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A floating-stroke, free-piston internal combustion reciprocating engine (FS-FPE) is currently under development with the primary goal of high engine efficiency, along with ultra-low emissions. High compression ratio, boosted, lean operation is targeted with kinetically-modulated combustion expected to be utilized as a principal mode of operation. To aid the engine's preliminary design stage modeling is conducted in order to explore the engine's operational characteristics and charge conditioning needs. Natural gas and gasoline are considered as potential fuels. A single-zone, homogeneous reactor model (HRM) is employed to approximate the in-cylinder processes, especially the ignition chemistry (timing) which is important for operation under these conditions. Sub-models are integrated into the HRM to describe fuel evaporation, heat transfer, and piston crevice / ringpack flows.

A small-scale flow rig has been constructed to investigate the swirl behavior of various intake manifold configurations. This effort is to support the development of a 10cc-size, single-valve reverse uniflow 2S engine. In this reverse uniflow geometry the incoming charge enters through a single valve in the engine head, and the burned gases are exhausted through symmetrically-arranged ports in the cylinder wall near bottom dead center. Port-directioning of the fresh charge, used in conventional (bottom-up) uniflow arrangements, is not available with this geometry, so another means to control the cylinder sweeping is sought. The flow rig has been constructed on a 2:1 scale, and three preliminary intake manifold configurations have been prototyped using a 3D printing machine. A straight manifold, a ramped tangential manifold and a basic helical design were manufactured.

A 10cc single-valve, reverse uniflow 2S engine is being developed to power a compact compressor system; the output from this device could be hydraulic or pneumatic power. In this design a free piston is used to directly compress the power fluid. In the initial configuration fresh charge will be delivered through a single, dual-acting spring-loaded poppet valve located in the center of the cylinder and the burned charge is exhausted through symmetrically-arranged ports located at the bottom section of the cylinder; two combustion chambers exist on opposite ends of the piston. Of particular interest in the early stages of the engine development is the gas transfer system; proper cylinder scavenging is required to ensure adequate engine operation. An initial design is being investigated using the commercial computational fluid dynamics software suite, STAR-CD/ESICE. This report will document some initial simulations and indicate areas requiring further refinement.

The charge dynamics within a Rapid Compression Expansion Machine (RCEM) have been investigated using an integrated computational fluid dynamics / chemical kinetics code, KIVA3V/CHEMKIN. A 0D ring-dynamic model, first developed at MIT, and subsequently modified at UIUC to include circumferential flow past unlubricated rings, was added to the code in order to account for flow into, out of and past the piston's ringpack. Simulations were conducted using two different compression ratios (25:1 and 50:1) for an unreacting (‘motored’) charge and at 38:1 for a reacting (‘fired’) charge, in this case with a lean H2/air mixture. A 19-step detailed kinetic mechanism was employed for the reacting simulation. The effects of various modeling parameters, including the mesh configuration, ring-dynamic parameters and turbulent/laminar assumptions were explored; the simulation results were compared to experimental data from the RCEM.

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.