Mixture formation and combustion behaviour analysis in a di ng engine with centrally mounted injector under different injection timings

The work presented in this paper was carried out by Politecnico di Torino, IFPEN, Renault and Continental within GasOn project of the European commission. The objective of this study has been to understand the fluid-dynamic behaviour in a natural gas engine using direct injection. The first part of the CFD activity has been focused on the characterization of the flow field and its interaction with the jet, with reference to different injection strategies. In the second part the ‘mixture breakdown’ at high speed has been detected, as the highest engine speed at which a sufficiently homogenous mixture can be obtained at the start of combustion. The third one has been related to the discussion of the mixing process and turbulence evolution at low speed and low load. The direct injection of NG in the combustion chamber allows several degrees of freedom to be considered, from the point of view of engine control. At full load, a late injection timing is preferable, whereas at partial load a better mixture quality is obtained for an early injection. For the engine under study, a significant deviation from the mixture homogeneity for engine speeds higher than 4500 rpm, can be detected.