Abrasive flow finishing

[r_tech at earthlink.net]

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I read in an article on the net (or was it a magazine)somewhere about =
the surface texture of ports in a cylinder head. It was something about =
the benefits of porting. What they mentioned was that the exhaust side =
would benefit most from having a smooth finish vs the intake.  One =
reason mentioned for leaving the intake side unpolished is to help the =
turbulance effect which serves to homogenize the fuel mixture for more =
thorough combustion and thus better power. If I find the article again I =
will post the address here so that who ever is interested may read it =
too.

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From: 	Dan
Sent: 	Wednesday, December 17, 1997 12:35 PM
To: 	diy_efi at efi332.eng.ohio-state.edu
Subject: 	Re: Abrasive flow finishing

I read an article recently in Design News concerning skin
friction drag reductions.  They quote another article in
Nature where skin friction drag was reduced by 13% on
aerodynamic surfaces by adding random small bumps to=20
the surface (vs a smooth surface).  Design News was considering
the fuel reduction costs possible for typical commercial aircraft.
A 13% skin friction drag equates to about a 6.5% overall
drag reduction.  Big numbers when a 1% drag reduction saves
a typical commercial aircraft about $100,000 annually in fuel
costs.

The idea is similar to the dimples used on golf balls which
enable the golf balls to fly farther than undimpled
balls.  I wonder what this might mean for engine intakes and
exhausts?  Maybe an extrude honing type smooth surface is
not the ideal surface even when injectors are near the valves.

The dimples have to be in a random pattern, else you increase
drag.  The theory is that random dimples (or chevrons) reduce
bursting near an aerodynamic surface.  Busting is caused by
low speed air streaks near the wall and is believed to be
responsible for creating intense turbulence.

Comments?

Dan L


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