Hydrogen Utilization: Combustion - Hydrogen Generation, Storage, and Utilization - page 144

1900

1800

1700

1600

measured
GRI 3.0
GRI 2.11
Konnov

1500

1400

1300

1200

0 0.02 0.04

Mass flux (g/cm2.s)

0.06

FIGURE 8.4 Flame temperature vs. mass flux at equivalence ratio ϕ = 0.6. The equivalence ratio is
defined as the ratio of the actual fuel/air ratio to the stoichiometric fuel/air ratio. Points: measurements;
lines: calculations using different models or reaction mechanisms: GRI-Mech 3.0 (thick solid line) or
GRI-Mech 2.11 (dashed line) or Konnov (thin solid line). Source : Reproduced with permission from
Haruta and Sano [10].

than 700 K. The approach was suggested to be general and can be used for
other fuels as well.

8.4 CATALYTIC COMBUSTION

Hydrogen combustion can be assisted by catalysis as in many chemical reac-
tions. Compared with flame-type combustion, catalytic combustion can
operate at lower temperature and reduce pollution due to NO x emission in
flame combustion [11]. Common catalysts used include Pt, Pd, Ni, and Co,
usually dispersed in metal oxide supports, for example, Al 2 O 3 , SiO 2 , ZrO 2 ,
and TiO 2 . One of the primary functions of the catalysts is to facilitate dis-
sociation of the H 2 molecule by weakening the H-H bond through adsorption
onto the catalyst surface. The supports help to disperse the metal catalysts
and enhance surface area, while in some cases, play a more active role by
functioning as catalysts themselves. For example, an earlier experimental
study has examined the effect of fundamental conditions of hydrogen-fueled
catalytic burners on their operating properties [12]. In diffusive combustion,
Pd-power coated Ni foam with relatively large pores could afford the highest