Counterflow heptane flame structure

Abstract

Results are reported for thermocouple and gas-chromatographic measurements of profiles of temperature and of concentrations of C7H16, C5H10, C4H8, C4H6, C3H6, C2H6, C2H4, C2H2, CH4, CO, and CO2 in two laminar counterflow n-heptane flames having measured flame temperature of 2100 K, at an oxidizerside potential-flow strain rate of 50 s−1. One was a diffusion flame, in which a fuel spray was transported by nitrogen, and the oxidizer stream was an oxygen/nitrogen mixture with an oxygen mole fraction of 0.47. The other was a partially premixed flame, in which the spray was transported by air at a fuel stream equivalence ratio of 2.8, und the oxidizer stream was air. The partially premixed system exhibited two-stage combustion: the green planar rich premixed flame separated 3 mm to 4 mm from the blue planar diffusion flame. Both Phase-Doppler particle analyzer (PDPA) measurement of droplet size, velocity, and number density and observations of planar laser-sheet scattering confirmed that evaporation was complete at a vaporization plane 2 mm to 3 mm upstream from the first reaction zone in both experiments, so that gaseous fuel entered the flame. Although flame structures computed with a detailed mechanism of 180 steps were in generally good agreement with the measurements, differences for some intermediates in excess of experimental uncertainty for the partially premised flame indicated that the fuel chemistry requires further attention.