Negative absolute pressure ???

Rams

Hi friends, am modelling combustion inside an cylindrical combustion chamber which has two nozzles one at inlet & one at out let,... Using Fluent 6.1 software

I need help from u people in solving some of my problems

am getting few problems in my problem,...

1. Am getting negative pressures (both static & absolute) at the throat of both the nozzles at inlet & out-let,.... what does the negative pressures at throat indicate,...

2. Am not getting the mass fluxes right,.. i.e., in the report fluxes,.. the mass flow rate is not matching with my experimental inlet & outlet condition,... what could be the reason for this ???

3. Am using fuel injection for injecting fuel to the combustion chamber,... some times the fuel injected is not getting evoporated,.. what should i do so that the injected fuel gets evoporated???

Please suggest me some thing so that i can complete my Project with in time,....

Waiting for reply,