In an internal combustion engine cylinder sometime sudden and violent knocks are experienced, this is known as "Detonation". This knock is set up by a high pressure wave giving loud pulsating noise as it strikes against cylinder walls, cylinder head and piston.
A mild detonation will simply heat the engine but if the detonation is severe, it may even result in fracture of the piston or other damages to the engine.Detonation also results in increased carbon deposits. If detonation continue for a long time it may overheat the cylinder and spark plug so as to ignite the Charge even before sparking and lead to pre-ignition. These are the disadvantages of detonation. A properly designed combustion chamber will reduce detonation considerably.
Following are the main factors, which affects detonation,
01) The fuel used in internal combustion engine will considerably effects on the chances of detonation. Alcohol and benzol do not cause detonation but it can not be use due its low calorific value and other objections to use as fuel. Again alcohol cannot blend with petrol in the presence of water.
02) The detonation is also promoted by increase in compression ratio. The compression ratio at which detonation just occurs is known as the Highest Useful Compression Ratio. Higher the compression ratio higher the chances of detonation and lower the output.
03) If the carbon deposits are in the cylinder and used excessive sparking temperature, the detonation will increased rapidly.
04) The position of the spark plug in a combustion chamber determines the distance the flame has to travel in order to reach the detonation zone. More the distance more the chances of detonation. A centrally placed spark plug works better. Spark plug must be placed near to exhaust valve but the exhaust must be located away from detonating zone.
05) Higher temperature of the walls of combustion chamber tends to raise the temperature combustion chamber tending to raise the temperature of Detonation zone.
06) The rate at which the combustion of the portion of the fuel, which is first to ignite immediately after the application of the spark, also affects detonation.
Hence from the above description we must know, the detonation is dangerous for internal combustion engine and must be removed or reduced.
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