2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

I agree. 2-stoke with it's disadvantages, has been discarded except for ships, were those disadvantages are not too big. Stationary engines (whatever stroke) can make a comeback in hybrid street cars. Stirling even, why not.

I don't think 2-stoke, high-ratio-turbo compound, direct injection, (relative) low rpm, otto/diesel Frankenstein engines is a step forward for F1 though.

Well, you could always read through the thread (as Pat seems to have), & learn how the inherent
50% power impulse frequency* of 2T is attractive to an F1 not yet ready to ditch ICE/pistons for
the anodyne 'kitchen appliance' appeal of FE.

*2T appeal being a given - in relation to hi-efficiency & in providing an F1 worthy - ambient sound.

[Big Tea]

I realise most here follow better than I, but I found this 'simplified' item interesting

https://www.youtube.com/watch?v=UF5j1DvC954

[manolis]

Hello all

This array (from the Youtube video of Big_Tea post):



"talks" for 1 to 1,000 (or so) oil to fuel ratio for the Achates Power 2-stroke engine(s).

(~0.2gr/kWh Brake Spec. Oil Consumption divided by ~200gr/kWh Brake Spec. Fuel Consumption)

Do I (or they) miss something?

Is there a 4-stroke that achieves such figures?

Thanks
Manolis Pattakos

[Dr. Acula]

Hello all

This array (from the Youtube video of Big_Tea post):

https://www.pattakon.com/tempman/Achates_BSFC.png

"talks" for 1 to 1,000 (or so) oil to fuel ratio for the Achates Power 2-stroke engine(s).

(~0.2gr/kWh Brake Spec. Oil Consumption divided by ~200gr/kWh Brake Spec. Fuel Consumption)

Do I (or they) miss something?

Is there a 4-stroke that achieves such figures?

Thanks
Manolis Pattakos

Pretty much every modern 4 stroke achieves such figures. It also depends on the oil used.
I'm not sure you realise that this is not a fuel/oil mixture they use. They simply use a external oil pump. So it's no surprise the values are about the same, because it's the same way to lubricate the whole thing as in any 4 stroke engine.

[Pinger]

Hello all

This array (from the Youtube video of Big_Tea post):

https://www.pattakon.com/tempman/Achates_BSFC.png

"talks" for 1 to 1,000 (or so) oil to fuel ratio for the Achates Power 2-stroke engine(s).

(~0.2gr/kWh Brake Spec. Oil Consumption divided by ~200gr/kWh Brake Spec. Fuel Consumption)

Do I (or they) miss something?

Is there a 4-stroke that achieves such figures?

Thanks
Manolis Pattakos

Pretty much every modern 4 stroke achieves such figures. It also depends on the oil used.
I'm not sure you realise that this is not a fuel/oil mixture they use. They simply use a external oil pump. So it's no surprise the values are about the same, because it's the same way to lubricate the whole thing as in any 4 stroke engine.

Good that it matches 4T oil consumption then. Some had worried that the piston rings would scrape oil off the cylinder and into the exhaust port.

[Dr. Acula]

Hello all

This array (from the Youtube video of Big_Tea post):

https://www.pattakon.com/tempman/Achates_BSFC.png

"talks" for 1 to 1,000 (or so) oil to fuel ratio for the Achates Power 2-stroke engine(s).

(~0.2gr/kWh Brake Spec. Oil Consumption divided by ~200gr/kWh Brake Spec. Fuel Consumption)

Do I (or they) miss something?

Is there a 4-stroke that achieves such figures?

Thanks
Manolis Pattakos

Pretty much every modern 4 stroke achieves such figures. It also depends on the oil used.
I'm not sure you realise that this is not a fuel/oil mixture they use. They simply use a external oil pump. So it's no surprise the values are about the same, because it's the same way to lubricate the whole thing as in any 4 stroke engine.

Good that it matches 4T oil consumption then. Some had worried that the piston rings would scrape oil off the cylinder and into the exhaust port.

Well, these values are generally measured with a brand new engine on a test bench. So take them with a grain of salt. But it's the same with 4 stroke engines. I mean if you would measure some used Audi engines with clogged up oil return holes in the piston, you would have an insanely high oil consumption.

[Rodak]

Yeah, well my Toyota RAV4 V6, as near as I can tell, has exactly zero oil consumption between changes @ 5000 miles and has 190,000 miles on the clock. I've been trying to come up with a reason to replace it but can't; exactly no problems at this mileage, replaced the plugs @ 110k miles (they were beautiful re mixture, I was amazed), timing chain instead of belt, faultless. Sure, brake pads/rotors, struts and normal stuff but still..... Really, cars now days are pretty amazing for longevity and lack of maintenance. 60,000 miles for tires.... If you want to do a scary calculation, look at how much gasoline (yeah, petrol) has gone through the system in 100,000 miles; it's astounding yet these things just keep going. My total lifetime mileage in the RAV4 is 25 mpg so I've burned about 8000 gallons of petrol @ $2.75/gal (in the US of A) at a cost of $22,000, about the cost of the car. Even worse (or whatever) is that means I have spent about 4000 hours in the car driving.... or about 7.7 hrs/week driving, which seems about right. Damn.

Note: No two stroke relevance.

[manolis]

Hello Dr.Acula

You write:
“Pretty much every modern 4 stroke achieves such figures. It also depends on the oil used.
I'm not sure you realise that this is not a fuel/oil mixture they use. They simply use a external oil pump. So it's no surprise the values are about the same, because it's the same way to lubricate the whole thing as in any 4 stroke engine.”


It is a surprise the values of specific lube consumption of the ported 2-strokes to be similar to those of the conventional 4-strokes.

The 2-strokes Detroit-Diesels (GM) use an “external oil pump” (no fuel/oil mixture) and have exhaust valves on their cylinder heads and intake ports on their cylinders.
Their specific oil consumption is more than high (their nick name among the engine repair technicians is still “oiler's”).

When the piston rings pass over the ports of the cylinder of a 2-stroke, oil will be lost.

The question remains: how Achates Power managed their Opposed Piston engines (of conventional architecture: the same as that of the Junker Opposed piston engines) not to lose oil from their ports.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, a couple of things, the big sleeve valve aero-engines of the 1940s-50s era
were no heavier on oil-consumption than those with poppet valves, flying at the time,
whether of air-cooled radial, or liquid-cooled inline construction types.

& of course, like the military, F1 has never been concerned with road-vehicle emissions
standards, since they impede power/efficiency - in fact its only fairly recently that F1
has insisted on a much lower level of oil-consumption (it was higher than total-loss 2T)
- but this restriction was not due to emissions concerns, rather to prevent the lost
lubricant being utilized as a defacto fuel additive, for a performance advantage.

[Pinger]

The question remains: how Achates Power managed their Opposed Piston engines (of conventional architecture: the same as that of the Junker Opposed piston engines) not to lose oil from their ports.

Quite. It's far from obvious.
On this topic, deleting the piston rings may help (as done a little halfheartedly by SWRI) but ringless is better suited to higher rpm engines but diesel combustion is not.

[saviour stivala]

They don’t lose oil (engine lubricating oil) by the piston uncovering the inlet exhaust ports only by the piston crown. The piston skirt does not uncover the inlet and exhaust ports. The piston pin bore in piston is sealed by a plug which acts as a pin retainer because it does travel over the ports the ports. The piston rings having to go over the ports is no problem wear wise. See the TS3 animation.

[63l8qrrfy6]

The oil control ring only runs outboard of the port, it's only the compression rings that actually run over the ports.
It is still impressive what they can achieve.

I do wonder though how good the compression ring durability really is though. I presume that cylinder pressure is quite low when the rings go over the ports so that should help.


http://achatespower.com/wp-content/uplo ... 1-0068.pdf

[Pinger]

I do wonder though how good the compression ring durability really is though. I presume that cylinder pressure is quite low when the rings go over the ports so that should help.

2T has a bad rep for ring wear based on hi-po engines with ports as wide as they can possibly be.
Uniflow permits the whole circumference of the cylinder to be used and if the ports are below a critical width un-pegged rings are possible, Blair reckoned that that would contribute greatly to ring durability.

[manolis]

Hello all.

Here is a slide from the Achates_Power Opposed Piston youtube video (posted a few posts ago by Big Tea):



A is the exhaust port.
B is the piston skirt.
C is the piston pin.

The piston skirt B abutting / sliding on the cylinder liner (not shown) transmits a thrust force F from the piston to the casing (the inclination of the connecting rod causes this thrust load F); F times the eccentricity of the piston pin from the crankshaft rotation axis makes the instant torque provided by the engine (more correctly: by the specific cylinder of the engine).

To take the heavy thrust loads without wear, it is necessary a thick oil film between the piston skirt and the cylinder liner, no matter where the oil rings (if any) are located.

The piston rings need a substantially thinner oil film on the cylinder liner to avoid scuffing.

So, you need adequate oil above the exhaust port A.
And this oil is scraped by the piston rings and passes over the “hot” open holes pof the exhaust port.
This simply says that you can’t avoid oil from escaping (total loss).

The same with the opposite piston that slides over the open intake (transfer) ports.


Unless they use some “smart” / magic oil that avoids falling into the open holes (i.e. the ports) of the cylinder, the specific oil consumption for this 2-stroke engine of Achates Power can’t be real / true.

The Junker Opposed Piston engines, the “famous” Ecomotors OPOC, the Detroit Diesels of GM had exactly the same problem.


Do I miss something?


As explained above, the trhust load is at the piston pin height.

What if the piston pin is shifted away from the ports?

This is what the OPRE:



and the PatOP:



opposed piston engines do (spot on the piston pins).

The OPRE and PatOP opposed piston engines use “crosshead” architecture that, without increasing the engine length, passes the thrust loads away from the ports, at the cool side of the cylinder.

At the surface of the cylinder where the port openings (holes) are, the OPRE and PatOP need only a thin oil film to protect the piston rings from scuffing.

This allows a “4-stroke-like” lubrication and lowers the specific oil consumption.

Thanks
Manolis Pattakos

[Pinger]

And this oil is scraped by the piston rings and passes over the “hot” open holes pof the exhaust port.
This simply says that you can’t avoid oil from escaping (total loss).

Yes.

The same with the opposite piston that slides over the open intake (transfer) ports.

No.
Surely it will end up back in the cylinder carried by the fresh charge of air.