A very accurate control of air fuel ratio in port injected spark ignition engines during transient is required to reach the toughest polluant emissions standards. The prediction of air fuel ratio behavior has been made with models for liquid fuel film, droplets and fuel vapor in the intake manifold of single point injected engines [1], where the droplet deposition rate on the manifold was only a parameter.
This paper describes a model for droplet deposition rate on the port walls and intake valve in port injected engines. The model described here takes into account the transient character of fuel injection in a real port geometry. The droplet diameter distribution is included with seven different droplet sizes, and varies across the spray, with a multicomponent fuel. The backflow of hot burned gas at valve opening is also taken into account by the model.
The depostion rate on the valve and the port walls as a function of space and time has been calculated for several operating conditions. The droplet diameter distribution, the injector angle as well as the injector-valve distance were also varied.
Finally a comparison of the equivalence ratio calculated with a global model including the deposition rate description with the measured equivalence ratio is given for a transient test, showing a really good correlation between calculated and measured air fuel ratios.