Instability and divergence observed in diffusion flame configuration

[vijayaraj1]

diffusion_example.zip
I'm noticing instability and divergence of diffusion flame configuration (H2 fuel at atmospheric conditions or high pressure conditions. Eg 15atm, 20 atm). The problem is traced down to global time step size. If I reduce it (say 1e-8), the solution is stable. But it takes forever to converge.

• One suggestion that was suggested by Ray was to use chemistryIntegrator='cvode' and splittingMethod='strang'. It helped when I run at higher time step size. But the overall convergence still takes longer. Also once can notice higher values of wdot[product_species] compared to the lower time step value.
• Is it possible to have an adaptive time stepping process based on how a certain criteria changes with time step?
  Relevant files are attached and more details of this issue can be found at:
  https://groups.google.com/g/cantera-users/c/T9ZgWnfG65k/m/52EeGehMBgAJ

Thanks
Vijay