Diesel Unsteady flamelet model

    • anilwakale

      Dear Support,

      I am using Diesel unsteady flamelet model for my research work to model mixture chemical kinetic model using n-dodecane/butanol blends. The aim of my study is to see how butanol blends affect the reduction of NOx and soot emission using the default zeldovich and one-step soot model from Ansys fluent v16.2 version. I took the help of engine simulations done from the workbench and simulated in fluent tutorials from youtube and created our own mesh and fluent cease file too.  We initially made case for very well known ECN sprayA  (https://ecn.sandia.gov/ecn-data-search/) experiments to model spray characterization of liquid and vapor penetration length and we got good match over it  following points we are facing problem in our engine simulations 

      1. for the better convergence of continuity equation we reduced the time step size nearby start of injection after which combustion will start but our simulations are getting stopped because of writing error. we are using processor in order to reduce the overall time of case. The simulations are run only for the Inlet valve closing (IVC) to exhaust valve open (EVO) that is compression and expansion part. But when I switch to  series mode the simulation is running fine but it takes 5times the overall time to complete one case which is not worth 

      2. We are comparing our simulated pressure with experimental pressure data from in-house experimental test set-up and the engine piston bowl geometry is the same and we maintain the same compression ratio in CFD too.  We are getting the mass loss problem in simulation. We ON the Crevice model too as our engine is custom made an extended top head engine.so the mass loss will be very high and can be seen from CFD too. Is it happening because of Crevice loss or else? 

      3. The NOx from zeldovich is ''volume-average mass fraction of pollutant NO'' in SI units what is unit and how do I convert that it into ppm level and same for the soot mass fraction also what is its SI unit? 

      4. I am getting a match of in-cylinder pressure of CFD vs Experimental pressure data only when i keep Initial value os gauge pressure of (-13000 pa) which is wrong . what exactly the solution for it? If we change to +value the cylinder pressure rases to 120bar for the same case where it matches with -ve gauge pressure.  

      5. if anyone has good experience on scalar dissipation rate from flamelet to understand the PDF generation and combustion will help me to understand how these parameters are affecting on all results. Most of the time I used the default value from fluent which may be wrong. 

      Pressure-velocity coupling is done using PISO scheme and second order Upwind scheme is used for other equations 

      In-cylinder temperature is reaching to 2200K as per adiabatic temperature too. 

      If anyone has done the IC engine simulation using Ansys fluent in past and can share the case file it will be helpful for me to do reverse engineering on my case and solve my problems

      For spray simulation, I used the droplet injection parameter in settings of particle type but when I used Multicomponent particle type I have to use different KH-RT constants for the same case or else my penetration length will increase. I don't have any explanation for it. 

      I hope I will get the solution over these problems soon 

      you can contact me on my email: me12m1002@iith.ac.in  

      Thank you 


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