PARALLEL SIMULATIONS OF PARTIALLY STIRRED METHANE COMBUSTION

Premixed methane combustion in a partially stirred reactor (PaSR) is s tudied numerically. The effects of turbulent stirring rate on NO, CO, and other quantities are computed. The chemistry is represented by a ' 'full'' scheme (27 species, 77 reactions) in the baseline study. Turbu lence is accounted for by the ''IEM'' (Interaction-by-Exchange-with-th e-Mean) submodel. The PaSR is described by a system of (N(s) + 1) x N( p) first-order coupled o.d.e.'s in time, where N(s) = number of specie s, and N(p) = number of particles. The model is well suited to paralle l computers, without which the present study would not have been pract ical. The speedup over serial computers is essentially linear in the n umber of processors used, until the number of particles per processor becomes small enough (< 10) to affect load balance. The conditions are 30 atm, 1200-K inlet temperature, 800-K equilibrium temperature rise, and 2-ms reactor residence time (in the PSR limit). In the PFR limit the flow just starts to ignite, while in the PSR limit temperatures ar e very near equilibrium. PaSR simulations are conducted in the range 1 00-5000 Hz (mixing frequency), and in each case converge to a stochast ic steady state and span the PFR-PSR limits smoothly. The correlation of NO with particle age decreases as frequency increases, and is withi n expected limits. The OH levels are uniform to within a factor of two in this frequency range, which is consistent with the ''distributed'' OH structures observed in turbulent diffusion flames. Simulations wit h a 25-step ''skeletal'' scheme agreed well with the baseline study ab ove 1,000 Hz, but are about 400 K low on mean temperature at 100 Hz. T he corresponding four-step ''reduced'' scheme failed to ignite in all cases, suggesting a need for reduced schemes which do not assume that the radicals are in a chemically steady state.