the blow-off limit particular to the employed burner. It is
obvious that with increasing XH2 , flame speed increases and
the blow-off equivalence ratio limit becomes leaner. When
hydrogen is increased, flame speed of the mixture increases
and flame is more stabilized, making it hard to be blown off
compared to the low XH2 flame. Increase of flame speed and
extension of blow-off limit at increased XH2 is responsible to
the above phenomenon. Furthermore, flame speed shows
a non-linear increase with equivalence ratio. This trend is
related to the variation of flame height. Flame speed directly
reflects the changes with variation of XH2 and equivalence
ratio.
Fig. 8 shows the structures of syngas flames at different
equivalence ratio with same composition. Similar to the effect
of hydrogen, the change of equivalence ratio also influences
flame layer structure. However, the reason for this trend is not
that of hydrogen change. The difference in flame structure as
mixture composition changed is due to the distinctive diffusive
nature of two fuels. For fuel-lean combustion, oxygen is
sufficient for reaction, and combustion tends to concentrate
along the flame conic reaction zone. For fuel-rich flame, the
excess unburned fuel reacts with the oxygen from the
surrounding area. This results in the production of a secondary
combustion layer and high concentration of OH radicals
locates at the flame cone tip and the diffusive flame boundary.