1. Evolution of Spark into Flame Kernel
P M V Subbarao
Professor
Mechanical Engineering Department
Spark is External Driven Event….
Flame is a Signature left by the Spark….

2. Electrical coil ignition system to Create A Spark
The evolution of the energy being fed into Gap to Generate a spark

3. Mechanism of Spark Development
i) pre-discharge, ii) breakdown, iii) breakdown/arc transition, iv) arc, v) arc/glow transition, and vi) glow

4. Voltage and Energy distribution in Spark Gap
During arc and glow phases, only a fraction of the spark energy is released to the gas.
The energy released in a thin region near the electrodes is essentially lost by fall voltage.
The potential difference between both electrodes, also called spark voltage is written
where Vcf is the cathode fall voltage, Vaf is the anode fall voltage and Vgc is the gas column voltage

5. Voltage distribution in Spark Gap

6. The gas column voltage
The anode fall voltage is similar for the arc and glow modes and equal to V for Inconel.
The cathode fall voltage is 7.6 V during arc phase and 252 V during glow phase for Inconel.
The gas column voltage is expressed by:

7. Energy Available for Gas Column
At breakdown, about 60% of the breakdown energy is released to the gas, providing the ignition energy Eign .
This is a function of the spark gap and of the breakdown voltage.
 During the glow phase, the voltage fall is localised in the vicinity of the electrodes.
Therefore it is assumed that the energy released within these regions is lost to the electrodes.
Finally, the energy transferred to the gas is deduced from the gas column voltage and the intensity following:
This energy Eign is used to determine if ignition is successful or not!!!!!

8. Evolution of Baby Spark into Baby Flame (Flamelet)

9. Conditions for Survival of Baby Flame
It is considered that a flame kernel can be formed around the spark, and ignition starts only if Eign(t) is greater than Ecritical (t).
Critical ignition energy depending on local thermodynamic properties in the vicinity of the spark.
In that case, an amount of burnt gas mass is deposited at the spark, which corresponds to a cylinder of radius 2L and length lspk.
L is known as the thickness of Baby flame.
The burnt mass generated by a successful spark is:

10. Geometrical Features of Electrodes
One curve corresponds to a series of experiments in which the electrode terminals were tipped with stainless steel spheres of 1.5 mm diameter.
In the other series, the electrodes were similarly tipped and in addition were flanged by glass plates.

11. The Minimum Spark Ignition Energy

12. Effect of velocity on energy to be supplied by Secondary Coil
Remark: when the mixture is moving ignition is more difficult
Energy Supplied by Coil, ES, mJ
Geometrical Model for Kernel due to spark ignition in flow.

13. Control of Turbulence Level for Efficient Ignition
Energy Supplied by Coil, ES, mJ

14. The Efficiency of Coil

15. The effect of the spark plug gap on the brake specific fuel consumption

16. The effect of spark energy on the brake specific fuel consumption

17. Other Ignition systems
Ignition By An Electrically Heated Wire
Ignition By Flame or Hot Jet
Plasma Jet Ignition
Photochemical Ignition
Microwave Ignition
Laser Ignition
Puff-jet Ignition

18. Laser Ignition
The importance of the spark time scale on the flame kernel size is well recognized.
A laser ignition source has the potential of improving engine combustion with respect to conventional spark plugs.
A laser based ignition source, i.e. replacing the spark plug by the focused beam of a pulsed laser.
Laser ignition, or laser-induced ignition, is the process of starting combustion by the stimulus of a laser light source.
It was tried to control autoignition by a laser light source.
The time scale of a laser-induced spark is by several orders of magnitude smaller than the time scales of turbulence and chemical kinetics.

19. The Concept of Laser Ignition

20. Arrangement and Control of Ingition Region

21. Phases in Laser Ignition
The different phases of laser ignition can be defined in chronological order
Electric breakdown and energy transfer from laser to plasma
Shock-wave generation and propagation
Gasdynamic effects
Chemical induction of branching chain reactions of radicals leading to ignition
Turbulent flame initiation

22. Time Scales in Laser Ignition

23. Selection of Wave Length

24. Effectiveness of Laser Ignition

25. Control of Ignition Region

26. Impact of Modern Methods on Engine Cycle