A work of pure genius! - Brilliant "Revetec" Engine

[manolis]

Pneumatic,

You write: In the image below, there is a clutch and pressure plate in the middle of the center gear, inline with the teeth. So the "reasonable selection for the location of the bearing" cannot be inline with the gear teeth, because there is a clutch plate there. So it must be cantilevered off a bearing at the back, which would be a bad design.

This slide is taken from the original CAD file by means of which the PRE13.exe animation was created.



and the following slide is after elevating a little the parts of the clutch



and here are the detailed support of the center gear (not shown in the animation)

You write: I know the images are concepts, and because of that they are not worth discussing. It is easy to make a concept, it is hard to figure out all the details and still have a good design.
The Revetec concept is fine, but the details shown thus far haven't been very impressive. It sounds like they are working through the details and making progress, so the final design may still be good, but until then there isn't much point commenting.

If we had the prototype to test, then what the use of asking opinions and critics. We have undergone the same when we asked for opinions and objections about Pattakon’s VVA system. You can’t imagine what the opposition and the snobbery was those days. Now we have the prototype cars ready for anyone to test drive them. And the initial design of VVA was actually the manufacturing design / blueprint (in most details) for all the VVA prototypes. When you get the time, take a look at the video
http://www.pattakon.com/vvar/OnBoard/A1.MOV.

The commenting and criticism of people skilled in the art is worthy only prior to the building of the real thing.

You write: Take the flying machine concept. It shows the handle bars out in front of the propellers. That wouldn't work, the handle bars need to be inline with the propellers - which is easy enough to fix.

If you look at the animations of the flying machine, you will see that there is a hole in the red frame (which comprises also the handle bars) from where – I thought it was obvious – the rider / pilot is hanged from, as in the a parachute or in a parapede, i.e. the rider is hanged exactly as you say, i.e. in line with the two propellers. The handles give the rider the ability to move his body relative to the engine/propellers and so to control his flying machine, just like a rider controls his bike.

You write: The concept animations make it look very simple, but when you add all the other bits needed to make it work you realise the actual product would be much much bulkier. For it to be a detailed design, they need to add;
* A fuel tank
* Carb's or EFI
* A starter motor (or starting device)
* a battery
* an alternator / generator (which has to be run off the crankshafts)
* cooling. air cooled fins will make the design much bulkier. water cooling needs a water pump and radiator
* spark plugs, probably 2 (one each side of cylinder)
* ignition system, leads, coil, something to time the spark
* guarding for the fans (as they slow down the machine will want to fall onto the ground unless you are strong enough to hold it up until it stops)

A fuel tank.
Having an engine of top thermal efficiency (read HONDA’s patents mentioned in my previous replies to Brad. These patents simply start with: ‘in order to increase thermal efficiency by increasing the constant volume portion of combustion it is proposed etc etc’).
It seems that saving, say, one third of the fuel for a specific ride/fly, deserves no discussion.

EFI
I.e. two injectors (for safety reasons) and two spark plugs (in case PRE is not compression ignition), a fuel pump and an EFI unit. How much all these weight? How much weights Hayabusa’s injection and ignition system.

A starter motor
You have the propeller within the reach of your hands to crank the engine, if necessary by both hands. The starter motor is a heavy luxury. Even in small airplanes.

An alternator / generator
Why the alternator cannot be directly driven by the lower end of the one crankshaft? And how much an alternator – with capacity to supply electric power to the EFI unit, to spark plugs (if any) and to a position/safety light – weights?

Cooling
Take a loon at this airplane engine. Through away the cylinder heads with their heavy and long fines – which protect from exhaust valve overheating – and keep only the cylinders with their short and light fins.



Overcooling is here the problem, not overheating.

Guarding for the fans
The hope is to have a very light propulsion system. If so, strong or weak riders can keep it in place until propellers stop rotating. A light version for light rider could help (the light rider needs less powerful engine and smaller rotors).

You write: So you can see the animations they show are rather pointless. They only show a very simple concept. It will still have vibrations. Although the pistons balance each other, the conrods will still produce unbalanced vibrations.

Wrong. Analysing properly the con-rod into two masses, the one at the piston pin and the other at the crankpin (both completely balanced as there is another piston making the opposite reciprocation inside the same cylinder) the only that is left is an inertia torque due to the angular acceleration of the con-rod. But again there is another con-rod at the other side of the cylinder producing the same – and opposite – inertia torque. The sum is permanently zero, I.e. if you left the engine run and the rotors rotate, the cylinder / block is absolutely free from vibrations, and this is a must for a portable flying machine.
Use the http://www.pattakon.com/educ/balance.exe program. It may help.

You write: To be honest I don't see the point of having the outer piston halfs. Normal two strokes get by just fine using the underside of the firing piston and crankcase to do the same job.
I think a conventional pair of two stroke engines set up so the pistons face each other would probably be better. The advantage of running the two stroke fuel/oil premix through the crankcase is that the premix lubricates the bottom end very well, and cools the piston.
....
. So now you probably need to add an oil sump and oil pump to the list of parts required for the engine. You also have to make sure you don't get too much oil around the cranks, or you will have a lot of power loss due to oil being flung around under the pistons.

I thought it was a step ahead the two stroke operation with four stroke lubrication. GM with its big Diesels think this way too. In the animations you can see the oil rings, two per piston, which never pass over the intake or exhaust ports. The oiling is as efficient as in the conventional four stroke engine, without oil loss. The piston crowns oil-cooling is as in present state of the art four stroke engines.
Beyond the uncontrolled oiling, the fouling of the plugs, the additional cost of oil, the emissions and the smell, what the premix oiling provides. One of the problems of the Wankel rotary engine is the need for two stroke oiling.
To my thinking, after the thermal efficiency, the best the Junkers-PRE provides is the outside piston crowns. Adding actually nothing, you get the best scavenging pumps I can imagine. They have a minimum dead volume which guarantees a top scavenging at all revs and loads. On the other hand, the large dead volume inside the crankcase is a major problem of the conventional two stroke (anything but flat torque curve).
The pair of the two conventional two stroke you mention, has two cylinder heads to dissipate energy on them, the Junkers PRE has none.
The pair of the conventional two stroke will necessarily use cross scavenging, a far less efficient and far less clean way than the through scavenging of the Junkers PRE engine (take a look at the 2nd world war airplane Junker design in a previous reply). Why to use two crankshafts at a large distance from each other with heavy synchronizing gearing between them? The only difference they make is the through scavenging and the elimination of the cylinder heads.
So yes, an oil sub is necessary – as in all four stroke – and an oil pump at the lower end of the one crankshaft. And the control of the oil quantity at the cylinder is already solved (long ago) in horizontal boxer engines of airplanes (like Lycoming), bikes (like BMW boxers) etc.
Think of Junkers-PRE as a two stroke functioning without the two stroke problems.

You write: I am not saying any of it can't be overcome, but I am saying that those animations are deceiving because they make it look really simple.

Deceiving animation!
For what reason?
A couple of years ago, trying to get thoughts, suggestions and criticism about the Pattakon VVA system, the objection was that ‘putting this system into a Honda B16 and B18 production engines is impossible’. Download the
http://www.pattakon.com/vvar/OnBoard/Assembly.exe collection of photos and think again.

If what you mentioned as problems of the Junkers-PRE are the most serious problems of this propulsion system, my view is that this Pattakon Flying Machine has potential.

Thanks
Manolis Pattakos

[pneumatic]

Manolis, you need to read my posts and learn to relax. I never said there was anything wrong with any of the design. Everything I have said is true.

The detail of the clutch and pressure plate is too simplified. The pressure plate needs a clamping surface which is not shown. The clutch plate needs friction linings which are not shown. The input shaft that will go through the clutch plate needs a pilot bearing in the flywheel, which there is no room for. A single deep groove ball bearing will not provide enough support for the flywheel. The ball bearings have radial and axial clearances that will be exaggerated by the big diameter of the flywheel, and it won't like the thrust load from the throw-out bearing. Not to mention that the hottest part of the engine (the center) is now covered with a flywheel and bearing support which will make cooling the area more difficult.

You are proving my point that there isn't much point talking about it without all the details, because every time I say something you give a new detail to counter my point.

Everything I said the engine still needed, it still needs. You just don't think the impact of adding those extra parts will be as much as I do. So we have a fundamental difference of opinion.

I don't have the time to sit down and calculate your forces in your engine at the moment , but from first glance the conrod forces don't look balanced.

I never said your design won't work. I doubt the flying machine will work, as I think you under-estimate the thrust required to lift a person. I think unguarded blades will be dangerous. But they are just my thoughts. I am not the keeper of all knowledge, I am not some expert that you need to gain permission from. If you ask for my thoughts, then accept them when you get them.

I will add that I do like the VVA concept. It is quite interesting.

[manolis]

Dear Manolis

Your graphs seem to look ok but we have discussed on here previously that a longer conrod ratio is for higher revving engines such as F1. If you look at the graph 1.65:1 is good for 7,000rpm and 2:1 is good for 18,000rpm so what type of characteristics will you get from such a piston acceleration curve?

My point is that an engine running such an acceleration curve must make it only suitable for a lot greater than 18,000rpm? Doesn't it?

Brad,

Sorry, it does not.

The piston acceleration data you used (piston acceleration versus crank angle for various con-rod to stroke ratios) were not correct. You wrote “Below 1.5:1 the initial velocity suffers also shown in the plotting of the ratio of 1.2:1 which is too low” and now you know this is far from being true.

As I understand, the connection you make between the piston acceleration and the breathing ability of an engine is not based on some theory, just on intuition. Not enough. If there is a connection between them, I like to know.

Having a specific four stroke PRE engine (i.e. given the con-rod to stroke ratio) I can move the peak torque at my desirable revs (let say 3000 rpm) just selecting properly the valve lift profiles. If I want the peak torque of the same engine to be at 6000 rpm, again I can: by proper selection of the valve lifts profiles (and the rest details that effect the free breathing, like intake manifold etc).
A typical tuner does exactly this work: he takes a normal engine with good torque at low revs and changes the camshafts, the intake manifold, the exhaust etc to finally achieve an engine having peak torque at higher revs and high maximum power at extreme revs, with drawbacks the reliability, the high consumption, the emissions, the poor drivability etc. The con-rod to stroke ratio has, compared to the valve train system, only minor effect on the breathing.

According your writing, a formula1 engine cannot breath well at 2,000 rpm because its con-rod to stroke ratio is too long (2.0 or more). This is absolutely wrong. It cannot breath because the overlap of its valves is selected to give the best at 15000 to 18000 rpm. If you change the camshafts of the formula1 engine with other ones providing no overlap and short lift, the formula1 engine could have a torque peak at – why not – 2,000 rpm. The fact that such engines are extremely over-square will decrease the thermal efficiency.

I.e. breathing is mainly a matter of the valve train system. The power train does have, but only minor, effect on breathing.

I.e. whatever con-rod ratio you choose I can make the engine breath good at your desirable revs.

Thanks
Manolis Pattakos

[manolis]

Not really a fan of the way the pistons separate. But I suppose they may come up with alternative designs....

My "bearings" point on the GRECO engine was that if you separate the shafts so they don't hit and the bearings are made at a size that is reliable and those components will not fit up the bore unless the engine is very very oversquare. At that point they'll have trouble getting the piston out the way to open the valves. We'll just have to wait to see how they address it. :-)

Brad,

An advantage of the GRECO is exactly that it can, with reasonable height, have a long stroke. Look at the animation of Greco in line three.

I am not sure you got it right what I wrote about the U-6 Greco.
If you want more strong drive shafts, all you need is to increase their distance.
For each mm increase of their distance, the thinner section of each drive shaft increases by exactly the same amount. So an increase of the drive shafts distance by – let say – 15 mm makes them much stronger than necessary in any application.

And as we talk about U-6 drive shafts strength, take into consideration that GRECO’s drive shafts undergoes only the 1/3 of Revetecs three lobes drive shafts torque, for the same pistons and bore (and even less as Revetec’s pistons are necessarily double pistons).

If the only drawback your expertise finds for the GRECO U-6 design is the ‘weakness’ of the drive shafts, U-6 GRECO has potential. Doesn’t it?

Thanks
Manolis Pattakos

[manolis]

Manolis, you need to read my posts and learn to relax. I never said there was anything wrong with any of the design. Everything I have said is true.

The detail of the clutch and pressure plate is too simplified. The pressure plate needs a clamping surface which is not shown. The clutch plate needs friction linings which are not shown. The input shaft that will go through the clutch plate needs a pilot bearing in the flywheel, which there is no room for. A single deep groove ball bearing will not provide enough support for the flywheel. The ball bearings have radial and axial clearances that will be exaggerated by the big diameter of the flywheel, and it won't like the thrust load from the throw-out bearing. Not to mention that the hottest part of the engine (the center) is now covered with a flywheel and bearing support which will make cooling the area more difficult.

You are proving my point that there isn't much point talking about it without all the details, because every time I say something you give a new detail to counter my point.

Everything I said the engine still needed, it still needs. You just don't think the impact of adding those extra parts will be as much as I do. So we have a fundamental difference of opinion.

I don't have the time to sit down and calculate your forces in your engine at the moment , but from first glance the conrod forces don't look balanced.

I never said your design won't work. I doubt the flying machine will work, as I think you under-estimate the thrust required to lift a person. I think unguarded blades will be dangerous. But they are just my thoughts. I am not the keeper of all knowledge, I am not some expert that you need to gain permission from. If you ask for my thoughts, then accept them when you get them.

I will add that I do like the VVA concept. It is quite interesting.

Pneumatic,

Believe or not, I deeply appreciate your replies.
You are of the few that risk a question about a technical matter.
I do thank you.


The motorcycle Junkers-PRE engine (i.e. PRE13.exe) with the center gear is not necessarily air cooled, so the projection that rotatably supports the center gear does not spoil the cooling.
On the other hand, the Flying Machine (Flyer1.exe) which needs to be air cooled (for lightweight) does not need clutch neither supporting shaft on the middle of the block.


But it seems we cannot agree on matters like the width of the clutch, the type of the roller bearing of the center gear, the weight of the cooling fins etc.
So let us concentrate on a matter of pure mathematics.

I clearly claim that the Junkers-PRE with the opposite rotating crankshafts is absolutely balanced, i.e. on its cylinder-block there are neither inertia forces, nor inertia moments, nor inertia torques of any order (at least as these terms are defined in Taylors books). In a nutshell, there are no inertia vibrations at all.

The Junkers-PRE with the opposite rotating crankshafts (like the one in the Flying Machine) is, with respect to inertia, as balanced as the Wankel rotary engine and a little better than the best V-12.
Furthermore: As long as the load is divided equally to both opposite rotating crankshafts (it is the case of the proposed Pattakon Flying Machine, it is the case of a single cylinder stationary dual electric generator, it is the case of an outboard engine driving two screws etc etc) the block/cylinder is absolutely free – as a whole – from inertia vibrations AND from power vibrations (notice here: a single crankshaft Wankel electric generator suffers from heavy power vibrations).

So the two counter-rotating crankshafts that share the same combustion chamber (i.e. they see the same instant pressure) have advantages in several applications.

The previous are applicable to the typical Junkers engines, too. These engines prevail in thermal efficiency over the single crankshaft conventional engines.

The Junkers-PRE with the long dwell around TDC, further improves the already top thermal efficiency of the typical Junkers engines. And besides Junkers-PRE brings the two crankshafts closer (making the synchronizing gearing shorter-simpler-lighter-quieter and reducing considerably the bending moments on the cylinder block) it also has an excellent built-in scavenging pump.

If I am true, doesn’t Junkers-PRE deserve a little attention?

Thanks
Manolis Pattakos

PS: beleive it or not I prepaired this reply based on your original - not the edited - message.

[revetec]

As we discussed before about conrod ratios, it does have a marked effect on the operation of an engine. If it didn't, then we would see F1 using shorter conrod ratios such as 1.3:1 to make an engine more compact and save weight. A selection of conrod ratio is made with consideration to operational RPM. I have tried a sine wave cam in one of our engines which is half way between a conventional engine and the Pattakon selections. We needed to supercharge the engine to get it to perform. I know that the Pattakon engine's outer piston supercharge's the centre end of the piston, but the pumping losses of supercharging will probably result in little benefit to overall efficiency when compared to a conventional engine with no supercharger. I'll be interested in the final design and look forward to seeing results once a Pattakon engine is built and tested.

There is plenty of ways to design and make an engine. I have seen many designs that look ok from a CAD model, but many fail in prototyping due to unforseen problems. I think this discussionis taken the wrong way! All we are doing is discussing possible points of failures of the project. Healthy discussion only results in good information and/or opinions that might spur on further thoughts and innovation that will help your cause. In our early development many people put in their opinions which helped me with further thoughts on which way the development program should be headed. Knowing all the possible faults with a product helps you design a better product.

Please note: If it isn't cheaper to produce, doesn't require too much retooling to manufacture, fit most existing applications layouts ( size / weight /c onfiguration / Rev range / peak power and torque RPMs, fit transmissions ), cheaper to run, more reliable than what we already have and marketable to the general public, then it's a big upward battle.

These days emissions and efficiency of conventional engines is pretty optimised. It takes a lot more research and development these days to reach a level that will be accepted by any engine manufacturing company(Usually 5-10% better). This means that an initial engine will just be an evaluation engine because no one can be expected to get it right the first time. Usually the forth version engine is getting it almost right. Costs vary from $300,000 to $1.5 million for each of any serious engine prototype. With each prototype, the design varies greatly due to innovation with the technology and feedback from testing advances and failures.

I'll be watching the Pattakon engine in the future to see how they travel.

[revetec]

Oh...Here is a little help.... The centre drive shaft... lower it to below the cylinders (you can still gear the cranks to it) and you can run a shaft under the combustion chamber and get the shaft long enough to be supported well. See a good free tip for you, which has resulted from healthly discussion on this forum.

[revetec]

My IT guy says our website update will be in two days. :-)
I will post the link when it's up and running.

[pneumatic]

Ok, I will make more comments. But they are just my thoughts at this stage.

I don't think the PRE-Junker engine will ever be useful for a car or motorcycle, as it is too wide for it's capacity. It is simply the wrong geometry to be practical.

I don't think air cooling will work with this layout, because the gears are in the way of the air flow.


You'd either need some complex shrouding, or to move the gears to the lower side.

I actually don't think air cooling will work at all, because as the center part of the cylinder thermally expands, the crankshafts move further apart and the gears will lose their mesh. I think Junker had a similar problem in his earlier engines.

I think you need a more rigid outer casing with water cooling to keep the expansion under control. Or you need a rigid case to run around the cylinders to the crankshafts, and let the cylinders grow in towards each other. Or you need to get rid of the gear connection and use a chain / belt with a tensioner. There are lots of options, but they all effect the size and practicality of the final design.

Having opposing pistons gave thermodynamic advantages back in the 30's, but I don't think the advantage is as significant these days. There are better ways to reduce thermal losses through the cylinder head, like ceramic coatings and even ceramic engine parts. Ceramic coatings on piston crowns, combustion chambers and valves are very common performance modifications.

I think the one-way valves will be troublesome and difficult to to control. If they don't close in time they will hit the piston. Reed valves on a normal two stroke can stay open at high rpm with no problem.

The "exhaust" side (not a very good name, but you should know what I mean) will pose problems. There is no room in the port for it to open. It needs a space to fold back into.

What will the one-way valves be made from, and how will they have a spring force applied?

Starting the device by the propellor will be hard. Since there is no guard, you can't sit it in the ground and crank it over. You need to hold the entire machine over your head with one hand, and crank it over by the propellor (which is probably out of reach) with your free hand.

As for efficiency, two-stroke petrol engines are not as efficient as two-stroke diesels. In a two stroke you get good power when you get to the point that some of the intake charge completely flushing the combustion chamber and starts to go into the exhaust (before the compression stroke). On a diesel engine this is fine because a diesel is direct injection, and only injects the fuel it needs. Therefore by wasting intake charge out the exhaust you only waste air, not fuel.

If you inject fuel (petrol) into the intake port, then losing intake charge out the exhaust is inefficient. If you use direct injection petrol you still need to figure out how much air is in the combustion chamber to inject the correct mixture of fuel. It is hard to do if some goes out the exhaust.

So two-stroke intake/exhaust timing and efficiency generally only go together in diesel engines. A diesel would be too heavy for the flyer.

Some interesting info on the junker;

The Junkers aircraft 2-stroke diesels comprised 6 in-line vertical cylinders, 12 pistons and 2 crankshafts coupled by a gear train, also used for the propeller reduction gear. The lower pistons opened the intake ports, the upper ones opening the exhaust ports. In order to get the optimum timing, the lower (intake) crankshaft was about 11° retarded relative to the upper exhaust one. So the latter received roughly 3/4 of the power and it was geared directly to the propeller shaft.

I'm sure retarding it 11degrees didn't do much for the balancing either.

[kingofthering]

hmmm. with an engine like this, it would be possible to create a scooter with the power of a motorcycle.

[manolis]

Brad,

You write: As we discussed before about conrod ratios, it does have a marked effect on the operation of an engine. If it didn't, then we would see F1 using shorter conrod ratios such as 1.3:1 to make an engine more compact and save weight. A selection of conrod ratio is made with consideration to operational RPM.

The typical formula1 engine has, as they say, a piston stroke of about 40 mm.
If the piston pin is 20 mm in diameter, the piston pin bosses have to be at least 30 mm in diameter. The crankshaft webs need to be less than
2*(conrod length – 0.5*(piston stroke)- radius of piston bosses),
i.e. 90 mm in diameter when the conrod to stroke ratio is 2 (i.e. con-rod center to center distance equals to 80mm). If the conrod ratio decreases to 1.5 (i.e. con-rod length decreases to 60 mm) the diameter of the crankshaft webs decreases to 50 only mm otherwise the crank hits the piston. I suppose their main crankshaft journals are near 50 mm in diameter.

I.e. the use of less than 2.0 con-rod to stroke ratio in such over-square engines is impossible spatially

Looking from another point of view, the 40 mm stroke means – for 2500 cc 8 cylinder capacity – a bore of 100 mm.
Most formula engines are in V-90 arrangement.
Take a crankpin of the crankshaft and connect two con-rods of 60 mm (center to center) at a 20 mm offset (i.e. the wirth of the con-rod) each one having one piston of 100 mm bore at their other ends.
When the pistons are close to their BDC, their piston skirts hit each other.
If this is confusing, take a look at the

http://www.pattakon.com/pre/PRE3.exe animation.

I.e. in formua1 the a con-rod to stroke ratio of around 1.5 is not possible, neither it offers more compact design or less weight.
I.e. the 2.0 or more con-rod to stroke ratio is not a choice, it is a necessity.

You write: I have tried a sine wave cam in one of our engines which is half way between a conventional engine and the Pattakon selections. We needed to supercharge the engine to get it to perform. I know that the Pattakon engine's outer piston supercharge's the centre end of the piston, but the pumping losses of supercharging will probably result in little benefit to overall efficiency when compared to a conventional engine with no supercharger. I'll be interested in the final design and look forward to seeing results once a Pattakon engine is built and tested.

How did you optimise the breathing of the harmonic revetec engine?
How many valve lift profiles (i.e. how many different camshafts) did you use to find the optimum camlobes?
I you had a pattakon VVA system on the cylinder head (like the one on the Pattakon Civic prototype) then you could easily optimise the breathing of your harmonic VVA at your desirable revs.
Optimising the breathing of an engine by manufacturing and replacing camshafts is nothing but a nightmare.

I.e. keeping ‘some’ camshafts (which are optimised for other than harmonic piston travel profile) and expecting the harmonic to breath well, is not correct.

I.e. the Pattakon PRE, which is not necessarily of Junkers-PRE design (take a look at the four stroke PRE versions) does not need supercharging to breath well. With the VVA as the tool, the optimisation of the breathing is a relatively simple and a really low cost procedure. When the final optimum valve lift profile is reached, the relevant valve lift profile is recorder and the correct cam shafts are designed.

Thanks
Manolis Pattakos

[manolis]

Pneumatic

You write: I don't think the PRE-Junker engine will ever be useful for a car or motorcycle, as it is too wide for it's capacity. It is simply the wrong geometry to be practical.

A 500cc Junkers-PRE engine (50+50=100mm stroke, 80mm bore) has a maximum dimension of 557 mm



The power and the torque of this engine are close to those of a conventional 1000 cc four stroke.
I measured the width of the Honda Civic VTEC engine. This engine has at its top a width of about 530 mm (670 with the distributor). This engine has also a depth of about 240 mm and a height of about 540 mm (if you can please please let me know the Hayabusa’s engine dimension).

In case of twin Junkers-PRE (i.e. two cylinders sharing the same crankshafts (having crankpin at 180 degrees for even firing) the maximum dimension of the Junkers-PRE remains at 557 mm while it becomes 1000 two stroke cc in capacity. I.e. more powerful and more smooth than the civic 1600 straight four. The rest dimensions of the Junkers-PRE are beyond comparison.

The compactness and the external form of the Junkers-PRE are advantages not drawbacks.

Compare the Junkers-PRE 500 cc with BMW’s Boxers 800 cc or 1000cc: the one is like the mother of the other, in all dimensions. In case of Junkers-PRE the engine could be mounted on a motorcycle even longitudinally as a part of the frame (this for Kingofthering).

You write: I don't think air cooling will work with this layout, because the gears are in the way of the air flow.

You'd either need some complex shrouding, or to move the gears to the lower side.

I actually don't think air cooling will work at all, because as the center part of the cylinder thermally expands, the crankshafts move further apart and the gears will lose their mesh. I think Junker had a similar problem in his earlier engines.

I think you need a more rigid outer casing with water cooling to keep the expansion under control. Or you need a rigid case to run around the cylinders to the crankshafts, and let the cylinders grow in towards each other. Or you need to get rid of the gear connection and use a chain / belt with a tensioner. There are lots of options, but they all effect the size and practicality of the final design.

The synchronizing gears is preferable at the top, close to the rotors. The four stroke lubrication helps here: the gearing case has oil that can cool the cylinder below as necessary. Many Suzuki aircooled motorcycle engines use the air-oil cooling.

As for the thermal expansion:
The thermal expansion was a problem for the typical Junkers PRE because the distance of the two crankshafts was huge compared to Junkers PRE. The typical Junkers long gearing had also to carry half of the power to the output shaft. The gearing of Junkers-PRE carries no power.
On the other hand, The synchronizing gears in the plot above are not in line. If you keep their centers at constant distance, no matter how much the distance of the crankshaft enlarges, their operation remains correct. But this is luxury.

You write : Having opposing pistons gave thermodynamic advantages back in the 30's, but I don't think the advantage is as significant these days. There are better ways to reduce thermal losses through the cylinder head, like ceramic coatings and even ceramic engine parts. Ceramic coatings on piston crowns, combustion chambers and valves are very common performance modifications.

I hear about adiabatic engine for some twenty years now. If they succeed, the Junkers-PRE will also take advantage of them. Today they are not in use despite the vast amounts of money that have been spend on this technology. Their investors know.

You write: I think the one-way valves will be troublesome and difficult to to control. If they don't close in time they will hit the piston. Reed valves on a normal two stroke can stay open at high rpm with no problem.

What will the one-way valves be made from, and how will they have a spring force applied?

The existing reed valves of the two stroke motorcycles are more than adequate for the Junkers-PRE as they operate reliably over 15,000 rpm.
By the way take a look at some other kind one way valves at

http://www.pattakon.com/vva/VVA_Idle/VVA_Idle.htm

You write: The "exhaust" side (not a very good name, but you should know what I mean) will pose problems. There is no room in the port for it to open. It needs a space to fold back into.

Sorry, be more specific. I don’t understand.

You write: Starting the device by the propellor will be hard. Since there is no guard, you can't sit it in the ground and crank it over. You need to hold the entire machine over your head with one hand, and crank it over by the propellor (which is probably out of reach) with your free hand.

OK, here is a problem. Maybe something like a kick starter.

You write: As for efficiency, two-stroke petrol engines are not as efficient as two-stroke diesels. In a two stroke you get good power when you get to the point that some of the intake charge completely flushing the combustion chamber and starts to go into the exhaust (before the compression stroke). On a diesel engine this is fine because a diesel is direct injection, and only injects the fuel it needs. Therefore by wasting intake charge out the exhaust you only waste air, not fuel.

If you inject fuel (petrol) into the intake port, then losing intake charge out the exhaust is inefficient. If you use direct injection petrol you still need to figure out how much air is in the combustion chamber to inject the correct mixture of fuel. It is hard to do if some goes out the exhaust.

So two-stroke intake/exhaust timing and efficiency generally only go together in diesel engines. A diesel would be too heavy for the flyer.

What we actually think is to use in the flying machine Diesel Junkers-PRE for the sake of fuel economy. I hear you saying ‘but the additional weight’. If the fuel weight can be reduced more than 3 Kp, the take off weight will be less than using petrol. Junkers-PRE can operate at lower compression than normal Diesels because of the dwell at TDC.
If it was the typical Junkers, the Diesel cycle would have a marked increase on engine’s weight. In case of the Junker-PRE the two close to each other crankshafts make the bending moments on the cylinder weaker etc etc. So all you need is a reinforced cylinder and two stronger crankshafts.

If direct petrol injection is used, the lambda sensor gives the feedback to the EFI and the injection duration is adjusted as in the present car. When the Pattakon Civic prototype uses ‘closed loop’ control, it automatically reads the Oxygen concentration at exhaust and adjust the injection duration.

You write: Some interesting info on the junker;
Quote:
The Junkers aircraft 2-stroke diesels comprised 6 in-line vertical cylinders, 12 pistons and 2 crankshafts coupled by a gear train, also used for the propeller reduction gear. The lower pistons opened the intake ports, the upper ones opening the exhaust ports. In order to get the optimum timing, the lower (intake) crankshaft was about 11° retarded relative to the upper exhaust one. So the latter received roughly 3/4 of the power and it was geared directly to the propeller shaft.

I'm sure retarding it 11degrees didn't do much for the balancing either.

If the absolute balance is necessary, the asymmetric timing is not the case. If necessary, a clap at exhaust can offer the control.
If the asymmetric timing is advantageous a little vibrations is the price.
In the flying machine it is better to have Diesel cycle with absolute balance.

Thanks
Manolis Pattakos

[pneumatic]

A 500cc Junkers-PRE engine (50+50=100mm stroke, 80mm bore) has a maximum dimension of 557 mm. ..... .... The power and the torque of this engine are close to those of a conventional 1000 cc four stroke.

A 500cc two stroke is not equivalent to a 1000c four stroke. That used to be a rule of thumb, and they used it for sizing the new capacity when motogp went from 500cc two-strokes to 1000cc four strokes. They were getting around 200HP from the two strokes, and 250HP from the four strokes which aren't tuned as hard. A 500cc two stroke is closer to a 800cc four stroke in practice (my observations).

You shouldn't say the maximum dimension is 557mm, because in reality it won't be. That sketch shows no material thickness on the ports or anything. It reality it will be a bit longer, how much longer depends on how everything will be detailed. But your right it can be made to fit in a car, but I don't think it's shape is practical and would be used in a car (just my opinion).

In case of twin Junkers-PRE (i.e. two cylinders sharing the same crankshafts (having crankpin at 180 degrees for even firing) the maximum dimension of the Junkers-PRE remains at 557 mm while it becomes 1000 two stroke cc in capacity. I.e. more powerful and more smooth than the civic 1600 straight four. The rest dimensions of the Junkers-PRE are beyond comparison.

Compare the Junkers-PRE 500 cc with BMW’s Boxers 800 cc or 1000cc: the one is like the mother of the other, in all dimensions. In case of Junkers-PRE the engine could be mounted on a motorcycle even longitudinally as a part of the frame (this for Kingofthering).

As I mentioned before, I think a 1000cc twin junkers-pre will only be comparable with a 1600cc engine power wise anyway. You are correct, you could lay it across the frame like a BMW boxer, but I don't think that's a good layout for a bike. That's why no other manufacturer does it. BMW do it because it's their trade-mark (and they are doing it less and less, introducing more conventional engines all the time).

I think the biggest problem for car or motorcycle use is that it is a 2-stroke. So it either needs to compete with a convential 2-stroke, or show a lot of advantages over a 4-stroke.

People buy two-stroke motorcycles because of their outright performance and light weight. A J-PRE engine will be bigger than a conventional 2-stroke, and won't make a significally different amount of power to offset the size and increase in complexity.

And these days two-strokes are being phased out. Why - because 4-strokes are more efficient, have more than ample power and require less maintenance. The extra complexity and extra weight / size is not a problem. And, they have a more user-friendly power band.

This is the big question mark over the J-PRE that no-one can answer until one is built. What will the power delivery be like? Will it be like a traditional 2-stroke?

I think in the end this engine would have to compete with another "alternative" engine design, offering similar size and power advantages. That engine is the Rotary (Wankel). The wankel has never been widely accepted despite it's size and power for size.

The synchronizing gears is preferable at the top, close to the rotors. The four stroke lubrication helps here: the gearing case has oil that can cool the cylinder below as necessary. Many Suzuki aircooled motorcycle engines use the air-oil cooling.

yes many motorcycles use oil / air cooling, but they still have fins for some air cooling. And if it uses oil cooling then it needs an oil cooler. So if you use oil cooling in the flyer then you need to add an oil cooler to the list of parts.

The gearing of Junkers-PRE carries no power.

If the J-PRE is used for a motorcycle or car, then it will transmit 50% power like the junker.

In the flyer it will transmit whatever power you have drawn off one of the cranks to drive the ancillaries of the engine (oil pump, alternator, etc).

On the other hand, The synchronizing gears in the plot above are not in line. If you keep their centers at constant distance, no matter how much the distance of the crankshaft enlarges, their operation remains correct. But this is luxury.

I don't know what you mean by "are not in line". They look in line. If the crank case heats up and grows, then the distance between the crank centres will grow and meshing will be a problem.

The existing reed valves of the two stroke motorcycles are more than adequate for the Junkers-PRE as they operate reliably over 15,000 rpm.

Have you seen existing reed valves? They won't fit in the space you have allocated. Reed valves have steel plates that are permanently in the "open reed valve" position. So you can't have the reed valves opening into the cylinder, as then the steel limit plates would be hit by the piston.

You write: The "exhaust" side (not a very good name, but you should know what I mean) will pose problems. There is no room in the port for it to open. It needs a space to fold back into.

Sorry, be more specific. I don’t understand.

If the exhaust reed or valve is oval like the port, then it cannot swing open on a pin. It simply won't open. The port needs a recess for the reed to open into. Draw it in 3D and you will see what I mean.

And if you change to traditional reeds, then you won't get the "zero volume" at TDC on the outer pistons. It will also make the engine a little bigger in width too. Again, this area needs to be detailed to see what problems will arise.

OK, here is a problem. Maybe something like a kick starter.

I think it needs a start motor and battery. Manual starting is not marketable.

[revetec]

Our REVETEC website has been updated!

The link to our Latest News page for the X4 is: http://www.revetec.com/?q=engine-dev


Four cylinders drive two cams. Output shaft is the lower shaft providing two strokes of each piston per 360 degrees of rotation (Same as a conventional and our previous engine).

Pistons are inline and balance out 2/3's of each other's weight. Top balance shafts balance out the other 1/3 (up and down movement).

Most downforce applied to and lost into a conventional engine's main journal is deflected into the opposing cam gaining more rotational force. Torque lever is extended throughout the stroke which transfers torque more effectively. As the point of peak presure moves up and down the stroke due to RPM, Load and fuel mixtures, the transfer is always kept at a higher amount than a conventional engine.


2.4 litre X4 engine; currently being designed (Shown without cylinder heads)
International patents on the X4 engine have been lodged.

Block is only 160mm front to back (2.4 litre) and is about 40% the size of most equivalent engines being currently manufactured.

Cheers

[pneumatic]

{from website}It was found that the cylinders could be arranged in a 60 degree X configuration using only two trilobe cams.

That's pretty cool . Using two cams for 4 pistons should be able to offer weight and space saving.

I can see the engine will offer the space and weight saving, but I am still not so sure about the magnitude of the efficiency advantages. Some of the efficiency gain of the trilobe vs crankshaft design will be lost by the need to gear the output shaft down, and also run the 2nd trilobe through two gears to make it spin the other way. We could talk theory until the cows come home, but test data will be the final word.

It will be interesting to see how noisy those gears are too, and if you need to go to helical gears (less efficient but quieter). Motorcycles use straight cut gears which do make a lot of whining noises, but motorcyclists love the mechanical noises so it is ok. The aircraft and trike guys probably won't care either, but car manufacturers and buyers might.

The power and the torque of this engine are close to those of a conventional 1000 cc four stroke.

Manolis, just one more thing on this subject. Yes a 2 stroke will make more power and torque than an equivalent sized four stroke, but in the real world the differences aren't so big.

Have you ridden many motorcycles before? Try riding a 250cc 2-stroke and a 250cc 4-stroke. The 2-stroke will ultimately be faster, but the 4-stroke is easier to ride around on, with a more gentle and easy to use power delivery.

Therefore just because a 1000cc two-stroke is enough to move a car as fast as a 2000cc (or 1600cc maybe) four-stroke, it doesn't mean it will be as nice or easy to drive.

There are a lot of factors that decide whether an engine is successful, and outright power and torque is only a small part. Manufacturers could make all engines very very powerful, but they don't. They want an engine to be smooth (power delivery and vibration wise), quiet, have good fuel efficiency, long service life, and a whole heap of other factors. A lot of these factors you will not know until you run a proto-type. The Junker-PRE might show advantages in all of these areas, it might not.

Trucks are a good example. Some trucks want a cheap light powerful and relatively efficient engine (workhorse type trucks), so they go for a supercharged 2-stroke diesel (which has oil in the crank area like the Junker-PRE). It meets that manufacturers criteria, but the engine is harsh and noisy.

Another manufacturer might want efficiency with refinement and quiet operation (more expensive long haul trucks), so they go for a turbo-diesel four stroke engine.

So the question is, what engine will the Junker-PRE compete with? I think it will need to compete with a supercharge diesel.

A supercharged diesel uses a positive displacement blower to do the 2-stroke scavenging. The Junker-PRE uses the outer pistons and some one way valves to do the same thing. I think a screw-type positive displacement blower would probably do the same job more efficiently, so I don't think the Junker-PRE will successfully compete with the tried and proven supercharged 2-stroke designs.

And since no-one uses supercharged 2-strokes in cars or motorcycles, I don't think anyone would want to use a Junker-PRE either.