Is that possible to use Fluent to model diesel engine combustion and emission formation? I know that Fluent has a turbulent combustion model and dynamics mesh. So is it powerful enough to stimulate the diesel engine combustion.

This seems highly unlikely, compression is probably a much more efficient stimulus.

Oh! You meant simulate, well that should be quite feasible, though Fluent's spray models still lag behind those in Fire and in Star-CD (probably the most commonly used tools for this type of simulation alongside of Kiva) in some respects. I have not seen any results produced with Fluent yet, so I am not quite sure if everything works out. This is not CFD for beginners though.