piston speed
piston speed
(OP)
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
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





RE: piston speed
There is always a specific thing that goes wrong first when you over rev an engine, and there a few candidates for what that might be. Only a couple of those know what piston speed is. Snapping a rod is a possibility, rod bearing failure, valve to piston clash, etc.
A good indicator of how heavily loaded an engine is is BMEP.
RE: piston speed
RE: piston speed
RE: piston speed
Be interested in comments,
Thanks Golfpin
RE: piston speed
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: piston speed
RE: piston speed
Would be very interested in what that highly modified valve train was. F1 type motors we know of because of the pneumatic systems used.
tbuelna I must agree that the load reversals because of the Otto cycle system are a greater issue and that is perhaps, as in the aircraft industry parts are"Lifed" and then turfed out before they can break. Hence replacement of certain parts at the end of one run down the drag strip by the top teams, this I have only heard of.
Cheers Golfpin
RE: piston speed
F1 can rev to 20,000rpm, but with 39mm strokes, that's still only a piston speed of 26m/s.
Motorbike engines, all around the same limit too.
RE: piston speed
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: piston speed
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: piston speed
So a combination of inlet mach index and 'outrunning the flame' is the most likely answer. If the mach index doesn't get you, the flame speed will.
RE: piston speed
http://cache.gawker.com/assets/images/12/2010/02/e...
RE: piston speed
Dragon, I like, that says it all! Greg and yourself and all others must consider yourselves as "mythbusters"
Golfpin
RE: piston speed
- Steve
RE: piston speed
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: piston speed
The posited reason that the combustion rate more or less keeps pace with rpm, is that the intensities of the bulk charge motion and turbulence in the cylinder are quite linked to the piston speed, which drives both the velocity of charge that is brought into the cylinder through the intake port(s), and subsequent modification of the charge motion after it has entered the cylinder, i.e. mainly during the upper part of the compression stroke. While I am not a combustion analyst at the 3D CFD and combustion kinetics level, I believe that the experts in these fields have satisfied themselves that the foregoing explanation is valid to some extent.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: piston speed
RE: piston speed
Is it definitely the case as the piston is approaching/passing around 27m/s though? Have there been any studies to specifically study this aspect?
RE: piston speed
RE: piston speed
RE: piston speed
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: piston speed
RE: piston speed
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: piston speed
RE: piston speed
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: piston speed
RE: piston speed
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?
RE: piston speed
RE: piston speed
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: piston speed
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
RE: piston speed