Gas inlet channel flash boiling atomization spraying method and gas inlet channel spraying device

Abstract

The invention provides an air inlet channel flash boiling atomization injection method. The method comprises the steps that state parameters of fuel to be injected out of an oil injector and the environment pressure in an air inlet channel are obtained; regulating and controlling the fuel to generate a superheat degree relative to the environment pressure, so that the fuel is in a flash boiling state when being sprayed out of the fuel injector; and the fuel injector injects the fuel in the flash boiling state to an air inlet channel. The invention further provides an air inlet channel injection device which comprises an air inlet channel, an oil injector and a flash boiling control system, and the air inlet channel is used for inputting air; the oil sprayer is arranged in the air inlet channel and used for spraying fuel to the air inlet channel. And the flash boiling control system is used for regulating and controlling the thermodynamic state of the fuel or the environment pressure in the air inlet channel, so that the fuel to be injected is in a flash boiling state. The problems that the atomization quality of low-pressure spray sprayed by an air inlet channel is poor, the cold start emission of an engine is high, and the oil control accuracy is poor are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of engines, and particularly relates to an intake port flash boiling atomization injection method and an intake port injection device. BACKGROUND

[0002] The fuel injection system is the core subsystem of the engine, and the port fuel injection (PFI) and the direct injection (DI) are two main modes of modern fuel injection. Among them, the direct injection technology can more accurately control the fuel injection and use the charge cooling effect to improve the compression ratio of the engine, so the DI engine is superior to the PFI engine in power and fuel economy, and has been widely used.

[0003] In recent years, the sales of plug-in hybrid electric vehicles (PHEV) in the Chinese market have grown rapidly, among which, the single-gear PHEV and the range-extended electric vehicle (REEV) have become the fastest-growing technology route. The common point of these two technologies is that the vehicle mainly relies on the motor drive, and the engine is less involved in the drive or is completely decoupled from the wheels, and is mainly used for range extension power generation. This reduces the requirement for the driving power of the engine, and more attention is paid to the cost, size economy and emission performance of the engine. Under this background, the PFI engine is again concerned by the industry because of its simple structure, low cost (adopts low-pressure injection without high-pressure fuel supply system), and better emission performance than DI engine in most working conditions (PFI engine has longer oil-gas mixing time and more uniform oil-gas mixing).

[0004] Although PFI engine is again concerned about the advantages of cost economy and emission performance, but it still has the problems of high emission in cold start condition and poor oil control precision, and the core reason for these problems is the poor atomization quality of PFI fuel injection. Both port injection and direct injection use the principle of pressure atomization, but compared with the high injection pressure of 35~50MPa of direct injection, the injection pressure of port injection is generally not more than 0.6MPa, which leads to the fact that the spray atomization quality of port injection is significantly worse than that of direct injection: the spray particle size of conventional GDI engine is less than 20μm, while the spray particle size of PFI engine is between 120~200μm. Although the spray breakup evaporation and oil-gas mixing time of PFI engine is significantly longer than that of DI engine, which makes PFI be able to achieve better oil-gas mixing effect in most thermal engine conditions, but in cold start condition, due to the combined effect of low temperature environment of intake port and rich injection strategy, the fuel atomization is not sufficient, and part of the fuel enters the cylinder in the form of droplets and does not burn completely, which significantly increases the emission in the cold start stage. In addition, poor atomization quality will also cause large droplets to adhere to the wall surface of the intake port to form an oil film. Since the wall-attached oil film is difficult to enter the combustion chamber with the intake air flow in time, this will cause a deviation between the injection quantity and the actual amount of fuel participating in combustion, thereby affecting the air-fuel ratio control of in-cylinder combustion and the rapid response of injection quantity adjustment, that is, the problem of fuel control precision of PFI engine.

[0005] Currently, the technologies to solve the problems of PFI engine cold start emission and oil control precision mainly include three technical routes: first, improve the atomization quality of PFI spray by increasing the PFI injection pressure or optimizing the nozzle structure; second, optimize the distance and angle between PFI spray and intake port wall, valve wall, etc., to reduce the amount of oil film attached to the wall, and optimize the atomization effect through secondary breakup by wall impingement; third, use PFI+DI, double PFI and other hybrid injection strategies, use direct injection instead of PFI in cold start and other conditions, so as to avoid the atomization disadvantage of PFI. However, these methods do not fundamentally improve the atomization quality of PFI spray, and the problems of PFI engine cold start emission and oil control precision caused by poor atomization quality of low pressure injection still exist.

[0006] The flash boiling atomization technology optimizes the atomization effect of the spray by increasing the fuel injection temperature, reducing the background environment pressure or adjusting the injection pressure to optimize the bubble growth. The principle is that the fuel in a certain superheated state will generate bubbles in the nozzle flow stage (such as increasing the fuel injection temperature, reducing the background environment pressure to increase the fuel superheat degree), if the bubble can be ensured to have enough growth time in the nozzle (such as reducing the injection pressure to prolong the residence time), the generated bubble will be broken into fine droplets due to the pressure difference between inside and outside after flowing out of the nozzle. Compared with the cold pressure spray, the primary broken droplets of the flash boiling spray come from the film bubble explosion, so the size is similar to the liquid film thickness, and is much smaller than the primary broken droplets of the cold spray. The flash boiling atomization technology realizes atomization by changing the thermodynamic state and kinetic process of the fluid, and the mechanism is essentially different from the dynamic breaking mechanism of the pressure atomization. It has the potential to fundamentally improve the atomization quality of PFI injection even with low injection pressure without changing the PFI injection pressure, thereby solving the problems of high engine cold start emission and poor oil control precision.

[0007] Therefore, the person skilled in the art is committed to providing an intake port flash boiling atomization injection method and an intake port injection device to solve the problems of poor low-pressure spray atomization quality of PFI injection, high engine cold start emission and poor oil control precision. SUMMARY

[0008] In view of the defects in the prior art, the technical problem to be solved by the present application is how to provide an injection method and device that can solve the problems of poor low-pressure spray atomization quality of PFI injection, high engine cold start emission and poor oil control precision.

[0009] To achieve the above-mentioned purpose, the present application provides an intake port flash boiling atomization injection method, comprising: obtaining the state parameters of the fuel to be injected by the fuel injector and the environment pressure in the intake port; controlling the superheat degree of the fuel relative to the environment pressure, so that the fuel is in a flash boiling state when it is injected from the fuel injector; the fuel injector injects the fuel in a flash boiling state into the intake port.

[0010] Further, the controlling the superheat degree of the fuel relative to the environment pressure specifically comprises: controlling the temperature of the fuel or the environment pressure in the intake port, so that the saturated vapor pressure of the fuel is greater than the environment pressure; controlling the injection pressure of the fuel injector to reduce the hydrostatic pressure in the nozzle of the fuel injector and prolong the residence time of the fuel in the nozzle, and promote the nucleation and growth of bubbles.

[0011] Preferably, the way of regulating the superheat degree of the fuel relative to the ambient pressure of the intake passage comprises one or more of the following: actively heating the fuel, adjusting the ambient pressure in the intake passage, adjusting the injection pressure of the fuel injector.

[0012] Further, the actively heating the fuel comprises: determining a target heating temperature according to the engine operating condition, and controlling a heating component to heat the fuel to the target heating temperature at which the fuel is in a superheated state.

[0013] The application also provides an intake passage injection device, comprising: an intake passage for inputting air, the intake passage having an ambient pressure therein; a fuel injector arranged in the intake passage for injecting fuel into the intake passage; a flash boiling control system for regulating the thermodynamic state of the fuel or the ambient pressure in the intake passage, so that the fuel to be injected is in a flash boiling state.

[0014] Preferably, the flash boiling control system comprises: a state adjusting actuator, the state adjusting actuator comprising a heating component; a controller for controlling the heating component to heat the fuel to be injected by the fuel injector when it is determined that the operating condition requires active flash boiling.

[0015] Further, the fuel injector is arranged in one of the intake passages, the inlet of the fuel injector is connected to an oil rail, and the inlet of the intake passage is connected to an intake manifold.

[0016] Preferably, the heating component comprises a positive temperature coefficient heating plate and a copper heat exchange sleeve, the positive temperature coefficient heating plate is used to heat the copper heat exchange sleeve, and the copper heat exchange sleeve is used to heat the fuel, the fuel heated by the copper heat exchange sleeve is delivered to the oil rail.

[0017] Preferably, the heating component is an electric heating coil, and the electric heating coil is arranged at the end of the fuel injector.

[0018] Preferably, the oil rail is provided with a temperature sensor and a pressure sensor, and the intake manifold is provided with a pressure sensor, the temperature sensor is used to measure the temperature of the heated fuel, the oil rail pressure sensor is used to measure the injection pressure of the fuel injected by the fuel injector, and the intake manifold pressure sensor is used to measure the ambient pressure in the intake passage.

[0019] The application has at least the following beneficial technical effects: The intake passage flash boiling atomization injection method of the application realizes multi-dimensional regulation through active heating, ambient pressure utilization or injection pressure regulation, does not change the PFI low-pressure injection characteristics, retains the low-pressure injection and low-cost advantages, and fundamentally improves the PFI atomization quality, optimizes the cold start emission and oil control precision performance of the PFI engine.

[0020] The application realizes the optimization of cold start performance, and the number of exhaust smoke particles of the flash boiling PFI is reduced by more than 90% compared with that of the conventional PFI under the cold start working condition; the flash boiling PFI combustion is more sufficient than the conventional PFI combustion, and there is no local over-concentration area caused by large droplets / wall film entering the cylinder, thereby avoiding the generation of soot emission.

[0021] The application realizes the optimization of oil control precision, and the average cylinder pressure variation coefficient (IMEPCOV) of the flash boiling PFI is reduced by about 30% compared with that of the conventional PFI, the combustion cycle fluctuation is lower, the in-cylinder oil supply amount is more stable and accurate, and the oil control precision performance is optimized; the average cylinder pressure variation coefficient of the flash boiling PFI is close to or even lower than that of the conventional DI.

[0022] The concept, specific structure and technical effects of the application will be further described below with reference to the accompanying drawings, so as to fully understand the purpose, features and effects of the application. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a process schematic diagram of the intake passage flash boiling atomization injection of the application embodiment; Figure 2 It is a structure schematic diagram of the intake passage injection device of the application embodiment 1; Figure 3 It is a structure schematic diagram of the intake passage injection device of the application embodiment 2.

[0024] Among them, 1-engine cylinder, 2-intake passage, 3-intake manifold, 4-throttle valve, 5-oil rail, 6-oil injector, 7-adiabatic shell, 8-positive temperature coefficient heating plate, 9-copper heat exchange sleeve, 10-temperature sensor, 11-pressure sensor, 12-electric heating coil. DETAILED DESCRIPTION

[0025] The preferred embodiments of the application are introduced below, so that the technical content of the application is clearer and easier to understand. The application can be embodied in many different forms of embodiments, and the protection scope of the application is not limited to the embodiments mentioned in the text.

[0026] In the drawings, components of the same structure are denoted by the same reference numerals, and components similar in structure or function are denoted by similar reference numerals. The size and thickness of each component shown in the drawings are arbitrarily shown, and the size and thickness of each component are not limited in the present application. In order to make the drawing clearer, the thickness of the components is appropriately exaggerated in some places in the drawing.

[0027] The present application provides a method for flash boiling atomization injection in an intake port, which is characterized in that the relationship between the thermodynamic state parameter of fuel and the ambient pressure in the intake port is regulated so that the fuel is in a superheated flash boiling state at the moment of injection. The specific means include: actively heating the fuel, using the low pressure environment of the intake port, or adjusting the injection pressure. Preferably, the fuel is heated to a superheated state, and by changing the thermodynamic state of the fuel, bubbles are generated in the fuel flow stage in the injector due to overheating. The overheated bubbles burst to form small droplets with a size close to the thickness of the liquid film after being injected out of the nozzle, effectively improving the atomization quality of low-pressure injection, and solving the problems of high emissions and inaccurate fuel control of existing PFI engines in cold start conditions due to poor atomization quality of fuel injection.

[0028] As shown in Figure 1 The specific process of flash boiling atomization in the intake port of the present application is shown. By actively heating, the fuel is superheated, and the fuel in a superheated state has the potential to form nucleation bubbles. Flash boiling bubbles are generated in the flow channel during the flow process in the injector. These flash boiling bubbles grow continuously, and if combined with a lower injection pressure, the bubbles will grow for a longer time in the flow channel, and will flow with the fuel to the outlet of the injector flow channel. After being injected out, the bubbles will quickly burst due to the pressure difference between the inside and outside of the bubbles, and break into small droplets. The broken droplets of the flash boiling spray come from the bubble burst, so the droplet diameter is similar to the liquid film thickness, much smaller than the droplets formed by the insufficient disturbance of the liquid core in the low-pressure cold PFI spray, and similar to the atomization level of the high-pressure cold DI spray. The present application optimizes the atomization quality of the PFI low-pressure spray using flash boiling technology, and the formed fuel spray droplets are smaller, have a shorter penetration distance, and have stronger evaporation phase change and higher gas phase ratio, which can effectively reduce the wall film formed by the valve back and the intake port inner wall due to the poor atomization and breaking of the PFI spray, and solve the problems of high emissions and poor fuel control accuracy of the PFI engine in cold start conditions. The present application can form a fuel spray with good atomization quality and high gas phase ratio in the intake port during the fuel injection stage. The fully atomized fuel enters the cylinder during the intake stage, and can form a uniform oil-gas mixture by taking advantage of the long oil-gas mixing time of the intake port injection and the upward movement of the piston during the compression stroke to fully promote the oil-gas tumbling, and finally realize the homogeneous mixture combustion with near-zero soot emissions in the combustion process.

[0029] The application also provides an intake port injection device, which comprises an intake port, an oil injector, and a flash boiling control system. The intake port is used for passing air to mix with fuel. The oil injector is arranged in the intake port and sprays fuel into the intake port. The flash boiling control system is used for regulating the state of fuel, for example, actively heating the fuel to be sprayed by the heating component to make it in a superheated state. The end of the intake port is provided with an engine cylinder for burning the fuel.

[0030] Generally, the number of oil injectors and intake ports is multiple. The inlet of the oil injector is provided with an oil rail for distributing fuel to multiple oil injectors. The inlet of the intake port is provided with an intake manifold for delivering air to multiple intake ports. The intake manifold can be further provided with a throttle valve for controlling the air delivery amount, air delivery pressure and air delivery flow rate of the intake manifold.

[0031] For example, the oil rail can be provided with a fuel pump for pumping fuel to the oil rail. The intake manifold can be provided with an air filter for filtering air before being delivered to the intake manifold. Figure 2The figure is a schematic diagram of the intake port injection device of the embodiment 1 of the application. The oil rail 5 connects the fuel injector 6 and the actuator of the flash boiling control system. The actuator (heating component) is composed of an adiabatic shell 7, a positive temperature coefficient heating plate 8 and a copper heat exchange sleeve 9. The temperature sensor 10 is installed on the oil rail 5. The pressure sensor 11 is installed on the intake manifold 3. During the operation of the engine, the automobile electronic control unit (ECU) serves as the controller of the flash boiling control system. According to the engine operating conditions, the type of fuel used and the pressure information in the intake port 2, the ECU executes the flash boiling control strategy. Specifically, the ECU first calculates the flash boiling intensity ratio under the current operating conditions. In the high back pressure operating conditions such as cold start, the ECU determines that active heating must be performed and determines the target temperature of the fuel heating, and transmits this signal to the positive temperature coefficient heating plate 8. The positive temperature coefficient heating plate 8 starts heating. The heat is transferred and swept through the copper heat exchange sleeve 9 of the tube bundle. The fuel exchanges heat with the copper heat exchange sleeve 9 when passing through the heating component, reaches the target temperature and enters the oil rail 5. In the hot engine operating conditions such as partial load, the ECU monitors the signal of the pressure sensor 11. If it is found that the intake port 2 has a high vacuum degree (i.e. low ambient pressure), the ECU determines that the low ambient pressure can meet the flash boiling condition. At this time, the heating power can be reduced or stopped to achieve energy-saving control. In addition, the ECU can also control the fuel pump. In the operating conditions that require intensified atomization and have low requirements for the penetration distance, the ECU instructs to reduce the fuel supply pressure to prolong the growth process of the bubbles in the fuel injector 6. The superheated fuel generates flash boiling bubbles during the flow process in the fuel injector 6. The flash boiling bubbles grow continuously with the fuel flow and rapidly burst into fine droplets and form vapor phase fuel after being sprayed out of the fuel injector 6 due to the pressure difference between the inside and outside of the bubbles. The fully atomized fuel enters the engine cylinder 1 with the intake stroke to form a homogeneous mixture, and finally realizes the homogeneous charge combustion with near-zero soot emission. The temperature sensor 10 is used to monitor the fuel heating temperature to ensure that the fuel is heated to the target temperature. Combined with the pressure sensor 11 monitoring the ambient pressure in the intake port 2, the current flash boiling spray overheat degree can be determined to determine the current spray form and atomization characteristics, and the closed loop and active control of the flash boiling spray overheat degree are realized. The embodiment realizes the intake port injection flash boiling atomization. The flash boiling technology is used to realize the fuel atomization effect similar to high-pressure direct injection at low injection pressure, solves the problems of poor atomization quality, high cold start emission and poor oil control precision of the existing PFI engine. In addition, the fuel heating component is integrated and arranged in front of the oil rail in the embodiment, so that the existing oil rail system only needs to be simply modified to adapt to the flash boiling PFI technology. The application of the cross-pipe bundle copper heat exchange sleeve improves the heat exchange efficiency between the positive temperature coefficient heating plate and the fuel, ensuring more stable fuel heating effect. Heating the fuel in front of the oil rail can also ensure that the temperature of the fuel injected by each fuel injector is consistent, especially in the operating conditions with high fuel injection requirements, which can stably supply superheated fuel.

[0032] As Figure 3The figure is a schematic diagram of the intake port injection device of the embodiment 2 of the present application. In this embodiment, the fuel heating is achieved by the electric heating coil 12 arranged near the cylinder head at the end of the fuel injector 6. In the actual operation of the engine, the automobile electronic control unit (ECU) determines the target temperature of the fuel heating according to the engine operating conditions, the type of fuel used and the pressure information in the intake port 2, and transmits this signal to the electric heating coil 12. The electric heating coil 12 directly wraps the end of the fuel injector 6 to achieve fuel heating. This embodiment also achieves flash boiling atomization of the intake port injection, so that the flash boiling PFI engine has the advantages of low cost and low emission of PFI injection technology, and the advantages of low cold start emission and precise oil control of DI injection technology. Compared with the embodiment 1, the fuel at the end of the fuel injector 6 is directly heated in this embodiment, which is more efficient, faster in response and more accurate in temperature control. However, the heat resistance requirement of the fuel injector 6 is higher, and the fuel flow is fast and the heat exchange is insufficient under the condition of large fuel injection, so it is difficult to ensure the stable supply of superheated fuel with large flow. Therefore, it is more suitable to use the fuel heating function occasionally in special conditions such as cold start to optimize the low-pressure spray atomization effect by using the flash boiling technology.

[0033] The preferred embodiments of the present application are described in detail above. It should be understood that those skilled in the art can make many modifications and changes without creative labor based on the concept of the present application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment based on the prior art according to the concept of the present application shall be within the protection scope determined by the claims.

Claims

1. A method for flash boiling atomization injection in an air intake duct, characterized in that, include: Acquire the state parameters of the fuel to be injected by the fuel injector and the ambient pressure in the intake manifold; The superheat of the fuel relative to the ambient pressure is controlled so that the fuel is in a flash boiling state when it is injected from the injector; The injector injects the fuel, which is in a flash-boiling state, into the intake manifold.

2. The intake flash boiling atomization injection method as described in claim 1, characterized in that, The regulation of the superheat of the fuel relative to the ambient pressure specifically includes: The temperature of the fuel or the ambient pressure inside the intake manifold is controlled such that the saturated vapor pressure of the fuel is greater than the ambient pressure. The injection pressure of the injector is controlled to reduce the hydrostatic pressure of the fluid in the injector orifice and prolong the residence time of the fuel in the orifice, thereby promoting the nucleation and growth of bubbles.

3. The intake flash boiling atomization injection method as described in claim 1, characterized in that, The method of regulating the superheat of the fuel relative to the ambient pressure includes one or more of the following: actively heating the fuel, adjusting the ambient pressure in the intake manifold, and adjusting the injection pressure of the fuel injector.

4. The intake flash boiling atomization injection method as described in claim 3, characterized in that, Actively heating the fuel includes: The target heating temperature is determined based on the engine operating conditions, and the heating components are controlled to heat the fuel to the target heating temperature. At the target heating temperature, the fuel is in a superheated state.

5. An air intake injection device, characterized in that, include: An air intake duct for introducing air, wherein the air intake duct is under ambient pressure; A fuel injector, located inside the intake manifold, is used to inject fuel into the intake manifold; The flash boiling control system is used to regulate the thermodynamic state of the fuel or the ambient pressure in the intake manifold so that the fuel to be injected is in a flash boiling state.

6. The intake manifold injection device as described in claim 5, characterized in that, The flash boiling control system includes: A state-regulating actuator, the state-regulating actuator including a heating component; The controller, when determining that active flash boiling is required, controls the heating element to heat the fuel to be injected by the injector.

7. The intake manifold injection device as described in claim 5, characterized in that, The fuel injector is located within one of the intake passages, the inlet of the fuel injector is connected to the fuel rail, and the inlet of the intake passage is connected to the intake manifold.

8. The intake manifold injection device as described in claim 6, characterized in that, The heating component includes a positive temperature coefficient heating plate and a copper heat exchanger jacket. The positive temperature coefficient heating plate is used to heat the copper heat exchanger jacket, and the copper heat exchanger jacket is used to heat the fuel. The fuel heated by the copper heat exchanger jacket is transported to the oil rail.

9. The intake manifold injection device as described in claim 6, characterized in that, The heating element is an electric heating coil, which is located at the end of the fuel injector.

10. The intake manifold injection device as described in claim 5, characterized in that, The fuel rail is equipped with a temperature sensor and a pressure sensor, and the intake manifold is equipped with a pressure sensor. The temperature sensor is used to measure the temperature of the heated fuel, the fuel rail pressure sensor is used to measure the injection pressure of the fuel injected by the injector, and the intake manifold pressure sensor is used to measure the ambient pressure inside the intake manifold.

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