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

摘要

Ignition delay times of lean (Φ = 0.1-0.4) heptane/air mixtures were measured in the temperature range 720 K ≤ T ≤ 1100 K at pressures of about 50 bar to determine self-ignition characteristics under conditions relevant to diesel and homogeneous charge compression ignition engines. The dependence of the ignition delay times on temperature and equivalence ratio is presented showing negative temperature coefficient behaviour and, in part, a two-stage ignition. This two-stage ignition occurs at temperature T < 900 K, with the pre-ignition becoming stronger compared to the main ignition with decreasing temperatures and equivalence ratios. The results are in good agreement with Cieski and Adomeit [Combust. Flame 93 (1993) 421] for mixtures with equivalence ratios of Φ = 0.5-3. Reaction schemes used in the literature only predict qualitatively the measured ignition delay times. The shape of the curve and the dependency on the equivalence ratio are very well represented by the simulations whereas the absolute experimental values are about a factor of 2 shorter. Two-dimensional ICCD pictures taken through a quartz window in the end flange shortly after the main ignition show that the ignition occurs in the middle of the shock tube.