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CFD modelling of diesel spray and combustion using homogenous gas phase reactions within the Euler-Eulerian framework

The spray dynamic behavior in terms of mixing and atomization influences the overall engine performance. Thus, the understanding of these processes represents essential knowledge in engine development. Diesel fuel is usually injected into the combustion chamber with high velocities arising from high injection pressure and small diameter nozzles. As a result, a high fuel-air relative velocity occurs causing the surface instabilities. This leads to fuel jet disintegration and droplet formation, their evaporation, and finally, fuel vapor combustion. In most of the engineering applications spray is modelled using the Euler- Lagrangian approach, where the motion of droplets is described using Lagrangian equations. Such approach suffers from disadvantages in the modelling of dense spray region. Therefore, the discrete phase could be considered as the continuous phase, divided into a number of classes characterized with the volume fraction, and treated with the Eulerian conservation equations. Employing this approach in the spray simulations, the liquid-gas interactions in the dense region are more adequately described. In this research, the fuel jet disintegration is modeled as the primary break-up of the liquid jet. The further disintegration of the ligaments formed by primary atomization is modelled by a secondary break-up model based on the common WAVE model. Droplet-droplet collisions are described employing the stochastic O’Rourke collision model adjusted for the Euler-Eulerain approach. The combustion of the evaporated fuel is modelled by using the homogenous gas phase reaction model. The effect of chemistry is considered such that at the beginning of each computational time step a single zone 0D reactor model is called for each computational cell. The model calculates source terms for the species transport equations and the enthalpy equation. The implemented combustion model is verified with the constant volume case, where the interior is filled with fuel-gas mixture on the elevated temperature. The validation of the model is performed by comparing the simulation results to the experimental data from the ECN database (European Combustion Network). One component fuel (n-dodecane) is injected through a 90 µm SAC nozzle into a pressurized reacting environment of 150 bar and a corresponding density of 22.15 kg/m3. The liquid fuel and vapor penetration, spray angle, mass distribution, velocity profiles, flame lift off and emission characteristics are analyzed.

Eulerian spray; combustion; gas phase reactions; modelling

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