Various standard terminologies and abbreviations are being used while understanding and elaborating the engine concepts.

Internal Combustion (IC)

The engines where combustion takes place in side the cylinder, they are known as Internal Combustion (IC) engines. Majority of the engines being used for various applications are IC engines only. Although in early stages of engine developments, pre combustion chambers were also being used to inject the pre ignited charge (air fuel mixture) into the cylinder.

Spark Ignition (SI): 

When a beam of external spark with the help of spark plug is used to initiate the combustion process in each cycle, it is known as spark ignition (SI). (c) Compression Ignition(CI): When in an engine, the combustion process starts with the self ignition of air fuel mixture due to high temperature in the combustion chamber caused by the high compression, it is known as CI engines. Diesel engines particularly are the CI engines.

Top-Dead-Center (TDC): 

During the reciprocating motion of piston in the cylinder, position of the piston when is at the furthest point away from the crankshaft, it is known as the TDC. In some engines top-dead-center is not at the top of the engine (e.g., horizontally opposed engines, radia l engines, etc.,), some sources call this position Head-End-Dead-Center (HEDC). Some sources call this position Top-Center (TC). When the piston is atTDC, the volume in the cylinder is a minimum called the clearance volume.

Bottom-Dead-Center (BDC): 

Same way, during the reciprocating motion, position of the piston when it stops at the point closest to the crankshaft refers to as BDC. Some sources call this Crank-End-Dead-Center(CEDC) because it is not always at the bottom of the engine. Some sources call this point Bottom Center (BC).

Direct Injection (DI): 

When fuel is injected directly into the main combustion chamber of an engine, it is known as DI engines.

Indirect injection (IDI): 

Rather than fuel injected directly into the combustion chamber or cylinder, the fuel is injected into the pre-combustion chamber of an engine for partial its burning.