Modeling and simulation of the evaporative fuel system in an automobile
This thesis work has been performed at the department of
diagnosis and dependability at Volvo Car Corporation, Torslanda.
The background of this project is based on interest in
ascertaining how different factors possibly can affect
a diagnosis method, which has been developed to find leaks
in the fuel tank and evaporation system. According to the OBD II
requirements leaks with an orifice diameter larger or equal to 0,5 mm,
must be detected. The idea of the diagnosis method is to create
an over pressure in the system with an air-pump. The current through
the pump is measured and correlates to the power consumed by the pump.
As the power is a function of the pressure difference over the pump,
the pump current correlates to the pressure in the tank.
Thus, the pump current can be used as a measure of the impenetrability.
Changes in the system pressure, not caused by the pump, are accordingly
disturbances to the method.The object of this work was to develop
mathematical models, describing the lapse where the system is
pressurized by the pump under the influence of different physical factors.
The model is for instance considering variations in temperature and height,
flow resistance in lines and valves, component characteristics,
fuel evaporation, leaks etc. Furthermore the pump current is
treated by the diagnosis evaluation algorithm with purpose to judge
whether there is a leak in the system. The model has been implemented
in Matlab/Simulink and it can consequently be used in dynamic
simulations according to the over pressure leakage detection concept.
Numerical experiments can be done in purpose to examine how changes in
environmental conditions or component characteristics will affect the
diagnosis method. Good agreement has been found between measurements
and simulated results. The diagnosis function produces correct decisions
under different conditions with disparity in leak sizes, additionally
confirming the reliability of the model.
Keywords: Leakage diagnosis, over pressure method, airflow, evaporation,
temperature, modeling, simulation
Senast uppdaterad: 2019-06-05