The PatOP engine is the single crankshaft version of the OPRE engine.

Thanks
Manousos Pattakos

The OPOC
The two external pistons of the OPOC are the good ones. Their arrangement and lubrication is similar to those of the cross-head engines. A drawback is the necessarily long and heavy piston pin that extends well outside the cylinder. Another drawback is the two long and heavy connecting rods per external piston (about 2.5 times longer than the single connecting rod of the internal piston) and the increased number of crankpins and bearings.
As compared to a piston performing a pure sinusoidal motion of the same stroke, the external piston of the OPOC moves more slowly around the Combustion Dead Center (CDC). This would improve the combustion efficiency, yet they come the internal pistons to spoil this advantage. The internal pistons of the OPOC move, around the CDC, more quickly than a piston performing a pure sinusoidal motion of the same stroke. Finally the volume between the two pistons and the cylinder increases, around the CDC, more quickly than in case of pistons performing pure sinusoidal motion.
There is also a difficult lubrication issue with the internal pistons of the OPOC, especially the one thrusting over the exhaust ports. The hot cylinder with the exhaust port slots is where the piston skirt has to touch (to slide, to abut) in order to pass to the cylinder the thrust loads generated by the inclination of the connecting rod. The problem is that increasing the quantity of the oil at the exhaust port area of the cylinder, the oil consumption (it escapes at the exhaust) is also increased and the quality of the oil degrades sooner.
In order to counterbalance the first order inertia forces and moments, the OPOC engine has to use internal and external pistons of the same reciprocating mass (it is the mass of the piston, of the piston pin and of the upper part of the connecting rod mass). Yet each internal piston has a small piston pin and a single short connecting rod, while each external piston has two long and heavy connecting rods and a big and heavy piston pin. The solution (?) is to add mass to the internal pistons. This increases the inertia loads and the friction loss. Besides, it is the offset between the two cylinders of the OPOC that generates a 2nd order unbalanced inertia moment. There is also a strong unbalanced inertia torque of 2nd order (just like in any four in-line conventional engine).
The OPOC engine is so long (wide) because it is based on an opposed cylinder to counterbalance the inertia loads. Despite all this complication (four pistons, two short connecting rods, four long connecting rods, two cylinders) the “vibration-free” or “balance quality” of OPOC is not exceptional.
Another issue is the different timing, during the scavenging, of the one cylinder as compared to the other: The cylinder that uses the internal piston to controls the exhaust ports aspirates differently than the cylinder that uses the external piston to control the exhaust ports. This asymmetry may be compensated at some revs and loads, yet it cannot at a wide rev and load range.
Finally, the scavenging process (i.e. the most critical and power consuming process in a two-stroke engine) of the OPOC is realized externally by a turbo-charger (not the ideal solution for engines that operate in a wide rev and load range).

The OPRE
Take now the OPOC engine, throw away the two internal pistons, throw away the four long connecting rods, throw away the two long and heavy piston pins and replace the unique multi-crank-pin crankshaft by a pair of single-crank-pin crankshafts located outside the pistons. What is left is the OPRE engine.
The OPRE needs not long connecting rods neither an opposed cylinder to be “vibration-free”. And its width is more than 30% smaller than an OPOC of the same piston stroke.
The combustion takes place at the slow dead center that provides a 30 to 40% additional time (as compared to the conventional engine) and a 20% additional time (as compared to the OPOC) to the fuel to get prepared and burned more efficiently. This extended piston dwell at the CDC allows a way higher rev range (it allows Direct Injection Diesels operating efficiently at 6000 rpm).
If the one combustion per crank rotation is not adequate, additional OPRE modules can be added in series to make a multicylinder OPRE engine.

By using the external side of the pistons (i.e. the wrist pin or cool side of the piston) as a “zero” cost, zero friction volumetric piston-type scavenging pump, the OPRE takes its final form. If the forced induction (turbo-charge) is desirable, it is OK for OPRE, because it can operate efficiently with and without turbo charging.

The integrated volumetric scavenging pumps of OPRE allow the operation either with symmetrical timing or with asymmetrical timing between the intake and the exhaust.

Especially in case of divided load (for instance as a power generation set, or range-extender, with one electric generator on each crankshaft) the NVH properties of the OPRE range-extender are the best among the internal combustion engines, the Wankel rotary engine included. The OPRE range-extender is not only perfectly free of inertia vibrations, which is also true for the Wankel range-extenders, but it is also free from power pulses vibration on its mounts (supports) which is not the case for the Wankel range-extenders: each combustion into the Wankel rotary engine causes a reaction torque (power vibration) on its supports.

An unconventional application: with a couple of counter-rotating propellers the reliable, lightweight, efficient and true vibration-free OPRE makes a portable Flyer (presented at http://www.pattakon.com/pattakonFly.htm ). We think the OPRE Portable Flyer can change the world. Yet we have to fly first, to prove it.

Despite what CEO Don Runkle (OPOC engine) claims, as compared to the OPOC engine
the pattakon Opposed-piston-Pulling-Rod-Engine (OPRE engine) is:
more compact,
lighter,
simpler,
cheaper,
is based on “built-in” scavenging pump of the piston type,
has a wider rev range,
is more vibration-free,
provides additional time to the fuel to get prepared and burned more
efficiently,
has better lubrication, etc.

For more (videos of the OPRE prototypes running on Diesel fuel,
dimensions, weight etc): http://www.pattakon.com/pattakonOPRE.htm

Thanks
Manousos Pattakos