2 stroke thread (with occasional F1 relevance!)

[Pinger]

Uniflow I respect for recognising the potential of OP architecture, building one, and it being the first crankcase scavenged one. It doesn't however totally eliminate the possibility of UBHC to the exhaust port. In fairness to Uniflow, I don't recall him ever claiming it did.

Other (eg Cummins) OP engines appear to have been swallowed whole by the military disappearing from commercial viability and, as diesels, require direct injection (obviously!) and further, will go the route of the very expensive common rail injection kit.

There just doesn't seem to be anything in the middle ground that can eliminate entirely UBHC without resort to direct injection which despite there being spark ignited diesel versions (again, swallowed by the military) will I think struggle with low volatility bio-fuels should they be pursued (I believe they should). Bio-fuels are closer to ready than synthetic fuels (the volatility of which is unknown to me) but will require very large capital investment to realise.
Bio-fuels or synthetic fuels will be carbon neutral but un-burned emission of either won't be acceptable so is as the problem of UBHC currently with 2T.

[J.A.W.]

Uniflow I respect for recognising the potential of OP architecture, building one, and it being the first crankcase scavenged one. It doesn't however totally eliminate the possibility of UBHC to the exhaust port. In fairness to Uniflow, I don't recall him ever claiming it did.

Other (eg Cummins) OP engines appear to have been swallowed whole by the military disappearing from commercial viability and, as diesels, require direct injection (obviously!) and further, will go the route of the very expensive common rail injection kit.

There just doesn't seem to be anything in the middle ground that can eliminate entirely UBHC without resort to direct injection which despite there being spark ignited diesel versions (again, swallowed by the military) will I think struggle with low volatility bio-fuels should they be pursued (I believe they should). Bio-fuels are closer to ready than synthetic fuels (the volatility of which is unknown to me) but will require very large capital investment to realise.
Bio-fuels or synthetic fuels will be carbon neutral but un-burned emission of either won't be acceptable so is as the problem of UBHC currently with 2T.

Pinger, you'd surely recall that Evinrude E-TEC outboards were very competitive vs 4T rivals on 'UBHC' emissions,
(& that's without taking into account such '4T Owners Manual' views from car-makers - BMW & Subaru - that 'up to
a litre of oil consumed every 1000km is deemed acceptable, & is per production tolerance/specification usage').

Of course the whole 'emissions' aspect is more political than properly scientific, with parameters imposed
via tightly constrained 'modeling', (such as failing to take into account combustion temperature effects on
UBHC particulates,(& as a few other examples will demonstrate) ranging from size/volatility through to
matters of solidity/toxicity/carbon-state/aerosol-state, & deleterious effects on lung-function).

True the military places operation function capability well above the concerns of 'civil' authorities here (& are
indeed exempt from them), but that does not mean they don't have practical reasons to replace 'ancient' design 2T
Detroit Diesels & mid-1970s turbo-shaft engines with their respective smoke/heat emission & fuel guzzling habits.

Bio-oils derived from plants - from the venerable castor plant, through to recent avocado-derived lubricants also
offer a practicable alternative to fossil-sourced lubricants, likewise...

[Pinger]

Pinger, you'd surely recall that Evinrude E-TEC outboards were very competitive vs 4T rivals on 'UBHC' emissions,
(& that's without taking into account such '4T Owners Manual' views from car-makers - BMW & Subaru - that 'up to
a litre of oil consumed every 1000km is deemed acceptable, & is per production tolerance/specification usage').

Add Tohatsu (Orbital system) and others besides - but despite everything, they appear to have been ousted by 4T and I just don't understand why.

Of course the whole 'emissions' aspect is more political than properly scientific, with parameters imposed
via tightly constrained 'modeling', (such as failing to take into account combustion temperature effects on
UBHC particulates,(& as a few other examples will demonstrate) ranging from size/volatility through to
matters of solidity/toxicity/carbon-state/aerosol-state, & deleterious effects on lung-function).

Given the much lower carbon footprint in the manufacturing of 2T engines versus 4T, there should be scope for some dispensation re any oil escaping via the exhaust. As you mentioned, 4Ts burn oil and the disposal of their sump oil (even when recycled, especially when recycled!) also has a carbon footprint.

True the military places operation function capability well above the concerns of 'civil' authorities here (& are
indeed exempt from them), but that does not mean they don't have practical reasons to replace 'ancient' design 2T
Detroit Diesels & mid-1970s turbo-shaft engines with their respective smoke/heat emission & fuel guzzling habits.

I guess the military aren't side-tracked by electrification....

Bio-oils derived from plants - from the venerable castor plant, through to recent avocado-derived lubricants also
offer a practicable alternative to fossil-sourced lubricants, likewise...

Yes (though somewhat prone to gumming) and the possibility of pure synthetics. Pure synthetics are rare. They are inevitably semi-synthetic blended with mineral oil to provide some solubility for the additive packages that pure synthetics lack. Adding mineral oil provides that solubility. 2T oils being 'single pass' don't require much in the way of additive packages.I think - though I'm not certain - this is how Stihl pass UBHC regs with its 4-Mix engines. Single pass pure synthetic oil with zero HC content.

[J.A.W.]

Pinger, you'd surely recall that Evinrude E-TEC outboards were very competitive vs 4T rivals on 'UBHC' emissions,
(& that's without taking into account such '4T Owners Manual' views from car-makers - BMW & Subaru - that 'up to
a litre of oil consumed every 1000km is deemed acceptable, & is per production tolerance/specification usage').

Add Tohatsu (Orbital system) and others besides - but despite everything, they appear to have been ousted by 4T and I just don't understand why.

Of course the whole 'emissions' aspect is more political than properly scientific, with parameters imposed
via tightly constrained 'modeling', (such as failing to take into account combustion temperature effects on
UBHC particulates,(& as a few other examples will demonstrate) ranging from size/volatility through to
matters of solidity/toxicity/carbon-state/aerosol-state, & deleterious effects on lung-function).

Given the much lower carbon footprint in the manufacturing of 2T engines versus 4T, there should be scope for some dispensation re any oil escaping via the exhaust. As you mentioned, 4Ts burn oil and the disposal of their sump oil (even when recycled, especially when recycled!) also has a carbon footprint.

True the military places operation function capability well above the concerns of 'civil' authorities here (& are
indeed exempt from them), but that does not mean they don't have practical reasons to replace 'ancient' design 2T
Detroit Diesels & mid-1970s turbo-shaft engines with their respective smoke/heat emission & fuel guzzling habits.

I guess the military aren't side-tracked by electrification....

Bio-oils derived from plants - from the venerable castor plant, through to recent avocado-derived lubricants also
offer a practicable alternative to fossil-sourced lubricants, likewise...

Yes (though somewhat prone to gumming) and the possibility of pure synthetics. Pure synthetics are rare. They are inevitably semi-synthetic blended with mineral oil to provide some solubility for the additive packages that pure synthetics lack. Adding mineral oil provides that solubility. 2T oils being 'single pass' don't require much in the way of additive packages.I think - though I'm not certain - this is how Stihl pass UBHC regs with its 4-Mix engines. Single pass pure synthetic oil with zero HC content.

Yeah, 'marketing/profits' - just as with MX bikes, most outboards are 'recreational products'..
But those considerations do not apply to military use of course (or at least, not as heavily, maybe).


Modern blend automotive 'castor-based' oils are not nearly so 'gummy' (model/toy 2Ts tend to use a large % of 'pure').
AFAIR, 'synthetic' market-available lubricants are still based on 'fossil gas' processing.

For sure single-pass lubes ejected via low-temperature combustion events - are far less 'toxic' particulate-wise.

[Pinger]

For sure single-pass lubes ejected via low-temperature combustion events - are far less 'toxic' particulate-wise.

And, chances are a cat could deal with them anyway.

[Sockmonkey]

It's been mentioned that adding an active exhaust valve reduces the simplicity of a 2 stroke, but is acceptable sometimes, so just for the heck of it, here's my take.
https://i.imgur.com/U5XR6CF.png
As far as I know, an external valve ring hasn't been done before.
Forces on it are radially symmetrical, and lubrication can get to it via a tube enclosing the gear shaft that turns it.
Sealing rings can be fitted above and below the ports, and having a large number of them keeps the rate it has to turn at much lower than crank speed.

I don't think there are any unsolvable issues, and this thread is a little old so I don't expect replies anytime soon, but I've read through most of it and the inventiveness is interesting to me and so I'm tossing in my two cents.

There are some other ideas I'd like to run by you guys if you wanna see them.

[gruntguru]

Active exhaust ports usually change the timing as well. Later opening at lighter loads.

Your design seems to require a fairly complex exhaust manifold.

[Zynerji]

After just reading about the new ammonia burning engines, could they be done as 2t?

[Sockmonkey]

Active exhaust ports usually change the timing as well. Later opening at lighter loads.

Your design seems to require a fairly complex exhaust manifold.

The exhaust manifold would be shaped like a ring, I imagine. We want the cylinder heads exposed for spark plug changes and such. Ideally, the cylinder would have a ridge running around the outside for the valve to sit on and for the exhaust manifold to attach to.

If we used spiral cut gears for the driving ones and the ones on the valve ring, having the drive gear slide up and down a little on a splined shaft could even get us adjustable exhaust timing.

There is one other idea that may be useful in smaller engines. It's a variation on the moving cylinder liner, except in this case it's part of the piston itself. If the picture isn't clear enough I'm happy to elaborate.
https://i.imgur.com/uFHjyZ3.gif
It requires that the cylinder have a concentric section that goes inside the "bucket" piston.
The advantage of this is that the intake and exhaust ports can be at opposite ends of the cylinder, and it has the same number of moving parts as a standard 2 stroke.

[Tommy Cookers]

I think I said what I wanted to say better in 2011
(cylinder porting dictates increased cylinder spacing making a multi-cylinder engine package disadvantageously large)

(C.F.Taylor said that the usual (eg Sabre) type of sleeve valve was lacking in port area. I think this was why Ricardo's interest turned to the 2 stroke open sleeve as realised in the Crecy)

All cylinder ported engines are relatively starved of port area as larger bore:stroke ratios are used (for higher power via higher revs). This is broadly a historical trend, associated with broad historical progress in fuel quality.

Poppet valves are advantageously aligned wrt gas flow and size, and to use overlap. Crucially, poppet valves areas are relatively larger at larger bore:stroke ratios.
Poppet valves are used in some 2 strokes

Would the 2 stroke prevail in current F1 ?

GP motorcycle 2 strokes always had relatively low bore:stroke ratios to allow sufficient port depths (a fraction of stroke). Shortening the stroke for more revs and power wouldn't work because the port areas would not increase. All these engines had b:s ratios close to 1
GP motorcycle noise limits introduced about 35 years ago were very hard on the 4 stroke, the last ever (flat 4, never raced) MV Agusta failed the noise test at full rpm when producing no power (driven electrically) ! The last MVs that actually raced made as much noise as a grid full of 2 strokes. They were competitive, having a stroke short enough to rev about 40% higher than the 2 strokes

[gruntguru]

. . . and of course you have to squeeze some transfer ports in, somewhere around the periphery - clashing with the exhaust collector.