1. Analysis of Ignition Systems
P M V Subbarao
Professor
Mechanical Engineering Department
Micro-Engineering of Extreme Natural Events….

2. The Extreme Art of Miniaturization
The average lightning bolt measures about an inch wide and five miles long.
The temperature of lightning can reach around 30,000 K.
The electricity in a single bolt can reach 200 million volts.
An average duration of time for a stroke of lightning is about 30 microseconds.
The average peak power of a stroke of lightning is about 1012 watts.
A single bolt of lightning carries an energy 5 billion joules.
Spark plugs in automobiles generally have a gap between 0.6 and 1.8 mm

3. Spark Plug

4. Physics of Sparking
In 1889, F. Pashchen published a paper which set out what has become known as Paschen's Law.
The law essentially states that, at higher pressures (above a few torr) the breakdown characteristics of a gap are a function (generally not linear) of the product of the gas pressure and the gap length.
Usually written as V= f( pd ), where p is the pressure and d is the gap distance.
Extensive additional experiments for different materials, lower pressures, different gases and a variety of electrode shapes have expanded the data set involved.

5. Paschen Curve
Paschen found that breakdown voltage was described by the equation
Pd (Pa-m)
Where V is the breakdown voltage, p is the pressure, d is the gap distance.
The constants a and b depend upon the composition of the gas.
For air at standard atmospheric pressure of 101 kPa, a = 43.6×106 V/(atm·m) and b = 12.8.
What is signature of an Ignition System ?

6. Measurement of Minimum Ignition Energy

7. Ignition energy in air at 1 atm, 20C
Fuel E’ (10-5J)
Methane 33
Ethane 42
Propane 40
n-Hexane 95
Iso-Octane 29
Acetylene 3
Hydrogen 2
Methanol 21

8. Theoretical & Practical Minimum Spark Energy
The minimum ignition energy is a measure of required energy for a localised ignition source to successfully create a temperature higher than SIT.
The practical minimum energy required to ignite an air-fuel mixture is much higher.
Effect of Various Parameters on MIE:
Distance Between Electrodes
Fuel
Equivalence Ratio
Initial Temperature
Air Movement

9. Duty of An Ignition System
The purpose of a spark ignition system is to provide enough energy into a small gas volume, in the vicinity of the electrode gap.
Energy provided by SIS must ensure a successful initiation of the combustion process.
This energy is initially stored as electrical energy in the ignition system and is converted into thermal energy when released into the spark gap.

10. Simplified electrical scheme of a coil ignition system
The evolution of the electrical energy of the secondary circuit
The energy is not entirely transferred to the spark: a substantial part is lost by Joule effect.

11. Mechanism of Spark Creation
ii) breakdown
i) pre-discharge
15kV
(1mJ)
50V

12. Mechanism of Spark Development
iv) arc
15kV
(1mJ)
50V
(1mJ)

13. Mechanism of Spark Development
v) arc/glow transition
iv) arc
50V
(1mJ)
500V
(30mJ)
15kV
(1mJ)
vi) glow

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