Three-Dimensional Simulation of Diesel Spray Ignition and Flame Lift-Off Using OpenFOAM and KIVA-3V CFD Codes

• Three-dimensional simulations of ignition and combustion of a dieselspray were conducted. The primary goal of the work was to compare twodifferent CFD codes: OpenFOAM, an object-oriented C++ based code, andKIVA-3V. The spray is modelled by the Eulerian-Lagrangian approach inboth codes, with several common submodels. Some important sub-modelsimplemented include \emph{inter alia} aKelvin-Helmholtz/Rayleigh-Taylor (KH/RT) model for spray break-up, animproved spray collision model, and a Partially Stirred Reactor (PaSR)model for turbulence-chemistry interaction. Both CFD codes solve thechemical reaction equations in a fully coupled manner. A cubic-shaped Cartesianmesh was used in the KIVA-3V simulations, while a polyhedral meshincluding a combination of hexagonal and prism-shaped cells wasconstructed for the OpenFOAM computations.The effects of high EGR and ambient temperature on the ignition and flamelift-off processes of a diesel spray were investigated. Sandia experimentsconducted in a high-pressure and high-temperature constant-volume vessel werechosen for the simulations and validations. A single spray was injected intothe vessel, and EGR was mimicked by reducing the oxygen concentration. Thediesel reference fuel (n-heptane) was considered. For the study, a medium-sizemechanism involving 83 species and 338 reactions was employed. The mechanismwas validated using the CHEMKIN II package and the reaction rate constantswere adjusted on the basis of measurements of auto-ignition delays ofn-heptane/air mixtures in shock-tube experiments (with equivalence ratiosranging from 0.2 to 0.4 at 50 bar, and from 0.5 to 2.0 at 13.5 bar and 41.0bar), laminar flame speeds (1 atm and 3 atm), and flame structure inburner-stabilized premixed flames (1 atm).The simulations demonstrate that both CFD codes are capable of spray ignitionand combustion studies, though both show stronggrid-dependence. The numerical results show that the ignition delay,flame lift-off and combustion temperature of the spray are stronglyinfluenced by EGR and ambient gas temperature. These predictions arein agreement with measurements. Nevertheless, differences are observedbetween the results predicted by OpenFOAM and those from KIVA-3V, forexample, the flame predicted by the former is thinner and longer than that by thelatter, which requires further investigation.

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TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

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