The “four-stroke propaganda” and the “conspiracy theories” cannot justify the complete absence of the two-strokes from motorcycles and cars.
The two-stroke has some technical issues yet to solve. This is why it is used only in marginal applications (2-stroke Mercury outboard engines, 2-stroke snowmobiles, a KTM 2-stroke model that needs a kit in order to cheat the rules, the Hirth small aircraft engines etc).
Talking for aircraft engines, here is a Cross Radial PatATeco:
Full balance (as the best V-8) and even firing.
A turbocharger is driven by the exhausts and feeds with compressed air the intake/transfer ports. Indirect injection inside each piston. Etc.
Thanks
Manolis Pattakos
Last edited by manolis on 21 Oct 2016, 14:07, edited 1 time in total.
If the exhaust could close earlier than the transfer, then things would improve a lot in the 2-stroke.
In the Opposed Piston engines this is easy. The one piston controls the exhaust port, the other piston controls the transfer ports. With the proper timing of the two crankshafts, the transfer can extend after the exhaust is closed.
With a single piston per cylinder, things are more difficult. But there is simple solution: the PatAT architecture:
The above “timing” is what the PatAT engine does, without the need of the reed valve you mention.
“With the PatAT the two-stroke operates on asymmetric timing (as shown, for instance, in the above plot at right, wherein: the exhaust port opens 55 degrees before the BDC and closes 55 degrees after the BDC, while the transfer starts 35 degrees before the BDC and ends 65 degrees after the BDC).
In the PatAT the source of pressurized air or mixture (the crankcase in most cases) communicates with the combustion chamber through transfer ports disposed in series with respective piston ports.
The transfer ports are controlled by the piston.
The piston ports are controlled by the connecting rod.
The source of pressurized air or mixture can, additionally, communicate with the combustion chamber through conventional transfer ports (that open by the piston after the exhaust port)
As the piston moves "downwards", it initially opens the transfer ports; but with the respective piston ports closed by the connecting rod, the combustion chamber cannot communicate with the crankcase (or, in general, with the scavenge pump).
The piston continues its downwards motion and opens the exhaust port; the pressure inside the combustion chamber drops quickly; the crankcase continues to remain sealed from the combustion chamber.
Later the connecting rod opens the piston ports (and the piston opens the conventional transfer ports, if any). The transfer takes place.
As the piston moves upwards, it initially closes the conventional transfer ports (if any).
Later the piston closes the exhaust port.
The crankcase is still communicating with the combustion chamber: after the closing of the exhaust port, air or mixture continues to enter (through the "connecting rod controllable" piston ports and their respective transfer ports) into the combustion chamber until the transfer ports to close by the piston.
While the engine remains as simple, as cheap and as compact as the conventional two-stroke, its operation is drastically improved.”
End of Quote.
I hope this is what you were asking about: a two-stroke capable to keep its transfer open after the closing of the exhaust (which is crucial for an efficient 2-stroke supercharging).
So after about a week on and off of reading this topic all the way through, I've decided to register for the forum.
I will preface by saying that I do not pretend to understand everything that has been discussed, and that might be a bit of an understatement...
That being said, I do have a few comments:
Manolis, I like your rotary valve design (patrova?) though I am curious, have you developed any provisions for variable timing? How about variable lift and duration? It seems there is a lot to be gained in a modern engine, in terms of powerband and flexibility with these technologies, which, mind you, aren't particularly new. Additionally, if wanting to change the flow characteristics of the patrova valves (pardon any misnomers, please) by either re-machining or replacing all together, how do the potential costs compare to sourcing a different set of camshafts as one would in a conventional "poppet valve" engine?
At risk of embarrassing myself, may I ask, can 2T engines not use an overhead cam and "poppet valve" setup like a 4T? I can understand that doing so would ruin the mechanical simplicity inherent in the 2T design, but not remove the 2T's main advantage of one combustion event per cylinder per crank rotation.
In addition, what are people's thoughts on how valves without valvetrains play into all of this, both for 4T and 2T designs. What I mean are things like Koenigsegg's "FreeValve" designs, where valve actuation is achieved not by mechanical action following camshafts etc. but rather electro-magnetically, electro-hydraulically, electro-hydraulic-pneumatically, etc. In theory, you would be rid of losses from having to mechanically operate valves (though gaining some elsewhere for pneumatic or hydraulic pumps, etc.) while having "infinite" control over intake and exhaust events. Again, not exactly a "simple" design, but if we're originally (supposed to be) talking about potential F1 engines, the level of technology would certainly seem appropriate.
You write:
“I like your rotary valve design (patrova?) though I am curious, have you developed any provisions for variable timing? How about variable lift and duration? It seems there is a lot to be gained in a modern engine, in terms of powerband and flexibility with these technologies, which, mind you, aren't particularly new.”
A simple way (there are others, too) to vary the overlap and the “lift” in a PatRoVa rotary valve is by shifting the valve relative to the cylinder head.
The zero total load on the bearings makes such lifting / lowering easy and accurate.
You also write:
“Additionally, if wanting to change the flow characteristics of the patrova valves (pardon any misnomers, please) by either re-machining or replacing all together, how do the potential costs compare to sourcing a different set of camshafts as one would in a conventional "poppet valve" engine?”
To replace the rotary valve seems easy and cheap. It is a single piece having simple shape, so it can’t be expensive in mass production.
Easier and cheaper would be to modify the ports of the PatRoVa.
Starting with a mild PatRoVa engine, by grinding the intake and exhaust ports of the rotary valve (and the chamber ports (or “windows”) at the sides of the roof of the combustion chamber), one could turn the engine to more sporty, even to pure racing.
Depending on where material is removed, the overlap can increase, or the duration can increase, or both.
To turn a poppet valve cylinder head to racing it needs more than a camshaft. I still remember the 460 Euro paid for a set of “egg shape” TODA valve springs for the modification of the Honda Civic V-TEC B16A2 engine to roller-VVA (more at http://www.pattakon.com/pattakonRoller.htm ) in order to allow 12mm valve lift and more than 9,000rpm.
In mass production the PatRoVa has many reasons to be several times cheaper than a cylinder head like those of Ducati Panigale.
So, I think there is no comparison in the cost.
You also write:
”At risk of embarrassing myself, may I ask, can 2T engines not use an overhead cam and "poppet valve" setup like a 4T? I can understand that doing so would ruin the mechanical simplicity inherent in the 2T design, but not remove the 2T's main advantage of one combustion event per cylinder per crank rotation.”
I think you mean something like the PatPortLess engine:
The time in the 2-stroke is about half, which means it is required double valve area to make the peak power at similar revs with the 4-stroke.
By covering the entire cylinder head with exhaust valves and the entire piston crown with intake valves, the 2-stroke gets port-less (which means true 4-stroke lubrication) and has the required high flow capacity to compensate for the shorter available time.
You also write:
”In addition, what are people's thoughts on how valves without valvetrains play into all of this, both for 4T and 2T designs. What I mean are things like Koenigsegg's "FreeValve" designs, where valve actuation is achieved not by mechanical action following camshafts etc. but rather electro-magnetically, electro-hydraulically, electro-hydraulic-pneumatically, etc. In theory, you would be rid of losses from having to mechanically operate valves (though gaining some elsewhere for pneumatic or hydraulic pumps, etc.) while having "infinite" control over intake and exhaust events. Again, not exactly a "simple" design, but if we're originally (supposed to be) talking about potential F1 engines, the level of technology would certainly seem appropriate.”
“In theory” yes: you would be rid of losses.
But in practice?
Most of the pneumatic / electromagnetic etc VVA’s (Variable Valve Actuation systems) introduce more losses than the mechanical systems.
There is another serious problem: the safety. If, for some reason, the sensors fail to inform the ECU about the true position of the piston, or the system fails to restore the valve, a catastrophic valve-piston-collision may happen.
There is another issue: the exhaust valves need a significantly stronger force to start opening because of the pressure inside the cylinder. Most of the pneumatic and electromagnetic VVA’s cannot deal with the exhaust valves.
We asked (at Engine Expo, Stuttgart Germany, 2009) the guys in the booth of Cargine (later: Koenigsegg's “FreeValve”) how they manage to open the exhaust valves; “it is an issue to be addressed”, they said.
On the other hand, as the revs increase a lot and as the size (and the lift) of the poppet valves increases (say, as in the Ducati Panigale 1199 / 1299), the energy that has to be given to, and then to be taken back from, the poppet valves gets extreme. Even a camshaft is difficult to manage it, not the pneumatic or the electromagnetic VVAs.
Such problems are unknown in the case of the PatRoVa rotary valve. Without inertia forces and without friction it can operate at extreme revs, higher than any set of piston / connecting rod / crankshaft / casing can withstand.
A normal size (350cc cylinder capacity) prototype PatroVa rotary valve was tested by rotating at 11,000rpm for several minutes in its cylinder head (which means 22,000rpm of the crankshaft, if crankshaft was present) with its temperature not exceeding 60 degrees Celsius.
Talking for poppet valves, high revs and variability of the valve lift and of the valve duration, I bet you will like the DVVA (desmodromic VVA) at http://www.pattakon.com/pattakonDesmo.htm
In regards to the PatRoVa system, I see how shifting the "vertical" location of the shaft would alter "lift." I'm curious, how does this work in conjunction with the timing belt/chain? By means of a spring or hydraulic tensioner or similar? If yes, then would that not affect timing? I'm not nitpicking, just curious.
Another curiosity is, with the orientation of the PatRoVa "disks" does this not imply that, at least on a banked cylinder arrangement as found in an inline or vee engine, the intake and exhaust pathways in the "head" are forced through essentially 90 degree angles to lead to their respective manifolds? Does this not hurt flow into and out of the engine?
In my mind I envision an alternate version of the PatRoVa that would employ "drums" that are (for lack of better word) cross-drilled with intake/exhaust tracts, allowing intake and exhaust ports to be located in more traditional positions for possibly better flow into and out of the head, though I believe spark plug and injector placement might become more problematic that way, as well as being harder to package all together.
Regardless, I feel that the PatRoVa system is wonderfully simple and effective, particularly for something intended to run high revolutions.
The DVVA arrangement of yours that eliminates valve springs all together is interesting, too, though it seems like it has an awful lot of "fiddly bits" though I suppose Ducati's Desmo engines are no less complex.
Speaking about the FreeValve (or similar systems) I agree, it seems like the risk of failure is potentially high, as are the forces that the actuators need to cope with. For what it's worth, Koenigsegg claims that they've run their Saab 9-5 test vehicle 55,000km with FreeValve controlling the intake valves, and 10,000km with FreeValve controlling both intake and exhaust. Mind you, this is not a racing engine under racing conditions by any means.
The “four-stroke propaganda” and the “conspiracy theories” cannot justify the complete absence of the two-strokes from motorcycles and cars.
The two-stroke has some technical issues yet to solve. This is why it is used only in marginal applications (2-stroke Mercury outboard engines, 2-stroke snowmobiles, a KTM 2-stroke model that needs a kit in order to cheat the rules, the Hirth small aircraft engines etc).
Thanks
Manolis Pattakos
Hi Manolis,
I don't know where you get your "conspiracy theories" from..
..but its a fact that 2T engines made GP motorcycle racing faster, & much less expensive, than 4Ts,
- which could only compete by having a huge capacity advantage allowing a much softer tune.
Then, 2Ts were actually specifically banned, & for example, the Moto 2 class, running a production-based
600cc 4 cylinder Honda 4T in a pukka race-bike chassis - replaced the GP 250cc 2T twins.
Racing at the Phillip Island GP in Australia this weekend, Moto2 are still yet to better the quickest 250 2T lap time around that fast-flowing natural track, set almost a decade ago, not much progress there then, eh..
2-strokes are used, where function ( esp' military applications) & business performance/costs come first,
& in such scale variation from tiny handheld chainsaws to massive container ship power-plants.
Motorcycles, esp' road-bikes are an 'emotional' purchase, & buyers are notoriously conservative & fickle.
Form often comes before function in such purchases, & makers/dealers want to milk their customers
perceived needs. Just look at the whole Harley-Davidson 'cruiser' genre...
The marketing dept guys tell the engineering/production guys what to build, based on sales projections.
The perceived market for a new 2T road-bike is likely below the ' go' production order threshold, or risk.
This is especially so when 2Ts are banned from competition, so that fans can't ask for what they see
winning on the track, as an alternative road-bike variant.
For cars, 2Ts may yet make a comeback, as CI emissions restrictions by diesel fuel concerns,
appear more amenable to being solved by 2Ts, such as those under development for Renault.
Research also continues for SI 2T machines, since those inherent virtues are fundamentally attractive.
Ed Hilary on being 1st to top Mt Everest,
(& 1st to do a surface traverse across Antarctica,
in good Kiwi style - riding a Massey Ferguson farm
tractor - with a few extemporised mod's to hack the task).
You write:
“In regards to the PatRoVa system, I see how shifting the "vertical" location of the shaft would alter "lift." I'm curious, how does this work in conjunction with the timing belt/chain? By means of a spring or hydraulic tensioner or similar? If yes, then would that not affect timing? I'm not nitpicking, just curious.”
and here is how it keeps the timing of the camshafts unchanged despite the lifting / lowering of the cylinder head relative to the crankcase:
“The synchronization between crankshaft and camshafts is simple and accurate:
A free roller (the red one, near the camshaft sprockets) has its center secured on the crankcase, i.e. its center remains immovable when the cylinder head moves up or down to change the compression ratio.
This free roller changes the direction of the belt / chain, coming from the crankshaft sprocket, for about 90 degrees before it meshes with the first camshaft sprocket.
Another free roller, beside the crankshaft sprocket, is the tensioner that takes the lash of the belt / chain (the conventional lash and the lash resulting from the approach of the camshafts to the crankshaft).
This simple geometry keeps the timing between crankshaft and camshaft unchanged, no matter what the compression ratio is, i.e. the valves open and close at the same crankshaft degrees either at 20:1, or at 7:1 or at any other available compression ratio.”
If it is not yet obvious how the above “method” applies in the case of the “VVA” PatRoVa”, let me know to further explain.
You also write:
“Another curiosity is, with the orientation of the PatRoVa "disks" does this not imply that, at least on a banked cylinder arrangement as found in an inline or vee engine, the intake and exhaust pathways in the "head" are forced through essentially 90 degree angles to lead to their respective manifolds? Does this not hurt flow into and out of the engine?”
This “short stroke” (for extreme revs) In-Line-Four with “cross-plane” crankshaft (different crankpin arrangement than in the M1-R1 of Yamaha) has 5 exhaust ports and four inlet ports:
Each cylinder uses two exhaust ports without interfering with its neighbor cylinders (because the combustions in neighbor cylinders differ for at least 270 crank degrees).
The port area (intake and exhaust) is extreme.
The form of the engine is completely conventional (exhausts at the one side of the cylinder head, intake at the opposite side of the cylinder head).
The offset between neighbor cylinders is limited only by the bore.
Spot on the way the rotary valves are supported: they are actually free to move along the splined-shaft (which is supported on small roller bearings) and to “play” angularly on the splined-shaft to find the “ideal position” relative to the combustion chamber they control.
The zero total force on each rotary valve makes this possible.
The only significant dimension is the distance between the opposed disks of each PatRoVa rotary valve separately.
You also write:
“
In my mind I envision an alternate version of the PatRoVa that would employ "drums" that are (for lack of better word) cross-drilled with intake/exhaust tracts, allowing intake and exhaust ports to be located in more traditional positions for possibly better flow into and out of the head, though I believe spark plug and injector placement might become more problematic that way, as well as being harder to package all together.”
A drawing would help.
One of the advantages of the PatRoVa architecture is the use of the combustion chamber windows for both: intake and exhaust. This keeps the temperature of the surfaces surrounding the combustion chamber uniform and low, allowing even higher compression ratios without knocking. And the combustion chamber becomes compact.
Using a pair of PatRoVa rotary valves per cylinder, one for the intake and one for the exhaust, is possible. However there are significant side effects (combustion chamber compactness, high temperatures at the exhaust side etc).
You also write:
“The DVVA arrangement of yours that eliminates valve springs all together is interesting, too, though it seems like it has an awful lot of "fiddly bits" though I suppose Ducati's Desmo engines are no less complex.”
All these “fiddly bits” are rid of bending loads.
And instead of sliding friction (which is the case in the Desmo cylinder heads of Ducati), in the DVVA there is “rolling” friction (when Honda moved from their old VTEC to the S-2000 VTEC they officially claimed a 75% friction reduction in the cylinder head).
The above plot gives an idea of the variability of the DVVA: infinite valve lift profiles (or modes) wherein the valve duration and the valve lift can change independently from each other. These infinite valve lift profiles are instantly available “on the fly” by rotating some control shafts.
The only variability in the Desmodromic cylinder head of the Ducati Panigalle Superleggera (price: some US70,000$) is the variable timing of the camshafts.
The DVVA is (quote from pattakon Home Page) “more desmodromic than Ducati Desmo (which is non-variable); and way more variable than BMW's valvetronic, Toyota's valvematic, Nissan's VVEL.”
Why the DVVA is “more desmoromic than Ducati’s Desmo”?
Look at the big springs required in the Desmo cylinder heads, wherein two “independent” linkages are used per valve: the one to open the valve and the other to close the valve:
In the case of the DVVA one linkage opens and closes the valve.
You also write:
“Speaking about the FreeValve (or similar systems) I agree, it seems like the risk of failure is potentially high, as are the forces that the actuators need to cope with. For what it's worth, Koenigsegg claims that they've run their Saab 9-5 test vehicle 55,000km with FreeValve controlling the intake valves, and 10,000km with FreeValve controlling both intake and exhaust. Mind you, this is not a racing engine under racing conditions by any means.”
If you look at the electro-mechanical-hydraulic MultiAir / TwinAir VVA-system of FIAT / INA / Schaeffler / Chrysler (or at its evolution PatAir and HyDesmo systems), the camshaft defines the envelope wherein the valve “moves”, protecting the engine from valve-piston collision (as much as in the conventional non-variable valve trains)
The mechanical hand-made VVA-roller-version installed on the Honda-Civic-1600cc-VTEC (B16A2 engine) was happy at 9,000rpm, controlling both, intake and exhaust valves:
“Development of a New Scavenging System.
This system is based on the principle of scavenging with a stratified charging process.
In the improved design, two reed valves are fitted at the upper ends o f the transfer ducts connecting the crankcase and the cylinder. as shown in Figure 1.
Atmospheric air enters the crankcase through the carburetor along with the fuel in the conventional way, as well as through the two reed valves fitted at the transfer ports.
When the piston moves from BDC to TDC, the pressure inside the crankcase is below atmospheric pressure and air from the atmosphere gets into the crankcase through the above-mentioned three paths.
When the air flows through the reed valves, the fuel-air mixture present in the transfer ducts as a result of the previous cycle is forced into the crankcase and air takes its place.
This process results in either a partial or a complete filling up of the transfer ducts by pure air.
During the downward stroke of the piston, pressure builds up in the crankcase and in the transfer ducts as soon as the inlet ports and the intake to the crankcase are closed.
Hence, the reed valves are also closed.
When the piston descends further, the transfer ports open and the pure air or very lean fuel-air in the transfer ducts enters the cylinder first.
This air pushes the exhaust gases out and becomes the main component to be short-circuited into the atmosphere through the exhaust port.
The fuel-air mixture, which follows the air, is retained inside the cylinder to a larger extent.
As a result, the amount of fresh charge loss during the initial scavenging period is reduced; hence, improved fuel economy and lower hydrocarbon emissions could be obtained.
Experimental investigations were carried out to optimize this new scavenging system by using both atmospheric air and compressed air through the extra reed valves.
The effects of engine capacity, load, speed, area of opening of the reed valve chamber, and secondary air flow rate through the reed valves were investigated in detail.
The amount of secondary air entering through the reed valves should be such that it displaces more exhaust gases to reduce fresh charge loss, and while doing so, it should have minimal effects on the mixture quality of the trapped charge in the cylinder.
It has been shown (Poola et al. 1993) that for large (250-cc) and medium (1 50-cc) capacity engines, a higher secondary air flow rate, achieved by regulating compressed air flow (part of the cooling air from the blower of the engine), is desirable. For example, the percentage improvement in brake thermal efficiency increases from 7.2 to 16.96% (at 2.8 kW, 3000 rpm), when reed valves permit atmospheric air and optimum compressed air, respectively, compared to the normal engine.
For a very small capacity (55-cc) engine, there must be a control on the quantity of secondary air from the atmosphere itself in order to obtain the maximum benefits with regard to fuel economy and HC emissions.
The HC emissions in the exhaust arise due to mixture short-circuiting, combustion of fuel-lubricant blend, trapping of unburned charge in the crevices, and flame-quenching.”
End of Quore.
The above system is, more or less, the stratified charge used in the Stihl’s 2-stroke chainsaws (your link at page 69):
It is correct that the two-strokes have advantages not met in the four-strokes. Especially for racing and military use.
However, it is also correct that there are crucial disadvantages not allowing the use of the two-strokes in “normal” applications like in motorcycles and cars: emissions, fuel efficiency, reliability, lubricant consumption etc.
The question is how to cure the disadvantages of the two-strokes (without losing their advantages) in order to make them better than the 4-strokes from every point of view.
Let’s make the discussion more specific.
Unless I am wrong, the KTM300exc brings nothing new.
What about its emissions and power if its engine is modified to PatATeco:
It has 4-stroke lubrication and plain bearings.
It is fully balanced.
It is indirectly injected (independent injection inside each piston).
It uses a lightweight and strong crankshaft (the heaviest part of the engine) with a single crankpin shared among the four pistons.
Its architecture does not allow fuel to go to the exhaust before participating in at least one combustion.
It is simple and cheap to make.
As compared with a similar-power four-stroke for light airplanes, like, say, a Rotax boxer:
Perhaps their R & D dept would like to run a software comparison with your design?
Maybe a technical university would sponsor do as research, a test-in-metal, too?
Here is a 2T Jawa 350cc road-bike on sale in Britain: http://www.jawamotorcycles.co.uk/350Classic.html
It is sold as an even more basic budget alternative to the archaic Indian built Enfield 4T.
Did you read this 2T research : http://cdn.intechopen.com/pdfs-wm/43662.pdf
Looking into smaller capacity/high rated CI engines for cars.
& wherein they note : " ...a number of minor issues concerning & liner durability..."
( both of which may well soon be an ex-issue when a new DLC-tribofilm is available)
& also: " ...the superiority of the 2T in comparison to the 4T..."
which extended into areas of driveability as well as fuel economy & gas/particulates emissions reduction.
It shows a 30 year old basic model 350cc Yamaha twin, updated for a bit more performance,
at which rating it was a well-mannered durable/reliable road bike, such as I have commuted to work
on for over a decade, & it is even fuel efficient ~ 5 Ltr/100 Km at highway speeds below P-V opening rpm.
There is no technical reason a 600cc 2T DI snowcraft engine could not do similar duty today.
"Well, we knocked the bastard off!"
Ed Hilary on being 1st to top Mt Everest,
(& 1st to do a surface traverse across Antarctica,
in good Kiwi style - riding a Massey Ferguson farm
tractor - with a few extemporised mod's to hack the task).
The tough questions they are asking of their proposal and the simulations and tests they are doing to address those questions, speak volumes for their capability, in my opinion.
J.A.W. wrote: .......2T Jawa 350cc road-bike on sale in Britain: http://www.jawamotorcycles.co.uk/350Classic.html sold as an even more basic .......
..........As an example, here is a dyno chart: http://rd350lc.net/Magazine/MCI0986-5.jpg
It shows a 30 year old basic model 350cc Yamaha twin, updated for a bit more performance,
at which rating it was a well-mannered durable/reliable road bike, such as I have commuted to work
on for over a decade, & it is even fuel efficient ~ 5 Ltr/100 Km at highway speeds below P-V opening rpm.
There is no technical reason a 600cc 2T DI snowcraft engine could not do similar duty today.
J.A.W - sorry for the messy 'quotes'
my (1975) RD 350 had a lumpy power curve such that it wanted to do 60 or 80 mph, not 70, and impossible eg as a road car characteristic
this made me wonder about the port timing eg relative to the earlier R5 and 'your' Jawa, and I found this http://cybermotorcycle.com/euro/brands/cz-jawa.htm
when I rode the first? H2 ? 750 Kawasaki in the UK the most surprising aspect was that it pulled like a freight train
this is now comprehensible, as it seems it was the 2nd version ie with more conservative and user-friendly port timing
regarding the Kawasaki bsfc being best at full power (ie how do these 'simple' engines actually work in normal use ?) ....
someone used the 492cc 3 cyl 3 carb Excelsior in a bike and fitted exhaust pipe restrictors acting at small throttle openings
in those days we had DKW cars
2 stroke DI cars died in 1958 when the 900cc Goliath was superceded - no later Japanese 2 stroke cars used DI ??
T-C, I have owned/operated many Yamaha 350s over the decades,
& I would suggest that you had a carb tune problem with your RD misbehaving like that.
The advent of electronically linked timing/exhaust port valving certainly tamed their 'torque hit',
while adding more, over a wider rpm spread.
The big H2 used its capacity to mask a soft tune, which while docile, was still powerful enough to provide a bit of fun with that characteristic rising torque curve giving a feeling of exponential thrust.
Nippon makers built large ( litre plus) 3 cyl FI 2Ts for water & snow craft, but AFAIR their biggest 2T car mill was the Suzuki 550/3, built at a time when they were putting a 2T 750/3 & a Wankel rotary-piston mill in their bikes..
Orbital ran a fairly large fleet of DI 2T cars for GM, using Suzuki 2T marine engines, ~20 years ago,
& showed good results, but the marketing people felt the lack of engine braking ( this was prior to regen-tech, such as the Prius uses) & lively 'torque hit' characteristics would be unnerving for ordinary 'econobox' drivers.
"Well, we knocked the bastard off!"
Ed Hilary on being 1st to top Mt Everest,
(& 1st to do a surface traverse across Antarctica,
in good Kiwi style - riding a Massey Ferguson farm
tractor - with a few extemporised mod's to hack the task).
Thanks for the explanation of various arrangements of PatRoVa that allow a more "straight-shot" entry and egress into the head.
The belt/chain tensioning methods you describe in your variable-compression concept is about what I imagined, thanks for showing that, too.
As for the idea of my own that I had mentioned, I unfortunately no longer have access to a SolidWorks license, so the best I could do for you is a hand drawing. That may be moot, however, as I realized this morning that what I was thinking would subject the "barrels" to the combustion chamber pressures in a vertical manner, which is one of the things that the PatRoVa avoids due to the nature of its design.
“In the second half of the ’90, AVL [4] developed a 980 cm3, three cylinder in-line proto type following a different path. The engine features an uniflow scavenging, obtained by means of inlet ports on the cylinder wall and exhaust poppet valves on head. The combustion chamber is based on a traditional HSDI four stroke design (i.e. bowl in the piston), fuel metering is provided by a Common Rail system while air boosting is obtained by a mechanical supercharging combined with a turbocharger.
. . .
Still in 2005, FEV announced the development of a four cylinder supercharged 2-Stroke Diesel engine, for military ground vehicles [7]. This engine, called OPOC (opposed-piston, opposed-cylinder), features uniflow scavenging (intake and exhaust ports at opposite ends of the cylinder), asymmetric port timing (exhaust ports open and close before intake) and electrically-assisted boosting. FEV claims a very high power to weight ratio (325HP, 125kg) and low fuel consumption.
. . .
While in the automobile field the 2-Stroke Diesel engine still hasn’t found an application to industrial production, beside some exceptions (in 1999 Daihatsu proposed the “Sirion” car with a 3-cylinder 2-Stroke 1.0L engine), this concept is starting to be applied in the aeronautic field, to power light aircrafts [9-14].”
End of Quote
The design of AVL is actually the old Detroit-Diesel.
The design of FEV (and EcoMotors) is a pair of old Junkers-Doxford engines:
sharing the same crankshaft for the sake of a better vibration-free-quality and of better power to weight ratio, in expense of an extremely long engine.
Some US100$ millions have been invested in EcoMotors OPOC engine, the 25 millions from US army, the 23.5 millions from Bill Gates of Microsoft.
They were planning to put their OPOC in mass production in 2014 (for trucks and cars). Then in 2015. Then in 2016. And so on.
They were talking for a US200M$ plant in China.
The truth is that they did not yet address significant technical issues of their engine, like the lubrication for instance.
The two-stroke Daihatsu Sirion E202:
was phased-out too soon.
Quote from the Internet:
“The E202 engine employs a hybrid scavenging system that combines a supercharger, a variable nozzle turbocharger and an intercooler together with a bypass control for internal exhaust gas re-circulation. This hybrid system improves the output and fuel consumption of the engine by using the exhaust energy efficiently, maintaining the scavenging pressure at an optimum level. The E202 also employs DVVT (Dynamic Variable Valve Timing) to control the four valves per cylinder and fuel is injected using a common-rail injection system.”
End of Quote.
It is a three cylinder, 987cc two-stroke having poppet exhaust valves (and a full-size four-stroke-like cylinder head to drive the poppet valves), a turbocharger, a supercharger, an intercooler.
The basic advantages of the 2-stroke, like simplicity, small size, low cost etc, are gone.
The RD350LC was an important engine in the 2-stroke history.
Great engine at its time, not competitive today.
The basic design/philosophy of the two-strokes needs fundamental changes/modifications to make them again competitive.
Isn't it obvious?
Two side crankshafts, multiple connecting rods per piston to eliminate the thrust loads, synchronisation gearing between the crankshafts etc.
They claim for specific lube consumption as low as in the four-strokes.
However now they appear focusing on the original Opposed Piston engine of Hugo Junkers.
Also on the form of the combustion chamber and on the injection.
A strange thing is that they limit themselves exclusively in Opposed Piston diesel engines, while their “injection” and “combustion chamber shape” could apply to the non-opposed-piston engines (two or four stroke), too.
Some US100M$ have been invested to Achates Power (Walmart etc) so far.
And unless I am wrong, they have not yet built a complete multicylinder engine to measure in the lab and then to put in real service for tests.
