DNS Study of the Ignition of NHeptane Fuel Spray under High Pressure and Lean Conditions
Yunliang Wang and Christopher J. Rutland University of WisconsinMadison
Direct numerical simulations (DNS) are used to investigate the ignition of
nheptane fuel spray under high pressure and lean conditions. For the solution
of the carrier gas fluid, the Eulerian method is employed, while for the fuel
spray, the Lagrangian method is used. A chemistry mechanism for nheptane with
33 species and 64 reactions is adopted to describe the chemical reactions. Initial
carrier gas temperature and pressure are 926 K and 30 atm, respectively. Initial
global equivalence ratio is 0.258. Two cases with droplet radiuses of 35.5 and
20.0 macrons are simulated. Evolutions of the carrier gas temperature and species
mass fractions are presented. Contours of the carrier gas temperature and species
mass fractions near ignition and after ignition are presented. The results show
that the smaller fuel droplet case ignites earlier than the larger droplet case.
For the larger droplet case, ignition occurs first at one location; for the smaller
droplet case, however, ignition occurs first at multiple locations. At ignition
kernels, a significant amount of OH is produced. NO is produced when temperature
is high enough at the ignition kernels. For the larger droplet case, more NO is
produced than the smaller droplet case due to the inhomogeneous distribution and
incomplete mixing of fuel vapor.
