Monolith Engines has developed a set of dual (Fig. 1) and quad (Fig. 2) opposed piston engines (watch Two and Four Cylinder Single Stroke Opposed Piston Engines on Engineering TV). The engines uses a dual, split crankshaft that is connected to the pistons by an arm that is connected perpendicular to the piston. The compact design is very efficient with very low vibration and wear characteristics. The engine can be fully enclosed and cooled by air or water. The approach supports 2- and 4-cycle designs. It is ideal of a range of application from unmanned air vehicles (UAV) to hybrid electric vehicles to motorcycles.

The new Gen II two-cycle design fits a 1.2 liter engine into a 24-in by 12-in by 5-in package. The proposed 200 HP engine weighs under 75 pounds for a gas engine version and 95 pounds for a diesel design. The piston head is air cooled using an air intake that moves air into the cylinder through the top of the piston head. The design incorporates air pumps in the upper part of the engine block. This allows air to travel in both travel directions. The approach provides more air volume than is needed for cleaning out the cylinder exhaust. The design can handle an exhaust turbo pump allowing for even higher power output and RPMs

The two-cycle engine design uses fuel injection. This eliminates valves and an oil/gas mixture.

Low vibration is the result of the opposed piston design and the balance crankshaft interconnected. This reduces bearing wear and requirements because of the balanced loading. Counter balances found on other engine designs are not necessary with Monolith Systems' design. Wear on the piston and rings is minimized because of this as well since there is minimal fricton between the piston and cylinder wall. The design uses four cylinder rings to keep the dual pistons in place. This also restricts lubrication oil to the crank case.

The reduced wear also has implications on block construction. The new engine block can extruded versus the more costing cast blocks used in most engines. The extruded block is also lighter and easier to manufacture.

The engine actually has two output shafts. These can be synchronized for single shaft outputs but many applications could take advantage of two shafts. For example, a dual push/pull propeller driven aircraft is one possiblity.

The design lends itself to electronic ignition and timing. The design scales well and larger implementations improve efficiency.

Opposed piston engines have been around almost since engines have been designed. Interest in these power plants is growing as designs like those from Monolith Systems deliver improved perfomance and efficiency.