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# Double Octothorpe Engine

8 axial cylinders, low centripetally induced friction.
 (+2, -1) [vote for, against]

This is an idea for a kind of Rotary Axial Engine. An axial engine is one in which the cylinders are arranged parallel to one another, around a central shaft. A rotary engine is one in which the engine cylinders rotate around a central shaft.

Other people have proposed engines of this kind before, but they suffer from high friction at high rpms, because in those designs, nearly all of the centripetal force keeping the pistons moving in a circle is supplied by friction between the cylinder wall and the piston sides.

Eddie Paul's Cylindrical Energy Module can be considered prior art.

The purpose of this idea is to supply the necessary centripetal force by way of simple rigid linkages, and appropriately chosen bearings.

Consider a piece of metal shaped similarly to a # symbol, with two vertical bars and two horizontal bars.

Move the horizontal bars a certain amount downwards, for a reason which I'll explain further down.

Take four pistons, attach them to the tops and bottoms of the vertical bars. Two of the pistons will of course be facing upwards, and two facing downwards.

Take four bearings, either tapered roller bearings, or spherical roller thrust bearings, and attach them to the ends of the horizontal bars. Attach a spherical wheel to each of these bearings. Two wheels will have their axles pointing leftwards, and two pointing rightwards.

Create thin grooves on the inner edge of each vertical bar. The groove should have a slightly varying depth, and be deepest near the horizontal bars.

Add a tiny hole through the bar, at the deepest point in each groove, leading towards the bearing. When oil is sprayed on the groove when the assembly is spinning, "centrifugal force" will pull the oil towards the hole, then through it to the bearing, providing lubrication.

Each vertical rod will *probably* have a counterweight, because the metal will probably be steel, which is slightly springy. When the engine is spinning at high speed, inertial will "pull" the pistons outwards, bending the verticals bars slightly. A counterweight between the horizontals might counteract this enough to keep each piston at the proper radius.

Create a duplicate of this entire assembly, flip it over top- to-bottom (so it's horizontal beams are "higher" than those of the first assembly), and interlock it with the first assembly. Rotate the second assembly 90 degrees to the first, so two of its wheels are towards you, and two are away from you.

Create two identical cams. Each cam will encircle our pair of #-assemblies. One cam will touch the top four wheels, the other cam will touch the bottom four wheels. Each cam has a double-sinusoidal curve on it's working surface, with two peaks and two troughs.

Each cam's working surface has a V-shaped groove in it, with a slightly varying angle to the V. The variation in the angle is chosen so that when the engine is spinning, the rotational speed of each ball shaped wheel will be some constant multiple of the average RPM, regardless of the wheel's angle around the engine axis. Without this variation, the wheel's speed would speed up or slow down, as it moved along the steeper or more level parts of the cam surface.

Purpose of the higher horizontal parts (or lower horizontal parts on the flipped assembly) should now be obvious -- if the assemblies were identical to one another, they'd collide as they oscillated vertically.

From here on out, the engine has few if any differences from Eddie Paul's CEM. While I could provide a link, I expect most of you would be happier to just read my own description here.

As each #-assembly rotates around its center axis, it oscillates up and down due to the action of the rollers on the cams. Because the two #-assemblies are 90 degrees apart physically, and because the cams have a *double* curve, the vertical motion of the two #-assemblies will be 180 degrees out of phase, so when one is going up, the other is going down.

There are two rotating engine heads, one for the top four pistons, the other for the bottom four. Each head obviously has four cylinder bores in it. Furthermore, each bore goes all the way through the head. Each head is attached to the other in such a way that they can't rotate relative to one another, but can move slightly closer together or further apart. The heads are pushed apart by short, stiff springs.

Each cylinder, on the side of the head away from the engine's center, has a high-pressure sliding seal around it.

The engine has two stationary port plates, one pressed against each engine head (or at least, pressed against the sliding seals of the cylinders). Each port plate has an intake port, an exhaust port, one or more fuel injectors, and one or more spark plugs.

 — goldbb, Mar 18 2016

Twelve piston "Cylindrical Energy Module", shown exploded http://contest.tech...piston_assembly.jpg
[goldbb, Mar 21 2016]

Twelve piston "Cylindrical Energy Module", shown with cams http://contest.tech...Engine_exploded.jpg
[goldbb, Mar 21 2016]

 The sheer number and complexity of moving parts tells against it.

A turbine has (effectively) one moving part. A two-stroke piston engine has three. This has ... many.
 — 8th of 7, Mar 19 2016

 //nearly all of the centripetal force keeping the pistons moving in a circle is supplied by friction between the cylinder wall and the piston sides.// This isn’t true.

 The force that pulls the revolving pistons in a rotary engine toward the fixed central crankshaft is exerted by the rods connecting the pistons and the crankshaft, not the walls of their cylinders.

Rotary engines, which were popular mostly in lightweight airplanes ca. 1915 (eg the Sopwith Camel and Fokker Dr.I), fell out of popularity mainly because their high rotating mass produces strong gyroscopic effect that made airplanes hard to control (ie they couldn’t turn left well), and because they had simple lubrication systems that caused them to have very dirty, oily exhausts.
 — CraigD, Mar 20 2016

Yeesh. Any chance of a sketch? (I'm good at visualising stuff, but this is pretty complicated...)

 CraigD, if we exclude wankels, there are two broad categories of rotary engines. One category has of pistons which move towards and away from a central crankshaft, and the other category has pistons which move parallel to the central crankshaft. The former are called "rotary engines" and the latter are called either "axial rotary engines" or "rotary axial engines."

 In a rotary engine which is *not* configured axially, what you said is exactly true.

 neutrinos_shadow, The images I linked to are of the (prior art) "cylindrical energy module" by Eddie Paul.

 The shown engine has six oscillating rods, whose ends are both pistons.

 My idea is similar to that, but first, I've got four rods instead of six, and diagonally opposed rods are mechanically connected to one another.

 8th of 7, if you've got a one-cylinder two-stroke engine, you've got three parts.

 If you've got an eight cylinder two stroke engine, you've got seventeen moving parts.

 The double octothorp engine has eight cylinders, and (if we count each roller as a separate moving part, and the connected engine heads as a single moving part) eleven moving parts.

 Looks like I'm ahead, but let me continue:

 However, I've described my engine idea as being four stroke, not two.

 Since comparing a two stroke engine to a four stroke isn't fair, I'll just have to describe what happens when we make a two-stroke double-octothorp engine.

 First, we replace the port plate with one that has two intake and two exhaust ports, and two spark plugs. This doesn't alter the part count, since the spark plugs aren't moving, and ports are just holes ;)

 Second, we add a supercharger, which increases the part count by two, resulting in 13 moving parts.

 Third, we note that the number of combustion events per rotation has doubled, to sixteen, because each piston makes two up strokes and two down strokes per rotation.

 Naturally, if we want to compare this form of double octothorpe engine to a conventional two stroke, it will have to be a sixteen cylinder conventional engine, which means at least 33 moving parts.

 By my count, 13 is much, much, less than 33.

I win!
 — goldbb, Mar 21 2016

I am completely lost after trying to follow that description, and I'm in the top 5% or less of all people when it comes to visualizing 3D things (according to a psychologist- administered IQ test, not just hubris). I have no idea in which axis the bars are offset from each other (even after the reason for the offset is supposedly obvious), how the pistons are oriented, or even about which axis the whole thing rotates. You really need to provide a diagram, even a crude ASCII one like Vernon does, or at least define a coordinate system and use it throughout the description.
 — notexactly, Mar 27 2016

 [annotate]

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