Hi Arun!

You need an estimation of the mass trapped in the cylinder in order to apply PV=mRT to the closed part of your cycle. From the geometry of your engine you should be able to retrieve the cylinder volume at each crank angle. For the trapped mass, you can get a rough estimate using the speed density (volumetric) method, again using ideal gas, with the conditions at your intake, that is: m_int = n_v*p_int*V_cyl/(R*T_int) where n_v is the volumetric efficiency either that you have from experiments or you can consider a value of around 0.9. Then, you should also add fuel mass and residual gases because m_cyl = m_int + m_f + m_res. If you have the required information (fuel should be available), add them. If not, just neglect them for now and start getting some results. Note that, in situations where you do not have EGR, m_int would be directly you air mass that you can obtain from your air mass flow sensor. You should be able to find plenty of information on the web and in the literature because this is at the base of quite many applications in combustion engine modeling.

Good luck!

Thank you Alvin Barbier for your time and for providing the answer. Just a quick followup What can be the T_int in this case.?

Thank you

p_int and T_int refer to your intake manifold pressure and temperature, V_cyl is the cylinder displaced volume.