Basics of Automobile Ignition System | Engineering UPdates

An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture in spark ignition internal combustion engine oil-fired and gas-fired boilers, rocket engines, etc. The widest application for spark ignition internal combustion engines is in petrol (gasoline) road vehicles: cars (autos), four-by-fours (SUVs), motorcycles, pickups, vans, trucks, and buses.

Compression ignition Diesel engines ignite the fuel-air mixture by the heat of compression and do not need a spark. They usually have glow plugs that preheat the combustion chamber to allow starting in cold weather. Other engines may use a flame, or a heated tube, for ignition. While this was common for very early engines it is now rare.

The first electric spark ignition was probably Alessandro Volta's toy electric pistol from the 1780's. So, let's see, how basic magneto ignition system works.

How it Works ?

- When the Ignition switch is turned on, current flows from to the Ignition coil. Current flows through the primary winding of the ignition coil where one end is connected to the contact breaker.

- A cam which is connected directly to the camshaft opens and closes the contact breaker points according to the number of engine cylinders.

- A condenser absorbs the back EMF from the magnetic field, thereby increasing the life of contact points by reducing burning of the points. When the cam lobe pushes CB switch, the contact breaker points opens, which causes the current from primary circuit to break.

- Due to break in current, an EMF is induced in the secondary winding having more number of turns than primary, which increases the battery's 12 volts to 22,000 volts.

- The high voltage produced by the secondary winding is then transferred to the distributor.

- A rotor inside the distributor rotate according to the ignition timing. When the rotor comes exactly in front of the distributor point, the voltage jumps due to the air gap from the rotor to the point.

- High voltage is then transferred from the distributor to the spark plug terminal via a high tension cable. A voltage difference is generated between the central electrode and ground electrode.

- The voltage continues to transfer through the central electrode which is sealed using insulator.

- When the voltage exceeds the dielectric strength of the gases between these electrodes, the gases are ionized. Due to ionization, gas becomes a conductor and allow the current to flow through the gap and spark is finally produced.