1. Development of Design Knowledge for GDI Internal Combustion Engines
P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi
Models to Predict New & Better Anatomy of Artificial Horse …..

2. How to develop Design Knowledge???

3. Thermodynamic Modeling : Development of Pseudo GDI Engine
Modeling of IC engine process can be carried out in many ways.
Multidimensional, Transient Flow and heat transfer Model.
Thermodynamic Transient Model USUF.
Fuel-air Thermodynamic Model.
Air standard Thermodynamic Model

4. Intake System of Modern Engines

5. Engine Intake Process : USUF Model
Any instant during intake, the equation of state for incylinder ideal gas is expressed as:
Rate of change of incylinder gas properties:

6. Geometrical Shape of A Puppet valve Passage
For lower valve lift the minimum area is the valve curtain area.
For larger lifts the minimum area is the valve seat area.
For Low Lift:

7. Air Flow Through Intake Valves : No MPFI
The air flow rate is related to the intake manifold stagnation pressure p0,in and stagnation temperature T0,in, Static pressure just down stream of the valve and a reference area AR.
AR is a characteristic of the valve design.
The real gas flow effects are included by means of an experimentally determined discharge coefficient CD.

8. Air Flow Through Intake Valves : with Fuel Injection
GDI Engine:
MPFI Engine:

9. Variation of In-cylinder temperature during Intake
First law for USUF :
GDI Engine:
MPFI Engine:

10. Operating modes of the GDI engine
Superior output mode : SOM
Injection in late intake stroke
Wider spray with high penetration for charge homogenization
A/F – Stoichiometric
Homogeneous A-F Mixture
Complete Vaporization of Fuel
Ultra Lean combustion mode : ULCM
Very lean stratified mixture : A/F ~ 30
Injection during compression
Compact spray, deflected from the piston top to the spark plug
Distinct Stratification
At spark , ignitable mixture conditions
It is two engines in one place

11. Feel the In-Cylinder Processes in GDI Engine:SOM
Start of injection
End of injection

12. Sizing of Nozzle Instantaneous fuel Flow rate:
Mass of Gasoline per cycle:

13. Simplified Engineering Droplet Path Tracking & fuel Evaporation model
In a simplified engineering model a representative diameter for the entire group is defined to compute evaporation rate.
Equivalent diameter of same number of uniformly sized droplets having same total surface area.

14. Simplified Engineering Droplet Path Tracking & fuel Evaporation model
In a simplified engineering model a representative diameter for the entire group is defined to compute evaporation rate.
Equivalent diameter of same number of uniformly sized droplets having same total surface area.

15. Prediction of Droplet Paths
After the spray break up there is a drag force exerted on the droplets from the surrounding gases.
This drag tends to decrease the relative velocity between the drop and the gas flow.
From the Newton's Second Law, the equation is:
Where dsmd is the droplet diameter, ug and usmd are the velocities of the gas flow and the liquid fuel droplet, respectively.
And the drag coefficient CD is given as:

16. Details of Heat and Mass Transfer across Droplet

17. The mass transfer number BM is equal to:
Droplet evaporation
The droplet evaporation rate is given by
where d is the droplet diameter, DAB the gas diffusivity, Sh* the non-dimensional Sherwood number, and Bm the mass transfer number.
The mass transfer number BM is equal to:

18. Tracking of Post Injection Events inside Cylinder

19. New Knowledge Required to Develop GDI Engines
Effect of Geometrical and Spray Parameters
Injector location,
Spray orientation,
Injection timing,
Droplet diameter,
Spray cone angle,
Type of spray,
Fuel temperature

20. Required Features of CFD Package
Capability to model flow in complex geometry
Capability to model turbulent flow
Capability of handling moving boundaries
Generalized multi-block capability
Spray model
Robust Algorithm

21. Deforming Mesh

22. Initialize all variables
Source terms of Gas Phase Equation = 0
Solve for Gas Phase Equations
Solve for Droplet Equations
Cal. Gas Phase Source Terms
Converged ? ya
Next Time Step No
Droplet Tracking Algorithm