Timing in IC Engines

In the IC Engine, as the piston moves up and down the cylinder, many other things have to take place simultaneously.

The fuel has to be injected, the injected fuel has to be ignited and air has to be drawn in for combustion. After combustion, the products of combustion have to be expelled.

When each of these processes occurs is known as the Timing of the engine.  The Timing of the engine is denoted in degrees with reference to the TDC or BDC of the engine.

A general timing of an IC Engine is as follows.

Inlet valve opening           30 degrees before TDC
Inlet valve closure            50 degrees after BDC
Exhaust valve opening     45 degrees before BDC
Exhaust valve closure      30 degrees after TDC

Injection of the Fuel        15 degrees before TDC