The Rand-Cam Engine: A Pistonless Four Stroke Engine 940518
The Rand-Cam engine is a positive displacement machine, operating on a four stroke cycle, which consists of a rotor with multiple axial vanes forming combustion chambers as the rotor and vanes rotate in a cam shaped housing. The cam housing, consisting of two “half-housings” or stators, contains a toroidal trough of varying depth machined into each stator. The two stators are phased so that the shallowest point on one trough corresponds to the deepest on the other. A set of six vanes, able to move axially through machined holes in the rotor, traverses the troughs creating six captured zones per side. These zones vary in volume with rotor rotation. Since each trough has two deep sections and two shallow sections with ramps in between, full four stroke operation is obtained between each pair of vanes in each trough, corresponding to twelve power “strokes” per revolution. Since intake, compression, power and exhaust strokes are separated in space along the trough length, intake and exhaust flow is achieved using ports and opportunities for simple variable port timing exist. Aside from dynamic considerations, trough and vane shape are influenced by thermodynamics and manufacturing considerations. The desire for a continuous line contact between the vane seal and trough (cam) throughout a rotation under constraint of a finite vane thickness has led to the construction of a prototype model to demonstrate this concept. Vane motion is then purely cycloidal. The cam profile is also influenced by the need to keep the pressure angle between the vane and bearing surface cam as low as possible, while providing enough dwell near “top-dead-center” to provide adequate compression ratio. Basic design of a prototype, including port and plug placement, are presented and compression ignition design considerations are reviewed.