Demonstration of a Free-Piston Rapid Compression Facility for the Study of High Temperature Combustion Phenomena

A free-piston rapid-compression facility (RCF) has been developed at the University of Michigan (UM) for use in studying high-temperature combustion phenomena, including gasphase combustion synthesis and homogeneous charge compression ignition systems. The facility is designed to rapidly compress a mixture of test gases in a nearly adiabatic process. A range of compression ratios, currently 16 to 37, can be obtained. The high temperatures and pressures generated by the RCF can be maintained for in excess of 50 ms, providing an order of magnitude increase in observation time over what can be obtained using shock tubes. The facility is instrumented for temperature and pressure measurements as well as optical access for use with laser and other optical diagnostics. This work describes the UM-RCF and its operation, establishes obtainable pressures and temperatures (over 1900 kPa and 970 K for predominately N2 gas mixtures, and over 785 kPa and 2000 K for Ar gas mixtures), and demonstrates the repeatability of the UM-RCF experiments (< 3% run-to-run variability in peak pressure) for combustion studies. The experimental results for time histories of temperature and pressure are interpreted using analytical isentropic models. Comparison between the isentropic predictions and the experimental data indicate excellent agreement and support the conclusion that the core region of the test gases is nominally uniform and is compressed isentropically.