2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

It would be interesting for Manolis to turbocharge his opposed piston and to measure the gains.

Yeah, but Manolis appears to dismiss the need for any kind of post-exhaust port attachments,
from a basic pipe to direct noxious levels of hot-blasting gases & noise away from the operator,
to a combination silencer/power-pipe - to anything heavier/more complex - like a turbo...

He has AFAIR, previously dismissed the idea of E85 fuel, on the basis that any power/cooling
gains were needless versus straight petrol, along with fuel volume/power density disadvantages.

Manolis would only consider a turbocharger useful for altitude compensation & currently does
not envisage any 'flyer' activity much above sea level, at least 'til he's got it proved.

Here's a picture of a 2T multi-fuel turbo-compound aero-engine by Napier, not opposed piston like
their much heavier surface dwelling Deltic turbo, nor a poppet valve engine like a 2T Detroit..

[Pinger]

It all depends on having overlap, a certain amount of air fuel will blow straight down the exhaust also.

But for the back pressure created by the turbo's turbine.
(I was reading a paper where Renault developed a 4T engine to run exclusively on natural gas. To simulate turbocharging on the dyno they provided 'shop air' for the inlet side and replicated the turbine's contribution to back pressure with a butterfly valve in the exhaust).

I tried to clarify which design path of 2 stroke was being followed to further this discussion on the 2 stroke turbo thread as there are 2 design paths for a 2 stroke, detroit diesel style or an expansion exhaust style.
I dont know what the opposed pistons characteristic is for overlap, maybe its perfectly suited to supercharging and not realised yet?

According to some Napier Deltic literature I was reading the exhaust piston had a 20 degree lead and closed before the inlet/transfer port did. This was also true of the Rolls-Royce Crecy where it was said to afford a 'small degree of supercharging'. Supercharging was also claimed to be a feature of the Deltic.Very small though as the period (in both engines) where the exhaust is closed and the inlet/transfer still open is very short. With a 2T, any blower is much more a scavenge pump than supercharger - unless/until turbo back pressure is utilised - or possibly a tuned pipe. But the pipe would do that without a blower anyway.

[Pinger]

The sonic-pulse is not going to do an immediate by-pass up a right-angle joint,

Not 'by-pass' but split and individual components of it travel up any branch it encounters. 'Tis the teaching of Blair and were it not so the 'compact branch manifold' as applied to groups of 3 and 4 cylinders would not work. Blair also points out that a sonic pulse has no mass thus no inertia and turning corners therefore doesn't trouble it.

but the gasses will
find that 'escape hatch' once the piston shuts the ex-ports, & quite obviously, Rotax must've tested
this arrangement against the existing type - which had the turbine at the tail-end of the expansion
chamber - finding sufficient advantage in it, to patent it for their own use.

Sooner than that and Rotax will have designed the system as they have to maximise the thermal energy to the turbine (rather than the gas lose a shed load of heat travelling through the expansion chamber) before arriving at a turbo as with other systems.

Still the question of what happens to the pulse on encountering the turbine remains. We know that a returned +ve pulse at exhaust port closing 'sees' an obstruction and reflects back down the pipe as the +ve pulse it was when it arrived. What of the -ve pulse arriving around BDC? Is there a clue there as to what happens with a turbo?

[J.A.W.]

The sonic-pulse is not going to do an immediate by-pass up a right-angle joint,

Not 'by-pass' but split and individual components of it travel up any branch it encounters. 'Tis the teaching of Blair and were it not so the 'compact branch manifold' as applied to groups of 3 and 4 cylinders would not work. Blair also points out that a sonic pulse has no mass thus no inertia and turning corners therefore doesn't trouble it.

but the gasses will
find that 'escape hatch' once the piston shuts the ex-ports, & quite obviously, Rotax must've tested
this arrangement against the existing type - which had the turbine at the tail-end of the expansion
chamber - finding sufficient advantage in it, to patent it for their own use.

Sooner than that and Rotax will have designed the system as they have to maximise the thermal energy to the turbine (rather than the gas lose a shed load of heat travelling through the expansion chamber) before arriving at a turbo as with other systems.

Still the question of what happens to the pulse on encountering the turbine remains. We know that a returned +ve pulse at exhaust port closing 'sees' an obstruction and reflects back down the pipe as the +ve pulse it was when it arrived. What of the -ve pulse arriving around BDC? Is there a clue there as to what happens with a turbo?

As Blair might tell you (if he was able) a 90 degree off-tube isn't a 'corner' to be swept about, a pulse
shot is purblind to it, while gas pressure isn't ( think 'manhole' covers being blown off)..

As a 180 degree twin, with a 2-into-1 manifold, exhaust pulses are regular, & having heat enter the
turbine, rather than the exhaust ports, is a good thing, & which as testing doubtless showed, was timed
properly for best results EGT-wise, prior to Rotax/BRP going though the cost of producing a patent.

[coaster]

That Napier design is like a straight jacket relying so much on its crankshaft phasing, im glad its no longer in vogue.
One crankshaft and a moveable sleeve port could offer so much more for efficiency.

[J.A.W.]

That Napier design is like a straight jacket relying so much on its crankshaft phasing, im glad its no longer in vogue.
One crankshaft and a moveable sleeve port could offer so much more for efficiency.

On a piston-to-crankshaft ratio, the compact Deltic didn't do so badly,
& that basic Jumo opposed piston layout appears to be back "in vogue"..

[coaster]

Perhaps for a certain inventor it may well be back in style, but come on, really? All those moving parts? The friction losses would be a big problem.

[gruntguru]

The moving parts count is lower than for 4 stroke engines.

[J.A.W.]

Indeed, no poppet valve gubbins above the piston crown, just another piston.

As for being "back in style" for "a certain inventor", seems well known Diesel manufacturer
Cummins has put their backing into a variant of this one linked below, as a replacement
for the hot/thirsty inefficient turbo-shaft engines currently used in US-built military tanks.

https://dieselnet.com/news/2021/03achates.php

[coaster]

Wow, this is why our inventor is silent, he's so busy with his company doing this now.
I'm glad he did not test pilot the personal flyer,
I had nightmares about that flyer.

[J.A.W.]

Wow, this is why our inventor is silent, he's so busy with his company doing this now.
I'm glad he did not test pilot the personal flyer,
I had nightmares about that flyer.

Dreams of flying (with minimal, or no, visible apparatus of support) are fairly common,
I'd have thought - albeit doing an 'Icarus' can tend to be a tad nightmarish, yeah...

Have you attempted to contact Manolis by PM from here, or via his own site?

Another member here is a home-builder/self-pilot of 2T aero-engines/rotorcraft - 'uniflow',
& he has some cool yet fully bona fide youtube evidence of his success in so doing...

[Big Tea]

Why 14 ltr? The hardest part of war is getting everything you want in the place you want. Logistics takes far more resources than combat. Every kg of fuel needed is a kg of something else not transported, and size is weight.

Why are they not looking at smaller size and more RPM and gearing it?

[gruntguru]

The Power (1000 hp) and fuel efficiency (40%+) targets alone will dictate the engine type and displacement. A smaller high rpm unit will not meet the efficiency target.

[J.A.W.]

Certainly every aspect of usage/packaging requirements must be taken into account,
& as the Cummins tech-bloke noted - the potential for modular increases in cylinder
count/power rating - keeping the same dimension for each 2 piston per cylinder, is
utilitarian, according to role requirement/weight/volume of the armoured vehicle.

[Dr. Acula]

Why 14 ltr? The hardest part of war is getting everything you want in the place you want. Logistics takes far more resources than combat. Every kg of fuel needed is a kg of something else not transported, and size is weight.

Why are they not looking at smaller size and more RPM and gearing it?

You need a lot of immediate torque/power in this particular application. The vehicle needs to really going forward when you press the pedal down from a standstill. That means you can't wait for a big turbocharger to spool up because until that happend you may have been unlucky and got hit. So you need quite a bit of displacement to achieve that. Also 1000hp out of 14.8l displacement is really not to shaby for such an engine.
Just for comparison the MTU Diesel engine of the Leopard 2 achieves 1500hp with a displacement of 47.6l. Sure, it's basically a 1970s Diesel engine, but that just shows how much more compact these modern engines can be.