Abstract of PhD Thesis

Detailed chemical kinetics combined with a computational fluid dynamics study of a twin piston rapid compression machine

Judith Wurmel, National University of Ireland, Galway (2004)

Rapid compression machines have been developed to mimic the conditions (very hot, high pressure) that exist in real engines but with few of the complications such as rapidly changing conditions (pistons moving up and down), complex flows of gases and aerosols (inlet and exhaust valves opening and closing), contamination by oil mists, abraded metal particles, etc. Thus an RCM is a simple but valuable research tool to simulate a single cycle in a combustion engine and has been widely used for autoignition studies, with the underlying assumptions that a constant adiabatic core temperature persists for long enough and is only slightly contaminated by a small cool boundary layer of unreactive gas. However, the temperature fields generated in conventional RCMs are not uniform, as shown by experiments and simulation studies and this can be a major complication in the interpretation of kinetic data. Hochgreb and Lee, following on earlier work by Park, have shown in CFD studies that the machining of a groove or crevice in the piston head sidewall can, through the suppression of corner vortices, considerably alter the flow fields and by implication the temperature fields.

In this study a 2–dimensional moving mesh CFD computer model was created and used to investigate the flow and resulting temperature fields in a rapid compression machine. The sensitivity of the horizontally opposed twin piston RCM to non–synchronized and non–uniform piston strokes was determined and factors which influence the design of an optimal piston head crevice were highlighted. The STAR-CD model was validated against experimental and simulated data, which were generatedby a second CFD  (KIVA) model.

Finally, the simulation tool was applied to study the auto–ignition behavior of hydrogen in our RCM.