Comparison of chemical mechanisms for n-dodecane at engine conditions using an unsteady flamelet model

摘要

In the present study, unsteady flamelet calculations were used to compare chemical mechanisms for n-dodecane at thermochemical conditions corresponding to the Engine Combustion Network Spray A reference case. The calculations were carried out for a broad range of scalar dissipation rates and the results were analysed in terms of ignition delay times and location in composition space. The results indicate only a weak dependency of the ignition delay times on the scalar dissipation rate, up to a certain value for which ignition cannot occur any more (χ_(ign)). While this behaviour is consistent for all investigated mechanisms, the value of χ_(ign) varies between them. A more detailed investigation of the effect of mixing showed a significant broadening of the heat release profile in composition space. Consequently, the ignition location shifts to much richer mixtures, even for low scalar dissipation rates. This shift is predicted for all mechanisms, though the extend varies between the mechanisms. The results reveal valuable information with respect to the ignition characteristics of each mechanism, but also indicate that further analysis is needed.