Each classification of rotary engines has inherent
advantages and disadvantages. The main objective of
any engine design should be an improved efficiency
over existing designs. While the rotary mechanism is
inherently a simpler mechanical device with no
connecting rod and valve train compared to a
conventional piston engine, it does falter when sealing
the working fluid chambers. The conventional piston
engine sealing design has evolved over the last one
hundred years and can be considered a two-dimensional
problem involving circumfencial sealing and translational
movement. However, the sealing in rotary engines is a
three dimensional problem involving the rotary
movement and sealing at least two perpendicular
surfaces. The sealing between two perpendicular
surfaces generally results in the “simple” rotary
mechanism becoming “complex.”