detonation,squish,cetane number,octane number

• Detonation in S I Engines It is due to auto-ignition of the fuel before the spark actually occurs.

• Squish:-As the piston approaches the TDC at the end of compression stroke, the volume around the outer edges of the combustion chamber is suddenly reduced to a very small value. Many modern combustion chamber designs have moSt of the clearance volume near the centre line of the cylinder.’ As the piston approaches the TDC the gas mixture occupying the volume at the outer radius of the cylinder is forced radially inward as this outer volume is reduced to near zero. This radial inward motion of the gas mixture of gas mixture is called “squish”. This helps in quickly spreading the flamç front.

• Cetane Number : of a fuel is defined as the percentage by volume of Cetane in a mixture ol’ Cetane and a-methyl naphthalene that produces the same ignition lag as the fuel being tested, in the same engine and under the same operating conditions. This is used filter diesel to express its ignition quality.

• Octane Number : is the percentage of iso-octane by volume in a mixture of isp.-. octane and n-hepane. which exactly matches the knocking intensity of a given fuel, in a standard Jgihc under given standard operating conditions. ignition quality of petrol is expressed by octane number. A fuel having octane number more than 100 is superior for less knocking tendency. The addition of various amounts of tetraethyl lead (TEL) to iso-octane produces fuels of greater antiknock quality than iso-octane alone. This is called doping.