Analysis on Factors Affecting Leak Detection of Vehicle Fuel Evaporative System

Many factors could affect the detection of a leak on a vehicle fuel evaporative system. This paper investigates the impacts of orifice diameter, tank ullage volume, initial decay pressure, and hot soak temperature. The leak in the fuel evaporation system of a gasoline vehicle was simulated by using the orifices with standard diameters. The pressure decay method was utilized in orifice diameter, ullage volume, and initial decay pressure experiments. This method utilizes an air compressor to establish a certain pressure for the system, after which the orifice is turned open and the pressure change overtime is recorded. Engine off nature vacuum method was utilized in hot soak experiments. After the hot soak in an aging room, the evaporation system was moved to a lower-temperature environment, then the pressure change was recorded. The results show that the larger the diameter of the orifice, the shorter the pressure decay duration. The pressure decay duration of test bench with a 1 mm orifice is just one-fifth of that with a 0.5 mm orifice, which means that the pressure decay method is suitable for leak detection. The pressure decay duration decreases with the ullage space of tank, so the leak detection is not suitable to be performed when the fuel level is too high nor too low. The ambient temperature has a certain effect on the results, but the absolute error is not significant. The result of leak detection is less affected if the criteria is chosen based on the pressure change characteristics of the first 50 s of pressure decay duration.