Numerical Simulation of the ECN Spray A Using Multidimensional Chemistry Coordinate Mapping: n-Dodecane Diesel Combustion

Abstract

A three dimensional numerical simulation of the ECN “Spray A” is presented. Both primary and secondary breakup of the spray are included. The fuel is n-Dodecane. The n-Dodecane kinetic mechanism is modeled using a skeletal mechanism that consists of 103 species and 370 reactions [9]. The kinetic mechanism is computationally heavy when coupled with three dimensional numerical simulations. Multidimensional chemistry coordinate mapping (CCM) approach is used to speedup the simulation. CCM involves two-way mapping between CFD cells and a discretized multidimensional thermodynamic space, the so called multidimensional chemistry coordinate space. In the text, the cells in the discretized multidimensional thermodynamic space are called zone to discriminate them from the CFD cells. In this way, the CFD cells which are at the similar thermodynamic state are identified and grouped into a unique zone. The stiff ODEs operates only on the zones containing at least one CFD cell. This zones are called “active zones”. Several CFD cells may fall into a unique zone. Thereby, speedup in the stiff ODEs integration is expected. In simulation of the “Spray A”, it is shown that the number of active zones is of the order of hundred times less than the total number of CFD cells. It is therefore a significant speedup in the simulation is expected. After the stiff ODEs integration the mean reaction rate computed in the zones are mapped back to the corresponding CFD cells. While the CCM approach significantly reduces the compositional time, the results are very promising. For example, the predicted spray penetration length, lift-off and the structure of the reaction zone agree well with the experimental measurements. The ignition delay time however was over-predicted. This may be attributed to the kinetic mechanism used in the simulation.