New Data on Flame Behaviour in Lean Burn S.I. Engine

The concept of lean-burn combustion in spark ignition engines had been developed for reducing both exhaust emissions and fuel consumption. However the operation of engines in this mode is limited due to the misfire phenomenon. Several studies have been conducted to improve the understanding of the interaction between flow-field, mixture preparation and the progress of combustion. Multidimensional optical diagnostics are an important tool and in the other hand, the work done on combustion modelling in engine becomes more and more relevant but mainly in the case of stoichiometric mixture. The objective of the present work is to provide new information on the flame structure in lean mixtures under different flow field configurations, particularly when the flame is in the laminar-turbulent transition. Classical Mie scattering tomography of flames was performed in a transparent 4-valve Spark Ignition engine. A comparison between the flame behaviour described by Fractal geometry concept and a more recent technique, Covarial analysis, which predicts better the effect of the turbulence level, is presented.