Experimental Observation of Negative Temperature Dependence in iso-Octane Burning Velocities

The average burning velocities of premixed, spherically expanding iso-octane flames are reported for flame radii from 0.75 to 1.75 cm between 400 and 900 K, near 1 atm. Measurements are performed in lean mixtures (0.9 equivalence ratio) using a helium-enriched oxidizer ( oxygen, nitrogen, and 41% helium) to inhibit thermodiffusive instabilities at high temperatures. A shock tube is used to heat the unburned gas to elevated temperatures....