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 January 29, 2009, 14:24 Adiabatic compression #1 Erik Guest   Posts: n/a Hi all, I'm simulating a compressing piston using a moving mesh of a 1/7th slice of the cylinder. When I perform a simulation where the in-cylinder air is compressed adiabatically, the pressure at TDC is too high, compared to the pressure calculated using the ideal gas law. When I look at the temperature, it is calculated very accurately and the volume during the compression stroke is exact the same as in the ideal gas law calculation and the mass inside remains constant. So that's very strange, as pressure is determined by temperature, volume, mass and cp. The density is calculated using the ideal f(T,P) function, the cp of the air is a polynomial from the chemkin database, the walls of the slice are cyclic boundaries, the piston and head are adiabatic walls, the solver timestep is 0.1 dCA. Is there someone who has a possible explanation, because I think I've tried everything right now (changing boundaries, scalars, heat capacity etc..) Thanks!

 January 29, 2009, 17:17 Re: Adiabatic compression #2 Pauli Guest   Posts: n/a "the cp of the air is a polynomial from the chemkin database" The chemkin database does not have a material "air". You are likely using the polynomial for N2.

 January 30, 2009, 02:31 Re: Adiabatic compression #3 Erik Guest   Posts: n/a That's true, I've used the polynomial for N2

April 21, 2015, 00:31
#4
Member

sanjeet Limbu
Join Date: Mar 2015
Posts: 91
Rep Power: 7
Hi I am trying to do a rapid compression of fuel mixture N2/AR/O2/nC7H16: 58/30/10.307/0.562 by mole fraction in partially premixed using 2D axi-symmetric
After creating PDF species model I updated operating condition for zones: Pressure, density by hand calculation 1.334Kg/m3, and the initialization of some input like temp 297K.

I am unable to get the temperature rise or pressure rise as needed.
There may be due to initial values wrong ... Please help me I am near to my report submission and not getting the combustion in the model
Attached Images
 species model.jpg (59.1 KB, 17 views) operating and initial values.jpg (33.9 KB, 12 views) temp profile.jpg (27.1 KB, 18 views)

 February 21, 2016, 23:56 #5 Member   Pradeep Join Date: Nov 2014 Posts: 43 Rep Power: 7 Its a problem related to your initialization, thermodynamic database file..kindly check it