spray modelling diesel engines
 

hello,
iam using wall film model in converge for my simulation which consists of early diesel injection inside cylinder( at about 70deg before tdc). I have found that only 25% of fuel has evaporated into vapour phase and combustion didnt happen. Iam using default values in converge for wallfilm and spray modelling.
What parameters i can change, to increase the vapour fraction so that combustion happens in simulation(combustion took place in experiment).

thanks
Anirudh

Hi Anirudh,

I assume most of your evaporation is taking place from film evaporation rather than spray evaporation. So, first of all, make sure you turn on the film evaporation. Here are some suggestions that might help you increase the fuel evaporation:
- You can scale the film heat transfer coefficient (default it 1.0) under the scaling tab in spray modeling window.
- We usually use rebound/slide for spray-wall interaction model in diesel engines, but if you want to use wall-film model, also turn on the adaptive film mesh to make sure you don't have film parcel accumulation in a spot and rather have a more even parcel distribution.
- You can also tweak the breakup model parameters to make the spray parcels break faster and into smaller droplets. For this, lower the time and size constant in the KH and RT models. If your droplets are smaller, they can evaporate faster.
- Increase the number of injected parcels to make sure that you don't have excessive amount of fuel mass in each parcel and each cell. This will help your parcels receive more heat transfer from the flow and potentially evaporate faster.
- In your spray.out, check how much of your parcels are in spray form and how much in film form. You can also check your postfiles for that. This should give you a better idea as to what should be the next steps to take. You can learn whether the evaporated fuel came from the spray or the film.

Thank you sir for your reply.

Can you clarify me one more doubt?
iam simulating diesel-natural gas dual fuel engine. I have taken reaction mechanism from converge example case. I have given all the boundary conditions and mass fractions of species and mass of diesel according to the experiment conducted.
I have checked in species_mass_region.out and the mass trapped inside cylinder is also correct for all species CH4, C02,o2,N2. Compression ratio(18.5) is also correct.
But the peak cylinder pressure from simulation is 15 bar higher than experiment.
I have used AMR, fixed embedding also during combustion.
What can i do to match with the experiment.
Kindly help me.

Thanks,
Anirudh.

Hi Anirudh,

Please email support@convergecfd.com using your official email address. The CONVERGE support team will be able to assist you better after assessing your case more thoroughly.