Study on Leak Detection of the Vehicle Fuel Evaporation System Based on the Positive Pressure Method

Abstract In this article, a study is carried out on the leak detection of the evaporation system based on the positive pressure method. The mathematical model of pressure variation in the evaporation system was developed. The effects of leak hole diameter, fuel level, and air pump operating voltage on the pressure buildup in the evaporative system were analyzed. The 1 mm and 0.5 mm leak detection methods were explored and experimentally validated. During the air pumping process, the pressure of the evaporation system gradually increases until it fluctuates steadily. The saturation pressure and buildup time are negatively correlated with the leak hole diameter. Fuel level does not affect the saturation pressure, but significantly affects the buildup time. The difference in pressure saturation time corresponding to 15% fuel level and 85% fuel level is 450 s. In the range of 9–16 V, the pressure-building capacity of an air pump is linearly and positively correlated with its operating voltage. The threshold method can be used for 1 mm leak detection, but detection accuracy is limited. When there is a leak hole close to 1 mm such as 0.8 mm and 0.9 mm, the evaporation system may be diagnosed with leaks greater than 1 mm. The reference hole method is not affected by the working capacity of the air pump, which is suitable for 0.5 mm leak detection. The research content contributes to the understanding and refinement of leak detection techniques based on positive pressure methods.