Engine Ignition System

1/4 inch spark plug

When we talk about the engine ignition system there are two fundamental types:

  1. compression ignition
  2. spark ignition.

This is the system for igniting an fuel-air mixture that has been compressed in the cylinder by the motion of the piston.

Compression Ignition

Ignition of a fuel charge by the heat of the air in a cylinder, generated by compression of the air, as in the diesel engine.

The rapid compression of air within the cylinders generates the heat required to ignite the fuel as it is injected.

Advantages over Spark Ignition:

  • Low specific fuel consumption at both full load and part load conditions.
  • Utilizes less expensive fuels.
  • Reduced fire hazard.
  • Long operating life.
  • Better suited for supercharging.
  • Better suited for two-stroke cycle operating, as there is no loss of fuel in scavenging.

The two-stroke Compression Ignition engine does not suffer from the disadvantages of the spark ignition engine which are fuel loss and idling difficulty and hence CI engine is more suitable for two-stroke operation.

High Tension Leads – High voltage wire from the ignition coil. May also indicate the secondary wire from the ignition coil to the distributor and wires from the distributor to the spark plugs.

Low Tension Leads – The wiring in the ignition system that is distinguished from the high tension wiring. The low tension leads carry only 6 or 12 volts.

Spark Ignition Engine

An engine whereby the fuel air mixture is compressed in the cylinder and then ignited with an electric spark.

Advantages over Compression Ignition:

  • Low initial cost.
  • Low weight for a given power output.
  • Smaller size for a given power output.
  • Easy starting.
  • Less noise.
  • Less objectionable exhaust gas odour and less smoke.

The two-stroke spark ignition engine suffers from two big disadvantages-fuel loss and idling difficulty.

Spark Plug – Electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark.


  1. “Theory and Design of Automotive Engines”, B Dinesh Prabhu, Assistant Professor, P E S College of Engineering, Mandya, KARNATAKA
About Nigel 308 Articles
Have been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

Be the first to comment

Leave a Reply

Your email address will not be published.