[MichaelC]

Hi,

I am currently working on a transient simulation of a V8 engine Intake Manifold. To increase the accuracy of the results I have imported intake pressure wave data as a function of crank angle(and hence time) from an engine simulation program into my opening boundary condition at each of the 8 openings. My query is in term of the reference pressure I should be using in the domain. During a valve opening event the intake will undergo a pressure drop below atmospheric pressure, hence if I set my domain reference pressure to 1atm, should my total pressure at the opening be a negative value to simulate a pressure below atmospheric i.e a vacuum? On the same merit if my intake boundary condition is atmospheric pressure, should this be set to 0, due to the reference pressure being 1atm?

[ghorrocks]

In most cases of IC engine modelling the reference pressure should be atmospheric pressure, which sounds like it is 1 atm in your case. This would mean that the intake pressure wave data will be negative when the pressure is below atmospheric and your intake boundary should be 0 Pa relative pressure.

Be careful with your terminology for pressure - you say "my total pressure at the opening..." which I think you intend to say "my relative pressure at the opening...". The term total pressure is defined as the static pressure plus the dynamic pressure (https://en.wikipedia.org/wiki/Total_pressure), so is a different thing.