Measurement and Simulation of n-Heptane Mixture Autoignition

The autoignition of n-heptane mixtures was studied over a wide range of conditions using a rapid compression machine (RCM). The experiments were performed using several n-heptane mixtures at average compressed gas pressures of 6.55 and 13.35 bar, compressed gas temperatures ranging from 605 to 757 K, equivalence ratio of one, and two inert dilution ratios of 79, and 84%. Two detailed kinetic mechanisms (LLNL and NUI Galway kinetic models) were used to simulate the measured data. Three-dimensional (3-D) and zero-dimensional (0-D) computational fluid dynamics models were used to simulate the autoignition at the studied conditions. The mechanism models performed well using 84% diluted mixture at both pressures, while 79% dilution performed well only at lower pressure. The NUI Galway mechanism model predicts a longer ignition delay with respect to the measured data at most of the studied conditions. The modeled ignition delays are longer using 3-D model with respect to the O-D model, which is due to the simulation of the flow pattern inside the combustion chamber. However, the difference between the two models becomes smaller at higher gas temperatures. The results show that the 3-D model is necessary to simulate the n-heptane mixture ignition delay and validate the kinetic model at the RCM low-temperature conditions. In addition, some of the measured ignition delays were compared with the shock tube data, and they are slightly shorter than the shock tube data.