In order to research the effect of pre-chamber system to development of flame jet

in-cylinder flow

combustion process and generation of emission

based on Computational Fluid Dynamics （CFD） program and chemical reaction kinetics

this paper built a numerical model of a large low-speed dual fuel marine engine modified by a normal diesel marine engine and explored the effect of different position cases of pre-chamber. The results show：When pre-chamber case cause flame jet collide

the flow field of colliding area is disturbed strongly

it also takes fuel rich mixed gas to this area

which restrains the generation of oxynitride（NOx）; If there is no collision between jet flame

the flame jet penetration will be longer and combustion achieve wider region multi-spot ignition in cylinder

which make heat release more focused

however it also brings higher level NOx emission. Besides

contact with wall such as cylinder head

liner

piston crown

will reduce the rate of jet flow observably.It also leadstoreducing of combustion temperatureandturbulentkinetic energyin cylinder

even causes combustion deterioration

which should be avoid.