1. Design rules to generate Turbulent Flame Speeds in SI Engines
P M V Subbarao
Professor
Mechanical Engineering Department
The Major Controller of Engine Speed & Torque…..

2. Clues to Develop a Healthy Turbulent Flow in An Engine Cylinder
Eddy turnover time:
Characteristic Chemical Reaction Time:
The ratio of the characteristic eddy time to the laminar burning
time is called the Damkohler Number Da.

3. Identification of A Control (Dimensionless) Parameter for Span
Turbulent Reynolds Number:
Important controlling dimensionless parameter:
Computational Methods will help in simulation of turbulent flames with various combinations of Da & ReT

4. Regimes of Turbulent Flame
108
Weak Turbulence
Reaction Sheets Da 1
Cyclonic Turbulence
Flamelets in Eddies
Distributed Reactions
10-4
108
ReT

5. Regime of Fast SI Engine’s Turbulent Combustion

6. Mechanism of Turbulent Combustion in SI Engines
Values of Da and Re for a typical SI-engine lie predominantly in the reaction sheet flame region
The size of an energetic eddy must have a turnover time equal to the time needed to diffuse unbrunt mixture into and burnt mixture out of flame zone.
During its turnover time an eddy of size L will interact with the advancing flame front.
This will be able to transport preheated fluid from a region of thickness in front of the reaction zone over a distance corresponding to its own size.

7. Model of the turbulent flame speed, ST
Turbulence Intensity ST

8. Effect of Equivalence Ration on Laminar Burning Velocity
Sflamelet,Lp,m/s
Methane

9. Methane

10. Engine Geometry to Control Turbulent Flow

11. Types of Intake Flows
There are two types of structural turbulence that are recognizable in an engine; tumbling and swirl.
Both are created during the intake stroke.
Tumble is defined as the in-cylinder flow that is rotating around an axis perpendicular with the cylinder axis.
Swirl is defined as the charge that rotates concentrically about the axis of the cylinder.

12. Tumble Motion
For most of the modern SI engines, tumble flows are more crucial than the swirl flows.
Tumble flow generates proper mixing of air and fuel, and for high flame propagation rate.
Also a well defined (single vortex) tumbling flow structure is more stable.
TR is defined as the ratio of the mean angular velocity of the vortices on the target plane to the average angular velocity of the crank.
The negative or positive magnitudes of TR indicate the direction of the overall in-cylinder tumble flow in a given plane as CW or CCW respectively.

13. Pentroof Pistons

14. Variation of tumble ratio with crank angle positions

15. Tumble in Double Ports

16. Generation of Swirl during Induction
Deflector Wall Port
Shallow-Ramp Helical Port
Directed port
Steep-Ramp Helical Port

17. Measures of Swirl
Two different values are calculated to assess the swirl intensity.
Swirl number or swirl coefficient and swirl component or swirl number.
The first, the swirl number, is the ratio of angular momentum to the axial momentum:
This angular momentum is calculated in the centre of the swirl (not on the cylinder axis).
The other is herein called the “swirl component” and is the swirl parameter relevant for experimental tests with a paddle wheel placed in the axis of the cylinder:

18. Selection of Valve Lift & Valve Geometry
Plain Directed
Shallow Ramp Helical
Steep Ramp Helical

19. Swirl Generation through Valve Seat

20. Valve Geometry Vs Turbulence

21. Control of Turbulence Level

22. Turbulence Level versus engine speed

23. Integral Scale Vs Speed

24. Engineering Correlations for Turbulent Burning Velocity
Groff and Matekunas obtained a relation that takes into account the effect of spark timing on the flame speed ratio.
They obtained the following relation for flame speed ratio
ST/SL = (u´/SL)(p/pm)0.82s
Where p is the pressure, kPa
pm is the corresponding motoring pressure, kPa
s is the spark advance factor given by
s =  0.4
where  is the spark advance, crank angle degrees before top dead centre.

25. Symptoms of Normal Combustion in SI Engines

26. Cyclic Variation of Flame Volume

27. Unexpected Engine Damage
Damage to the engine is caused by a combination of high temperature and
high pressure.
Piston
Piston crown
Cylinder head gasket
Aluminum cylinder head

28. Dangerous Accidents