1. On the Journey of Fuel Droplets in Ports – Phase 2
P M V Subbarao
Professor
Mechanical Engineering Department
Clues for the Difference in Injected and In-Cylinder Fuel-Air Equivalence Ratios ….

2. Teaching : Sharing of Knowledge
How wonderful that we have met with a paradox. Now we have some hope of making progress. -- Prof. Niels Bohr
Everything we call real is made of things that cannot be regarded as real Prof. Niels Bohr
Never express yourself more clearly than you are able to think. - Prof. Niels Bohr
The best weapon of a dictatorship is secrecy, but the best weapon of a democracy should be the weapon of openness. -- Prof. Niels Bohr

3. Physics of Liquid Droplet Impingement on A Wall
The wall impingement process is classified as four regimes:
The regime transition criteria are determined based on the Weber number of the incident droplet and the surface condition:

4. Deposited Film Mass Fraction
 /DSMD = 1.18
 /DSMD = 0.78
 /DSMD = 0.5

5. Nature of I.C. Engine Fuel Films

6. Nature of I.C. Engine Fuel Films

7. Physics of Liquid Droplet Impingement on A Wall
A second level of transition occurs after growth of a critical thickness of film.
These regimes are mainly due to interaction of large droplets with fuel film.
A special number is defined using Reynolds number and Weber number to identify the second level of transition.
Splash is the most important and also the most complex.
Spread and Splash are commonly observed in SI engine ports.

8. Physics of Liquid Droplet Impingement on A Wall
splash is the most important and also the most complex.
Spread and Splash are commonly observed in SI engine ports.

9. Spreading Dynamics of Films
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:

10. Computation of Total Deposited Film Mass Fraction
The ratio of the reflected to the impinging mass is given by
Ohnesorge numbers
Assignment 2
Submit a research report on:
Mathematical models to calculate mass fractions of deposited fuel films in I.C. Engines.
Date of Submission: 17th September 2018.

11. The Splash
Splash results in the rebounding of many smaller secondary droplets from the impinging location.
The size and velocities of the secondary droplets are statistically distributed.
The splash threshold Hcr
 : non-dimensional surface roughness = (roughness height/incident droplet diameter),
/DSMD : non-dimensional film thickness =(film thickness/incident droplet diameter)

12. Secondary Breakup of the Droplets
The process of evaporation begins just after primary breakup and hence SMD is based on primary breakup.
The primary SMD droplet is assumed to be analogous to a spring mass system.
The aerodynamic force on the droplet is the external force.
The surface tension is represented by a spring force.
The viscosity can be modelled by the damping forces.
The droplet is assumed to oscillate under the effect of these forces, with its acceleration given by:
CF, Ck, Cd, and Cb are model constants.

13. Next Generation Droplets
The injected droplet oscillates normal to its injection direction.
All droplets subject to oscillation with y > 1, break up into smaller droplets.
Child droplets will have same normal velocity asithat of the parent droplet.
The SMD of the child droplets is determined from energy conservation, as below:
K is a constant

14. Development of Fuel Film
Injected fuel
Fuel in Films