Engine knock cause

In the past, tetraethyl lead was added to gasoline to slow its burning rate in order to prevent engine knock and increase performance. This caused serious and harmful pollution, and lead has since been eliminated as a gasoline additive in most countries. Most exterior (and some interior) house paints once contained high levels of lead as well. Today, the amount of lead in paint is controlled, with not more than 0.05% allowed in the paint material. 

What is engine knock What causes the engine knock problem ... 

In some circumstances, the octane number of the gasoline used in the engine must be increased to prevent knock caused by accumulated deposits. This phenomenon is called Octane Requirement Increase (ORI). Both prevention and reversal of ORI are difficult to achieve. 

The octane number (rating) of a gasoline indicates how smoothly it burns and how much engine knock it produces. (Engine knock is caused by premamre detonation of fuel in the combustion chamber.) 2,2,4-trimethylpentane, isooctane, has excellent combustion properties and was arbitrarily assigned an octane number of 100. Heptane, CH3(CH2)5CH3, has very poor combustion properties and was assigned an octane number of zero. 

The more compact the hydrocarbon molecule, the less likely it is to cause spontaneous combustion and engine knock. Consequently, it is desired to isomeri e straight-chain hydrocarbon molecules into more compact molecules through a catalytic process called reforming. 

I knocking is the premature j spontaneous explosion of the petrol mixture during the com-I pression stroke in a petrol en-I ginc before the mixture is ig-j nited by a spark. Knocking causes significant loss of power I and may result in damage to i the engine. 

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