Auto-ignition characteristics of diesel fuel in an O₂-CO₂ mixture

To study diesel fuel auto-ignition in an O₂-CO₂ mixture, a TZ (temperature zone) model is proposed. The effect of O₂ and CO₂ on reaction rate is considered. The relationship between temperature and ignition delay time is obtained. Different reduced mechanisms based on steady-state assumptions are applied in three temperature zones (T ≤ 800 K, 800 K < T ≤ 1100 K, T > 1100 K). The TZ model is coupled to KIVA-3V code for simulation calculations. To support the simulations, a constant-volume combustion bomb test bench is set up to visualize diesel fuel auto-ignition in air (21%O₂-79%N₂), a 53%O₂-47%CO₂ mixture, and a 61%O₂-39%CO₂ mixture. Ignition delay time and the flame image in these three conditions are compared and analyzed. Then the flame temperature contour and the flame lift-off length in a 53%O₂-47%CO₂ mixture and a 61%O₂-39%CO₂ mixture are analyzed. The results show that diesel fuel auto-ignition can be achieved in the tested O₂-CO₂ mixture. The TZ model can predict the auto-ignition characteristics of diesel fuel in a 53%O₂-47%CO₂ mixture and a 61%O₂-39%CO₂, with errors of 12% and 10%, respectively. In these two conditions, the ignition delay time and flame lift-off length are shorter than they are in air.