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Automotive / Buying and Maintaining a Car


Subject:  Re: Fun at the Auto Show Date:  1/29/2004  9:23 PM
Author:  duke345432 Number:  31094 of 74070

Hemispherical combustion chambers had been used in radial aircraft engines for decades before Chrysler designed an automotive engine that used them.

Ideally, the combustion process would burn all of the fuel-air mixture instantaneously throughout the combustion volume so as to minimize combustion pressure loss due to heat transfer into the cylinder head, piston, and cylinder. This is never achieved in practice, so some efficiency is lost.


first part is correct, with the additional comment that the aircraft system usually used four valves, and many had sodium filled exhaust valves. Almost all had inserts for valve seats.

If all the fuel burned as you say, the crown of the piston would last minutes. Detonation is killer in any engine. Like a small bomb going off. Octane is a measure how slowly the fuel burns to prevent this event.

In a diesel engine it is desired to have the fuel burn fast in the 1000 degree compressed air. Note that as the fuel is injected it lights off. As more fuel enters the pressure remains high, the piston moves increasing the volume. Pressure at mid stroke generates the maximum torque. Before the piston reaches this position all the fuel is in the cylinder. Except for tractor pulls and the like. Then the pump in oil much longer. That is why they belch black soot and flames. That is another game.
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