In this work, air and fuel were delivered into TBIM at
stoichiometric air-fuel ratio, i.e. 17.3:1. Nevertheless, the
air-fuel ratio of the mixing before entering the engine could be
differed from this value owing to poor mixing. A good mixing
would give a stoichiometric mass fraction of methane (Mch4.s)
locally throughout the mixing region. The Mch4.s was calculated
as follows: