Crank windage

[fordboy628]

FB, I agree with you

Take a look at the piston, very short skirt which you would think might not guide the piston through rock-over too well.
It would appear that there is a running surface? above the rings?    Yes, it looks like the upper ring land was "touching" the cylinder wall.   My experience is that this is OK as long as the cylinder wall surface is not "compromised" for ring sealing.   It is a simple concept, difficult to "perfect".    A different way to consider piston skirt length is to calculate the piston skirt area, (perhaps including top land area?), as a percentage of the "bore bearing area", (piston bearing area * the stroke length).    The immediate possibility is that very short stroke lengths would allow very short piston skirt lengths (bearing areas) while still providing adequate stabilization, and reduced drag.    I see LOTS of development time here.
Not what I call conventional, but it works.

Cheers, J

J,

What else I noticed in the photo:

A/    "Only" 2 rings for reduced drag
B/    rings are very narrow, maybe .5mm compression, 1mm oil control?   Probably very low radial tension as well.
C/    Notice that the oil control drillings in the piston skirt, are partially below the ring groove.   This enhances pressure differential driven oil control.
D/    "inboard" pin bosses, shorten pin length and therefore weight.
E/    Vertical stiffening ribs between piston skirt and the bottom of the ring lands.
F/    Titanium (?) con-rod.
G/    Con-rod bolts appear large for the big end diameter.   A dead giveaway that the assembly is turning huge rpm's, as larger fasteners are required to resist the loads at
        very high rpm's.
H/     Even though the con-rod is Ti, LOTS of strategic machining to reduce the mass of the con-rod.
I/      Based on the strategic machining, it doesn't appear that they are too concerned about "streamlining" the rod shape to reduce "rotational windage".   These engines
        undoubtably have very high negative pressures inside the engines.
 
F/B

[Rex Schimmer]

Is cavitation in the feed side oil pump a problem on wet sump engines with a lot of crankcase vacuum?  It seems cavitation might happen before the desired oil pressure is obtained. 

If you're pulling a vacuum on a sealed wet sump motor, the oil pump is pumping from a lower pressure to the same lower pressure at the bearings.  I can't see how it knows any difference.  Relative pump pressure should remain the same.   Your gauge will read lower because it will be comparing the lower absolute pump pressure to outside ambient pressure.  For example, if your pump will pump 60psi normally, and now you're pulling a negative 5psi on your crankcase, your pump will be pumping from -5 psi, but since the entire crankcase is at -5psi, it will just put out 55psi gauge (still a difference of 60psi). Shouldn't be a problem.  Dry sump may be a different situation because you have a separate scavenge pump which, if pumping into an external tank vented to the atmosphere, will have to overcome the vacuum to return the oil to the tank, at least on motorcycle systems. 

The challenge that the oil pump has when pumping from a reservoir (oil pan)  is that there is only 14.7 psi available in the very best of cases plus any possible additional pressure that may be created by having the pump below the highest level of the oil and in most wet sump engines the pump is located above the oil level so there is nothing but the internal pressure in the engine case to make the oil go to the pump inlet. So with this 14.7 psi you have to over come the resistance through any kind of inlet strainer, flow resistance from the tubing that takes the oil from the inlet in the pan up to the pump inlet and also pressure to actually raise the oil to the pump inlet. Now if you very carefully measured what these pressure drops were they would be pretty small but you only have the, at best, 14.7 psi to over come them and then you need enough pressure remaining to actually get the oil into the open chamber that is made by the rotating teeth of a gear pump, of vanes of a vane pump or pistons of a piston pump. And you have to fill this volume fast enough so that the pressure (negative pressure in this case, vacuum) does not get so high that it draws the entrapped and dissolved air that is in the oil to "pop" out of the oil in the form of a bubble that will have to be recompressed along with the oil. That "pop" that you hear is cavitation and it can and will destroy pumps. Gear pumps are pretty resilient to cavitation, vane and pistons pumps can be destroyed in seconds from cavitation. So if you reduce case pressure you can certainly cause the oil pump to cavitate. Pumps are great at making pressure, fracking pump can pump a 50/50 mixture of water and sand to 15,000 psi, but they don't suck for $hit.

Rex 

[Jack Gifford]

Just a reminder that the goal of this experiment doesn't concern the making of power- rather, it is to attain better oil control, mainly less aeration. This particular engine (DOHC) will have the potential for much improvement in this regard, compared with the V8 I ran (pushrod), due to keeping all of the top-end oil drainback away from the crankcase (a separately scavenged chamber will collect all top-end drainback oil- cam bearings, followers, etc). The only "free" oil in the crankcase proper will be that which emanates from the rod/main bearings. Therefore, this is the perfect opportunity to also evaluate reducing the aeration created by the counterweights.

Hmm... I wonder if, a few years from now, I'll be trying to study how much aeration originates in the top end- cam followers, valve springs, etc....

[fordboy628]

Jack,

A separated (and sealed from the crankcase) "cam box/head area" is definitely the way to go, IMHO.   Oil that doesn't return to the crankcase can't rain down on the spinning crank assembly.   You will need a separate, appropriately sized, scavenge stage for this area, and a collection area for the oil.    A coarse screen in the "collection area" prevents the scavenge pump from ingesting "debris", in the event of a failure/breakage.   It can save an expensive pump from damage.
 
Fordboy

[jacksoni]

Jack- Kevin Johnson of Ishihara-Johnson crank scrapers ( www.crank-scrapers.com ) which MM is talking to about a scraper for his Midget, has done a lot of work and research about windage and associated issues which are the subject of this thread. I think you have said you will be using some sort of scraper/windage tray arrangement. You might talk to him about it and see what he thinks with your specific special circumstance.

[Jack Gifford]

Jack- thanks. Looks like a useful site.

[wobblywalrus]

Many years ago I polished a crank, rods, etc. to reduce windage.  The theory was that less oil would adhere to the shiny surfaces and there would be less windage.  It was a lot of effort.  Does anyone know about a scientific type comparison they verifies if this practice works?   

[roygoodwin]

Googling for "Oil Aeration in an Internal Combustion Engine" turns up some interesting things, the first 3 are from MIT and the next couple are from SAE.  Also there's a "Circle Track" (the magazine) article on windage and oil pan design http://www.circletrack.com/techarticles/ctrp_0603_oil_pan_design_windage_tech/viewall.html  

This one looks interesting http://gasturbinespower.asmedigitalcollection.asme.org/mobile/article.aspx?articleid=1424669

Maybe there's something in those.  I *think* you may have to pay to see the SAE & ASME papers

[Jack Gifford]

I apologize for not titling this thread "Reduction of oil aeration". I didn't realize that the term 'windage' specifically refers to power loss.

[Seldom Seen Slim]

Well, yes -- but more often "windage" refers to the drift of a projectile due to (cross)winds.

[tauruck]

The late Grumpy Jenkins wrote in his book "The Chevrolet Racing Engine" that he built a plexiglass screen into an oil pan and used a dye (I think) in the oil and filmed the rotating assembly with a special high speed camera.
What he saw was that the oil hangs together like a rope wrapped around the crankshaft.
There's detail on all the other weird stuff that goes on inside the pan.

Page 119 if you have his book.

[fordboy628]

I think the link to the Ishihara-Johnson has been posted before on this thread, but this one is specifically their tech page:

http://www.crank-scrapers.com/What%20is%20a%20crank-scraper.html

The whole concept, presented clearly and concisely.   AND, the reasons why the crank will NOT "throw off" all the oil, even at very high rpm.

There is also a link to a 2010 European engineering paper on the subject:

http://www.ilasseurope.org/ICLASS/ilass2010/FILES/FULL_PAPERS/097.pdf

There is no charge to download this pdf.    It's a 12 page article filled with "esoteric engineering speak".   If you persevere there is good info in the article.   I doubt very much though, whether any racer cares about average "particle size".
 
Fordboy

[tauruck]

That's some interesting reading.


Thanks Fordboy.

[Jack Gifford]

I bookmarked the Ricardo paper- thanks. I've read very little of Sir Harry's stuff- guess I really should, though.

Oops- I see that the paper was from 2010, and from the Ricardo Laboratory, not actually authored by the late Sir Harry.

[fordboy628]

I bookmarked the Ricardo paper- thanks. I've read very little of Sir Harry's stuff- guess I really should, though.

Oops- I see that the paper was from 2010, and from the Ricardo Laboratory, not actually authored by the late Sir Harry.

1./  The High Speed Internal Combustion Engine, Sir Harry Ricardo, 1953 (420 pages) is always in the top 5 of my recommended reading list for those who wish to get into the engineering end of engines.     It is however, hopelessly out of date regarding materials, designs, etc.   BUT, Sir Harry can show you how to think differently about effects.    IMHO, it is a worthwhile read for that.

2/    Design and Tuning of Competition Engines, Philip H. Smith, 1971 (468 pages) is another worthwhile read.   Again dated, but strong on the basics.

3/    IC Engine Combustion, Fuels, Materials, Design, C.F. Taylor, 1985 (783 pages)    A classic.  Standard of collegiate texts.

4/    IC Engine Thermodynamics, Flow, Performance, C.F. Taylor, 1992 (574 pages)    The companion volume to #3.

5/    Climax in Coventry, Walter Hassan, 1975 (158 pages)   Covers the Coventry Climax engines of the 50's & 60's.   And lays out the foundation of the relationships in
       the British Racing Engine Industry of the period.

There are many more contemporary volumes now in print, that are far more modern regarding materials and design.   Too many to list actually.    These are the basics I recommend, and you can go anywhere from here.
 
Fordboy