Ignition systems

Ignition system is designed for igniting air/fuel mixture in combustion chamber of the engine. Most of the Ignition Systems consist of two main parts: LT (Low Tension) and HT (Hi Tension).
LT components: Battery, Alternator, IGN Switch, (Ballast Resistor), IGN Coil primary windings, Capacitor (Condenser) and contact braker (contacts, pulse generators)
HT components: IGN Coil Secondary winding, Distributor Cap and Rotor, HT leads, Spark plugs.


Mechanically Operated Ignition
Kettering  (points) Ignition System
 Ignition Coil is being switched with the contacts (or points). Since Coil primary winding resistance is low (around 0.8 Ohms), so LT current would be hi. Points switch this current directly and were out quickly.

Ignition Coil (or step up transformer) is made of two windings primary and secondary. primary windings is lower resistance and about few hundred windings. Secondary winding is higher resistance and consist of few thousands of windings. .

current from battery goes through IGN Switch powering up the Ignition Coil primary. As starter motor spins the engine, the distributor cam changes its position opening and closing the contacts. once contact is closed and LT circuit is complete, the coil creates the magnetic field. Distributor cam rotates more and opens the contacts. This coses magnetic field of LT collapse, sudden collapse of magnetic field in LT induces voltage in HT. then this high voltage passed to the centre of the distributor cap through the HT wire and then through rotor back to the correct contact at distributor cap, through the HT wire to spark plug electrode.

in some applications capacitor (condenser) is used to increase duration and quality of the spark. condenser is connected in parallel with contacts. so capacitor is charging when contacts are closed. when the contacts open then condenser discharging to the IGN coil, then back EMF of the coil is charging capacitor again. so it goes back and forth until it is depleted.