Development of multi-zone chemistry mapping for turbulent partially premixed combustion

A direct numerical simulation (DNS) coupling with multi-zone chemistry mapping (MZCM) is presented to simulate flame propagation and auto-ignition in premixed and partially premixed fuel/air mixtures. In the MZCM approach, the physical domain is mapped into a low dimensional phase space with a few thermodynamic variables as the independent variables. The integration of the chemical reaction rates and heat release rate are done on the grids in the phase space. It is shown that for premixed mixtures, two independent variables can be sufficient to construct the phase space to achieve a satisfactory mapping. The two variables can be temperature of the mixture and specific element mass ratio of H atom for fuels containing hydrogen atom. However, for partially premixed mixtures where combustion may be in both premixed and non-premixed flame modes, a third phase space variable is required to map the physical cell into the phase-space. It is shown that scalar dissipation rate of the element mass ratio of H atom can be used as the third dimension of the phase space. An investigation is carried out on the behavior of MZCM and the choice over the element on which the local element mass ratio should be based on. An aliasing error in the MZCM is investigated. It is shown that if the element mass ratio is based on the element involved in the most diffusive molecules, the aliasing error of the model can approach to zero when the grid in the phase space is refined. To validate the MZCM model the results of DNS coupled with MZCM (DNS-MZCM) are compared with full DNS that integrates the chemical reaction rates and heat release rate directly in physical space. Good agreement between the results from DNS and DNS-MZCM is obtained while the computational time is reduced at least 70%