The levels of IGN and λ are fuel dependent to cover the optimal and widest possible range for each fuel.
A combined wide range of IGN and λ is not possible for hydrogen, due to the occurrence of abnormal
combustion at the extreme combinations (e.g. an early ignition for rich mixtures). Consequently, λ has
been varied at the lean side for hydrogen to cover the widest possible range for IGN. Stoichiometric
measurements will later be conducted to confirm the findings beyond the lean mixtures. An overview of
the extreme levels of the continuous factors is given in Table 2.