Stirling based cogen systems offer significant potential advantages over internal combustion engines in efficiency, life, noise and emissions. The ability of Stirling machines to maintain higher efficiencies at lower power levels than internal combustion engines significantly expands the potential market for micro-cogen. System cost reduction and electric prices higher than the U.S. national average will have a far greater effect on commercial success than any further increase in Stirling engine efficiency. In contrast to a conventional reciprocating compressor, a linear compressor is a positive displacement, piston-type compressor in which the piston is driven directly by a linear motor. Capacity modulation is intrinsic to the design via a feedback loop which uses a triac-based driver to control the piston stroke.
Modulation is the first of three efficiency related features unique to the linear compressor.
The second is that all the forces on the piston are axial, substantially reducing bearing loads and friction losses and allowing use of gas bearings or low viscosity oil. This results in extremely low friction losses compared to other compressor types. Many linear motor configurations are potentially applicable to linear compressors. Problems associated with some of these are discussed. Properties of, and experimental data relating to a particular configuration that has proven itself in many applications are presented.