The effects of liquid-fuel thermophysical properties, carrier-gas composition,and pressure, on strained opposed-flow non-premixed flames

摘要

A computational model is developed to study flame-droplet interactions in non-premixed opposed-flow flames. Although the stagnation-flow configuration is idealized, the operating conditions are chosen to be relevant to practical combustion. By considering droplet thermophysical properties ranging from heptane to diesel fuel, the results provide quantitative insight about the expected behavior of synthetic fuels. Initial droplet diameters range from 10 um to 20 urn, the loading densities range between 10~5 and 10~7 cm~(-3), strain rates are on the order of 1000 s~(-1) and pressure ranges from atmospheric pressure to l0atm. The gas-phase chemistry for all cases is represented using detailed heptane kinetics. Increasing pressure sfgnificantly narrows the flame zone. Heptane is highly volatile and small droplets evaporate well before entering the flame zone. Diesel fuel is significantly less volatile and small droplets can survive up to the edge of the flame. However, for the conditions studied, the flame structure is only weakly affected by the droplet thermophysical properties. Including oxygen in the droplet carrier gas permits some premixed chemistry, which slightly broadens the flame structure and produces more stable flames.