A Crevice Blow-by Model for a Rapid Compression Expansion Machine Used for Chemical Kinetic (HCCI) Studies

A crevice blow-by model has been developed for a Rapid Compression Expansion Machine. This device can be used to study chemical kinetics with application to Homogeneous Charge Compression Ignition and other alternative combustion processes. In order to accurately resolve the ignition conditions and understand the oxidation process, accurate models for heat transfer and crevice flow, including blow-by past the ringpack, must be utilized. Crevice flows are important when high compression ratio or boosted operation is investigated. In previous work the heat loss characteristics of the RCEM were characterized; this study concerns the crevice flows within the RCEM. A ring-dynamic model, first developed at MIT and recently modified at UIUC to account for circumferential flow pas unlubricated rings, was employed. The 0-D model was coupled to a four-zone heat release code and tuned so that good agreement could be achieved between a computed ‘modified-entropy’ pressure and the experimentally measured pressure for a number of high compression ratio (20-50:1) ‘motored’ runs. The model was then used with two ‘fired’ cases (natural gas / air) to understand how the crevice dynamics change and how the model affects the understanding of the combustion process. In a companion paper the ringpack model is incorporated into an integrated chemical kinetics / computational fluid dynamics (CFD) code to investigate the influence of the crevice flows on the in-cylinder charge motion and temperature profiles that develop during the compression and expansion strokes of the RCEM.