Fuel supply system for a steam car washer and flow control method for the system

Abstract

The present application discloses a fuel supply system of a steam car washer and a flow control method for the system, relates to the technical field of fuel supply, and aims to solve the problems of short service life of an oil pump, unstable combustion caused by intermittent oil supply when the rated flow of the oil pump is much larger than the combustion demand flow in the prior fuel supply system, and the problems of complicated debugging and easy parameter drift of an adjustable backflow scheme. The system of the present application comprises an oil tank, a gear pump, a main oil supply path, a first one-way valve, a three-way joint, a backflow branch, a fixed throttle hole, a second one-way valve and a PWM speed regulator. The opening pressure of the second one-way valve on the backflow branch is smaller than the opening pressure of the first one-way valve on the main oil supply path, so that the backflow branch is preferentially conducted, the fixed throttle hole determines the oil return flow, and the coarse distribution of the fuel flow is realized. The present application realizes continuous operation of the oil pump to prolong the service life, stable and pulse-free combustion, no manual debugging and no parameter drift of the system, low cost, and is suitable for small fuel combustion equipment such as steam car washers.

Description

Technical Field

[0001] This invention belongs to the field of fuel supply technology, specifically, it relates to a fuel supply system for a steam car wash machine and a flow control method for the system. Background Technology

[0002] In small-scale fuel-fired equipment such as steam car washers and portable fuel boilers, the fuel supply system typically uses a miniature gear pump to deliver fuel from the tank to the nozzle for atomization and combustion. In practical applications, a prominent technical challenge lies in the fact that the rated output flow rate of the miniature gear pump is often far greater than the actual flow rate required by the burner. For example, a certain model of miniature gear pump has a rated output flow rate of 240 ml / min, while the combustion flow rate required by a typical steam car washer's fuel boiler is only 30-66 ml / min—a difference of several times. How to achieve a highly efficient, stable, and long-life supply of fuel with a large pump and a small flow rate has long been a technical problem that the industry has failed to fully resolve.

[0003] In existing technologies, the following solutions are mainly adopted to resolve the above contradictions: Option 1: Intermittent oil supply control. This involves using an electronic switch to periodically start and stop the oil pump (e.g., starting for 25 milliseconds and stopping for 75 milliseconds every 100 milliseconds), reducing the effective oil supply by averaging over time. However, this option has serious drawbacks: during frequent start-stop cycles, the DC brushed gear pump experiences an inrush current several times its rated current with each start, leading to rapid erosion and wear of the motor brushes and commutator, significantly shortening the actual lifespan of the oil pump (typically far below its nominal continuous operating life, such as 800 hours). Simultaneously, periodic oil cut-offs cause severe fluctuations in oil supply pressure, resulting in inconsistent flame size and, in severe cases, even flameout.

[0004] Option 2: Overflow Valve Backflow Regulation. An adjustable overflow valve is connected in parallel at the oil pump outlet, allowing excess fuel to return to the fuel tank through the overflow valve. While this option achieves continuous fuel supply, the adjustable overflow valve has the following problems: the adjustment knob is prone to mechanical drift during equipment transportation and operation vibrations, leading to changes in the return fuel volume and affecting combustion stability; each commissioning requires specialized tools such as flow meters, making operation cumbersome and unable to meet the standardization requirements of mass production; the adjustable component increases potential failure points and leakage risks.

[0005] Option 3: Replace with a low-flow oil pump. Directly purchase or customize a low-flow oil pump that perfectly matches the combustion requirements. However, DC micro gear pumps with a rated flow rate below 50ml / min are extremely scarce in the market, and their price is often several times that of a conventional 240ml / min oil pump, making mass production not cost-feasible.

[0006] In summary, existing technologies cannot simultaneously meet the four conflicting technical requirements of long oil pump life, high combustion stability, system adjustment-free operation (no drift risk), and low-cost mass production. Therefore, there is an urgent need for a fuel supply technology that can achieve stable, reliable, adjustment-free, and cost-controllable operation even when the rated flow rate of the oil pump is much greater than the combustion demand flow rate, in order to ensure that the steam car wash machine can continuously and stably output steam for car washing operations.

[0007] Therefore, in order to solve the above problems, the present invention provides a fuel supply system for a steam car wash machine and a flow control method for the system. Summary of the Invention

[0008] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide a fuel supply system for a steam car wash machine and a flow control method for the system.

[0009] The objective of this invention can be achieved through the following technical solutions: The fuel supply system for a steam car wash machine includes: tank; A gear pump, the input end of which is connected to the oil tank via a filter; The main fuel supply line connects the output end of the gear pump to the fuel injector; The first check valve is connected in series in the main fuel supply line. Its opening direction is from the gear pump to the fuel injector, and its opening pressure is the first pressure value. A three-way connector is installed on the main oil supply line between the output end of the gear pump and the first check valve; The return branch has its inlet end connected in parallel with the main oil supply line via the tee connector, and its outlet end connected to the oil tank. A fixed throttling orifice is connected in series on the return branch; The second check valve is connected in series on the return branch. Its opening direction is from the gear pump to the oil tank, and its opening pressure is the second pressure value, which is less than the first pressure value. A PWM speed controller, electrically connected to the gear pump, is used to adjust the input voltage of the gear pump to change its speed.

[0010] As a preferred embodiment of the present invention, the first pressure value is 0.015-0.025MPa, the second pressure value is 0.005-0.01MPa, the rated output pressure of the gear pump is 0.05-0.07MPa, the orifice diameter of the fixed throttling orifice is 0.30-0.35mm, and the output frequency of the PWM speed controller is not less than 20kHz.

[0011] As a preferred embodiment of the present invention, the fuel nozzle is an internal mixing nozzle, which has a mixing chamber inside. The mixing chamber adopts an upward flow mixing structure in which high-pressure gas enters from the bottom up, fuel enters from the side, and is sprayed out from the top after mixing. The outlet of the mixing chamber is connected to the boiler. The system also includes a high-pressure gas source for supplying high-pressure gas into the mixing chamber, with a supply pressure of 0.18-0.20 MPa.

[0012] The flow control method for the fuel supply system described above includes the following steps: S1. Determination of fixed throttle orifice diameter: Based on the rated output flow rate of the gear pump, the target combustion flow rate, the first pressure value, the second pressure value, and the equivalent pneumatic back pressure of the fuel nozzle, the diameter of the fixed throttle orifice is determined so that when the gear pump is running at full speed under rated voltage, the fuel output by the gear pump is divided into two paths: one part of the fuel returns to the fuel tank via the return branch, and the other part of the fuel flows to the fuel nozzle via the main fuel supply line. The sum of the fuel flow rate returning to the fuel tank via the return branch and the fuel flow rate flowing to the fuel nozzle via the main fuel supply line is equal to the rated output flow rate of the gear pump, and the fuel flow rate flowing to the fuel nozzle via the main fuel supply line meets the target combustion flow rate. S2. Main fuel supply circuit configuration: Start the gear pump to pump fuel from the fuel tank through the filter, and after passing through the three-way connector, it is divided into two paths, one of which enters the main fuel supply circuit and the other of which enters the return branch circuit. S3, priority conduction of the return branch: Since the second pressure value of the second check valve is less than the first pressure value of the first check valve, the return branch is preferentially conducted, and the fuel flows back to the fuel tank through the fixed throttle orifice and the second check valve. S4, PWM linear fine-tuning: By adjusting the input voltage of the gear pump through the PWM speed controller, the speed of the gear pump is changed, thereby linearly fine-tuning the actual fuel flow to the fuel injector.

[0013] As a preferred embodiment of the present invention, in step S1, the calculation of the orifice diameter of the fixed throttle orifice further includes: determining the cross-sectional area of ​​the throttle orifice based on the required return oil flow rate, the pressure difference between the two ends of the fixed throttle orifice, and the fuel density.

[0014] As a preferred embodiment of the present invention, in step S1, the determined diameter of the fixed throttle orifice is such that when the gear pump is running at full speed under rated voltage and the duty cycle of the PWM speed controller is 100%, the actual fuel flow rate to the fuel injector is equal to the upper limit of the combustion target flow rate.

[0015] As a preferred embodiment of the present invention, S3 further includes a shutdown anti-siphon: when the gear pump stops, the second check valve blocks the return branch to prevent fuel in the tank from flowing back into the pipeline system due to the siphon effect.

[0016] In a preferred embodiment of the present invention, in step S4, the actual fuel flow rate to the fuel injector increases as the duty cycle of the PWM speed controller increases.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly extended oil pump life: The present invention adopts a continuous oil supply method, and the oil pump operates continuously and stably during system operation. This effectively solves the damage to the oil pump caused by frequent current surges and mechanical shocks in the intermittent start-stop scheme, enabling the oil pump to fully utilize its nominal continuous operating life and greatly improving the long-term reliability of the steam car wash machine.

[0018] 2. Stable Combustion: The fixed throttling orifice in the return branch of this invention works in conjunction with the first one-way valve in the main oil supply circuit to keep the oil supply pressure at the nozzle end constant under steady state, effectively solving the pressure pulsation phenomenon in the intermittent oil supply scheme. The flame presents a continuous and stable blue combustion state, without the risk of fluctuating size or flameout, thereby ensuring that the boiler continuously and stably generates heat and the steam output pressure is stable.

[0019] 3. System requires no debugging and is drift-free: In this invention, the return oil volume of the return branch is uniquely determined by the diameter of the fixed throttling orifice. This orifice diameter is calculated and precisely machined based on system parameters during the design and manufacturing stages. After equipment assembly, a consistent return oil flow rate can be obtained without any manual debugging. The entire system has no adjustable components that require user adjustment (such as adjustable overflow valves, adjustable needle valves, etc.), fundamentally eliminating the risk of drift caused by mechanical vibration and the risk of human error in adjustment. At the same time, it ensures the consistency of mass production, allowing the steam car wash machine to be used directly after leaving the factory without on-site calibration.

[0020] 4. Low cost and easy implementation: The only additional parts in this invention are two standard one-way valves and one precision throttle orifice, all of which are standardized parts with extremely low cost. Compared with the existing technology that uses adjustable relief valves, solenoid valves, and customized small-flow oil pumps, the cost advantage of this invention is extremely significant, and the parts are easy to procure or process.

[0021] 5. Flexible and linear adjustment: Based on the coarse distribution achieved by the fixed reflux distribution, the PWM speed controller can perform linear, continuous and fine electronic adjustment of fuel consumption, thereby linearly controlling the boiler's heat output and steam pressure. This meets the flexible adjustment needs under different car wash conditions (such as heavy oil stains requiring high temperature and high pressure steam, and interior cleaning requiring low pressure steam). The fuel consumption and PWM duty cycle have a good linear relationship, which is convenient for users to control precisely. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a system schematic diagram of the fuel supply system of the steam car wash machine of the present invention; Figure 2 This is a flowchart of the flow control method for the fuel supply system of the steam car wash machine of the present invention.

[0024] Figure label: 1. Fuel tank; 2. Gear pump; 3. Main fuel supply line; 4. Fuel nozzle; 5. Mixing chamber; 6. High-pressure air source; 7. Boiler; 8. First check valve; 9. T-connector; 10. Return branch; 11. Fixed throttle orifice; 12. Second check valve; 13. Filter; 14. PWM speed controller. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention: Example: Please see Figure 1-2 This embodiment provides a fuel supply system for a steam car wash machine and a flow control method for the system. Specifically, it is applied to a steam car wash machine with a target fuel consumption of 30-66 ml / min, using white oil or diesel-heated oil as fuel.

[0026] 1. System Hardware Configuration The fuel supply system for this steam car wash machine includes: Fuel tank 1: Used to store fuel, it is a standard container with a volume of 5L, and has a fuel outlet at the bottom and a fuel return port and a vent at the top; Gear pump 2: A miniature DC gear pump, model KGP200-D24, is used. Its rated voltage is DC24V, rated output flow rate is 240ml / min, rated output pressure is 0.06MPa (approximately 0.6kg), and rated power is approximately 15W. This model of gear pump is a mature standard component on the market. The input end of gear pump 2 is connected to fuel tank 1 through a filter 13. The filter 13 is a 100-mesh stainless steel filter screen used to filter out impurities in the fuel and prevent clogging of the throttle orifice and nozzle. Main fuel supply line 3: uses an oil-resistant rubber hose with an inner diameter of 4mm to connect the output end of gear pump 2 to fuel nozzle 4; First check valve 8: It is connected in series on the main fuel supply line 3. Its opening direction is from gear pump 2 to fuel injector 4. The opening pressure (first pressure value) is set to 0.02MPa (about 0.2kg). Three-way connector 9: Located on the main oil supply line 3 between the output end of gear pump 2 and the first check valve 8, used to divide the oil line into two lines; Return branch 10: Its inlet end is connected in parallel with the main oil supply line 3 through a three-way connector 9, and its outlet end is inserted about 30mm below the liquid level in the oil tank 1 to prevent air from being sucked back into the pipeline system through the return oil pipe; Fixed throttling orifice 11: It is connected in series on the return branch 10. In this embodiment, a thin-walled precision throttling orifice with a diameter of 0.33mm is used, and the tolerance is controlled within ±0.005mm. The orifice diameter is pre-calculated and precisely machined according to the system parameters, and no manual adjustment is required after the equipment is assembled. The second check valve 12 is connected in series on the return branch 10. Its opening direction is from gear pump 2 to oil tank 1. The opening pressure (second pressure value) is set to 0.01MPa (about 0.1kg), which is less than the opening pressure of the first check valve 8, 0.02MPa. PWM speed controller 14: Electrically connected to gear pump 2, used to adjust the input voltage of gear pump 2 to change its speed. In this embodiment, a high-frequency PWM module with an output frequency of 20kHz is selected. This frequency is far beyond the range of human hearing (20Hz-20kHz), which can completely avoid the audible whistling sound generated when the motor speed is adjusted, thus improving the user experience. The PWM duty cycle adjustment range is 0-100%. Fuel nozzle 4: It adopts an internal mixing nozzle with a mixing chamber 5 inside. The mixing chamber 5 adopts an upward flow mixing structure in which "high pressure gas enters from the bottom up, fuel enters from the side, and sprays out from the top after mixing". The outlet of the mixing chamber 5 is connected to the combustion chamber of the boiler 7. The nozzle diameter of the fuel nozzle 4 is 0.6mm. This upward flow structure can make the fuel and high pressure gas fully turbulently mixed in the mixing chamber to form a uniform oil-gas mixture, which is beneficial to subsequent stable combustion. High-pressure gas source 6: used to supply high-pressure gas to the mixing chamber 5. In this embodiment, the high-pressure gas source is provided by a small oil-free air compressor. After the pressure is regulated by the pressure regulating valve, the supply pressure is stabilized at 0.18-0.20MPa. The high-pressure gas is used to atomize fuel and provide pneumatic back pressure to the mixing chamber. Boiler 7: This is the main component of the steam car wash machine. It contains a combustion chamber and a heat exchange chamber. The combustion chamber burns an oil-gas mixture to produce high-temperature flames and flue gas. The heat is transferred to the water in the heat exchange chamber through the heat exchange wall. After absorbing the heat, the water vaporizes to generate high-temperature and high-pressure steam. The steam outlet of Boiler 7 is connected to the steam spray gun through a high-temperature resistant hose. The steam spray gun is a standard steam car wash spray gun with a replaceable nozzle (1.0mm orifice) at the front end and a trigger valve at the rear end. When the operator pulls the trigger, the high-temperature and high-pressure steam generated by the boiler is sprayed out through the spray gun to clean the vehicle surface.

[0027] 2. System piping connections The complete connection relationship of the system is as follows: oil tank 1-filter 13-gear pump 2-tee connector 9.

[0028] The two outlets of tee connector 9 are connected to two branch lines respectively: Main fuel supply line branch: tee connector 9 - first check valve 8 (opening pressure 0.02MPa) - fuel injector 4 - mixing chamber 5 - boiler 7; Return branch: tee connector 9 - fixed throttling orifice 11 (orifice diameter 0.33mm) - second check valve 12 (opening pressure 0.01MPa) - oil tank 1.

[0029] 3. Flow control methods This embodiment employs the following flow control method to enable the system to achieve stable, long-life, and commission-free operation even when the rated flow rate of the oil pump (240 ml / min) is much greater than the combustion demand flow rate (30-66 ml / min): S1: Determination of fixed orifice diameter During the system design phase, the orifice diameter of the fixed throttling orifice 11 is calculated and determined based on the following known parameters: Rated output flow rate of gear pump 2: (At rated voltage of 24V and full speed operation); Upper limit of target combustion flow rate: ; The opening pressure of the first check valve 8: P1 = 0.02 MPa; The opening pressure of the second check valve 12: P2 = 0.01 MPa; Equivalent pneumatic back pressure of fuel injector 4 under high-pressure gas environment: (Determined by the high-pressure gas source of 0.18-0.20MPa and the nozzle structure, obtained through experimental calibration).

[0030] The calculation process is as follows: When the gear pump is running at full speed, the pump outlet pressure It is approximately equal to its rated output pressure of 0.06 MPa. After the fuel flows through the tee joint, it splits into two paths. According to the principle of parallel pipeline in fluid mechanics, the flow distribution of the two branches is determined by their respective resistance characteristics.

[0031] For the return branch, fuel flows sequentially through the fixed orifice 11 and the second check valve 12. After the second check valve opens, its own pressure drop is very small (negligible), and the effective pressure difference across the fixed orifice is approximately:

[0032] According to the flow rate formula for thin-walled orifices:

[0033] in: The flow coefficient is 0.62 (for thin-walled orifices). The cross-sectional area of ​​the throttling orifice is... ; The pressure difference across the orifice is 0.05 MPa. The density of fuel oil (white oil approximately 800 kg / m³) 3 ).

[0034] make Substituting into the formula and solving inversely, we obtain the required orifice diameter:

[0035] The calculated value is d≈0.33 mm. 。

[0036] After actual processing and assembly testing, the measured return oil flow rate of the 0.33mm orifice under a pressure difference of 0.05MPa was 172-176ml / min, which is in good agreement with the design value.

[0037] Meanwhile, the orifice design ensures that when the gear pump 2 is operating at full speed under rated voltage and the duty cycle of the PWM speed controller 14 is 100%, the actual fuel flow rate to the fuel injector 4 (approximately 66 ml / min) is exactly equal to the upper limit of the target combustion flow rate. This guarantees that the system will not operate beyond the flow rate under full-speed conditions, avoiding incomplete combustion or black smoke.

[0038] S2: Main fuel supply circuit configuration When the system starts, the PWM speed controller 14 outputs a certain duty cycle (e.g., 50%), and the gear pump 2 starts to operate, pumping fuel from the fuel tank 1 through the filter 13. After the fuel flows through the three-way connector 9, it faces two branches simultaneously: Main fuel supply circuit: It needs to overcome the opening pressure of the first check valve 8 (0.02MPa) and the pneumatic back pressure at the fuel injector 4 (about 0.05-0.06MPa), with a total resistance of about 0.07-0.08MPa; Return branch: It needs to overcome the opening pressure of the second one-way valve 12 (0.01MPa) and the flow resistance of the fixed throttling orifice 11. The total resistance is about 0.01-0.06MPa (increases with increasing flow rate).

[0039] S3: Return branch is prioritized for conduction. Because the opening pressure of the second check valve 12 (0.01 MPa) is lower than that of the first check valve 8 (0.02 MPa), the return branch is preferentially opened when the oil pressure has not been fully established at the initial stage of system startup. The fuel output by the gear pump 2 first flows through the return branch 10 with a lower opening pressure, through the fixed throttle orifice 11 and the second check valve 12, and returns to the fuel tank 1.

[0040] At this point, due to the significant outlet back pressure (equivalent back pressure at the nozzle end of approximately 0.05-0.06 MPa) and the opening pressure of the first check valve, the total resistance of the main fuel supply circuit is much greater than that of the return branch. Therefore, most of the fuel (approximately 174 ml / min) will return to the fuel tank through the return branch, with only a small amount of fuel (approximately 66 ml / min) entering the main fuel supply circuit.

[0041] This "priority conduction and automatic allocation" mechanism does not require any sensors or electronic control algorithms. It relies entirely on the pressure characteristics of mechanical components to automatically achieve coarse flow allocation, and has the advantages of fast response, no delay, and high reliability.

[0042] Anti-siphon during shutdown: When gear pump 2 stops, the second one-way valve 12 automatically closes under the action of spring force, blocking the return branch 10. This effectively prevents fuel in tank 1 from flowing back into the pipeline system due to the siphon effect (the outlet of the return oil pipe is below the liquid level), avoiding starting difficulties or unstable combustion caused by air intake in the fuel line during the next start-up.

[0043] S4: PWM linear fine-tuning Based on the coarse distribution of fuel flow in the return branch, the effective value of the input voltage of the gear pump 2 is changed by the PWM speed controller 14, thereby changing its speed. Since the output flow of the gear pump is proportional to the speed (i.e., the PWM duty cycle) (approximately linear within a small range), the actual fuel flow to the fuel injector 4 also increases approximately linearly with the increase of the PWM duty cycle.

[0044] In this embodiment, the gear pump outputs 240 ml / min when operating at full speed under a rated voltage of 24V. After coarse distribution via reflux, the nozzle end receives approximately 66 ml / min. When the PWM duty cycle decreases, the gear pump speed decreases, and the total output flow rate decreases proportionally. However, since the resistance characteristics of the reflux branch and the main fuel supply circuit remain essentially unchanged, the ratio of their flow rates remains approximately constant. Therefore, the fuel flow rate at the nozzle end exhibits a good linear relationship with the PWM duty cycle.

[0045] The measured data verified this linear relationship, as shown in Table 1 below: Table 1: Relationship between PWM duty cycle and fuel consumption and steam pressure ; As can be seen from the data in Table 1, the deviation between the measured fuel consumption and the theoretical linear value is within ±1%, indicating excellent linearity. This provides users with an intuitive and predictable adjustment experience; that is, steam pressure can be linearly controlled simply by adjusting the electronic knob to change the PWM duty cycle.

[0046] 4. Steam generation and car wash process Combustion and heat generation stage: Fuel oil enters the mixing chamber 5 through fuel oil nozzle 4, where it mixes thoroughly with high-pressure gas (0.18-0.20 MPa) from high-pressure gas source 6 to form an oil-gas mixture. This mixture is then injected into the combustion chamber of boiler 7 from the outlet of mixing chamber 5, where it is ignited by an ignition device (a conventional ignition needle) for continuous and stable diffusion combustion. The flame temperature generated by combustion can reach 800-1000℃, and the high-temperature flue gas scours the boiler heat exchanger walls.

[0047] Steam generation stage: Boiler 7 has an independent water chamber, into which clean water is injected by a water pump. The heat generated by combustion is transferred to the water in the water chamber through the heat exchange wall. After absorbing heat, the water temperature rises above the boiling point and vaporizes to generate high-temperature, high-pressure saturated steam or slightly superheated steam. Boiler 7 is equipped with a safety valve and a pressure switch (both conventional components). When the steam pressure exceeds the set value (e.g., 1.6 MPa), the safety valve automatically releases pressure to ensure safe operation.

[0048] Steam Output and Car Washing: The generated steam is delivered to the steam spray gun connected to the boiler outlet 7 via a high-temperature, high-pressure hose. The operator holds the spray gun, aims the nozzle at the area of ​​the vehicle surface requiring cleaning, and pulls the trigger. The trigger opens the valve, and high-temperature, high-pressure steam is ejected at high speed through the nozzle, impacting oil, mud, and other contaminants on the vehicle surface. The thermal energy of the high-pressure steam softens and melts oil, while its kinetic energy washes away dirt, achieving efficient cleaning. For different working conditions (such as cleaning a heavily soiled engine compartment requiring high temperature and pressure, and cleaning interior fabrics requiring lower temperature and pressure), users can adjust the duty cycle of the PWM speed controller 14 to linearly change the fuel supply and combustion power, thereby obtaining steam with different pressures and flow rates to flexibly adapt to various car wash scenarios.

[0049] 5. Verification of technical effectiveness The system of this embodiment was tested, and the results verified that the present invention achieved the expected technical effect: 5.1 Oil pump life test The system of this invention was compared with a control system that used an intermittent fuel supply scheme (duty cycle of 25%, i.e., running for 25ms and stopping for 75ms every 100ms). Both systems ran continuously, simulating a real-world usage scenario of 8 hours of work per day.

[0050] Test results: Control system (intermittent oil supply): After running for about 200 hours, the gear pump made a noticeable abnormal noise. Disassembly and inspection revealed that the brushes were severely worn, the commutator surface was burned, the flow rate dropped by about 30%, and it could no longer supply oil stably.

[0051] The system of this invention (continuous operation): After running for 800 hours, the gear pump still runs smoothly. Disassembly and inspection showed that the brush wear was slight and the flow rate reduction was less than 5%, which is consistent with the rated continuous operating life (800 hours) of the gear pump.

[0052] The oil pump life of this invention is more than four times that of the intermittent oil supply scheme.

[0053] 5.2. Combustion stability test Flame stability was continuously monitored using flame ion current detection and a flue gas analyzer.

[0054] Test results: Intermittent oil supply scheme: oil pressure pulsation amplitude reaches ±30%, flame ion current fluctuates violently, flame exhibits periodic "breathing" phenomenon, CO emission fluctuates greatly, and occasional flameout occurs.

[0055] The invention features an oil pressure fluctuation of less than ±3%, a stable flame ion current, a continuous blue and stable combustion state of the flame, stable and compliant CO and NOx emissions, and continuous operation for 100 hours without a single flameout.

[0056] 5.3 No-Debugging and Anti-Drift Test Ten devices assembled according to the present invention were randomly selected. Under the condition of introducing 2.0MPa high-pressure gas, the gear pumps were directly connected to the 24V rated voltage and operated at full speed (without PWM speed regulation). The actual oil output at the nozzle end of each device was measured.

[0057] Test results: The measured oil output of the 10 devices were 64.3, 65.4, 65.1, 66.2, 64.3, 65.8, 66.6, 65.2, 64.8, and 65.3 ml / min, with an average of 65.3 ml / min and a standard deviation of 0.71 ml / min. All devices were within the target range (60-70 ml / min). This means that the equipment can be put into use directly after assembly without any manual debugging or calibration.

[0058] The 10 devices were installed on a vibration table and subjected to simulated transport vibration with a frequency of 10-55 Hz and an amplitude of 2 mm. After 48 hours of continuous vibration, the oil output from the nozzle was measured again. The results were completely consistent with those before vibration (deviation ≤1%), proving that there was no mechanical drift problem with the fixed orifice.

[0059] 5.4 Adjustment Linearity Test Within the duty cycle range of 10%-100%, fuel consumption at the nozzle end was measured every 10%, and this was repeated three times, with the average value taken. The results are shown in Table 1 above. The linear correlation coefficient R between fuel consumption and PWM duty cycle is... 2 =0.9992, with excellent linearity.

[0060] 5.5 Steam Performance Test The steam pressure stability was tested under different PWM duty cycles at an ambient temperature of 25℃ and an inlet water temperature of 20℃.

[0061] Test results: When the PWM duty cycle is fixed at a certain value (e.g., 68%), after continuous operation for 30 minutes, the steam pressure fluctuation range is ≤ ±0.05MPa, and it can stably output steam for car washing operations. When switching between different duty cycles, the steam pressure quickly follows the change and stabilizes within 10-15 seconds, without overshoot or oscillation.

[0062] 6. Safety and error-proofing design This embodiment also integrates the following safety designs: Backfire prevention: The first check valve 8 on the main fuel supply line opens at a pressure of 0.02 MPa. When the system is operating normally, the gear pump output pressure (approximately 0.06 MPa) is much greater than 0.02 MPa, keeping the check valve open. When the system shuts down or the boiler gas pressure abnormally rises, causing the nozzle pressure to exceed 0.06 MPa, the first check valve automatically closes, effectively preventing high-pressure gas from the nozzle and potential flame backfire from entering the fuel supply line, ensuring line safety. Additionally, the fuel tank 1 is positioned higher than the fuel nozzle 4. When the gear pump 2 stops, the first check valve 8 is closed, preventing fuel from the tank from flowing into the fuel nozzle 4.

[0063] Anti-siphon: The second check valve 12 on the return branch has an opening pressure of 0.01 MPa. When the oil pump is working normally, this valve is open to allow oil return; when the oil pump stops, the valve closes under the action of spring force, and the outlet of the return oil pipe is inserted below the oil level in the tank. Even if there is a siphon effect, the second check valve can reliably block it, preventing fuel backflow and avoiding starting difficulties or unstable combustion caused by air intake in the oil circuit during the next start-up.

[0064] Overpressure protection: Boiler 7 is equipped with a mechanical safety valve with a set opening pressure of 1.6MPa. When the steam pressure abnormally rises above 1.6MPa, the safety valve will automatically open to release pressure and prevent the risk of boiler explosion.

[0065] Low oil level protection: A float-type oil level switch (not shown in the figure) can be installed in the oil tank 1. When the oil level is lower than the set value, the power supply to the gear pump will be automatically cut off and an alarm will be issued to prevent the oil pump from running dry and being damaged.

[0066] In summary, this embodiment successfully applies a gear pump with a rated flow rate of 240 ml / min to a steam car wash machine with a required flow rate of only 30-66 ml / min. It also achieves the goals of long pump life, high combustion stability, no system debugging required, good linear adjustment, and low-cost mass production, demonstrating good industrial practical value and market promotion prospects.

[0067] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0068] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fuel supply system for a steam car wash machine, characterized in that, include: Fuel tank (1); A gear pump (2) is connected to the oil tank (1) via a filter (13); The main fuel supply line (3) connects the output end of the gear pump (2) to the fuel nozzle (4); The first check valve (8) is connected in series on the main oil supply circuit (3), and its opening direction is from the gear pump (2) to the fuel nozzle (4), and the opening pressure is the first pressure value; A three-way connector (9) is installed on the main oil supply line (3) between the output end of the gear pump (2) and the first check valve (8); The return branch (10) is connected in parallel with the main oil supply line (3) through the three-way connector (9) at its inlet end, and its outlet end is connected to the oil tank (1); A fixed throttling orifice (11) is connected in series on the return branch (10); The second check valve (12) is connected in series on the return branch (10). Its opening direction is from the gear pump (2) to the oil tank (1). The opening pressure is the second pressure value, and the second pressure value is less than the first pressure value. A PWM speed controller (14) is electrically connected to the gear pump (2) for adjusting the input voltage of the gear pump (2) to change its speed.

2. The fuel supply system of the steam car wash machine according to claim 1, characterized in that, The first pressure value is 0.015-0.025MPa, the second pressure value is 0.005-0.01MPa, the rated output pressure of the gear pump (2) is 0.05-0.07MPa, the orifice diameter of the fixed throttling orifice (11) is 0.30-0.35mm, and the output frequency of the PWM speed controller (14) is not less than 20kHz.

3. The fuel supply system of the steam car wash machine according to claim 1, characterized in that, The fuel nozzle (4) is an internal mixing nozzle with a mixing chamber (5) inside. The mixing chamber (5) adopts an upward flow mixing structure in which high-pressure gas enters from the bottom up, fuel enters from the side, and is sprayed out from the top after mixing. The outlet of the mixing chamber (5) is connected to the boiler (7). The system also includes a high-pressure gas source (6) for supplying high-pressure gas into the mixing chamber (5), with a supply pressure of 0.18-0.20 MPa.

4. A flow control method for a fuel supply system according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Determination of fixed throttle orifice diameter: Based on the rated output flow rate of gear pump (2), combustion target flow rate, first pressure value, second pressure value and equivalent pneumatic back pressure of fuel nozzle (4), the diameter of the fixed throttle orifice (11) is determined so that when gear pump (2) is running at full speed under rated voltage, the fuel output by gear pump (2) is divided into two paths: part of the fuel returns to the fuel tank (1) via the return branch (10), and the other part of the fuel flows to the fuel nozzle (4) via the main fuel supply line (3). The sum of the fuel flow rate returning to the fuel tank (1) via the return branch (10) and the fuel flow rate flowing to the fuel nozzle (4) via the main fuel supply line (3) is equal to the rated output flow rate of gear pump (2), and the fuel flow rate flowing to the fuel nozzle (4) via the main fuel supply line (3) meets the combustion target flow rate. S2, Main fuel supply circuit configuration: Start the gear pump (2) to pump fuel from the fuel tank (1) through the filter (13), and after passing through the three-way connector (9), it is divided into two paths, one of which enters the main fuel supply circuit (3) and the other enters the return branch circuit (10); S3, the return branch is preferentially opened: Since the second pressure value of the second check valve (12) is less than the first pressure value of the first check valve (8), the return branch (10) is preferentially opened, and the fuel flows back to the fuel tank (1) through the fixed throttle orifice (11) and the second check valve (12). S4, PWM linear fine adjustment: The input voltage of the gear pump (2) is adjusted by the PWM speed controller (14) to change the speed of the gear pump (2), thereby linearly fine adjusting the actual fuel flow to the fuel injector (4).

5. The flow control method according to claim 4, characterized in that, In S1, the calculation of the diameter of the fixed throttle orifice (11) also includes: determining the cross-sectional area of ​​the throttle orifice based on the required return oil flow rate, the pressure difference at both ends of the fixed throttle orifice (11) and the fuel density.

6. The flow control method according to claim 4, characterized in that, In S1, the diameter of the fixed throttle orifice (11) is determined such that when the gear pump (2) is running at full speed under rated voltage and the duty cycle of the PWM speed controller (14) is 100%, the actual fuel flow rate to the fuel nozzle (4) is equal to the upper limit of the combustion target flow rate.

7. The flow control method according to claim 4, characterized in that, The S3 also includes a shutdown anti-siphon: when the gear pump (2) stops, the second check valve (12) blocks the return branch (10) to prevent the fuel in the tank (1) from flowing back into the pipeline system due to the siphon effect.

8. The flow control method according to claim 4, characterized in that, In S4, the actual fuel flow rate to the fuel injector (4) increases as the duty cycle of the PWM speed controller increases.

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