piston speed 2

[golfpin]

A very happy new year to all,

I picked up on thread that Greg Alcock replied to, referring to my hero of engineers, Lanchester, he , I understand put forward a theory in about 1905, that engine speed was not limited by Revs but by piston speed, and that the upper limits for the time, based on then known materials was 4000 feet per min. However one had to divide the piston speed by the square root of the Stroke: to Bore ratio to get a better measure of the stresses involved. My Question is does this theory hold true for today,s engines given the huge advancement in materials. I did this calc some years ago on the specs of my 1100 Suzuki and was very interested to see that the suzuki redline translated into 3999 feet per min.
Your thoughts, comments,
All the best Golfpin

 

[inline6]

what good is mean piston speed as a measure over say actual peak piston speed?

 

[GregLocock]

Laziness. Are the two not directly related?

Cheers

Greg Locock


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[inline6]

i think it will depend on specifics of geometry and therefore not directly related but i have not worked it out yet

 

[GregLocock]

I suggest you do that.



Cheers

Greg Locock


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[inline6]

rod length will affect peak piston speed

 

[GregLocock]

Over the practical range of rod length/stroke ratios is it a big deal?

Cheers

Greg Locock


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[inline6]

almost certainly the engine with higher MPS will have a higher peak speed but i also imagine a few % would be significant if you are pushing the envelope on what is considered a extremely high "mean piston speed"

 

[Komodo86]

A 100mm stroke at 7500rpm has an MPS of 25m/s.

The peak piston speed with a 150mm rod is 41.22m/s. With a 200mm rod is 40.42m/s.

A change of about 1.9%. Is that significant?

 

[inline6]

this thread is about MPS limits, i cant see how ignoring a 2% higher peak piston speed for a given MPS makes sense. close enough is not good enough in some applications.

 

[GregLocock]

So why didn't YOU work that out?

Cheers

Greg Locock


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[turbomotor]

Hi Golfpin,

I enjoyed reading the responses to your post. I agree fully with Ivymike (very first response), and I can back it up with a little anecdotal data. The Teledyne Continental horizontally opposed 6 cylinder 520 cid engine with 4 inch stroke is offered as a recommended 1600 hour TBO engine when rated at 2700 rpm (uncorrected mean piston speed of 1800 fpm or 9.1 mps), but the recommended TBO drops to 1200 hour when the engine is rated at 3400 rpm (2267 fpm or 11.5 mps) and about the same BMEP.

(TSIO-520-UB versus the GTSIO-520-L).

But the real point of my response is to share some of Sir Harry's comments about piston speed and the relationship between piston speed and engine breathing (and power).

Regards,

Dick

 

[inline6]

Greg Locock, i was merely alluding to that when considering port Mach number and flame speed it would be more relevant to look at actual velocity, peak velocity or average over a more narrow crank angle of the when those things are occurring rather than washing away some details away by using MPS.