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مکانیک::
گاز انتهایی
Most critical is heat transfer from the hot exhaust valve and piston to mixture in the end-gas region.
Knock in an SI engine is the spontaneous ignition of the unburned "end-gas" ahead of the flame as the flame propagates across the combustion chamber.
Knock results in increased local heat fluxes to regions of the piston, the cylinder head, and liner in contact with the end-gas.
Increases to between twice and three times the normal heat flux in the end-gas region have been measured.13,52 It is thought that the primary knock damage to the piston crown in this region is due to the combination of extremely high local pressures and higher material temperatures.
Knock occurs when the end-gas autoignites prior to its being burned up by the normal flame-propagation process.
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