Characteristics of the deposited fuel liquid film when GDI spray impacts viscous oil film

Highlights: • LIF is proved applicable to measure the fuel mass after spray impacting a thin oil film. • Oil film leads to more deposited fuel mass than dry surface after spray impingement. • Higher injection pressure and thinner oil film lead to less deposited fuel. • Oil viscosity has different effects on deposited fuel with different injection pressure. -- Abstract: Quantitative two-dimensional characteristics of the deposited fuel film on a surface with pre-existing thin oil film after the impingement of a GDI (gasoline direct injection) spray were investigated with laser induced fluorescence (LIF) technique. Since the oil and the incident test fuel could mix during impingement, we examined the theory of the LIF technique and found it could no longer provide information on the mixture thickness but could still help us measuring the mass of the deposited fuel. Mixture of isooctane and 3-pentanone was chosen as the test fuel and silicone oil of different viscosity was selected as the surrogate liquid for the oil to eliminate disturbing LIF emission. The sprays with injection pressure from 7 to 15 MPa, injected mass from 2.9 to 6.4 mg were tested, the pre-existing oil film with viscosity of 10 and 100 cSt and thickness between 10 and 50 μm were studied. A lower fuel mass deposited ratio was found under higher injection pressure and thinner oil film, while the effects of the injected mass and viscosity of oil viscosity were found to be more complicated and were analysed with the help of single drop experiments from literature.