Questions on Naphtha Steam Cracking Simulation: Feedstock Complexity, Variable T/P Profiles, Termination Criteria, and Coke Formation Pathways

[alirezalotfii]

Hi everyone,
I am a simulation engineer currently working on modeling an industrial naphtha steam cracking unit for olefin production using RMG-Py. I have run into a few conceptual and technical challenges during the setup of my input.py file and would greatly appreciate some advice from the developers and experienced users in the community.
Here are the issues I am facing:

1. Naphtha Feedstock Representation & Combinatorial Explosion
   Real naphtha contains hundreds of individual paraffinic, naphthenic, and aromatic compounds. Attempting to define all these components as initial species in the RMG input file leads to a massive combinatorial (state) explosion, making the simulation computationally impossible.
   My Question: What is the industry standard/best practice for simplifying naphtha in RMG? Should I use a surrogate mixture (e.g., a 3-to-5 component PIONA surrogate)? If so, is there a recommended surrogate formulation for steam cracking that works well with RMG's current databases?
2. Handling Variable Temperature and Pressure Profiles
   Naphtha steam cracking is highly endothermic, causing a significant temperature drop along the PFR (Plug Flow Reactor) tube, accompanied by a pressure drop. However, the SimpleReactor in RMG assumes isothermal and isobaric conditions by default.
   My Question: How should I define T and P during the mechanism generation phase?
   Is it best practice to generate the mechanism using a constant average T and P, and then export the resulting CHEMKIN/Cantera file to run in a separate 1D PFR solver with the real T/P profile?
   Or is there a way to feed a T/P profile directly into RMG's reactor model during the generation phase?
3. Defining Termination Conditions for Pyrolysis
   I am unsure what the most physically meaningful termination criteria are for a pyrolysis system in RMG.
   My Question: What are the typical termination conditions used for steam cracking simulations? Should I terminate based on a target conversion of my primary feed components (e.g., 90% conversion), or is it better to terminate based on a target residence time (e.g., typical industrial coil residence times of 0.1 to 0.5 seconds)?
4. Simulating Coke (Coking) Reaction Pathways
   I would also like to model the coke formation process inside the cracker tubes.
   My Question: Can RMG be used to simulate the complete coke formation process, including both the gas-phase precursor growth (such as Polycyclic Aromatic Hydrocarbons or PAHs) and the surface deposition/solid carbon growth? Specifically, is it possible to generate or isolate just the reaction network and pathways leading to coke and its precursors?
   Thank you very much in advance for your time, guidance, and support!