Abstract: This paper aims to analyze the effect of the position of leak hole on the pressure and flow field characteristics in vapor space of vehicle evaporative control system when adopting vacuum decay method in leak monitoring. Firstly, the numerical model for total pressure in vapor space is built to obtain the boundary conditions of transient models. Then transient models with 1 mm leak hole for upward and sideward leaks are analyzed. Finally, verification test with 1 mm reference hole is conducted. Results show that in decay time 30-39 s the pressure in vapor space is basically equal everywhere except in the vicinity of leak hole and pipeline. The maximum pressure in the pipeline with valves is higher than that in circulating pipe. Vacuum decay rate in upward leak is higher than that in sideward leak. Decay time 30-39 s is the preferred leak monitoring period.

Key words: vehicle, leak monitoring, vacuum decay, leak hole