is introduced through the intake valve, and then a flame nucleus is generated under the heat produced by the oxidation-reduction reaction, which is then ignited.

10. The method for igniting a dual-chamber pre-combustion chamber of a methanol engine based on microwave plasma according to claim 9, characterized in that, The first preset air-fuel ratio is (5-6.5):1; the second preset air-fuel ratio is (6-7):1.

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