Promoting “adiabatic core” approximation in a rapid compression machine by an optimized creviced piston design

Rapid compression machine (RCM) is a widely-used experimental instrument for measuring ignition delay time (IDT) in the low-to-intermediate temperature range. In this work, to enhance the validity of the “adiabatic core” approximation in RCM, a piston crevice for suppressing the piston-driven vortex and therefore promoting the temperature homogeneity in the combustion chamber was firstly optimized by numerical simulation with a dynamic mesh strategy. Results show that crevice volume should be large enough to contain most of the boundary layer cold gas during the compression so as to assure the temperature homogeneity in the reaction chamber. While the shape of the crevice (with sufficiently large volume) only weakly affects the temperature homogeneity. An optimized piston was tested across wider ranges of pressure, the chamber length, and inert gas under experimental conditions. Based on the optimized piston crevice, a RCM was established and tested. Test results have confirmed that the crevice shape does not affect the IDT measurements, provided the crevice volume fixed. In addition, the present IDTs show consistency with those using other RCMs, as well as with the numerical predictions obtained by using the well-recognized and validated kinetic mechanisms, which support the validity of the present RCM facility for ignition delay measurement.