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Old   February 5, 2017, 15:44
Smile simple pulse jet combustion model
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Abin Alex
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this is my first post, i hope I'm able to convey my problem,I want to do a combustion (for simplicity methane + air )
I have made the geometry of a pulse jet engine as well as fluid domain of the pulse jet model where i want to do the analysis, and I want to do a combustion analysis using spark plug as the source of ignition, at the front section a cylindrical spark plug this is where i need help, i have enclosed the image of the model and the fluid domain to make it more understandable. I couldn't find much detail about on any tutorials so I'm looking out for help here.pulsejet engine.jpg

Boundary condition
1. Thin tube is fuel inlet (methane gas) dia :2.5 mm
2. Outside tube air inlet dia 10mm
3. at front spark plug. this is where I need help to define, spark plug definition, cylindrical shape radius 7.5 mm length 8mm from (0,0,0) to (0,0,8)
4. outlet
5. rest all wall
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Old   February 5, 2017, 20:00
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Lucky Tran
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You need to plan the whole thing out from beginning to end.

Describe what combustion model you want to use. For most models, a spark is simply forcing some cells in the domain and prescribing something like a temperature, a reaction progress, or just a heat source. You can have a dedicated cell zone for this spark or you can just mark the cells in the cell zone (by defining a small sphere or cylinder for example) and using that to specify which cell zones to patch.

Do you want just an initial spark or a continuous spark? For a continuous spark you need to fix and hold the value.
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Old   February 6, 2017, 14:57
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Abin Alex
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thank you, for the reply i couldn't reply soon since i had my project review in college. so back to the progress till which i have done
1. i have completed the mesh of the the fluid domain and created the name selection. a picture enclosed,
oh ok, I'll show from what i understood from "by defining a small sphere or cylinder for example) and using that to specify which cell zones to patch", if this is correct I'll proceed to the meshing and regarding the combustion model, i want to do a species transport, all i aim to get from this analysis is get all the variable like temperature, pressure and can visualize how actually deflagration occurs inside the pulsejet model, i found one youtube link which visualize the pulsejet combustion, i wish to produce a similar. link to the video is enclosed
yes! pje only require initial spark, if all the conditions are correct, there will be a backflow from both the tail section and inlet, the sucked in fresh air-fuel mixture mixing with hot slug gasses from the tail section will ignite the mixture wherever it is in the stoichiometric ratio, and it will act as multiple source of ignition and the cycle repeats better than previous one which only had one spark plug. I require assistance in setup.
Pressure based transient setup
models: energy on, viscous : k-epsilon (2en) k-epsilon model : standard, standard wall function and all values default selected.species: partially premixed combustion, pdf table creation mass fraction fuel: N2: .767 , O2: .219, C3H8: 0.014 | Oxid: N2 0.767, O2:.233, defining spark ignition: fixed spark size cylindrical shape and coordinates given. Boundary condition: (I just assumed that the fuel line is at 2 bar pressurized fuel line.) fuel inlet : pressure inlet 201325 Pa, specification method turbulence intensity 10. hydraulic dia 2.5mm, under species mean mixture fraction:1 , Air inlet :velocity inlet magnitude :10 m/s ,specification method turbulence intensity 10. hydraulic dia 20mm, Outlet: pressure outlet ( i have a confusion what to define in the specification method , since in the pulse jet i expect a back flow , and my tail section is like a frustum cone of length 241mm so i chose intensity and length scale back flow turbulent intensity:10%, back flow turbulent length scale:241mm, under species back flow progress variable:1
under solution: after initialization time step 0.001s and to for first run gave 20 iteration ,no. of time steps: 10. (i haven't patched a region for sparkplug yet) Skipping to Solution Controls, by clicking Equations and deselect the Premixed Combustion and PDF options so that the only equations solved for are flow, swirl velocity, and turbulence as a preliminary solution. this is my first run, ill update the results. hope anyone enlighten me how to do the correct procedure for using spark plug. thank you one again for patiently reading.
Attached Images
File Type: jpg Screenshots.jpg (106.9 KB, 9 views)
File Type: jpg patch.bmp.jpg (83.3 KB, 9 views)
File Type: jpg Screenshot (52).png.jpg (67.7 KB, 8 views)
File Type: jpg Screenshot (53).png.jpg (57.4 KB, 6 views)
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Last edited by abin alex; February 9, 2017 at 06:30. Reason: defining spark plug and first run
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combustion model, pulsejet, sparkplug

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