Ancient History

RABBITT_Andrew at mv8.orbeng.com.au RABBITT_Andrew at mv8.orbeng.com.au
Fri Sep 6 03:17:48 GMT 1996


>cylinder contains free oxygen and free hydrocarbon radicals and the
>whole lot reacts at once.  Bad news , knock , damage etc. 

Not exactly true.  Combustion pressure, temperature and radiation are 
required to initiate knock, which is where areas in the combustion 
chamber auto-ignite causing several flame fronts to develop 
uncontrolled.

>What is wanted is not the fastest burn possible but a good
>start and prolonged long enough to finish some way down the power
>stroke. 

In theory, you want as fast a burn-rate as possible (to minimise 
BSFC), however the pressure rise rate will limit this.  High pressure 
rise rates will excite the block, head etc at various natural 
frequencies, increasing the engine noise.  (Diesel engines are the 
extreme of this)

> ....quickly igniting the droplets as it goes.  They continue to burn 
>and any droplets too big will be exhausted without having provided 
>all the power they could have done.

Large fuel droplets cause soot formation.






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