Numerical simulation and laser-based imaging of mixture formation, ignition, and soot formation in a diesel spray
Laser-based imaging of fuel vapor distribution, ignition, and soot formation in diesel sprays was carried out in a high-pressure, high-temp. spray chamber under conditions that correspond to temp. and pressure in a diesel engine. Rayleigh scattering and laser-induced incandescence are used to image fuel d. and soot vol. fraction. The exptl. results provide data for comparison with numerical simulations. An interactive cross-sectionally averaged spray model based on Eulerian transport equations was used for the simulation of the spray, and the turbulence-chem. interaction was modeled with the representative interactive flamelet (RIF) concept. The flamelet calcn. is coupled to the Kiva3V computational fluid dynamics (CFD) code using the scalar dissipation rate and pressure as an input to the RIF-code. The flamelet code computes the instationary flamelet profiles for every time step. These profiles were integrated over mixt. fraction space using a prescribed beta -PDF to obtain mean values, which are passed back to the CFD-code. Thereby, the temp. and the relevant species in each CFD-cell were obtained. The fuel distribution, the av. ignition delay as well as the location of ignition are well predicted by the simulation. Furthermore, simulations show that the exptl. obsd. injection-to-injection variations in ignition delay are due to temp. inhomogeneities. Exptl. and simulated spatial soot and fuel vapor d. distributions are compared during and after second stage ignition.
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