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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.

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.

A free piston internal combustion (IC) engine operating on high compression ratio (CR) homogeneous charge compression ignition (HCCI) combustion is being developed by Sandia National Laboratories to significantly improve the thermal efficiency and exhaust emissions relative to conventional crankshaft-driven SI and Diesel engines. A two-stroke scavenging process recharges the engine and is key to realizing the efficiency and emissions potential of the device. To ensure that the engine's performance goals can be achieved the scavenging system was configured using computational fluid dynamics (CFD), zero- and one-dimensional modeling, and single step parametric variations. A wide range of design options was investigated including the use of loop, hybrid-loop and uniflow scavenging methods, different charge delivery options, and various operating schemes. Parameters such as the intake/exhaust port arrangement, valve lift/timing, charging pressure and piston frequency were varied.

Knock integrals and corresponding ignition delay (τ) correlations are often used in model-based control algorithms in order to predict ignition timing for kinetically modulated combustion regimes such as HCCI and PCCI. They can also be used to estimate knock-inception during conventional SI operation. The purpose of this study is to investigate the performance of various τ correlations proposed in the literature, including those developed based on fundamental data from shock tubes and rapid compression machines, those based on predictions from isochoric simulations using detailed chemical kinetic mechanisms, and those deduced from data of operating engines. A 0D engine simulation framework is used to compare the correlation performance where evaluations are based on the temperatures required at intake valve closure (TIVC) in order to achieve a fixed CA50 point over a range of conditions.

A high pressure capable, free piston rapid compression expansion machine (RCEM) has been used to investigate the autoignition, or Homogeneous Charge Compression Ignition (HCCI) behavior of a wide range of fuels. Thermal efficiencies and emissions characteristics were reported previously, but the heat release rates (HRR) and mass fractions burned (χ) seen under the experimental conditions were not specifically determined. This work investigates the characteristic heat losses in this device for use in determination of the HRR and χ. The heat flux is derived from surface temperature thermocouple data; a spatially-uniform, global convection model is correlated to this. Data from lean n-pentane and n-hexane in air mixtures were used to calibrate the model. The RCEM-calibrated model was compared to similar models that were calibrated to IC engines operating on HCCI, and to predictions from the CFD code KIVA3V.

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.

Simulation of chemical kinetic processes in combustion engine environments has become ubiquitous towards the understanding of combustion phenomenology, the evaluation of controlling parameters, and the design of configurations and/or control strategies. Such calculations are not free from error however, and the interpretation of simulation results must be considered within the context of uncertainties in the chemical kinetic model. Uncertainties arise due to structural issues (e.g., included/missing reaction pathways), as well as inaccurate descriptions of kinetic rate parameters and thermochemistry. In fundamental apparatuses like rapid compression machines and shock tubes, computed constant-volume ignition delay times for simple, single-component fuels can have variations on the order of factors of 2-4.