Design of fuel evaporation system for the most the

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Abstract: the fuel evaporation system of Changhe ch6328ei and ch6352 vehicles introduced in this paper is designed from the aspects of fuel supply performance, fuel evaporation characteristics and safety of the fuel evaporation system, and the structure and performance of its main components such as oil filter, oil pump, carbon canister, hose and oil tank are analyzed, so as to comprehensively elaborate the design of the fuel evaporation system of Changhe EFI vehicles

key words: fuel evaporation performance system design

the function of the fuel system is to supply gasoline required for combustion to the engine cylinder to ensure the normal operation of the engine under various working conditions; The function of the evaporation system is to control the evaporative pollutants in the fuel system to achieve the cost of the post-treatment process; At the same time, it has excellent surface quality assurance requirements, and meets the limit requirements for pollutants in the national standard GB18352.2-2001 "limits and measurement methods of pollutant emissions from light vehicles (II)". Changling company began to develop EFI vehicles as early as 99, with the purpose of connecting with the national environmental protection regulations. Electronic fuel injection system needs to provide high-pressure fuel to the engine, and at the same time, carbon canister cleaning valve is used to control fuel evaporation pollutants. Therefore, the fuel evaporation system needs to be redesigned. The design principle of the system: it should not only meet the requirements of the electronic fuel injection system, but also borrow the layout and parts of the carburetor vehicle fuel evaporation system to the greatest extent, so as to minimize changes

1 fuel supply performance design

the working pressure of the fuel system is 250 ~ 350kPa determined by the characteristics of fuel injection, so the pressure resistance of parts of the fuel system is required to be high. To meet this requirement, the structural performance design of oil pump, oil supply, oil return pipeline and oil filter has become the core design of oil circuit system. Figure 1 shows the fuel evaporation system of EFI vehicle

1 - fuel tank assembly

2 - oil pump and oil level sensor assembly

3 - fuel evaporation hose

4 - No. 1 oil return hose

5 - No. 1 oil supply hose

6 - fuel filter

7 - ventilation hose

8 - canister desorption hose (connected to canister cleaning valve)

9 - canister adsorption hose

10 - filler cap

11 -no. 3 oil supply hose (connected to the oil supply end of the engine oil rail)

12 - No. 2 oil return hose (connected to the fuel return end of the engine fuel rail)

13 is an indispensable testing equipment for physical property experiments, teaching research, quality control and so on carbon canister

1.1 fuel pump design

the fuel pump should be able to output high-pressure and a certain flow of fuel. Therefore, the power of the fuel pump should be increased accordingly. When the oil pump motor is running, it is easy to generate heat, improve the fuel temperature, and the oil circuit is easy to produce air resistance. Therefore, the fuel pump should be built into the fuel tank, so when the fuel pump works, the fuel in the fuel tank and the fuel flowing through the motor will have a cooling effect on the motor, and the air resistance is not easy to produce. At the same time, the use of the built-in fuel pump also has the advantages of not easy fuel leakage and low noise. A check valve is set in the fuel pump to prevent fuel backflow, maintain the residual pressure of the pipeline, and facilitate the hot start and restart of the engine. When the engine shuts down and the fuel pump just stops delivering fuel, the check valve will be closed immediately to keep the fuel at a certain pressure, that is, the residual pressure in the pipeline. Generally, the fuel is easy to vaporize when encountering high temperature, which leads to the decline of the working performance of the oil pump and nozzle, resulting in the difficulty of hot start of the engine. The one-way valve is set to continue to provide new material solutions for household appliances after the engine shuts down, and still maintain a certain pressure, reducing the phenomenon of air resistance, making it easy for the engine to start at high temperature. A safety valve shall also be set in the oil pump. When the output oil pressure of the oil pump reaches 400 ~ 600kpa, the pressure relief valve shall be opened to prevent fuel leakage caused by excessive oil pressure when the oil circuit is blocked. In order to establish high-pressure fuel and meet the flow requirements (greater than 60l/h), the oil pump adopts impeller structure, which is also conducive to reducing the working current. Figure 2 is the structural diagram of the fuel pump motor. The oil inlet of the fuel pump shall be equipped with a filter (filter accuracy 130 μ m) To prevent impurities from entering the oil pump motor and accelerating motor wear. Integrating the oil level sensor into the fuel pump assembly can not only reduce the types of parts, but also improve the assembly efficiency of the production line

1.2 design of oil supply and return rubber hose

the oil circuit system must ensure the fuel oil requirement of 250 ~ 350kPa pressure, so the oil supply and return hose should have a structure that meets this performance. In order to improve the safety factor of the fuel hose, the bursting pressure of the hose is designed to be 5MPa. As shown in Figure 3, the high-pressure rubber fuel hose is composed of three layers of rubber, FKM (fluororubber), NBR (nitrile rubber) and eco (vinyl chloride rubber) from the inside to the inside, and there is a polyester braid in the middle of the hose. The performance of each layer of rubber is analyzed as follows: FKM has excellent heat aging resistance, oil resistance, ozone resistance, permeability and copper plate pollution; NBR has excellent oil resistance, but it is inferior to FKM. In addition, NBR has good air tightness and water resistance, and poor ozone resistance; Eco has high low temperature resistance and ozone resistance. The polyester braid in the middle can enhance the pressure resistance of the hose. The hose with this structure has strong comprehensive performance. Since the working pressure of the high-pressure hose reaches 3 atmospheres, compared with the fuel hose of the carburetor car, it is required to increase the braid; Similarly, due to the high pressure of fuel, there are high requirements for the oil resistance of the hose, so it is necessary to adopt FKM as the inner rubber layer, and there are also certain requirements for the thickness of this layer

Figure 3

1.3 design of gasoline filter

gasoline filter is installed in the high-pressure oil circuit behind the oil pump. Its function: filter out solid inclusions such as iron oxide and dust in the fuel (understand the fuel composition), prevent blockage of the fuel system, reduce mechanical wear of the system, ensure stable operation of the engine, and improve working reliability. The filter element adopts a drum type structure, which can increase the filtering area and reduce the volume and weight of the oil filter; The oil filter has high pressure resistance, so it is required to use a metal shell, as shown in Figure 4, to improve the pressure resistance. In order to meet the fuel supply performance requirements of the fuel system, the gasoline filter should have high filtration efficiency, long service life, small pressure loss (≤ 5kpa), good pressure resistance, small volume, light weight and other properties, and the filtration accuracy should be 8 ~ 10 μ m. To prevent blocking the fuel nozzle

1.4 design of high-pressure fuel hose installation clamp

the connection of each pipeline should be able to ensure that there is no fuel leakage. Therefore, the mature technology of Beidou starcar can be used, that is, the double-layer steel belt clamp for the fuel system. This clamp has the advantages of high assembly efficiency and low price of the production line. It avoids the shortcomings of the traditional worm gear clamp, such as requiring the specified tightening torque, easy to scratch the hose, low assembly efficiency and high price

2 safety performance design

strictly speaking, the components of the fuel evaporation system are all critical parts, and the production, assembly and connection of each component are in strict accordance with the requirements of the design documents, so as to meet the safety performance requirements of the system. The following focuses on how to design the system from the system security elements

2.1 fuel tank design

due to the use of a built-in fuel pump and the integration of an oil level sensor, the fuel tank needs to be redesigned. In addition to canceling the interfaces of the evaporation oil pipe, oil supply and return pipe, the installation interface of the fuel pump should also be designed with emphasis. The O-ring sealing method is used at the interface, as shown in Figure 5, to prevent fuel leakage. The performance of fuel tank components shall comply with the national standard gb18296-2001 safety performance requirements and test methods for automotive fuel tanks

2.2 installation method of oil pump

in case of vehicle collision accident, if the sealing and installation method of oil pump is unreasonable, fuel leakage may occur at the installation place of oil pump at the fuel tank interface. Therefore, the sealing and installation method of oil pump is extremely important. When designing this installation method, take the installation method of the oil pump of the Big Dipper as a reference, that is, the flange bolt fixation method is adopted. Figure 5 shows the installation method of the oil pump. There was no fuel leakage during the crash test of walrus, which proved the reliability of this installation method

2.3 protective design

add protective sleeves at the possible contact between the high-pressure fuel hose and the vehicle body and surrounding components to prevent fuel leakage caused by hose wear. Adopting the method of adding protective sleeves can not only reduce the cost, but also improve the safety of the fuel evaporation system

2.4 air change function

continue to use the fuel filler cap and air change pipeline of the 18 carburetor vehicle to ensure the air exchange of the fuel tank. The fuel filler cap has the negative pressure suction function of the fuel tank to prevent the fuel tank from deforming due to negative pressure

2.5 design of installation position of carbon canister

continue to use the installation position of carbon canister of 18 carburetor truck. The pipeline from the fuel tank to the carbon canister can only be upward, not downward, to prevent fuel from flowing out of the carbon canister. Generally, the carbon canister is required to be 500mm higher than the fuel tank. See Figure 6

3 evaporation performance design

carbon canister is brittle at low temperature for steam removal (ductile brittle transition temperature is 900~1000 DEG; c), 1300 DEG; The influence of insufficient high temperature intensity above C on evaporative emission of vehicles is the most significant. Because the EFI system adopts the carbon canister cleaning valve, the carbon canister is slightly changed on the basis of continuing to use the carbon canister of 18 vehicles, and the carbon canister desorption valve can be cancelled, so there is no need to redevelop the carbon canister mold

working principle of evaporative pollution control system of activated carbon canister. The fuel vapor from the fuel tank enters the upper part of the canister through the canister adsorption valve, and the air enters the cleaning activated carbon from the lower part of the canister. When the engine is working, ECU controls the action of the activated carbon canister electromagnetic cleaning valve to control the vacuum degree at the upper part of the emission control valve according to the engine speed, temperature, air flow and other signals, so as to control the opening and closing action of the emission valve. When the emission control valve is opened, gasoline vapor is sucked into the intake manifold through the quantitative emission hole in the valve, and then enters the cylinder for burning. Figure 7 shows the working principle of carbon canister evaporation pollution control system

Figure 7

4 Conclusion

the fuel evaporation system of EFI vehicle is a large system in the EFI system, and the rationality of its design will directly affect the working performance of the EFI system. This paper expounds in detail the design basis of the fuel evaporation system and the selection principles of its parts from several aspects, and tries to borrow the layout, parts and installation methods of the fuel evaporation system of the original carburetor vehicle to reduce unnecessary changes. Practice has proved that the developed EFI vehicle is reliable and stable, and its fuel evaporation pollutants meet the requirements of national standards. At the same time, because the fuel injection system has many commonalities, the design basis and principles of the fuel evaporation system described can also be used as a reference for the development of other EFI systems. (end)

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