i have given atmospheric pressure as reference pressure and i m doing an diesel engine combustion analysis.. In the starting of analysis i m getting a negative pressure always and then it slowly increasing. Why its like that? In motoring analysis also i m getting the same.. Any input error?? awaiting ur valuable response..

Try to scale the Density blending factor to 0.1 with a CD scheme..if it doesn't work use strong under-relaxation factor for density..(0.75-0.70)