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Old 21st May 2011, 18:35   #46
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Default Re: What limits rpm for an internal combustion engine?

^^ For reference (All credits to respective authors) :-

1. SAE Technical paper series 930995 "Diesel Engine oil consumption depending on piston ring motion and design" by Hideki Yoshida, Masaki Yamada, Hiroyuki Kobayashi (March 1-5, 1993)

2. "Piston ring motion and its influence on Engine tribology" by S. Furuhama, M. Hiruma SAE no. 790860

3. "Piston ring dynamics and its influence" by J.M. Curtis SAE No. 810935

Trust this helps.

Spike
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Old 21st May 2011, 20:27   #47
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Default Re: What limits rpm for an internal combustion engine?

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Originally Posted by dhanushs View Post
Vina, I think the engine rpm is limited not due to the resisting torque, but due to the fact that the power developed at higher rpm's is not enough to accelerate the moving parts more.

Think of it this way. You have an engine with a flywheel of given mass revving at its max rpm. So.. the question is will the rpm increase if you replace the flywheel by another one with lesser mass?

Yes. Because, A=F/M. here at a given rpm (max), F of an engine is constant. So if we reduce M, then A will increase.
So long as A>0 (no matter how small it is) the speed (or rpm) will keep increasing. Irrespective of M.

Mass or moment of inertia by themselves do not prevent attaniment of a higher speed or rpm. They do slow the process down (so the acceleration will be sluggish) but they do not prevent the peak speed from building up.

You need a resisting force (or torque) to stop the acceleration.
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Old 21st May 2011, 21:06   #48
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Default Re: What limits rpm for an internal combustion engine?

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Originally Posted by SPIKE ARRESTOR View Post
It has been scientifically proved that, smaller the cylinder dia, higher is the oil consumption, more so for cylinder bores having dia less than 100 mm. So, piston speeds / RPM needs to be controlled.

Spike
Interesting!
How many passenger car engines have bores over 100 mm?

I thought that was a truism, that beyond a certain rpm, oil consumption increases. A mix of piston ring flutter, and too much oil on the cylinder wall overwhelming the oil control ring. Is this something else?

Regards
Sutripta

Edit: I see you have given references. Aren't SAE papers a paid subscription?

Last edited by Sutripta : 21st May 2011 at 21:08.
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Old 21st May 2011, 21:54   #49
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Default Re: What limits rpm for an internal combustion engine?

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Originally Posted by Sutripta View Post
Interesting!
How many passenger car engines have bores over 100 mm?
Good one Dada, most are below 100 mm (hence the need to limit the piston speed). The study was conducted on fleet operators for oil change intervals / soot deposition in oil and oil consumption. On the basis of this several recommendations for oil quality and drain interval were arrived.

Quote:
I thought that was a truism, that beyond a certain rpm, oil consumption increases. A mix of piston ring flutter, and too much oil on the cylinder wall overwhelming the oil control ring. Is this something else?
Somewhat, the piston ring gap and land volume for 1,2 were found as the contributing factors. Oil control ring was untouched.

Quote:
Edit: I see you have given references. Aren't SAE papers a paid subscription?
Only 5$ per article (they want it, not me).

Spike

Last edited by SPIKE ARRESTOR : 21st May 2011 at 22:02.
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Old 24th May 2011, 19:33   #50
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Default Re: What limits rpm for an internal combustion engine?

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Originally Posted by SPIKE ARRESTOR View Post

Only 5$ per article (they want it, not me).

Spike
It was more like $15, and I couldn't understand most of the abstract, so I have no intentions of buying it.

Can you summarise (if at all possible) for a layman what causes the extra oil consumption for smaller diameter rings?
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Old 25th May 2011, 00:36   #51
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Default Re: What limits rpm for an internal combustion engine?

One important factor affecting engine rpm is the inertia of moving parts. F1 car engines use very light, compact, stiff parts made of alloys. Resultantly the engine rpm is very high. Correct me if I am wrong.
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Old 25th May 2011, 10:29   #52
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Default Re: What limits rpm for an internal combustion engine?

Agreed. However, a super light flywheel with not work for road going vehicles.
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Old 27th May 2011, 10:01   #53
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Default Re: What limits rpm for an internal combustion engine?

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Originally Posted by Sutripta View Post
^^^
Hi,
Re: rpm limits, I actually have nothing further to add to what I've said in post #4. Also, I normally log in at night, and sometimes during lunchtime.

I thought we were not discussing diesels. Square/ Oversquare diesels which immediately come to mind are the Peugot/ Mahindra engines, and Cummins V series.

Breathing: You are on the right track. The air column needs a certain velocity (momentum) so that it continues filling in the cylinders even when the piston is moving up. Which is why the inlet valve has to be kept open beyond BDC. So two things- a) if you make your ports/ runners too big (a common rookie modifying mistake) you loose velocity, and breathing suffers. You make it too small, and it acts as a restriction, and breathing again suffers. b) Valve has to be kept open after BDC. Longer (in terms of crank degrees) if you want to optimise breathing at higher rpms. Similar, (but more complex) reasoning for exhaust. So breathing can only be optimised for a small band of rpm, and will have a detrimental effect for other rpms.

Turbos a different can of worms. Not just rpm, but there is a time function (delay) as well. Will wait for others to chip in.

You are right. Failure/ reliability is statistical. With a spread.

For a thread on rpm, lets leave it at that. For the nature of diesel combustion, maybe it will be discussed in another thread which is also active right now.

Do check out the Miller/ Atkinson cycles. Again, not rpm related.

Regards
Sutripta

I was trying to find stuff on petrol engine breathing characteristics on the internet and they all talk about formation of standing wave patterns.

Here's what I don't understand - at rpm below 12000 (i.e. 200Hz frequency, and 100Hz breathing/exhaust pulse rate) in air at 1 atmospheric pressure, the speed of sound is 340m/s (roughly) - base on this one wavelength is 3.4m and half wavelength is 1.7m

How do the standing waves form in the intake manifold given that its dimensions are nowhere close to these numbers?
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Old 27th May 2011, 20:31   #54
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Default Re: What limits rpm for an internal combustion engine?

^^^
You are talking of 'tuned' inlets, and I think we should let the modifiers/ tuners handle this.

Still, why don't you think in the time domain. I do. The pressure pulse travels along the guide, and at any discontinuity, reverses with a phase inversion.

Best (understand this phenomenon/ practice) on the exhaust side. Never was/ still am not comfortable on the inlet side.

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Sutripta
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Old 28th May 2011, 01:32   #55
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Default Re: What limits rpm for an internal combustion engine?

Quote:
Originally Posted by Sutripta View Post
^^^
You are talking of 'tuned' inlets, and I think we should let the modifiers/ tuners handle this.

Still, why don't you think in the time domain. I do. The pressure pulse travels along the guide, and at any discontinuity, reverses with a phase inversion.

Best (understand this phenomenon/ practice) on the exhaust side. Never was/ still am not comfortable on the inlet side.

Regards
Sutripta

I was thinking in terms of time/frequency/space - to make a standing wave you need space in multiples of half-wavelength

The only way there can be a standing wave in the size of a manifold is if the speed of the pulse wave is much less than that of sound - I think that may be possible because sound doesn't involve mass transfer (on an average the particles stay in their mean position), and pulse waves do.
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Old 28th May 2011, 22:48   #56
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Default Re: What limits rpm for an internal combustion engine?

^^^
Hi,
Group and phase velocities?

What is determining your choice of frequency?

Don't get the last part of your statement.

Regards
Sutripta
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Old 28th May 2011, 23:00   #57
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Default Re: What limits rpm for an internal combustion engine?

Quote:
Originally Posted by Sutripta View Post
^^^
Hi,
Group and phase velocities?
Lost you there - you'll have to explain. For a constant frequency, what is the difference? and why are you raising this (normally when you ask questions there is a clue, this one I am missing totally)


For analysis of musical instrument resonance in high school I remember we used multiples of half wavelengths to figure out length of the organ, flute etc.


Quote:
Originally Posted by Sutripta View Post

What is determining your choice of frequency?

Don't get the last part of your statement.

Regards
Sutripta
The frequency is merely the frequency of the inlet valve - at 6000rpm, it will be 100Hz/2 = 50Hz, at 12000rpm it'll be 100Hz.





What I meant in the last part was that when we derive speed of a wave in a medium, the assumption is that all particles in that medium are stationary, i.e. they oscillate but their mean position doesn't change. That assumption is not valid in the manifold, the gas is moving and moving very fast. So the "effective velocity" may be far less for the pressure waves (which are not pressure waves in true sense but actual mass transfer thingies)
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Old 28th May 2011, 23:33   #58
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Default Re: What limits rpm for an internal combustion engine?

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Originally Posted by vina View Post
Lost you there - you'll have to explain. For a constant frequency, what is the difference? and why are you raising this (normally when you ask questions there is a clue, this one I am missing totally)

No! Genuine question. Purity of tone.

Long long time back, when I had gone through back of envelope calculations (but for the exhaust side) don't remember there being any anomalies. Trying to recollect.

Inlet: had problems with the assumptions. Never explored.


The frequency is merely the frequency of the inlet valve - at 6000rpm, it will be 100Hz/2 = 50Hz, at 12000rpm it'll be 100Hz.

Think needs to be revisited.
Linear superposition. Like waves in an ocean, in an ocean current. Longitudinal waves also no mean movement.

As I said, the tuners and modifiers should have these at their fingertips. Wait for then to chip in.

Regards
Sutripta

BTW, what sort of spectral purity can one expect from a half lambda dipole?
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Old 29th May 2011, 00:00   #59
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Default Re: What limits rpm for an internal combustion engine?

^^^^

Why did you say "needs to be revisited" - did I do anything wrong?

12000rpm = 12000/60 Hz = 200Hz. On every alternate rev in a 4-stroke, the inlet opens - so we get 100Hz.

I'm not assuming that all 4 cylinders will generate pulsation, though that can arguably make it 400Hz (two intakes per rev), the thing is I have seen pictures of each cyl with its own inlet.


Quote:
Originally Posted by Sutripta View Post
BTW, what sort of spectral purity can one expect from a half lambda dipole?
I'm not sure what you mean by spectral purity here. Do you mean bandwidth?

All wires radiate at all frequencies, not just half wave dipoles. The question is one of emissivity and directional gain. In fact for most consumer applications the antennas are what are known as "short antennas" - they become omnidirectional and very wideband.
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Old 29th May 2011, 00:19   #60
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Default Re: What limits rpm for an internal combustion engine?

Quote:
Originally Posted by vina View Post
^^^^

Why did you say "needs to be revisited" - did I do anything wrong?

12000rpm = 12000/60 Hz = 200Hz. On every alternate rev in a 4-stroke, the inlet opens - so we get 100Hz.

What causes it, and when. And when do we want its (positive) contribution.


I'm not assuming that all 4 cylinders will generate pulsation, though that can arguably make it 400Hz (two intakes per rev), the thing is I have seen pictures of each cyl with its own inlet.

You're right. Either it will open to a plenum, or to atmosphere (hopefully through filter)

I'm not sure what you mean by spectral purity here. Do you mean bandwidth?
Yes, but trying to align the discussion with sound.

(OT. - My rule regarding antennas:- Every signal carrying conductor will radiate, and receive, in copious quantities. Except the antenna, which will fall way short of its expected values.
Regards
Sutripta
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