Experimental investigations of the influence of pressure on critical extinction conditions of laminar nonpremixed flames burning condensed hydrocarbon fuels, jet fuels, and surrogates

Critical conditions of extinction are measured for high molecular weight hydrocarbon fuels, jet fuels and surrogates at pressures up to 0.4 MPa. The hydrocarbon fuels tested are n-heptane, cyclohexane, n-octane, iso-octane, and n-decane. Jet fuels tested include JP-8 and Jet-A. The surrogates tested are the Aachen surrogate, consisting of 80% n-decane and 20% 1,3,5-trimethylbenzene by mass, and the 2nd generation POSF 4658 Princeton surrogate consisting of 49.6% n-dodecane, 24.3% iso-octane, 19.8% n-propylbenzene, and 6.3% 1,3,5-trimethylbenzene by mass. The counterflow, condensed-fuel configuration is employed. Air diluted with nitrogen at 298 K is injected onto the surface of a pool of heptane. The mass fraction of oxygen in the oxidizer stream is represented by YO2,2. A flame is stabilized in the stagnation point boundary layer that is established above the liquid-gas interface. At a selected value of pressure p, and at a selected value of YO2,2, the flow velocity of the oxidizer stream is increased until extinction takes place. The strain rate at extinction is calculated. The experiment is repeated for a range of pressures. The general ordering of extinction strain rates of hydrocarbon fuels was observed and found to be in general agreement with the predictions of kinetic models and experiments conducted at atmospheric pressure in earlier experiments and computations. An initial linear increase of extinction strain rate with pressure is observed at pressures up to 0.175 MPa, followed by a general flattening of the curves up to 0.35 MPa. At pressures above 0.35 MPa, extinction strain rates of some fuels begin to decrease with increased pressures. These general trends are consistent with results previously measured for n-heptane, n-hexane, and n-decane flames in a similar configuration.