Modeling Standards and Recommendations

Based upon past ECN workshop activities and discussions, particularly ECN2 guidelines, CFD activities should be performed and post-processed according to the following standard definitions and recommendations:

• C_d, C_v and C_a nozzle flow coefficients: The value of the density which is used for the calculation is to be reported.
• Liquid penetration: Maximum distance from the nozzle outlet to the farthest axial position where projected liquid volume in the cross-stream direction decreases to a specific value. The projected liquid volume is defined as PLV = ∫ LVF · dy, where LVF is liquid volume fraction and PLV is projected liquid volume. Two values for PLV are considered:
  • ∫ LVF · dy = 0.2e-3 mm³ liquid / mm² 
  • ∫ LVF · dy = 2.0e-3 mm³ liquid / mm²
• Vapor penetration: Maximum distance from the nozzle outlet to where the fuel mass fraction (or mixture fraction) is 0.1%.
• High-temperature ignition delay: Two different definitions are utilized. (1)First time at which Favre-average OH mass fraction reaches 2% of the maximum in the domain after a stable flame is established. (2) The time of maximum gradient dT/dt in temperature.
• Flame lift-off length: First axial location of Favre-average OH mass fraction reaching 2% of its maximum in the domain.

For consistency in comparison, we recommend similar simulation baselines (boundary conditions, grid, physical models) as defined in modeling contributions to ECN2. For RANS Lagrangian spray computations, we recommend minimum cell sizes (0.25 mm) and time steps (dt = 5E-7 s) in order to ensure fairly converged and comparable spray results.