2 stroke thread (with occasional F1 relevance!)

[Pinger]

I wouldn't put it past the F1 engineer to 'accidentally' leak oil into the combustion chamber to produce more heat during combustion. I would! even if my personal preference is not to polute, It would be my last way to gain power.

Talking of oil consumption...
Would a turbocharged EU4 compliant 2005 4T using engine oil at the rate of 2% of fuel under Lambda control (no air mass flow sensor) sense the oil as fuel and reduce fuel flow accordingly?
Would the lowered octane rating cause the timing to be retarded? If yes to the above, would a more modern engine strategy prevent the above?

[Muniix]

Does anyone know (or have a formula for) the relationship between gas velocity through the transfer ports/windows and the prevailing piston speed in a simple crankcase scavenged 2T?
Is it as linear as gas speed through an inlet valve in a 4T - or does the crankcase volume complicate matters? Any ideas?

Fluid flows are complex, air is compressible, surfaces cause friction, flow coefficients through ports and around bends, pressures and inertias all complicate the matter. For a given configuration a simplified model can be made.

[Pinger]

Does anyone know (or have a formula for) the relationship between gas velocity through the transfer ports/windows and the prevailing piston speed in a simple crankcase scavenged 2T?
Is it as linear as gas speed through an inlet valve in a 4T - or does the crankcase volume complicate matters? Any ideas?

Fluid flows are complex, air is compressible, surfaces cause friction, flow coefficients through ports and around bends, pressures and inertias all complicate the matter. For a given configuration a simplified model can be made.

The engine I'm looking at has a mean piston speed of 12.5m/s at 6000rpm and the ratio of area of piston to transfer windows is 3:1. Is a gas velocity of 37.5m/s at 6000rpm viable?
Can I similarly link it to mean piston velocities at other engine speeds? Does the effect of the crankcase volume skew these figures, and if so, in which direction?
Am I in assuming 37.5m/s at 6000rpm assuming a mean gas velocity with the initial flow velocity on transfer port opening much higher (due to the narrow open depth of the port/window)?

Just looking for ballpark figures here - to get my ball rolling!

[Muniix]

I wouldn't put it past the F1 engineer to 'accidentally' leak oil into the combustion chamber to produce more heat during combustion. I would! even if my personal preference is not to polute, It would be my last way to gain power.

Talking of oil consumption...
Would a turbocharged EU4 compliant 2005 4T using engine oil at the rate of 2% of fuel under Lambda control (no air mass flow sensor) sense the oil as fuel and reduce fuel flow accordingly?
Would the lowered octane rating cause the timing to be retarded? If yes to the above, would a more modern engine strategy prevent the above?

You dont need a air mass flow sensor to calculate air flow, a air box pressure and temperature sensor is all that is needed. From that one calculates the air flow, maybe not in a 2006 engine management system.

But if this was its normal condition then that is hopefully what the fuel maps are calibrated for. That is the problem with static fuel maps adjusting to engine wear, they are calibrated from a new engine from the production line, maybe a few and averaged, there is currently a lot of research trying to achieve correct engine management on worn engines.

Going with sensors that detect cylinder pressure, or heat release, real sensors or virtual ones calculated with physics models are far more accurate. Compute being cheap now, gigaflops are available, 100's even for a few dollars.

[Pinger]

But if this was its normal condition then that is hopefully what the fuel maps are calibrated for. That is the problem with static fuel maps adjusting to engine wear, the are calibrated of an new engine from the production line, there is a lot of effort trying to get engine management to work correctly on worn engines.
.

The engine in question is the Suprex as fitted to early smart fortwos - which have lousy oil control rings.
Your reply appears to support my theory (Lambda senses oil as fuel, fuel is leaned off, timing is retarded) as to why the exhaust valves ultimately burn on these engines once they start using oil.

Not reassuring that more modern systems would cope no better.

[manolis]

Hello all.


Take a look at the following video of Achates Power:



https://youtu.be/6zWCcZw6sdU

from the 60 to the 100 seconds.


It shows animated the Achates Power Opposed Piston Engine with the two side crankshafts:








All this complication is for the elimination of the thrust loads between the cylinder liner and the piston skirts (which, in turn, allows the substantial reduction of the specific lube consumption (plot in previous post)).


Compare with the PatOP cross-head architecture:




Thanks
Manolis Pattakos

[Muniix]

Hello all.


Take a look at the following video of Achates Power:

https://www.youtube.com/watch?v=6zWCcZw ... e=youtu.be

https://youtu.be/6zWCcZw6sdU

from the 60 to the 100 seconds.


It shows animated the Achates Power Opposed Piston Engine with the two side crankshafts:

http://www.pattakon.com/tempman/Achates_Power_10.gif

http://www.pattakon.com/tempman/Achates_Power_11.gif

http://www.pattakon.com/tempman/Achates_Power_12.gif


All this complication is for the elimination of the thrust loads between the cylinder liner and the piston skirts (which, in turn, allows the substantial reduction of the specific lube consumption (plot in previous post)).


Compare with the PatOP cross-head architecture:

http://www.pattakon.com/patop/PatOP1.gif


Thanks
Manolis Pattakos

Which has a huge amount of ring friction area, 3 ring packs with 1 huge bore.

It has reduced turbulence at start of combustion due to reduced piston velocity towards TDC compared to mean piston velocity. This slows combustion significantly requiring the engine to run at higher speeds and greater losses consuming more fuel less effiently.

Slower combustion causes higher heat loss, Lower thermodynamic efficiency.

All those large big end bearings have clearly not been through any size or friction optimisation, the bigend larger than the mains, insane more excessive friction and masses increasing inertial forces combined with its need to run at higher speeds this is terrible design.

Rating. 0 out of 5, fail, try again

[J.A.W.]

I stopped replying to manolis and added him to the ignore list. I am more than happy to continue any arguments with the rest of you.

You have not read my posts - the engine I am questioning is the engine that you are describing. Now please let me know why you thing such engine will have better oil consumption

Your posts are as clear as mud.. & I am close to putting you on ignore, if 'n' when - I ever put anyone on..

However I do fondly recall this opposed piston 2T diesel from my youth, that AFAIR, had no over-oiling issues,
nor 'carboning up' - providing the correct oil - 'Shell Rotella' - was used..

www.oldengine.org/members/diesel/rootes ... s3/ts3.htm

& they had a real sporty sound too, for an old truck.. https://www.youtube.com/watch?v=mfKmkitnqQY

You demanded 'cool technical comments'.

'I had a similar engine when I was little and it was okish' is not a cool technical argument.

Give me something based on physics and logic.

"Demanded"?

Mf, reading your posts on this thread, I get the distinct impression that you are either not
really interested in (or are temperamentally incapable of) reasonable collegial discussion,
- let alone discourse remotely scholarly in tone..
..& that in effect, you post in manner - tantamount to trolling..
..seemingly in a 'fit of pique' - due to your perceived sense of somehow being slighted here..

Clearly demonstrating the morbid sensitivity of the egotist - on your own behalf, yet you crassly continue
( heedless of advice to keep civil, & cease the crudely vulgar emotive tone & content)
.. to post angry tirades which add nothing of actual technical value to the thread..
& indeed.. frankly appear to be verging on.. psycho-pathological..

I'd wager Mf, that you are not unfamiliar with this feedback, either..
..further, I'd suggest you put your energy into seeking to develop an improved level of..
..emotional maturity/insight growth, rather than your current iconoclastic bent..
..which appears to be rooted in unresolved frustration - over you own machine's shortcomings..

Edit: fixed typos.

[gruntguru]

Suppose you have a cylinder with bore b and stroke s and a single piston.
You have another engine with 2 cylinders, same bore b and half the stroke.

The 2 cylinder engine has 2 times more rings and implicitly 2 times more ring gap area and 2 times more groove vertical clearance area.

Which engine has a higher oil consumption and higher ring pack friction ?

Ah - so you want to compare oil consumption of an engine with twice as many pistons and half the displacement per piston? I suppose that would use a bit more oil but it would be higher revving and make more power . . no I don't see the point - best to compare the oil consumption of two engines with the same number of pistons and the same displacement per piston etc.

Ok then !
You now have a single cylinder single piston owith the same bore and same displacement. (Twice the stroke)

How much oil will it consume compared to an opposes piston engine of the same displacement?

The only logical comparison would be a single cylinder (twin piston) OP engine vs a 2 cylinder conventional engine with identical bore, stroke, total displacement, displacement per piston, mean piston speed etc etc.

[gruntguru]

Hello all.
Here is the “in-cylinder-flow” :
http://www.pattakon.com/tempman/In_Cyli ... mmetry.gif
(if the image is not clear click on: http://www.pattakon.com/tempman/In_Cyli ... mmetry.gif )
The gas flow is shown only in the one half of the cylinder.
The gas flow in the other half of the cylinder is identical (mirrored about the bisecting plane).

It never is the same, how could anybody believe this, stop making up stuff to suppport your opinions.

The velocities of the gas molecules that are on the bisecting plane are parallel to the bisecting plane (zero velocity normal to the bisecting plane).

It is like having an “imaginary curtain” separating / isolating the cylinder in two halves: the one half fills by the gas entering though the one intake valve, the other half fills by the gas entering through the other intake valve.

If this “curtain” was real, it would spoil the flow (boundary layer friction), because in such a case the molecules on the bisecting plane should have zero velocity.

The PatRoVa rotary valve:

http://www.pattakon.com/PatRoVa/PatRoVa_Taper_STE.gif

is perfectly symmetrical.

There are two tangential gas streams (one per chamber port), the one filling the one half of the cylinder, the other filling the other half of the cylinder (the one abutting on the other).

And because they are symmetrical, they do not interfere with each other.

http://www.pattakon.com/PatRoVa/PatRoVa_Tumble.gif

Thanks
Manolis Pattakos

They are never symetrical.

Anyone doing proper 3D CFD knows this is complete rubbish, the turbulence is a complex 3D structure over the whole cylinder. Modelling over only have fails to identify the larger structures.

You are misrepresenting again.

There was once a time for compute cost and capability reasons they only modelled half the cylinder, this is no longer relevant and full cylinder simulations are performed. I assume you knew this and tried to gull those who are not so knowledgable on 3D CFD and it use in in cylinder flows.

Stop Misrepresenting the truth.
Bending whatever you can harvest from the internet to support your incorrect biased opinions.

Either you don't know what you are talking about or you are on some kind of vendetta. Manolis' assumptions around symmetry are often used for simplification and entirely valid for the purposes he was presenting. I am not sure what the strident tone and bold accusations are all about. I have read many of his posts and have never seen deliberate misrepresentation.

[J.A.W.]

From an official data base source: http://www.marinecouncil.org.au/engine-database/

Two engines compared, 250hp class S.I.,outboard motors:

1, 2T cylinder ported, crankcase scavenged DI - Evinrude G2.
2, 4T OHC variable valve timing fuel injected - Honda.

Both are premium CARB 3-star emissions rated: HC/NOx & CO, respectively.

1, Evinrude 2T; HC/NOx 12.2; CO 48.7.
2, Honda 4T; HC/NOx 13.2; CO 91.7.

HC is hydrocarbon - from burning fuel & oil, - & as can be seen..
.. the 2T does not show excessive oil loss via its construction of cylinder ports being swept by piston/rings..

[Muniix]

Hello all.
Here is the “in-cylinder-flow” :
http://www.pattakon.com/tempman/In_Cyli ... mmetry.gif
(if the image is not clear click on: http://www.pattakon.com/tempman/In_Cyli ... mmetry.gif )
The gas flow is shown only in the one half of the cylinder.
The gas flow in the other half of the cylinder is identical (mirrored about the bisecting plane).

It never is the same, how could anybody believe this, stop making up stuff to suppport your opinions.

The velocities of the gas molecules that are on the bisecting plane are parallel to the bisecting plane (zero velocity normal to the bisecting plane).

It is like having an “imaginary curtain” separating / isolating the cylinder in two halves: the one half fills by the gas entering though the one intake valve, the other half fills by the gas entering through the other intake valve.

If this “curtain” was real, it would spoil the flow (boundary layer friction), because in such a case the molecules on the bisecting plane should have zero velocity.

The PatRoVa rotary valve:

http://www.pattakon.com/PatRoVa/PatRoVa_Taper_STE.gif

is perfectly symmetrical.

There are two tangential gas streams (one per chamber port), the one filling the one half of the cylinder, the other filling the other half of the cylinder (the one abutting on the other).

And because they are symmetrical, they do not interfere with each other.

http://www.pattakon.com/PatRoVa/PatRoVa_Tumble.gif

Thanks
Manolis Pattakos

They are never symetrical.

Anyone doing proper 3D CFD knows this is complete rubbish, the turbulence is a complex 3D structure over the whole cylinder. Modelling over only have fails to identify the larger structures.

You are misrepresenting again.

There was once a time for compute cost and capability reasons they only modelled half the cylinder, this is no longer relevant and full cylinder simulations are performed. I assume you knew this and tried to gull those who are not so knowledgable on 3D CFD and it use in in cylinder flows.

Stop Misrepresenting the truth.
Bending whatever you can harvest from the internet to support your incorrect biased opinions.

Either you don't know what you are talking about or you are on some kind of vendetta. Manolis' assumptions around symmetry are often used for simplification and entirely valid for the purposes he was presenting. I am not sure what the strident tone and bold accusations are all about. I have read many of his posts and have never seen deliberate misrepresentation.

I can show many references to back up my claim that modelling half the cylinder does not show the larger 3d turbulent structures dating back to 2000. This is not opinion it is fact.

It is like having an “imaginary curtain” separating / isolating the cylinder in two halves: the one half fills by the gas entering though the one intake valve, the other half fills by the gas entering through the other intake valve.

Does not agree with those published limitations.

Fabricating the concept of a Curtain is complete misrepresentation of the knowledge and efforts 3D fluid flow researchers perform to increase our knowledge.

The limitations of modelling only half the cylinder are well documented in the literature, I suggest you familiarise yourself with them. I work with 3d fluid flow engineers. I know what I'm talking about. I run simulations. I've optimised the code, I've verified simulations against experimental data to validate the code.

Please can we stick to facts.

I remember someone using the energy conservation laws to argue against using the favourable piston motion and velocity of offset crankshafts to gain extra power from the fuel being burned. Completely ignoring the fact the energy comes from the introduced fuel.

[J.A.W.]

Does anyone know (or have a formula for) the relationship between gas velocity through the transfer ports/windows and the prevailing piston speed in a simple crankcase scavenged 2T?
Is it as linear as gas speed through an inlet valve in a 4T - or does the crankcase volume complicate matters? Any ideas?

P, perhaps this link may be of interest/value..
http://www.bucketracing.blogspot.com.au ... s-aka.html

[Muniix]

Does anyone know (or have a formula for) the relationship between gas velocity through the transfer ports/windows and the prevailing piston speed in a simple crankcase scavenged 2T?
Is it as linear as gas speed through an inlet valve in a 4T - or does the crankcase volume complicate matters? Any ideas?

P, perhaps this link may be of interest/value..
http://www.bucketracing.blogspot.com.au ... s-aka.html

I was going to suggest you search for published papers on cfd research identifying the relationship. They may have models you can use. Unfortunately I got distracted, didn't follow my normal "What's important now" helping someone is more important than correcting biased opinions. Now their negatively affecting others with their opinions.

[J.A.W.]

Does anyone know (or have a formula for) the relationship between gas velocity through the transfer ports/windows and the prevailing piston speed in a simple crankcase scavenged 2T?
Is it as linear as gas speed through an inlet valve in a 4T - or does the crankcase volume complicate matters? Any ideas?

P, perhaps this link may be of interest/value..
http://www.bucketracing.blogspot.com.au ... s-aka.html

I was going to suggest you search for published papers on cfd research identifying the relationship. They may have models you can use. Unfortunately I got distracted, didn't follow my normal "What's important now" helping someone is more important than correcting biased opinions. Now their negatively affecting others with their opinions.

Are you by any chance - actually 'Mudflap', too Marc?
Anyhow..
..both of you need to chill out, & stay on topic.. sans needless additions of personally directed, rancorous commentary..