To achieve 50% of thermal efficiency in gasoline engines, it is expected to realize super lean-burn with equivalence ratio 0.5 or less. However, the extension of ignition delay and the increase of cycle-to-cycle variation are issues to be solved. To investigate these phenomena, this study shows the trend of the turbulent Karlovitz number as a function of crank angle on the turbulent combustion diagram proposed by Peters. The turbulent Karlovitz number is calculated from laminar burning velocity, flame thickness, turbulence intensity and integral length scale. In the case of super lean burn, laminar burning velocity is slow, flame thickness is enlarged, the turbulent Karlovitz number is increased compared with stoichiometric combustion. Therefore, combustion regimes exist in Thin reaction zones as shown in Fig. 3.

Kenji Sugata
Graduate school
Keio University