1. Basic Principles for Design of Ignition Systems
P M V Subbarao
Professor
Mechanical Engineering Department
Design of Micro-Sparking Systems….

2. Mechanism of Spark Development
ii) breakdown
i) pre-discharge
III arc transition
v) arc/glow transition
iv) arc
vi) glow
500V
(30mJ)
50V
(1mJ)
15kV
(1mJ)

3. Evolution of Gap Current

4. Reaction Vs Action

5. Thermal Arc (Plasma)
Thermal Arc is a type of plasma that has a exceptionally high temperature.
In general temperature of this arc zone is several thousand degrees ~35000K.
This plasma is characterized by a condition of thermal equilibrium between all the different species contained in the gas.
Sufficiently higher values of gas density generates a sub-atomic level Resonance.
This resonance leads to the frequency of collisions between electrons, ions, and neutral species composing the plasma.
This frequency leads to an efficient energy exchange.

6. 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 voltage drop due to contact resistance.
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

7. Voltage distribution in Spark Gap

8. 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:

9. 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!!!!!

10. Energy Available for Gas :Growth of Spark
At breakdown, the spark length is equal to the spark gap and then, the spark is stretched by convection and by the turbulent motion of the flow .

11. Energy Responsible for Ignition

12. Size of Spark between thin cylindrical electrodes : Quiescent fuel-air Mixture

13. Size of Spark between thin conical electrodes : Quiescent fuel-air Mixture

14. Actual Length of spark In Engine Cylinder
The spark is stretched by convection :
The spark is also stretched by turbulence in the gap :
The spark wrinkling evolution equation
where Kspk,T and Kspk,M are the spark strain by the turbulent and by the mean flow respectively

15. Model for Spark Diameter
At a very early stage (1 to 10 ns), a cylindrical channel of about 40 m in diameter develops together with a pressure jump and a rapid temperature rise.
Pressure and temperature of hot plasma at this early stage may be estimated by constant volume addition of breakdown energy Ebd .
The high local pressure generated leads occurrence of normal shock wave.
As the ratio of temperature of ambient temperature to plasma temperature is very low, the diameter of the spark is estimated as:

16. Volume of the Spark
Considering the spark as a cylindrical channel of length lspark, the channel radius is:
In the spark discharge studies it is found that inside spark Tspark = 35,000 K for a gas with 300 K & and 0.1 MPa.
Every fuel injection system must ensure these conditions are sustained after breakdown of spark for successful ignition.

17. 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.

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

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

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

21. 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

22. 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.

23. The Concept of Laser Ignition

24. Arrangement and Control of Ingition Region

25. 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

26. Time Scales in Laser Ignition

27. Selection of Wave Length

28. Effectiveness of Laser Ignition

29. Control of Ignition Region

30. Impact of Modern Methods on Engine Cycle