Learning Forum

[sharanvenkatesh.211me344]

Hey guys!
I am trying to simulate the suction and compression stroke in a 4-stroke SI DI engine using hydrogen as the fuel. Everything is fine until the fuel is injected. The temperature solution begins to diverge, causing the fuel to evaporate.

This error shows up when I run the simulation.
I have tried reducing the mesh size and timestep size.
The boundary conditions seem fine as well.
Please let me know why this error is occurring.

I really appreciate any help you can provide.

[jcooper]

Hi:

Have you checked the Forte.log file to see what the timestep is heading into the fuel injection?  It is possible that this is too large and causes immediate overflow. If you limit your maximum timestep, this may help:

Droplets may evaporate too quickly or burn too fast, depending on how the spray is set up.  Make sure that the droplet size distribution and inlet temperature is reasonable.

 

You can also modify the spray parameters, specifically the spray breakup parameters, to see if this helps.

If you mouse-hover over the various settings, you will see how each one may affect the breakup rate (This also applies to all other settings in Forte):

 

I hope this helps.

Best Regards,

Judy

[sharanvenkatesh.211me344]

Hey Judy!
Thanks for the kind reply.
The injector diameter that the simulation used was according to a research paper on hydrogen injection. Increasing the diameter of the injector from 120 microns back to 300 microns helped mitigate that issue. So it definitely was an incorrect spray model.

After clearing the issue of the incorrect spray model, I ran into an issue where the log kept throwing up 'Recycling requested by spray vaporization.' The timestep keeps decreasing, and the simulation does not progress. Is this condition normal? I had no problem running the simulation using the gasoline chemistry set. Could using hydrogen as the fuel in the spray model be the problem? The chemistry set being used is 'Hydrogen_MFL2021.cks.'

I would appreciate any help!

Thanks in advance.

[jcooper]

 

Hi:

Yes, Hydrogen combustion is very fast, so simulations are often numerically difficult. 

Hydrogen is a liquid only at very cold temperatures or high pressures, so injecting it under other conditions will cause instantaneous evaporation. Under these (near-liquid conditions) vaporized H2 behaves as a real gas, so density and Cp  change very rapidly with increasing temperature.  This is most likely the cause of the tiny timesteps.

I would check and see if H2 can actually be in a liquid state at the temperature and pressures of the injection.