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A miniature homogenous charge compression ignition (HCCI) free-piston engine compressor aimed at an ankle-foot orthosis application is described. Analysis of the human ankle shows that a fluid power source in the neighborhood of 10 W is needed. To account for compressor and actuator inefficiencies, the power output at the engine cylinder is designed to be 30 W. A compact engine compressor package has been designed and mathematically modeled. Experiments using existing engine components characterized the leakage model. Through the dynamic simulation of the engine, major parameters of the engine have been specified. Simulations indicate that the HCCI free-piston engine compressor, designed in a prototype package scale of about 80×40×20 mm is a viable compact and efficient fluid power supply. Simulation results demonstrate that the overall efficiency of the engine compressor is expected to be 5.9% and that the package should have a higher energy density than batteries.

Analytical ferrography was used as a wear measurement tool while implimenting a procedure to calculate the wear particle generation rate and filter efficiency during laboratory diesel engine testing. The engine testing methodology with quantitative ferrography proved to be a sensitive wear measurement technique in detecting a reduction in the wear particle generation rate for a better anti-wear (API SF/CD) oil from that of a baseline API SD/CD oil. Ferrography and spectroscopy were useful as diagnostic tools for the detection and correction of the unexpected circulation of copper contaminant in the lubrication system. A journal bearing failure was detected with qualitative ferrography and verified with an engine teardown while spectroscopy did not detect the bearing failure.