1. Spray Impingement & Formation of Films In Ports
P M V Subbarao
Professor
Mechanical Engineering Department
Control of wall-film distribution area ….

2. Instantaneous Rate of Fuel Evaporation in Port
In PFI gasoline engines, a large portion of the spray impinges on the walls of the port or the intake valves.
Such wall wetting phenomena are found to be major contributors for high unburned hydrocarbon emissions.
Instantaneous rate of fuel evaporation in a port is the sum of evaporation rate of fuel droplets and evaporation rate of fuel films

3. Spray Wall Impingement & Formation of Films
The shape, size and location of impingement sites depend on;
Fuel spray cone angle.
Injection timing, back flow
Injection distance,
Impingement incidence angle.
For every impingement site, there exist;
the impingement probability and
the passing-by probability.
The impingement probability is proportional to spray covered wall area and the downstream flow cross-sectional area.

4. Basic mechanisms in the spray–wall interactions

5. Kinematics of Droplet Impingement
A droplet impacting on a solid surface first undergoes deformation and spreads out at a certain velocity under the impingement-induced pressure gradients.
This spreading flow either remains stable or becomes unstable, leading to different impingement regimes:
Stick, spread, rebound, and splash determined by Re & We, characterising the impingement conditions.

6. Details of Impingement
Two basic issues spray impingement processes.
Occurrence of type of Impacting regime.
Post-impingement characteristics, namely,
the rebound velocity magnitude and its direction for the rebound regime,
the fraction of the mass deposited on the wall and
the size and velocity distributions of the secondary droplets for the splash/breakup regime.

7. Fluid Dynamic Simulations in Ports

8. Velocity distribution during Intake Process

9. Possible Regions of Fuel Film in Port Injected Engiens

10. List of Impingement Points

11. Film Dynamics
There are two different forces exerted on a fuel wall film.
On the gas side, the gas flow tends to drive the film moving along the same direction.
On the wall side, the viscous friction tends to resist the film movement.
The force balance on the film gives the equation for the film motion:

12. Deposited Film Mass Fraction
The ratio of the reflected to the impinging mass is
given by
Ohnesorge numbers

13. Film Evaporation The film vaporization rate is determined by
where hf is the heat transfer coefficient, and Yfs the the mass fraction of the fuel vapor near the film surface.
Where p and pfs are the total local pressure and the pressure of the saturated fuel vapor near the surface of the wall film.
pfs can be calculated from the Clausius–Clapeyron equation presented in the following form

14. Estimation of Film Temperature
For the wall film, the energy equation is described by:
Where hfg & kf is the heat transfer coefficient and the liquid fuel thermal conductivity.
The terms in right hand of equation are the heat transfer rate from gas to fuel film on the gas side, the heat transfer rate used for vaporization and the heat transfer from wall to the film respectively.

15. Distribution of Fuel

16. Film distributions at various Zones

17. Wall Film Thickness Different Locations

18. Fuel Film at 1465 Crank Angles

19. Migration of Fluid Film

20. Effect of Injection Timing

21. Effect of Injector Location

22. Effects of impingement angle

23. Fuel Evaporation in Prot Injection Engine