Vortex formation in a rapid compression machine: Influence of physical and operating parameters

The performance of a rapid compression machine (RCM) with a creviced piston is assessed over a range of operating conditions through computational fluid dynamics simulations with systematic demonstration of the effects of compressed gas pressure, temperature, stroke length, and clearance on altering vortex formation and temperature homogeneity inside the reaction chamber. Simulated results show that as compressed gas pressure is reduced, the temperature homogeneity deteriorates due to the combined effect of thicker boundary layer and increased flow velocities. A further optimization of the creviced piston geometry is then required to completely suppress the roll-up vortex. Stroke length and clearance volume are also noted to significantly affect vortex formation. A basis for quantifying the extent of the roll-up vortex is suggested and the operating regime of an RCM with a creviced piston, that is free from the roll-up vortex, is delineated. This work emphasizes the importance of assessing the performance of an RCM over the associated range of operating conditions in order to obtain reliable chemical kinetics data.