Ingmar Schoegl

The fully resolved dynamics of an elliptical particle suspended in an upward flow in an expanding channel, with successively increasing degrees of freedom of motion from a completely fixed state to an eventually fluidized state, are examined using particle resolved direct numerical simulation. The signed distance function immersed boundary method (sdfibm), implemented in OpenFOAM, is validated against results from COMSOL for the case of a pinned ellipse. The aspect ratio of the ellipse (defined as the ratio of the major to the minor axis (γ=Ra/Rb) is held constant at 2, while the minor axis is kept as Rb=0.15 (with respect to the inlet width, Wi = 1). A particle Reynolds number defined as Rep=(2Ra)Vmax/ν (where Vmax = 1 is the centerline velocity) is varied up to 300. The simulations exhibit rich dynamical behavior with stable, steady solutions up to Rep around 67, above which vortex shedding begins, with the ellipse responding with its oscillatory motion in response to the stresses and torques acting on it by the fluid. For the case of free translation in the x direction, multiple oscillatory states are found, where the particle is confined in the left or right half of the flow domain, depending on the initial placement of the particle. The forces on the particle get progressively complicated as the degree of freedom of movement of the ellipse increases, indicating that traditional drag correlations with fixed particles may not be valid in situations when they have mobility if one desires higher fidelity in coarse-grained models.

The project “Microliter Fuel Characterization and Property Prediction” addresses DOE’s stated interest in enabling small volume (100 tests/device/month) measurements of transportation fuels and blends that are relevant to co-optimized fuels and engines. In this context, the ability to quantify the performance of a fuel in terms of autoignition metrics (e.g. octane number/sensitivity), combustion properties (e.g. flame speed) and physical properties (e.g. volatility and viscosity) is of significant interest. Predictions of fuel performance in a combustion engine require a link to be made between small volume measurements and combustion behavior of a fuel blend at engine relevant conditions.

The potential of a novel method to quantify the auto-ignition and extinction of fuels is investigated both experimentally and numerically. Results are discussed for both gaseous and liquid fuels, including ethane and primary reference fuels (PRFs). An externally heated microchannel with a controlled temperature profile is used as a microreactor. Experiments are performed for

Heat recirculating reactors have many potential applications as thermal oxidizers, combustors, and fuel reformers due to their extensive operating range. Low emissions and fuel flexibility make such devices highly desirable as heat sources as well as chemical reactors. The dependence on the solid/gas heat transfer implies that wall characteristics and operating conditions significantly influence the stable range. In this paper, the importance of various combustor parameters is examined through an analytical model, and an experimental reactor is fabricated from a new ceramic-metal composite using additive manufacturing. A full range of possible operation modes, from flashback to blow-off, was observed together with characteristic temperature distributions at various firing rates. The new combustor showed improved operational flexibility as compared to a traditionally assembled counterpart. Low CO and NO_x emission levels were observed together with an audible sound in the range between 825 Hz and 1000 Hz. The combustor operated for over 70 hours without visible damage to the material. The overall thermal performance, low emissions, and high power density make the heat recirculating reactor a viable solution for combustion applications.