Knock is a metallic clattering noise in internal combustion engines under stress. It is the result of a collision between the advancing flame front of gasoline ignited by the spark plugs in the cylinder and the flame front of a spontaneous explosion of gasoline from the opposite side of the cylinder caused by compression from the rising cylinder head.
Anti – knock Compound ( AKC) act as a catalyst which suppresses secondary spontaneous explosions in the cylinder of internal combustion engines. The result is that a single flame front from the spark plugs sweeps unopposed across the cylinder head. The absence of two explosions means that there is no “knock” or loss of power.
Tetra Ethyl lead (TEL) was investigated as an anti-knock by Thomas Midgely of Cornell University ca 1920. The first public sales of gasoline containing anti-knock were made in Dayton Ohio in Feb 1923.
Anti-knock Compound consists of an organic lead compound –Tetra Ethyl lead and a scavenger. The lead compound suppresses the knock and acts as an octane enhancer. In order to prevent the deposits of lead oxide, which were formed in this process, from building up on the spark plugs and valve surfaces it was found necessary to convert the oxide to a more volatile substance.
This substance had to be volatile at engine temperatures in order to be discharged with the exhaust gases.Chloride and Bromide salts suggested themselves with the result that organic scavengers,such as Ethylene dibromide (EDB) and came into use.
The original purpose of building Octel Amlwch was to extract bromine from sea water to be used to produce EDB to go into TEL as an AntiKnock compound for leaded petrol.