expansion of fuel/air mixture

[Greg Hermann]

At 4:35 PM 2/21/02, Camden Lindsay wrote:
>I was (probably inaccuratley) trying to figure in-cylinder pressure at full
>throttle bottom dead center (beginning of exhaust stroke), thinking about
>how cams are designed in terms of open/close ramp, time and such.  Is there
>any fairly accurate way to approximate this, depending on engine swept
>volume, compression ratio, volumetric efficiency and fuel ratio?
>thanks again
>camden

Yep, there is a reasonably accurate way, but it's not a short way !

You need to calculate your way around the cycle, and figure out what you
have left at BDC . To ballpark it, with an NA engine, at sea level, and at
WOT, the number will likely be somewhere between 50 and 90 psia (ABSOLUTE)
at (or near) BDC when the exhaust valve opens.

Greg

>
>
>
>
>
>>Better define what you are talking about better.
>
>
>>
>>For instance, at ignition, there is (ideally) no expansion beccause the
>>combustion chamber doesn't allow it--so there is a rise in temperature and
>>a consequent rise in pressure. The rise in temp is determined by the heat
>>of combustion available and the mass and specific heat of the gas present.
>>The rise in pressure is then determined by the gas law.
>>
>>Greg
>>
>
>
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