Accumulation Grooves

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
riff_raff
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gruntguru wrote:Brian. Agreed - there is someone kicking around a ringless piston design using multiple grooves of specific shape.

In place of the rings, each piston has numerous small, angled grooves, semi-circular at their apex. With the small clearances between them, the movement of the piston creates high-speed eddies -- air pressure working like metal rings to cut leakage and loss during the compression and combustion strokes.

From. http://www.motoring.com.au/news/2013/au ... ings-40773

Not much useful detail unfortunately.
Here's how this "ringless" design can be analyzed. It can be simplified as a system of orifices and volumes in series. Each orifice area is defined by the clearance between the piston and bore, and each volume is the space provided by each accumulator groove. If you start with the deltaP existing across the first orifice, and then calculate the flow rates and pressure losses from each accumulator groove to the next in series versus time, you'll find that the flow will eventually stagnate. This would theoretically imply a perfect gas seal, if you ignore the gas trapped within the accumulator grooves that does not contribute to the work output of the engine.
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johnny comelately
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Re: Accumulation Grooves

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one thing that is a point of interest are the different profiles for the grooves, some are semi circular others are veed

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PlatinumZealot
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johnny comelately wrote:accumulation grooves, does anyone know the facts on how they work in regard to sealing?
as an example the model aero pistons that have no rings and just an accumulation groove.
there does not seem to be any leakdown, which is surprising
Almost like a labyrinth seal I guess. It is used to create turbulence and dissipate pressure energy of any gasses that might flow into it. As for the oil side of it now.. I have no idea how it works to scrape the oil... or does it scrape the oil at all?
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johnny comelately
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Re: Accumulation Grooves

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PlatinumZealot wrote:
johnny comelately wrote:accumulation grooves, does anyone know the facts on how they work in regard to sealing?
as an example the model aero pistons that have no rings and just an accumulation groove.
there does not seem to be any leakdown, which is surprising
Almost like a labyrinth seal I guess. It is used to create turbulence and dissipate pressure energy of any gasses that might flow into it. As for the oil side of it now.. I have no idea how it works to scrape the oil... or does it scrape the oil at all?
any oil scraping is incidental to me.
do labyrinth seals actually touch the shaft? i think some do and some dont.
if there is 500psi pressure in a combustion chamber it would be amazing if the pressure dissipation theory was the answer

gruntguru
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You need a stratified charge system to ensure no fuel enters the groove area.
je suis charlie

johnny comelately
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:wink:
gruntguru wrote:You need a stratified charge system to ensure no fuel enters the groove area.
with the boundary layer and squish the combustion has very different characteristics in those areas.
most engines, model aero included that use accumulation grooves dont have stratified charge by design.
just white man magic i think :wink:

hardingfv32
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johnny come lately wrote: any oil scraping is incidental...
Not if you believe their purpose is to reduce oil migration into the combustion chamber and those reducing detonation.

Brian

riff_raff
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johnny comelately wrote:do labyrinth seals actually touch the shaft? i think some do and some dont.
if there is 500psi pressure in a combustion chamber it would be amazing if the pressure dissipation theory was the answer
Labyrinth shaft seals do not have any contacting surfaces. They work by creating a complex flow path that inhibits flow of fluids thru the tiny spaces between the seal parts.
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gruntguru
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johnny comelately wrote::wink:
gruntguru wrote:You need a stratified charge system to ensure no fuel enters the groove area.
with the boundary layer and squish the combustion has very different characteristics in those areas.
most engines, model aero included that use accumulation grooves dont have stratified charge by design.
just white man magic i think :wink:
I was referring to automotive engines where hydrocarbon emisions and wasted fuel cannot be tolerated.
je suis charlie

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PlatinumZealot
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Another thing to consider is piston clearance.

F1 engines are so tight they can barely be turned at room temperature. The surface finish on the cylinder walls are like a robot baby's bottom so imagine the microscropic gap around the piston. The BMEP of F1 engines are big, but so is the piston bore. The CSA of the gap is extremely small compared to the bore.
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riff_raff
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gruntguru wrote:I was referring to automotive engines where hydrocarbon emisions and wasted fuel cannot be tolerated.
Your point about HC emissions in auto engines is excellent. The performance of oil control rings in auto engines is now a very critical factor. Oil control ring design for auto engines has improved significantly over the past few years to the point where oil consumption of current auto engines is essentially nil.
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A: Start with a large one!"

johnny comelately
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https://www.youtube.com/watch?v=WQGW-60xxcQ
this video details an axial carbon seal used in a jet turbine engine for oil control.
the grooves have an interesting layout

Tommy Cookers
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Joined: 17 Feb 2012, 16:55

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PlatinumZealot wrote:Another thing to consider is piston clearance.
F1 engines are so tight they can barely be turned at room temperature. The surface finish on the cylinder walls are like a robot baby's bottom so imagine the microscropic gap around the piston. The BMEP of F1 engines are big, but so is the piston bore. The CSA of the gap is extremely small compared to the bore.
broadly speaking .... with recent N/A F1 (extreme bore:stroke ratio of about 2.5, and extreme piston acceleration and rpm)
the piston is tight at room temperature primarily because it is made out-of-round
this because the piston is minimised to a pin boss structurally integrated (conceptually, flush) with the crown
because it's structurally far from symmetrical, so its expansion is far from symmetrical
the parts of the piston carrying the rings are a minimally small proportion

none of this need apply currently as the b:s ratio (about 1.6) , and rpm and minimum engine height are conservative/traditional
imo

riff_raff
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johnny comelately wrote:https://www.youtube.com/watch?v=WQGW-60xxcQ
this video details an axial carbon seal used in a jet turbine engine for oil control.
the grooves have an interesting layout
Carbon face seals are commonly used as oil seals on high speed shafts on aircraft turbine engines that cannot tolerate any oil leakage. Modern carbon face seals do not have any grooving. Instead they rely on a very precise finish of the mating surfaces and a controlled amount of axial preload provided by a spring. A properly designed and maintained carbon face seal can tolerate surface contact velocities of 20 kft/min for 10,000 hours or more of operation.
"Q: How do you make a small fortune in racing?
A: Start with a large one!"

johnny comelately
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Re: Accumulation Grooves

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riff_raff wrote:
johnny comelately wrote:https://www.youtube.com/watch?v=WQGW-60xxcQ
this video details an axial carbon seal used in a jet turbine engine for oil control.
the grooves have an interesting layout
Carbon face seals are commonly used as oil seals on high speed shafts on aircraft turbine engines that cannot tolerate any oil leakage. Modern carbon face seals do not have any grooving. Instead they rely on a very precise finish of the mating surfaces and a controlled amount of axial preload provided by a spring. A properly designed and maintained carbon face seal can tolerate surface contact velocities of 20 kft/min for 10,000 hours or more of operation.
in the example on youtube, it is a axial seal with grooves that i was referring to.