Detonation: An uncontrolled explosion of the unburnt air-fuel mixture in the engine cylinder occurring after the regular combustion of some of the charge caused by the spark at the spark-plug. It becomes audible through vibration of the combustion chamber walls.

De NOx catalyst: A catalyst which, unlike a conventional catalyst used in a three-way catalytic converter is able to remove NOx from the exhaust gases even in the presence of oxygen.

Deep cycling: The process of discharging a battery almost completely before recharging.

Dead centre: The extreme top or bottom of the piston stroke.

Darlington pair: Two transistors wired together are called the Darlington pair, which allows a very small current to control large current.

Cylinder head: The detachable portion of the engine, usually fastened to the top of the cylinder block and containing all or most of the combustion chambers. On overhead valve engines, it contains the valves and their operating parts. On overhead camshaft engines, it contains the camshaft as well.

Cylinder block: The basic engine casting containing the cylinders, coolant jackets, crankshaft main bearings as well as machined surfaces for mounting other components such as the cylinder head, oil pan, transmission, etc.

Cylinder: A circular tubular opening in the cylinder block in which the piston moves in a reciprocating manner.

Cubic capacity: It is the sum of the displacement of all the engine cylinders.

Crankshaft pulley: A pulley attached to the front end of the crankshaft, which drives the fan, the alternator and other devices by means of a fan belt.

Crankshaft position sensor: A sensor ring with lobes, which sends information related to the exact position of the crankshaft so as to achieve accurate ignition/injection timing.

Crankshaft counter-balances: A series of weights attached to or forged integrally with the crankshaft placed in such a manner as to offset the reciprocating weight of each piston-connecting rod assembly.

Crankshaft: The main engine shaft from which power is taken. It converts the reciprocating motion of the engine pistons into rotary motion for automobile use.

Crankcase: The lower part of an engine in which the crankshaft and related parts operate.

Coolant-controlled EGR: A system which prevents exhaust gas recirculation until engine coolant temperature reaches a specific value.