Shock-tube study of the autoignition of n-heptane/toluene/air mixtures at intermediate temperatures and high pressures

Abstract

The ignition delay times of mixtures containing 35% n-heptane and 65% toluene by liquid volume at room temperature (i.e., 28% n-heptane/72% toluene by mole fraction) were determined in a high-pressure shock tube in the temperature range 620 ⩽ T ⩽ 1180 K at pressures of about 10, 30, and 50 bar and equivalence ratios, ϕ, of 0.3 and 1.0. The equation τ / μs = 9.8 × 10 −3 exp ( 15 , 680 K / T ) ( p / bar ) −0.883 represents the data for ϕ = 0.3 in the temperature range between 980 and 1200 K. At lower temperatures no ignition was found at 10 bar within the maximum test time of 15 ms, whereas for 50 bar, a reduced activation energy was observed. A pressure coefficient of −1.06 was found for the data with ϕ = 1.0 . No common equation for the data at ϕ = 1.0 could be found analogous to that for ϕ = 0.3 because the ignition delay times show no Arrhenius-like behavior. A comparison with ignition delay times of n-heptane/air and toluene/air for ϕ = 1.0 and 30 bar shows that the values of the mixture of the two components are between the values of the single substances. Furthermore, the results confirm the negative temperature coefficient behavior found for the mixtures at 30 and 50 bar, similar to n-heptane/air. A comparison for the other pressure and equivalence ratio values of this study was not possible because of the lack of data for pure toluene. These experimental data have been used in the development of a chemical kinetics model for toluene/ n-heptane mixtures as described in a companion paper.