ASYMPTOTIC ANALYSIS FOR THE BURNING OF N-HEPTANE DROPLETS USING A 4-STEP REDUCED MECHANISM

A four-step reduced mechanism is obtained from a minimal chemical-kinetic description, where the effects of the elementary rates are treated as parameters in the expressions for the global rates. This mechanism is used to analyze the extinction characteristics of a single n-heptane droplet burning under quasi-steady, spherically symmetrical conditions. The outer transport zones are described by the classical Burke-Schumann flame model. The reaction layer consists of a merged inner zone, on the fuel-rich side of the flame, where fuel and H atoms are consumed thereby producing H-2 and CO along with H2O And CO2, and an oxygen-consumption zone, on the fuel-lean side, where H-2 and CO are oxidized to produce additional H2O and CO2 along with H radicals. For the inner zone, a parameter mu is identified which describes the ratio of the thickness of a fuel-consumption layer to that of an H-recombination layer. Analytical solutions for the rate of scalar dissipation at extinction are obtained in the limiting cases mu --> 0 and mu --> infinity. From the results of the analysis, extinction diameters for n-heptane droplets are estimated for different pressures and ambient oxygen concentrations.