Dynamics and Interactions of Fuel Droplets in Engine Ports

1. On the Journey of Fuel Droplets in Ports- Phase 1 P M V Subbarao Professor Mechanical Engineering Department Clues for the Difference in Injected and In-Cylinder Fuel-Air Equivalence Ratios ….

2. Air –Fuel Interactions in the Manifold • As the droplet group moves in the air stream, it decelerates or accelerates depending on local flow geometry. • At the same time, the droplets vaporization is initiated. • As the droplets move to the end of the pipe, some of the unvaporized droplets are assumed to impinge on the intake port wall bend to form droplet deposition films. Because of the heat transfer from the wall and from the air stream, these liquid films continuously vaporize.

3. The Trajectories of Droplets Travelling in Ports

4. Fuel Droplet Dynamics : Prediction of Trajectory The location and angle of injector on the port are considered as the inputs. The momentum equation for the ith set of droplets is given by md,iis mass of the ith diameter droplet

5. Dynamics of (SMD) Droplet During the spray penetration, there is a drag force exerted on the droplets from the surrounding gases, which tends to decrease the relative velocity between the drop and the gas flow. The drag coefficient CDvaries with the droplet Reynold’s number as

6. Other Forces Acting on SMD Droplet The buoyancy and pressure forces are given by This is to be integrated over time to obtain the velocity and position of the droplet

7. Velocity of SMD Drops

8. Sequential & Simultaneous Activities • Initial period (t< ): • Droplet evaporation and Wall interactions. • Next period (t> ): • Droplet evaporation, wall interactions, generation of secondary droplets and Film evaporation.

9. Instantaneous Rate of Fuel Evaporation in Port In PFI gasolineengines, a large number of droplets impinge on the walls of the port or the intake valve(s). 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. • It is essential to predict the potential sites for film deposition and corresponding physics of film formation.

10. Identification of Possible Regions of Fuel Film Deposition

11. List of Impingement Points

12. 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.

13. Basic mechanisms in the spray–wall interactions

14. Maxwell’s Theory of Particle Surface Interactions A particle impacting on a solid surface first undergoes an elastic deformation and rebound.

15. Kinematics of Liquid Droplet Impingement • It is very different from Maxwell’s theory. • 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.

16. Characterization of Liquid Droplet Impingement • Two basic issues arise in liquid droplet 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.