This technology was created in an effort to combine the high flow characteristics of axial compressors and positive displacement advantages of piston compressors in a single machine. As most turbine systems can function as compressors (or pumps), the converse is not necessarily true. While vane, screw or scroll type compressors function quite well for certain applications, they cannot be used as turbines. The Musser Turbine can function as either a turbine or compressor, in much the same way a piston or axial system may be used in either application. The following relates generically to performance of several common compressor types.
A fundamental disadvantage of piston compressors (Figure 1) is the limited area available for valves. Generally located at the top of the cylinder, circular poppet valves use only a fraction of the area available for fluid movement into and out of the cylinder. Even the highest performance engines today (4 or 5 valves per cylinder) use only 50-60% of the total area available at the top of the cylinder. Additional valves dictate the use of additional camshafts to actuate them. The conversion of reciprocating piston motion into rotation at the crankshaft also results in design and manufacturing challenges to attain a reasonably balanced machine. Counterweights must be incorporated on the crankshaft unless a 180° opposed (Boxer Type) cylinder configuration is used. Counterweights on the crankshaft result in increased rotating mass.
On the other end of the operational spectrum, axial compressors (fans basically) are capable of handling very large flows (Figure 2). Since no valves are required, the flow is limited only by the diameter, speed and efficiency of the rotating elements. Axial compressors have a fantastic advantage in that their operation is extremely simple. One disadvantage, however, is that they must rotate very fast to produce significant pressures. The requirement to turn at very high speeds usually results in expensive materials and complex fan geometries to attain good efficiencies.