Fundamental simulations in a quiescent cell under adiabatic conditions were made to understand the effect of temperature, equivalence ratio and the components of the recirculated exhaust gas, viz., CO2 and H2O, on the combustion of n-Heptane. Simulations were made in single phase in which evaporated n-Heptane was uniformly distributed in the domain. Computations were made for two different temperatures and four different EGR levels. CO2 or H2O or N2was used as EGR.
It was found that the initiation of the main combustion process was primarily determined by two competing factors, i.e., the amount of initial OH concentration in the domain and the specific heat of the mixture. Further, initial OH concentration can be controlled by the manipulating the ambient temperature in the domain, and the specific heat capacity of the mixture via the mixture composition. In addition to these, the pre combustion and the subsequent post combustion can also be controlled via the equivalence ratio.
In order to verify these findings in a two phase scenario, Direct Numerical Simulation (DNS) type procedures were applied to a two-dimensional domain in which liquid n-Heptane droplets were pre-distributed. Simulations were performed using an enhanced version of the parallel code for turbulent reacting flows, called S3D, which was developed at Sandia National Laboratories at Livermore. The code comprises a DNS quality Eulerian method to solve the carrier gas flow field, while the Lagrangian method is used to track the liquid fuel droplets. Two-way coupling between the liquid and the gas phases were established via the mass, momentum and energy equations. A detailed chemistry mechanism involving 33 species and 64 reactions was used to describe the chemical reactions.