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Technical Paper

A Small-Scale Flow Rig for Swirl Studies of a Single-Valve, Reverse Uniflow 2S Engine

2008-04-14
2008-01-0609
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.
Technical Paper

Developing a 10cc Single-Valve, Reverse Uniflow, 2S Engine

2008-04-14
2008-01-0953
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.
Technical Paper

Evaluating the Heat Losses from HCCI Combustion within a Rapid Compression Expansion Machine

2006-04-03
2006-01-0870
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.
Technical Paper

Design and Operational Characteristics of a Novel Floating-Stroke, Free Piston Internal Combustion Reciprocating Engine

2013-04-08
2013-01-0284
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.
Technical Paper

A Numerical Study of a Free Piston IC Engine Operating on Homogeneous Charge Compression Ignition Combustion

1999-03-01
1999-01-0619
A free piston, internal combustion (IC) engine, operating at high compression ratio (∼30:1) and low equivalence ratio (ϕ∼0.35), and utilizing homogeneous charge compression ignition combustion, has been proposed by Sandia National Laboratories as a means of significantly improving the IC engine's cycle thermal efficiency and exhaust emissions. A zero-dimensional, thermodynamic model with detailed chemical kinetics, and empirical scavenging, heat transfer, and friction component models has been used to analyze the steady-state operating characteristics of this engine. The cycle simulations using hydrogen as the fuel, have indicated the critical factors affecting the engine's performance, and suggest the limits of improvement possible relative to conventional IC engine technologies.
Journal Article

Insights into Engine Knock: Comparison of Knock Metrics across Ranges of Intake Temperature and Pressure in the CFR Engine

2018-04-03
2018-01-0210
Of late there has been a resurgence in studies investigating parameters that quantify combustion knock in both standardized platforms and modern spark-ignition engines. However, it is still unclear how metrics such as knock (octane) rating, knock onset, and knock intensity are related and how fuels behave according to these metrics across a range of conditions. As part of an ongoing study, the air supply system of a standard Cooperative Fuel Research (CFR) F1/F2 engine was modified to allow mild levels of intake air boosting while staying true to its intended purpose of being the standard device for American Society for Testing and Materials (ASTM)-specified knock rating or octane number tests. For instance, the carburation system and intake air heating manifold are not altered, but the engine was equipped with cylinder pressure transducers to enable both logging of the standard knockmeter readout and state-of-the-art indicated data.
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