It is an opposed piston engine: a
cylinder and two oppositely reciprocating pistons form a combustion chamber.
OPRE's unconventional geometry (its crankshaft is disposed between the wrist pin
and the combustion chamber while the wrist pin of conventional is disposed
between the crankshaft and the combustion chamber) shifts the combustion to the
slow dead center.
With two intermediate gears, case of the prototype at top, the crankshafts are counter-rotating.
With a single intermediate gear, case of the animation just above, the two crankshafts rotate at the same direction.
Compared to the conventional, the OPRE engine provides some 30 to 40% longer
piston dwell at Combustion Dead Center (CDC), i.e. additional time for the
preparation of the mixture and the combustion of the fuel at better
After 4500 rpm the power output of all direct injection Diesels drops
steeply because a good part of the fuel is burned late (when the piston is away
from the CDC) and inefficiently. OPRE's geometry shifts this limit above 6000
rpm and proportionally the peak power, it also improves the medium revs thermal
efficiency of the direct injection Diesel.
one more crown at the wrist pin side of each piston, a pair of reciprocating
volumetric scavenging pumps is created at the two ends of the cylinder. The
ratio squared of the bore at the pump region to the bore at the combustion
region of the cylinder defines the scavenging ratio. Besides their simplicity,
efficiency, lightweight and low cost, OPRE's integrated scavenging pumps offer a
flat torque curve along a wide rev range, from very low revs to high revs now
inaccessible for Diesel engines.
of the wrist pin - i.e. of the thrust loads - away from the hot combustion
chamber and away from the ports, solves another problem of the opposed piston
engines: it allows "four stroke" like lubrication and oil consumption. OPRE's
piston skirt can avoid the touch with the hot cylinder wall because the thrust
loads are taken at the other side of the piston, onto the cool, rid of slots and
well lubricated cylinder wall of the scavenging pump. In comparison, the
piston skirt of the conventional opposed piston engine thrusts heavily onto the
hot, especially at exhaust side, cylinder wall, around the port area where the
openings restrict the contact surface, requiring plenty of lubricant and
inevitably resulting in lubricant consumption.
At first look OPRE's pistons seem heavy. The truth is that the gas
pressure loads are way stronger than the inertia loads, even at the rev
The short distance of the two
crankshafts of the OPRE - for a given piston stroke - makes robust, efficient
and light the coupling of the two crankshafts.
Click on the photo below to download the relevant video (QT format, 4.6 MB) showing the engine free on the desk, running on Diesel fuel (compression ratio 17:1, direct injection, rid of glow plug, rid of electrical system).
The additional big flywheel is secured on the "exhaust side" flywheel. It makes easier the manual cranking, it makes possible the true low rev operation and allows power/torque measurements.
* The oil pump is driven by the "intake side" crankshaft (it is installed inside the cover/bearing behind the one big gear).
* The high pressure fuel pump is driven by the "exhaust side" crankshaft (by means of a cam lobe behind the other big gear).
* The built-in scavenging pumps (two reciprocating piston compressors) add no extra cost or friction and operate efficiently throughout all revs. The ratio of the "combustion bore" to the "scavenging pump bore" defines the scavenging-supercharging ratio.
* The balance is perfect. In case of symmetrical load - like twin electric generators, twin propellers, twin rotors - the base of the engine is rid not only of inertia vibrations of any order, but it is also rid of "power" (combustion) vibrations of any order too. * The lubrication (and the oil consumption) is as in four stroke engines. The oil rings never pass over the ports and flooding with oil is needed only at the compressor side of the piston (the cool side) where the thrust loads are taken. * The total weight of the prototype (the big flywheel excluded) is 22 Kp (a 15 Kp total weight seems feasible).
* The long dwell of the pistons at combustion offers some 40% more time to the fuel to get prepared and burned efficiently. In other words this engine can burn efficiently the fuel at 40% higher revs (i.e. Diesel with peak power at more than 6000 rpm).
* The synchronizing gearing is nothing more than the couple of small "free" gears (the big gears are balance webs).
* At the same revs the piston speed is half of the conventional engine of same stroke (less friction).
The OPRE-II and OPRE-III prototypes standing free on the floor, operating on Diesel fuel
Complete power-train for small cars comprising a 500cc OPRE Direct Injection Diesel and a conventional gearbox/differential.
Flames from exhaust ports. Click on the images above and below to download QuickTime Videos of the engine running on Diesel fuel.
The two stroke operation, the perfect balancing, the built-in scavenging pumps, the true compact dimensions, the light weight, the simplicity (reliability), the smaller friction due to the half piston speed, the low cost, the ability for higher "efficient" revs (more power), the four stroke lubrication, the easy/light/cheap synchronization of the two crankshafts etc, etc make this engine a true alternative for all applications.
A 500cc two stroke can easily make some 80 Nt*m (8 Kp*m) torque. At 6000 rpm this torque makes some 50 KW (70 PS). 50 KW from 20 Kp means 0.4 Kp per KW. And 0.4 Kp/KW with direct injection Diesel efficiency sounds interesting, especially for an engine with such a low cost.
In a nutshell, the OPRE engine is the classical "free piston engine" without its problems.
Click on the image below to download a WMV video (700 KB) with the engine driven by two electric drills (balance quality).
Click on the image below to download the
PRE14.exe animation (0.9 MB) of the above engine.
Click on the image below to download the
PRE17.exe animation (1.2 MB) of the above engine.
Click on the image below to download the Hydrid Heart animation (2.7MB). The OPRE engine works as an "almost" free piston engine (after opening the animation press SpaceBar for help).