乘用车燃油蒸发排放OBD诊断替代车检泄漏试验

汽油的蒸发排放是汽车碳氢排放的主要来源，为此国六排放法规和车检法规都提出了对燃油蒸发排放控制系统泄漏监测和测试的要求。国六排放法规要求汽油车燃油蒸发排放系统的泄漏量小于直径1 mm小孔的泄漏量，车检法规要求完成燃油蒸发排放控制系统外观检验、进油口压力测试及燃油箱盖测试。基于进油口压力测试和燃油箱盖测试在实际车检中的复杂性，提出将OBD诊断信息使用在实际车检中。根据车检法规中燃油箱压力和泄漏流量损失限值，利用伯努利方程和非稳态气体泄漏的气体压力常微分方程计算燃油箱压力和泄漏流量，并对压力损失测试中的蒸汽体积提出修正。在修正的蒸汽体积条件下，1 mm小孔在不到国六排放法规规定时间120 s造成的气体泄漏就会使得蒸发系统的压力损失达到限值，0.533 6 mm直径的泄漏小孔即会使得燃油的泄漏流量达到国六排放法规限值60 mL·min^-1。研究结果表明：当蒸发系统出现大于直径1 mm小孔泄漏，OBD报出蒸发系统泄漏故障时，可认为车辆无法通过进油口压力测试和燃油箱盖测试；燃油蒸发排放控制系统车载OBD泄漏诊断信息可以替代车检进油口压力测试和燃油箱盖测试。

Replacement of Annual Leakage-inspection Test with Passenger-car Fuel-vapor-leakage On-board Diagnostics Information

Gasoline evaporative emissions are the main source of vehicle hydrocarbon emissions. As such, the China Ⅵ regulations for emissions and vehicle inspection have proposed requirements for leakage monitoring and testing of fuel evaporative emission control systems. The China Ⅵ regulation limits the evaporative leakage quantity of gasoline vehicles to be less than that of a 1.0 mm diameter hole. Vehicle-inspection regulations require appearance inspection, fuel filler port pressure test, and tank cap test of the fuel evaporative emission control system. Based on the complexity of the oil inlet-pressure test and fuel-tank cap test in actual vehicle inspections, the application of on-board diagnostics (OBD) information is proposed in these types of inspections. According to the limits of the fuel-tank pressure and leakage-flow loss in vehicular inspection regulations, the pressure and leakage flow of the oil tank are calculated using the Bernoulli equation and ordinary differential equation of gas pressure for unsteady gas leakage, and the vapor volume in the pressure loss test is modified. Under the condition of modified vapor volume, the pressure loss of the evaporation system reaches the limit in the case of gas leakage due to a small hole of 1 mm in less than 120 s, as specified in the regulations. In addition, the leakage-flow rate of fuel oil will reach the regulatory limit of 60 mL·min^-1 with a leakage hole diameter of 0.533 6 mm. The results show that the vehicle cannot pass the inlet-pressure and fuel-tank cap tests when the leakage hole of the evaporation system is larger than 1 mm. Moreover, the OBD reports the leakage fault as that of the evaporation system. Therefore, it is concluded that the leakage information by the OBD of the fuel evaporative emission control system can replace the fuel inlet-pressure and fuel-tank cap tests.