Date:         Fri, 21 Jun 1996 23:26:51 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Arnold Schultz <aschultz@smartt.com>
Subject:      Re: Cooling Intake Air?

My $.02
        When a turbo charger is compressing the air the temperature rises
sharply. In the combustion chamber prior to ignition you would like to have
lots of dense cool air and low pressure, in such that the power is derived
from the increase in pressure due to the increase in temperature when the
ignition or burn happens... so to let high temp air into the combustion
chamber would decrease power, also if the temps are to high going in you can
have preignition just from the rise in temp during the compression stroke.
The intercooler is to keep the intake air from getting to high in temp, in
such keeping the intake air as dense or cool as possible to maximize the power.
        As for the "freezing of the carburetor" ALL carburetors have this
problem. It is all because of some guy by the name of "Burnilli", He stated
that as the velocity of air increases temp and press decrease. SO... in your
carburetor at the venturi or by the main jets you get a decreases in
pressure and that lets the fuel get sucked(pushed for you physics types)
into the air stream. But the temp gets lower as well and if the OAT (outside
air temp) is low and the humidity is high then it may be possible that the
air temp at the venturi goes below freezing and allowes the water in the air
as it passes the supper cooled metal parts to cling and build up on them to
a point that the engine gets choked off. As in Aircraft most all cars have a
carburetor heat system, the older ones were quite simple... the air came
from around the exhaust manifold. Note: if the OAT is already below freezing
you should not use carb heat as this will bring the intake air temp above
freezing just to freeze in the carb again.
        Turbo or super chargers in aircraft are there mainly to compensate
for the decrease in power due to the decrease in air density at altitude. So
that the engine has the same engine inlet pressure as it did at sealevel.


 
>Seems to me the warmer the incoming air, the less dense it is, hence
>would have less oxygen per unit volume....  I cannot see how this would
>help.  Sounds like it would hurt things more.  BTW, as I understand it,
>this is what the "intercooler" in the intercooled turbo-charging
>units do -- cool the air being pumped into the cylinders.
>
>About the only place cool air into the cylinders is bad is airplanes --
>freezes the carburator too, I heard...
>
>Cooling the incoming air sounds like a good idea, at least in theory.
>whether one can actually cool it enough to make a difference and not hurt
>the air flow _around_ the engine is questionable...
>
>Cetin
>
>
>At 10:54 AM 6/21/96 -0500, you wrote:
>>I would actually think that this would both not help the heat situation and
>>make your motor run worse, not better.  By the former I mean that
>>difference it might make will be minimal.  By the latter I mean that warmer
>>air tends to absorb aersolized gasoline (such as that coming out of your
>>injectors or down in your carb) much more rapidly, efficiently and
>>completely, thus giving a more combustible air/fuel mix.
>>
>>Of course, this is just slightly informed speculation on my part...
>>
>>Eric
>>
>>
>>
>>
>Cetin Seren				Direct:	412-635-3479
>Software Development Engineer         	Main:	412-772-6600
>Outbound Technology Group		fax:	412-635-3350
>FORE Systems, Inc.			email:  cseren@fore.com	
>Research Park, 5800 Corporate Drive	URL:	http://www.fore.com
>Pittsburgh, PA 15237-5829		
>
>