Grail Engine

How it Works: Casually looking at the Grail engine, you'd swear it was a traditional two-stroke engine—carbon fiber reed valve intake, alternating combustion and exhaust strokes, and an extremely compact design. However, it's when you notice the large, upward-facing intake valve in the center of the piston that things go a little sideways. To start, the engine works by using the negative crankcase pressure of the upward moving piston to suck air past the reed valve. Upon ignition, the piston is forced down, in turn closing the reed valve. As the inertia of the piston compresses the air trapped in the crankcase chamber, it's forced through an oil-separating loop ending at the bottom side of the piston. When the pressure of the crankcase overcomes that of the combustion chamber, the piston intake valve opens, forcing air through the center of the piston, pushing exhaust out and fresh air in. As the piston moves up, the intake valve and overhead exhaust valve close, fuel is injected and the mix is ignited by a spark plug.

Claimed Benefits: Because the piston and compression chamber constantly have cool air moving through the center of their masses, heat soak is reduced, which allows fuel injection to occur at any time and in turn reduces NOx emissions. The engine can operate on literally any combustible, including propane, natural gas and diesel. It's light for its power output, a 25-pound engine can develop 65 hp, a 40-pound engine can develop 100 hp. The design is modular—self-contained single piston engines can be daisy-chained along a crankshaft to create a multicylinder inline engine. It's cheap to produce—there are very few parts involved and many can be simple castings. Effectively separating the oil from the intake charge will be a critical step, however, if this engine is to ever pass emission requirements.

Status: Considering the Grail engine has only been in development for 24 months, it's in pretty good shape. The company is currently performing dyno and durability testing and will be marketing it to whomever will listen.