BMW 2002 FAQ

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[quote="Reggie"]Some science is the result of necessity and some due to serendipity.  While the odds favor Nobel prize winners and those schooled in the subject, that is not always the case.  Smokey Yunick proved that "seat-of-the-pants" science is not always a junk.

I do not know much about combustion chamber design or laminar flow.  Nor do I have any experience with German WWII piston driven aircraft other than having seen them.  I do recall having seen some dimpled chambers in outboard motor cylinder heads at a machine shop.  The "dimples" were very small and angular - not hemispherical.  The dimples resembled "[i]knurling[/i]" marks.  Other than having seen them, I have no information about them.

Evidently, the concept of "golfing combustion chambers" is neither new nor particularly novel:

http://en.wikipedia.org/wiki/Cylinder_head_porting[i]

"It is popularly held that enlarging the ports to the maximum possible size and applying a mirror finish is what porting is. However that is not so. Some ports may be enlarged to their maximum possible size (in keeping with the highest level of aerodynamic efficiency) but those engines are highly developed very high speed units where the actual size of the ports has become a restriction. Often the size of the port is reduced to increase power. A mirror finish of the port does not provide the increase that intuition would suggest. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the 1. boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow but an optical finish is wasted effort and money.
The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO (see boundary layer and laminar flow). This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past which develops a velocity profile (or gradient) across the duct. In order for surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center. Only a very rough surface does this."[/i][/quote]

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