2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

Any pictures of a v4 2stroke crank? eg. NSR500
Are they a splayed inline 4 to achieve separate big ends and crankcase compression?

Paired side-by-side, just like the old TZ 750, but with V-cylinders - allowing space for needful gas-flow...

The NSR 500 appeared featuring various iterations of V-angle, crank-angle & balancer shaft...

[J.A.W.]

Hi Manolis, per your rotary piston design, have you run 'Fibonaci/prime' numbering computations
on the ideal quantity of lobes, or perhaps even the 'staging' of lobes on a shaft, compressor through to power section, turbine-wise?

[manolis]

Hello Tommy Cookers.

You write:
“a rotary engine with more than the usual Wankel 3 rotor faces - has via the 'crankshaft' gearing a higher torque/lower rpm output ? (than the usual)
this is very valuable for aviation, allowing greater thrust efficiency by using a bigger prop, without needing a reduction gear”


If I understand it correctly, not necessarily.

The architecture of the PatWankel talks for extreme power to weight ratios. It also talks for good sealing at lower revs (wherein the Wankel engine suffers).

For an airplane, a bigger capacity / lower revving PatWankel with the propeller directly driven by the inner body seems interesting.
The good sealing together with the fast – complete combustion “talk” for way lower specific fuel consumption than the Wankel rotary, which also means substantially lower take-off-weight (including the fuel) and way lower running cost (fuel).
With the two only moving parts and the air-cooling it “talks” for reliability.

Thanks
Manolis Pattakos

[manolis]

Hello J.A.W.

You write:
“Hi Manolis, per your rotary piston design, have you run 'Fibonaci/prime' numbering computations
on the ideal quantity of lobes, or perhaps even the 'staging' of lobes on a shaft, compressor through to power section, turbine-wise?”

No.
For the moment we deal with the typical arrangements, like triple, five, seven chamber designs, say like:



The above animation is useful for timing-check reasons:

The angle step is 10 degrees (as in the conventional engine, 180 degrees separate the TDC (wherein the volume of a working chamber is minimized) to BDC (wherein the volume of the same working chamber is maximized).

Start counting “frames” (and degrees) the moment the inner body is “horizontal” with the ports at right.

The timing shown is conservative.
The “overlap” may seem big, but it is quite small. This is so because during the “overlap” either the intake ports, or the exhaust ports, or both, are almost closed by the inner surface of the outer body.
The overlap in this engine is way different than in a, say, Ducati Panigale:



wherein overlap means, more or less, the “short circuit” between the intake and the exhaust (the area marked by the yellow ellipses) and inevitable loss of unburned mixture,
while in the above PatWankel overlap means a through or uniflow “scavenging” of the chamber by the fresh charge (more or less as in the opposed piston engines) that sweeps / pushes out the burned gas and reducing this way the residual gas.


The following animation shows a timing of a Five-chamber PatWankel (the step is 5 degrees now):



The following animation shows a timing of a Seven-chamber PatWankel (the step is 10 degrees, with 180 degrees being the angle from TDC to BDC):



Thanks
Manolis Pattakos

[Pierce89]

Can you show us anything in metal that is actually running? Theoretical CAD designing without simulation or empirical testing is really just making pretty pictures more than it is engine development.

[manolis]

Hello.

Quote from http://www.nextbigfu...ker-liquid.html

December 19, 2016:

Revolutionary engine maker Liquid Piston seeks commercialization partners after landing $2.5 million DARPA funding for 40HP engine that will be 30 lbs instead of conventional 2700 lbs for diesel

End of quote.


Without special care on the weight reduction, this direct-injection Diesel engine:



youtube video at:

https://m.youtube.co...h?v=2ByEgfTTq1I



(Opposed piston, 2-stroke, 636cc (with 850cc built-in scavenging pump), extended dwell at TDC, 4-stroke like lubrication, full balance etc)

weighs 20kg and is for way more than 40PS.


Regarding the LiquidPiston:

Last month LiquiddPiston received another $2.5 million from DARPA for their rotary engine.
More important: LiquidPiston also received a $25,000 cash prize from Shikorsky along with the opportunity to explore opportunities for LiquidPiston's technology with the Shikorsky product line

Thanks
Manolis Pattakos

[uniflow]

Manolis, this is hardly new technology is it. I think the first opposed piston engine ever built worked like this one.

[manolis]

Hello Uniflow.

You write:
“Manolis, this is hardly new technology is it. I think the first opposed piston engine ever built worked like this one”


No.

Here is one of the first Opposed Piston engines, patented by Hugo Junkers in 1927. Under his license it was produced in England as Junkers – Doxford to propel ships.



The two pistons perform a substantially different motion which, among others, result in heavy second order unbalanced inertia forces, in tall structure, in excessive lubricant consumption etc.


Here is a modern version of it:



It is the OPOC of EcoMotors.

What is the OPOC?
It is two Junkers-Doxford sharing a common crankshaft for the sake of a better vibration-free quality.

$23.5millions were lost by Bill Gates of Microsoft on the OPOC design.
Another $25millions were lost by DARPA on the same design.
Some $50millions were lost by other investors of EcoMotors.

Why lost?

Unless I am wrong, they have nothing in production yet; they would produce engines during 2014 (Navistar etc), then during 2015 (cooperation with a Chinese manufacturer), then during 2016 and so on.
The initial plan was to produce engines for trucks and cars.
Then, due to emissions, they turn direction to engines for electric generators etc.
But if you look at their design, they have several issues yet to address


I was tired reading, again and again, articles presenting the “great” OPOC engine.

A couple of years ago I wrote in “TheKneeSlider” where they were re-re-re-presenting the “promising” OPOC engine:

“In EcoMotors they have the funds, they have the publicity (every time a guy in EcoMotors “coughs”, every magazine in the world publishes -or reproduces- an article for OPOC), they have the support (only the name of Bill Gates “opens” every door). What they don’t have is a good engine design.
Unless I am wrong, after several years there is not yet an OPOC in a car or truck for tests by an independent third party.
Get in the place of the independent inventors / researchers / makers and think how they feel seeing in the press, again and again and again, about the OPOC of EcoMotors, about how many parts less than the other engines it comprises (which is a false claim), about how many less fuel it will consume (which is also a false claim), about how “green” it will be (which is also a false claim), and so on.”



The PatOP is different :



The two pistons perform identical (or very similar, depending on the design) motion.
The design enables a substantially lower overall height (see in the animation the piston rings of the “lower” piston; they “get” almost into the crankshaft).

The design is “cross-head” for both, the upper piston and the lower piston.
The cross-head design transfers the thrust loads away from the ports, at the cold side of the cylinder and enables 4-stroke-like lubrication.

With one only pair of opposed pistons the PatOP has a better balancing quality than the basic module of the OPOC which comprises two pairs of Opposed Pistons.

The OPRE / PatOP / PatPortLess (see at the http://www.pattakon.com web site) use pulling-rod architecture which extends substantially the dwell of the piston around the combustion dead center.

The LiquidPiston rotary engine (my last post) claims “constant volume combustion” while the volume of its working chamber varies harmonically (pure sinusoidal), which, at the combustion dead center, offers some 12 to 15% longer dwell (i.e. additional time to the fuel to get burned at high compression ratios).

The PatOP engine gives some 15% more time than the LiquidPiston engine (and than the Wankel engine), and some 30% longer dwell than the conventional reciprocating piston engines.



If the LiquidPiston (harmonic volume change, green curve in the above plot) is considered / advertised as a "constant volume combustion" engine, then what about the PatOP / OPRE engine? (the blue curve in the plot, which is substantially "slower" around the combustion dead center than the green/harmonic curve).

When you burn the diesel fuel in a PatOP running at 6,000rpm, the injected fuel feels as it burns inside a conventional engine running at only 4,500rpm (a great advantage for its peak power relative to the conventional Diesels).


For more, you can read at http://www.pattakon.com/pattakonPatOP.htm and http://www.pattakon.com/pattakonOPRE2.htm (or read the granted patents).


In the prototype PatOP engine:



the bore is 79.5mm (the piston rings are from a VW1.9Tdi),
the stroke is 64+64=128mm,
the capacity is 636cc,
the built-in scavenging pump bore is 130mm (its stroke is 64mm as it is secured at the lower end of the lower piston),
it has a 1.33 over-scavenging ratio (850cc scavenging pump capacity , 636cc combustion chamber capacity).


I would like to know your thoughts / objections about the PatOP.

Thanks
Manolis Pattakos

[Brian Coat]

Achates seems to me to have a more credible development program than Eco.

[Muniix]

Achates seems to me to have a more credible development program than Eco.

Agree on that one.

Having a higher dwell time is not that a significant a improvement in combustion, going on the more current combustion research papers reveals this, the latest F1 teams with Turbulent Jet Ignition, Ultra lean and multi phase combustion use a combination of constant volume and constant pressure, i.e. the polytropic index to extract greater work, and power the exhaust energy recovery systems to achieve higher efficiencies, low NOx etc. Constant volume can create more emissions and chemical species one wants to avoid, ones that consume the heat energy and thus some of the potential work available is lost, worse it is converted into toxic substances. It depends on the intended fuel that is to be used.

Some comments on the Rotary engine sealing

One thing that seems an issue is with the huge seal array, how does one cool it and achieve the necessory seal force, normally one uses the gas pressure and slots to allow the gas to get in and behind the sealing elements, this will be trickly as their is a active combustion chamber operating at different stages of pressure on each side of the seal, and this would allow gas to be exchanged between those two chambers. The thermal expansion of the seals and the previously mentioned minimal cooling available. Its not like you can run cooling channels along side or behind the gas seals as done on the Bishop rotary valve that saved them enormously in the implementation complexity, maybe that cooling is what made the Bishop possible, it provided the cooling function lubrication would normally have provided. The crevice volume areas where the 'end gas' which is at high pressure resides and can leak past seals contains a very high density (being at high pressure) is lost into blow by areas or between chambers through any gaps between seals, possibly caused by thermal expansion.

[Muniix]

Here is a V4 500cc 160HP 2T Motorcycle by Ronax -- Dual Countra-rotating crankshafts

It uses a narrow 80-degree V-angle (NSRs were 112-degree and YZRs 70-degree). Bore and stroke is 54 x 54.5mm, the same as the YZR and NSR, while the Ronax uses twin counter-rotating crankshafts supported inside CNC billet alloy crankcases that also house a cassette-style gearbox and a wet multi-plate clutch to make the bike more useable on the road. Ronax are claiming 160-rear-wheel-horsepower at 11,500rpm for the bike, which is incredible!

Seams the dual crank shafts are making a comeback, maybe people are realising some of the advantages in certain applications, and with crankshaft bearings being the smallest contributor to engine losses.

http://bikereview.com.au/ronax-v4-500cc-two-stroke/

[manolis]

Hello Brian Coat.

Achates Power has similar size with EcoMotors (some 100 millions US dollars , so far) and similarly famous investors (WalMart etc).

They had several arrangements of Opposed Piston engines, most of them with two counter-rotating crankshafts at the sides of the cylinders, multiple connecting rods (in order to eliminate the thrust loads on the cylinder liner) etc, like:



According the Internet they received some 14 millions from the US Army for an Opposed Piston engine for tanks etc. It is strange that this Opposed Piston for the US Army has the typical design of the old Junkers-Jumo engine.



Hello Muniix

The Ronax 500 has two crankshafts (as, say, the Bimota 500, or the Suzuki RG500), but they say nothing about multi-connecting-rods per piston.
I suppose the overall friction of the Ronax, as compared to a single crankshaft engine, increases.



Talking for the sealing in the Wankel, LiquidPiston and PatWankel rotary engines, here are some interesting, I hope, details:


With their different arrangement of the seals, LiquidPiston creates new “sealing” problems (not existing in the Wankel engine).

According the following drawing (from the patent of LiquidPiston):



there is an immovable “peak” seal, 825, which abuts on the cylindrical working surface 202R of the inner body,

there is also a side seal, 801, in a groove of the inner body, which follows the motion of the inner body.


A LiquidPiston side seal, as the seals of the conventional Wankel, undergoes a substantially variable (in direction and in amplitude) acceleration around the seal and around the cycle.

Here is the inertia force an apex seal of a conventional Wankel applies to the epitrochoidal casing :



(at some angles the inertia vectors outwards, at some other angles it vectors inwards),


and here is the acceleration required in order a point at the top edge (the outmost edge) of the side seal of a LiquidPiston engine to follow the motion imposed by the spinning / orbiting rotor:



and here it is shown, for comparison, the acceleration required in order a point at the innermost edge of the side seal of a LiquidPiston engine to follow the motion imposed by the spinning / orbiting rotor:



The following drawing helps in understanding the previous plots (the red circles show the path the outmost edge of the side seal follows, the cyan circles show the path the innermost edge of the side seal follows) :



R1 is the "crank-arm" of the eccentric shaft, R2 is the distance of the specific point of the seal from the center of the rotor.
In the LiquidPiston the casing (blue, yellow) is stationary. The rotor (not shown) performs a combined spinning-and-orbiting motion.



The gaps between the apex-seals /corner-seals / side-seals of the Wankel engine are gaps between bodies moving together (they are all inside grooves / holes of the rotor).


In the LiquidPiston, the side seal moves together with the inner body (the rotor), while the rest seals are stationary.
Any clearance of the synchronizing gear-wheels,
and any clearance in the bearings supporting the rotor (the bearing by which the rotor is rotatably mounted on the eccentric shaft and the bearings by which the eccentric shaft is rotatably mounted on the immovable casing),
and any “play” of the side seal inside its groove,
and any flexing of the eccentric shaft (or power shaft) due to inertia and/or combustion loads,
all are added to the required gap between the side seal and the “button seal”.
Note: around each chamber there are four such gaps.

The result is even more gas leakage than in the conventional Wankel.


Now think how the seals are arranged and are working in the PatWankel:



In the PatWankel with the working surface on the inner body, all the seals are inside grooves made on the outer body and perform a pure rotation (during a cycle, the inertia force remains constant in direction and constant in amplitude). Etc.


By the way, without an eccentric shaft, there is no flexing of the eccentric shaft.
Without inertia loads on the bearings, the clearance between the inner and the outer bodies is smaller.
Without eccentric shaft, no balance webs are required.

Thanks
Manolis Pattakos

[Muniix]

Now think how the seals are arranged and are working in the PatWankel:

http://www.pattakon.com/PatWankel/PatWa ... _Sport.gif

In the PatWankel with the working surface on the inner body, all the seals are inside grooves made on the outer body and perform a pure rotation (during a cycle, the inertia force remains constant in direction and constant in amplitude). Etc.


By the way, without an eccentric shaft, there is no flexing of the eccentric shaft.
Without inertia loads on the bearings, the clearance between the inner and the outer bodies is smaller.
Without eccentric shaft, no balance webs are required.

Thanks
Manolis Pattakos

Ok, two rotating bodies with seals between them, the air entering from the centre into the rotor with a kind of pre-chamber internal to the rotor that contains the combustion ignition system/spark plug. With the laminar flame speed of Gasoline at around 0.3 metres/second, too slow for combustion engines to be viable, they use turbulence generating mechanisms to enhance combustion speed. This is typically measured as mass averaged turbulent kinetic energy.

What is the turbulence generation mechanism?

What would be the TKE ?

Issue with sealing such a large seal array, how does one cool it and achieve the necessory seal force?

These are very significant issues with the design in order for it to be viable. I'm sure many would be interested in how these issues are to be solved.

The LiquidPistons 3-5hp for 70cc using the same architecture, doesn't bode well.
Seems obvious what needs improving and what the issues are with this concept.
If these issues are addressed it might worth while.
Someone might have some good ideas to remedy these serious issues.

The considerations;

Normally one uses the gas pressure and slots to allow the gas to get in and behind the sealing elements, this will be trickly as their is a active combustion chamber operating at different stages of pressure on each side of the seal, and this would allow gas to be exchanged between those two chambers. Not good for emissions or power!

The thermal expansion of the seals and the previously mentioned minimal cooling available. Its not like you can run cooling channels along side or behind the gas seals as done on the Bishop rotary valve that saved them enormously in the implementation complexity, maybe that cooling is what made the Bishop possible, it provided the cooling function lubrication would normally have provided. Or possible the end gas could cool the seals shrinking them compared to the rotor which will grow larger as it absorbs combustion heat. The end gas is cool generally as no combustion occurs, it is quenched due to proximity to soo much combustion surface around it.

The crevice volume areas where the 'end gas' which is at high pressure resides and can leak past seals contains a very high density (being at high pressure) is lost into blow by areas or between chambers through any gaps between seals, possibly caused by thermal expansion.

The Blow-by areas are large near the centre of the rotor, how is this going to be managed?

Good engineering practice, brings good engineering solutions and discussions. Others just ignore issues.


Mahle's Jet Ignition, uses the presure difference between main chamber and pre chamber throught the gas exhange holes provides useful turbulence generation to support fast combustion of the pre chamber and exchange of the radicals and combustion products and fresh air.

Having a lower dwell time, is kind of self defeating if the piston/rotor is approaching at the same slower velocity as it leaves, it is imparting less kinetic energy into the turbulence, so it will take extra time for combustion to progress, cancelling out the advantages of the improved dwell time! It effectevely is running the engine at a slower speed with less TKI and slower combustion with spark ignition anyway, different story for compression ignition.

Whereas with offset crankshafts of modern crank-train engines optimising friction reduction or dual-offset counter rotating crankshafts that have large offsets, the piston approaches tdc at the highest speeds in its motion (the rod is becoming more vertical), and leaves tdc very slowly (the rod attains its most vertical or inline with the cylinder axis some time after tdc) in the speed quandrant profile caused by the rod being at different angles due to the offset. This imparts high TKI into the gasses during compression and for any exhaust gas energy recovery systems, and a slower retreat from tdc, maximising extraction of work from the combustion forces, the best of both approaches and the negatives of neither.

[manolis]

Hello muniix

You write:
“What is the turbulence generation mechanism?”

The inner body (red) sweeps (progressively, at the beginning of the compression, abruptly at the end of the compression) the gas from the working chamber into a compact small cavity.
Depending on the design of the cavity, you can achieve as much turbulence as you like (say, as in the “bowl” on the piston crown of the direct injection Diesels).


You also write:
“Issue with sealing such a large seal array, how does one cool it and achieve the necessory seal force?”

More easily and efficiently than in the Wankel rotary.

Take another look at the accelerations the seals in the Wankel and in the LiquidPiston undergo (previous posts).

In the PatWankel with the working surface on the inner body, things are way better, because each point of a seal undergoes a constant in amplitude (and permanently directed to the rotation axis of the outer body) acceleration.

With all the seals into grooves on the outer body, their cooling is easy and efficient.

And as they slide “sweeping” all the working surface on the inner body (the red surface in the animations), they cool the inner body, too (think how the piston rings cool the piston in a reciprocating piston engine; something like this).


You also write:
“Whereas with offset crankshafts of modern crank-train engines optimising friction reduction or dual-offset counter rotating crankshafts that have large offsets, the piston approaches tdc at the highest speeds in its motion (the rod is becoming more vertical), and leaves tdc very slowly (the rod attains its most vertical or inline with the cylinder axis some time after tdc) in the speed quandrant profile caused by the rod being at different angles due to the offset. This imparts high TKI into the gasses during compression and for any exhaust gas energy recovery systems, and a slower retreat from tdc, maximising extraction of work from the combustion forces, the best of both approaches and the negatives of neither.”

Despite the fact that dual-counter-rotating-crankshafts with multi-connecting-rods-per-piston designs are known for a century, or so, none of them “survived” in the long term.

There are simpler designs that eliminate the thrust loads (like the kinematic mechanism used in the Harmonic PatTwo engine and in the first PatRoVa prototype engine).

A good effort was that of Achates Power, but even they seem to dislike their dual crank / multiple connecting-rod design (their engine design for the US army is based on the old Junkers Jumo, wherein each piston is connected to one only crankshaft).

On the other hand, the recent giant marine engine X92 of Wartsila uses a connecting rod having a center-to-center distance equal to the piston stroke (3,468mm; the leaning angle of the connecting rod varies from –30 to +30 degrees relative to the cylinder axis), which means way heavier thrust loads (but no additional friction, due to the crosshead design and to the true hydrodynamic lubrication there). Its Brake Thermal Efficiency, running on heavy fuel, is more than 50%.

Simpleminded question:
Is the complication, the side effects (for instance, think about the consequences of the torsional flexing of two long crankshafts which are synchronized at one end, on the motion / thrust loads of a piston driven by their other end), the added friction (which includes the additional bearings required and the need to pass half of the power through the gearwheels), etc.



You also write:
“Having a lower dwell time, is kind of self defeating if the piston/rotor is approaching at the same slower velocity as it leaves, it is imparting less kinetic energy into the turbulence, so it will take extra time for combustion to progress, cancelling out the advantages of the improved dwell time! It effectevely is running the engine at a slower speed with less TKI and slower combustion with spark ignition anyway, different story for compression ignition.”

The LiquidPiston engine (just like the Wankel rotary engine) has a pure sinusoidal relation between the increase of the volume of the working chamber and the rotation angle.



To take an idea for the size of the XMv3 engine: the spark plug to spark plug distance is about 100mm, the width (i.e. the height of the piston along the rotation axis) is about 20mm.
With a compression ratio of 9.2:1, the cavity wherein the mixture is concentrated at the end of the compression is less than a cube having a side of 14mm.

Look at the specifications (capacity per working chamber: 23cc, extreme overall surface to volume ratio) and focus on the Peak Brake Thermal Efficiency (18% at 5,000rpm).

Then calculate what this 5,000rpm means for the working gas (with reference to the leakage and to the thermal loss).

It is like operating an over-over-square, with problematic sealing, 23cc reciprocating piston engine at only 5,000/1.5=3,300rpm and achieves 18%peak thermal efficiency.

Here is a plot (I think from NSU) regarding the BTE of the Wankel-NSU KKM 502 of Spider (498cc, single rotor) which has a per chamber capacity more than 20 times bigger than the LiquidPiston XMv3 mini engine:



The red letters (BTE) at the right margin of the plot were calculated / added.

In normal size (say 500cc per working chamber, which means some 3 times smaller surface to volume ratio) the LiquidPiston, and the PatWankel with the substantially smaller leakage, seem capable for way higher BTE. Don’t they?


Thanks
Manolis Pattakos

[Muniix]

Hello muniix

You write:
“What is the turbulence generation mechanism?”

The inner body (red) sweeps (progressively, at the beginning of the compression, abruptly at the end of the compression) the gas from the working chamber into a compact small cavity.
Depending on the design of the cavity, you can achieve as much turbulence as you like (say, as in the “bowl” on the piston crown of the direct injection Diesels).

So in regard to the pre and main chambers, which btw are normally implemented with the pre chamber inside of the main so it is close by and normally only 1-3% of the main chambers volume to keep energy loss to a minimum, and sealing issues simple. You have gone with the complete opposite approach, large pre-chamber, separate and isolated and a large distance away. This is really breaking the mould with pre-chamber design. This brings lots of issues, doubling up the sealing requirements, achieving good fluid flows into the pre-chamber, between pre and main for work and scavenging, and inlet air flow into the pre-chamber.

Back to turbulence and fluid flow, creating turbulence is well known and researched subject, it is generating turbulence without loosing energy in the flows that is the complex issue engineers are allways dealing with.

The issues here are now beyond just a simple examination, they need a huge effort in simulation to understand how it actually works and the pressure gradients that will effect the fluid flows. This will need a customised 3D simulation system, nothing normal with this design, so simulation and modelling will be a costly challenge.

The seals, having up to 100 bar of gas pressure acting on the exposed seal faces and forcing them towards the side of their slot and between the seal and the surface they are meant to seal against, causing the gas seal to effectively collapse. Their are all sorts of pressure scenereos that have to be dealt with, one chamber operating at near full throttle, then a closed or near closed throttle on the next chamber. The design seems to ignore the pressures involved which will swamp most everything else.

Friction from the seals being forced against the sides of the slots, and the friction of the surface it is sealing agains has to be taken account of. With the seals in slots on the outer surface and the image shows it rotating, the gyroscopic action is going to negatively effect the sealing force. The point where the seals meet and the gap will cause blow-by, heat will effect thermal expansion and effect this gap. Achieving the necessary seal force evenly over the large array is going to be difficult. Lots of issues when one looks into it.

You also write:
“Whereas with offset crankshafts of modern crank-train engines optimising friction reduction or dual-offset counter rotating crankshafts that have large offsets, the piston approaches tdc at the highest speeds in its motion (the rod is becoming more vertical), and leaves tdc very slowly (the rod attains its most vertical or inline with the cylinder axis some time after tdc) in the speed quandrant profile caused by the rod being at different angles due to the offset. This imparts high TKI into the gasses during compression and for any exhaust gas energy recovery systems, and a slower retreat from tdc, maximising extraction of work from the combustion forces, the best of both approaches and the negatives of neither.”

Despite the fact that dual-counter-rotating-crankshafts with multi-connecting-rods-per-piston designs are known for a century, or so, none of them “survived” in the long term.
...
Is the complication, the side effects (for instance, think about the consequences of the torsional flexing of two long crankshafts which are synchronized at one end, on the motion / thrust loads of a piston driven by their other end), the added friction (which includes the additional bearings required and the need to pass half of the power through the gearwheels), etc.

The whole auto industry essentially went bust during the GFC, because they have optimised, near eliminated change from their production plant equipment, to keep their capital heavy investments to a minimum, they failed to change to market needs and demands. Many companies died during this period, others were bailed out, merges, split ups.

In single cylinder implementations, the issues are simpler, ford, gm and others have been actively researching multi cyclinder dual crank arrangements in the last decade for NVH reasons and Hybrid use. If fact the BMR Suzuki used such an implementation and it won the 1998 Super mono champion ship, due to its superior power from the improved thermodynamics the kinematics provide. The reduced piston friction which is the highest contributor to losses.
The Yanmar / Neander Shark Diesel outboard motor recently launched uses such a dual crank, dual rod/piston engine. It also has very novel lubrication of the crank-train, it is in the patent, is sort of dry.

Simulation is the only way to really answer the question, does the very small increase in bearing friction (which is the lowest contributor to engine losses) over ride the advantages, like elimination of balance shafts, the improved thermodynamics, the enhanced crank/rod angle with pressure curve. reduced piston skirt length and hence friction etc. There are allways issues that fail to be considered if one doesn't do simulations of the whole system with accurate and detailed models.

Thanks