A detailed numerical study was carried out for the effect of hydrogen enrichment on flame structure and NOx formation in counterflow CH4/air diffusion flames. Detailed chemistry and complex thermal and transport properties were employed. The enrichment fraction was changed from 0 (pure CH4) to 1.0 (pure H2). The result indicates that for flames with low to moderate stretch rates, with the increase of the enrichment fraction from 0 to 0.5~0.6, NO emission index keeps almost constant or only slightly increases. When the enrichment fraction is increased from 0.5~0.6 to about 0.9, NO emission index quickly increases, and finally NO formation decreases again when pure hydrogen flame condition is approached. However, for flames with higher stretch rates, with the increase of hydrogen enrichment fraction from 0 to 1.0, the formation of NO first quickly increases, then slightly decreases and finally increases again. Detailed analysis suggests that the variation of the characteristics in NO formation in stretched CH4/air diffusion flames is caused by the change of flame structure and NO formation mechanism, when the enrichment fraction and stretch rate are changed.

1.
Jackson
G. S.
,
Sai
R.
,
Plaia
J. M.
,
Boggs
C. M.
,
Kiger
K. T.
,
2003
, “
Influence of H2 on the response of lean premixed CH4 flames to high strained flows
”,
Combust, Flame
,
132
, pp.
503
511
.
2.
Ren
J. Y.
,
Qin
W.
,
Egolfopoulos
F. N.
,
Mak
H.
,
Tsotsis
T. T.
,
2001
, “
Methane reforming and its potential effect on the efficiency and pollutant emissions of lean methane-air combustion
”,
Chemical Engineering Engineering Science
,
56
, pp.
1541
1549
.
3.
Guo
H.
,
Smallwood
G. J.
,
Liu
F.
,
Ju
Y.
,
Gu¨lder
O. L.
,
2005
, “
The Effect of Hydrogen Addition on Flammability Limit and NOx Emission in Ultra Lean Counterflow CH4/Air Premixed Flames
”,
Proc. Combust. Inst.
,
30
, pp.
303
311
.
4.
Guo, H., Smallwood, G.J., Gu¨lder, O¨.L., 2006, “The effect of reformate gas enrichment on extinction limits and NOx formation in counterflow CH4/air premixed flames”, Proc. Combust. Inst., 31, in press.
5.
Gu¨lder
O¨. L.
,
Snelling
D. R.
, and
Sawchuk
R. A.
,
1996
, “
Influence of hydrogen addition to fuel on temperature field and soot formation in diffusion flames
”,
Proc. Combust. Inst.
,
26
, pp.
2351
2358
.
6.
Guo
H.
,
Liu
F.
,
Smallwood
G. J.
, and
Gu¨lder
O¨. L.
,
2006
, “
A numerical study on the influence of hydrogen addition on soot formation in a laminar ethylene-air diffusion flame
”,
Combust. Flame
,
145
, pp.
324
338
.
7.
Ju
Y.
, and
Niioka
T.
,
1994
, “
Reduced kinetic mechanism of ignition for nonpremixed hydrogen/air in a supersonic mixing layer
”,
Combust. Flame
,
99
, pp.
240
246
.
8.
Fotache
G. G.
,
Kreutz
T. G.
, and
Law
C. K.
,
1997
, “
Ignition of hydrogen-enriched methane by heated air
”,
Combust. Flame
,
110
, pp.
429
440
.
9.
Naha
S.
, and
Aggarwal
S. K.
,
2004
, “
Fuel effects on NOx emissions in partially premixed flames
”,
Combus. Flame
,
139
, pp.
90
105
.
10.
Giovangigli
V.
, and
Smooke
M. D.
,
1987
, “
Extinction of strained premixed laminar flames with complex chemistry
”,
Combust. Sci. Tech.
, Vol.
53
, pp.
23
49
.
11.
Kee, R.J., Grear, J.F., Smooke, M.D., and Miller, J.A., A Fortran Program for Modelling Steady Laminar One-Dimensional Premixed Flames, Report No. SAND85–8240, Sandia National Laboratories, 1985.
12.
Guo
H.
,
Ju
Y.
,
Maruta
K.
,
Niioka
T.
and
Liu
F.
,
1997
, “
Radiation Extinction Limit of Counterflow Premixed Fuel-Lean Methane-Air Flame
”,
Combust. Flame
,
109
, pp.
639
646
.
13.
Gregory P. Smith, David M. Golden, Michael Frenklach, Nigel W. Moriarty, Boris Eiteneer, Mikhail Goldenberg, C. Thomas Bowman, Ronald K. Hanson, Soonho Song, William C. Gardiner, Jr., Vitali V. Lissianski, and Zhiwei Qin http://www.me.berkeley.edu/gri_mech/.
14.
Kee, R. J., Warnatz, J., and Miller, J. A., A Fortran Computer Code Package for the Evaluation of Gas-Phase Viscosities, Conductivities, and Diffusion Coefficients, Report No. SAND 83-8209, Sandia National Laboratories, 1983.
15.
Kee, R. J., Miller, J. A., and Jefferson, T. H., A General-Purpose, Problem-Independent, Transportable, Fortran Chemical Kinetics Code Package, Report No. SAND 80-8003, Sandia National Laboratories, 1980.
This content is only available via PDF.
You do not currently have access to this content.