|
[Sponsors] |
January 5, 2012, 03:54 |
Deflagration - to - detonation transition
|
#1 |
New Member
Nguyen Phuoc Lam, Eric
Join Date: Jan 2012
Posts: 5
Rep Power: 14 |
Hi everybody,
My name is Eric and I am working on valveless pulse detonation engine for my final year project. I am trying to simulate the deflagration - to - detonation transition process with FLUENT. The model is a 2D, axisymmetric tube with one close end and the other end is set to ambient condition. The species transport and laminar finite - rate model is used to simulate the combustion process. After initializing the problem with stoichiometric H2/O2 mixture occupying the whole tube, I patch a region of high temperature (1000K) to the close end of the tube to simulate a spark ignition. However, as the simulation is run, the temperature of the flow field ahead of the combustion wave gradually increases up to approximately 1000K when auto-ignition occurs, preventing steady-state CJ detonation wave to be established. I would be much appreciated if anyone could enlighten me on the possible explanation of the raise in temperature of the flow field ahead of the combustion wave leading to the auto-ignition. Regards, |
|
April 12, 2012, 08:40 |
Ddt
|
#2 |
Member
Prateek
Join Date: Mar 2012
Location: Bangalore
Posts: 32
Rep Power: 14 |
hi Eric, I am prateek, I am also modelling DDT but with fully vaporised fuel i.e. kerosene air vapor mixture. Can you tell what boundary conditions you r using. I Hope we can sort out the problem.
|
|
April 16, 2012, 06:27 |
|
#3 |
New Member
Nguyen Phuoc Lam, Eric
Join Date: Jan 2012
Posts: 5
Rep Power: 14 |
hi there,
I apply adiabatic condition for the wall and the pressure outlet for the open end of the tube. What combustion model did you use? |
|
April 16, 2012, 08:33 |
Ddt
|
#4 |
Member
Prateek
Join Date: Mar 2012
Location: Bangalore
Posts: 32
Rep Power: 14 |
Hi,
I am using density based solver and species transport model with finite rate/ eddy dissipation model. adiabatic wall conditions and pressure outlet but m not able achieve anything yet. r u using patch for ignition. |
|
April 16, 2012, 09:36 |
|
#5 |
New Member
Nguyen Phuoc Lam, Eric
Join Date: Jan 2012
Posts: 5
Rep Power: 14 |
hi there,
from my experience, if you are using finite-rate/eddy-dissipation model, the reaction rate will be controlled by the eddy - dissipation rate as it results in lower values for reaction rate. for me, I managed to simulate direct detonation by patching a region of high pressure and temperature at the closed end of the tube and use the finite rate model i used the eddy - dissipation model to simulate the initial flame acceleration when passing through the obstacle field, my results indicated that the flame speed asymptote to a constant value but fail to achieve CJ detonation speed. One of my conclusion (if correct) is that detonation can only be modeled with finite-rate model, not eddy-dissipation model |
|
April 17, 2012, 10:15 |
Ddt
|
#6 |
Member
Prateek
Join Date: Mar 2012
Location: Bangalore
Posts: 32
Rep Power: 14 |
ok...gud! May be that could be the reason i have not achieved it yet.Are you using density based solver ans stiff chemistry solver. Have tried using different solution control method like turbulent kinetic energy and dissipation rate or by changing CFL number. And also the time step size that you are using.
|
|
April 17, 2012, 21:46 |
|
#7 |
New Member
Nguyen Phuoc Lam, Eric
Join Date: Jan 2012
Posts: 5
Rep Power: 14 |
hi there,
I realized that for the eddy - dissipation model, the initial flame initiation and propagation (prior to flame interaction with the first obstacle) is really slow and indeed it depends on the values of k and epsilon that you initialized the flow with (you may want to increase the ratio of epsilon/k to increase the flame speed). I used the density based solver as well, 2nd order implicit time stepping but I did not utilized the stiff chemistry solver. Just want to check if you have patched a small fraction of steam to the ignition zone to enable the reaction to start? |
|
May 17, 2012, 13:51 |
Ddt
|
#8 |
Member
Prateek
Join Date: Mar 2012
Location: Bangalore
Posts: 32
Rep Power: 14 |
hi,
I am not patching it with steam, rather m using jetA mixture only i.e. the same stoichiometric composition and initiating with high temperature and pressure coz i felt why to add extra species. In my case, m able to produce combustion wave but its not detonation since velocity is still less than local speed of sound. Are you getting flame propagation speed of more than mach 1? |
|
April 24, 2015, 15:46 |
|
#9 |
Member
sanjeet Limbu
Join Date: Mar 2015
Posts: 91
Rep Power: 11 |
Hi
I am trying to do autoignition for mixture fuel using chemkin mechanism.... can u tell me the changes I need to do in my model as I am not getting temperature raise- autoignition. My initial condition is 14.1bar at 766.1K for nheptane/N2/O2/AR: 0.00562/58/10/30 by mole fraction |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
How to predict the transition line in CFD? | k.vimalakanthan | Main CFD Forum | 2 | November 23, 2011 06:00 |
Missing Information in SST Transition Model Formulation | Josh | CFX | 2 | September 14, 2010 12:49 |
Code release: Flow Transition and Turbulence | Chaoqun Liu | Main CFD Forum | 0 | September 26, 2008 18:15 |
to LANGTRY ROBIN :help, hypersonic transition SST | ben akih | CFX | 0 | September 21, 2006 05:59 |
modelling transition with v2f turbulence model | pablo | FLUENT | 0 | August 7, 2006 16:44 |