Experimental validation and analysis of seven different chemical kinetic mechanisms for n-dodecane using a Rapid Compression-Expansion Machine

Abstract

Seven different chemical kinetic mechanisms for n-dodecane, two detailed and five reduced, have been evaluated under Engine Combustion Network (ECN) thermodynamic conditions by comparison to experimental measurements in a Rapid Compression-Expansion Machine (RCEM). The target ECN conditions are imposed at Top Dead Center (TDC), which cover a wide range of temperatures (from 850 K to 1000 K), oxygen molar fractions (0.21 and 0.15) and equivalence ratios (0.8, 0.9 and 1), while the pressure is fixed to keep a constant density at TDC equal to 22.8 kg/m3. The results obtained have been used to validate the chemical kinetic simulations, which have been performed with CHEMKIN, by comparing both cool flames and high temperature ignition delays, as well as the heat released in each stage of the combustion process in case of having a two-stage ignition pattern. The experimental results show good agreement with the chemical kinetic simulations. In fact, the mean relative deviation in ignition delay between experiments and simulations among all the chemical mechanisms is equal to 18.0% (3 CAD) for both cool flames and high temperature ignition. In general, closer correspondence has been obtained for the ignition delay referred to the high-temperature stage of the process, being the cool flames phenomenon more difficult to reproduce. Moreover, the differences between the reduced mechanisms and the most detailed one have been analyzed, concluding that the enhanced specific reaction rates of the most reduced mechanisms cause differences not only on the ignition delays, but also on the Negative Temperature Coefficient (NTC) behavior and on the heat released during cool flames.