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Most of liquid jet breakup models now available in combustion codes only apply to high pressure sprays (Diesel … ). When gasoline is injected in the intake pipe of a chamber (S.I. engines), the relative pressure between the injector and the intake gas flow is quite low (3-4 bars). In this case, the spray looks like a long continuous liquid non-evaporating phase. Generally, the jet collapses, giving droplets, far from the tip of the injector. Vaporization is negligible within the pipe. Thus, the assumption generally made that the fuel is gaseous in the chamber fails. The fluid phase can no more be considered fully atomized and dispersed. We propose here a breakup model for low Weber non-evaporating fuel jets. It takes into account the continuous nature of the spray. The liquid core is represented by cylindrical blobs. The main assumption is that the breakup of a blob is caused by the growth of its surface. A new equation gives the evolution of the surface for each blob.

A model of turbulent premixed flame initiation and early stage of propagation is proposed. Initiation submodel consists in representing of spark action with the heat deposit of the energy and duration appropriate for conditions relevant to SI engine, that is with the spark duration being non-negligible compared with turbulent time-scale. Chemistry is represented with reduced kinetics scheme of six reactions coupled with the pdf approach. The results of simulations obtained with this model are discussed. In particular, they show the model proposed is able to yield reasonable values for low concentration limits of ignition as well as critical spark energy needed to obtain self-sustaining flame propagation.