Synergistic Effects of Fuel Stratification and Preferential Diffusion for Ultra-Low NO x Formation in Hydrogen Flames

Tianze Yu; Long Zhang; Hua Zhou; Zhuyin Ren; Xiaohua Gan

doi:10.1016/j.eng.2026.01.023

Engineering ›› :202601023 DOI: 10.1016/j.eng.2026.01.023

Article

research-article

Synergistic Effects of Fuel Stratification and Preferential Diffusion for Ultra-Low NO x Formation in Hydrogen Flames

Author information +

History +

PDF

Abstract

The unique transport properties of hydrogen give rise to fuel re-stratification and super-adiabatic flame temperature (SAFT) in premixed flames—phenomena that are generally not absent in fossil-fuel combustion. These effects undermine the effectiveness of conventional fuel/air fully premixed technology for achieving low NO x emissions in hydrogen energy and propulsion systems. In this study, a scaling law for SAFT, incorporating the Lewis number (Le) and Zel’dovich number (Ze), is revisited for fully premixed hydrogen laminar flames under flow straining conditions. The impact of SAFT on NO x formation, with particular emphasis on thermal NO x governed by the Zel’dovich mechanism, is systematically analyzed. A theoretical expression is derived to estimate the thermal NO x reaction rate as a function of SAFT. With these new insights, a novel concept based on the synergistic effects of fuel stratification and preferential diffusion is proposed to achieve ultra-low NO x emissions in hydrogen combustion. The effectiveness of this concept is demonstrated in multi-slot flames, where a designed nonuniform equivalence ratio (𝜙 ) at the inlet configuration reduces peak temperature by 53-236 K and NO emissions by 15%-54% over the typical gas-turbine operating range of 0.4 < 𝜙< 0.7, compared with a fully premixed inlet configuration. This counter-intuitive approach provides new insights into hydrogen flame control and offers a promising pathway to achieving ultra-low NO x emissions in hydrogen energy and propulsion systems.

Keywords

Zero carbon emission / Hydrogen flames / Fuel stratification / Preferential diffusion / NO x emission

Cite this article

Download citation ▾

Tianze Yu, Long Zhang, Hua Zhou, Zhuyin Ren, Xiaohua Gan. Synergistic Effects of Fuel Stratification and Preferential Diffusion for Ultra-Low NO x Formation in Hydrogen Flames. Engineering 202601023 DOI:10.1016/j.eng.2026.01.023

登录浏览全文

4963

注册一个新账户忘记密码

References

Publishing order | Descend order by publishing year | Descend order by cited within

[1]	International Energy Agency. Net zero by 2050:a roadmap for the global energy sector. Report. Paris: International Energy Agency; 2021.

[2]	Öberg S, Odenberger M, Johnsson F. Exploring the competitiveness of hydrogen-fueled gas turbines in future energy systems. Int J Hydrog Energy 2022; 47(1):624-44.

[3]	Zhou H, Xue J, Gao H, Ma N. Hydrogen-fueled gas turbines in future energy system. Int J Hydrog Energy 2024; 64:569-82.

[4]	Jiang J, Wan B, Yu T, Zhang L, Zhou H, Cai J, et al. Effects of structural variations on NO x formation in coaxial dual-swirl hydrogen flames. Int J Hydrogen Energy 2025; 148:150047.

[5]	Jiang J, Zhang X, Yu T, Sun B, Zhou H, Ren Z. Structural impact on flame dynamics and mode transition in dual-swirl hydrogen flames. Aerosp Sci Technol 2025; 162:110206.

[6]	Berger L, Attili A, Gauding M, Pitsch H. LES combustion model for premixed turbulent hydrogen flames with thermodiffusive instabilities: a priori and a posteriori analysis. J Fluid Mech 2025;1003:A33.

[7]	Wen X, Berger L, Cai L, Parente A, Pitsch H. Thermodiffusively unstable laminar hydrogen flame in a sufficiently large 3D computational domain-part I: characteristic patterns. Combust Flame 2024; 263:113278.

[8]	Rieth M, Gruber A, Williams FA, Chen JH. Enhanced burning rates in hydrogen-enriched turbulent premixed flames by diffusion of molecular and atomic hydrogen. Combust Flame 2022; 239:111740.

[9]	Wang X, Zhou H, Berger L, Pitsch H, Ren Z. Transported probability density function investigation on turbulent premixed hydrogen flames with thermodiffusive instability. AIAA J 2025; 63(8):3445-60.

[10]	Shi S, Schultheis R, Barlow RS, Geyer D, Dreizler A, Li T. Assessing turbulence-flame interaction of thermo-diffusive lean premixed H 2 /air flames towards distributed burning regime. Combust Flame 2024; 269:113699.

[11]	Zhang X, Wang X, Zhou H, Ren Z. Effects of soret and differential diffusion on boundary layer flashback of H 2 /CH 4 swirling flames. Proc Combust Inst 2024; 40(1-4):105327.

[12]	Zhang X, Chen Y, Liu J, Zhou H, Hou L, Ren Z. Laminar flame speed modeling of pre-vaporized jet fuel/hydrogen mixtures under engine conditions. Fuel 2025; 380:133149.

[13]	Matalon M, Matkowsky BJ. Flames as gasdynamic discontinuities. J Fluid Mech 1982; 124:239-59.

[14]	Chung SH, Law CK. An integral analysis of the structure and propagation of stretched premixed flames. Combust Flame 1988; 72(3):325-36.

[15]	Sun CJ, Law CK. On the nonlinear response of stretched premixed flames. Combust Flame 2000; 121(1-2):236-48.

[16]	Law CK, Sung CJ. Structure, aerodynamics, and geometry of premixed flamelets. Pror Energy Combust Sci 2000; 26(4-6):459-505.

[17]	Day MS, Bell JB, Gao X, Glarborg P. Numerical simulation of nitrogen oxide formation in lean premixed turbulent H 2 /O 2 /N 2 flames. Proc Combust Inst 2011; 33(1):1591-9.

[18]	Wen X, Berger L, Cai L, Parente A, Pitsch H. Thermodiffusively unstable laminar hydrogen flame in a sufficiently large 3D computational domain-part II: NO x formation mechanism and flamelet modeling. Combust Flame 2024; 265:113497.

[19]	Vance FH, Scholtissek A. On the potential of using mixture stratification for reducing the flashback propensity of hydrogen flames. Appl Energy Combust Sci 2025;22100327.

[20]	Lipatnikov AN. Stratified turbulent flames: recent advances in understanding the influence of mixture inhomogeneities on premixed combustion and modeling challenges. Pror Energy Combust Sci 2017; 62:87-132.

[21]	Bechtold JK, Matalon M. The dependence of the markstein length on stoichiometry. Combust Flame 2001; 127(1-2):1906-13.

[22]	Law CK. Propagation, structure, and limit phenomena of laminar flames at elevated pressures. Combust Sci Technol 2006; 178(1-3):335-60.

[23]	Jomaas G, Law CK, Bechtold JK. On transition to cellularity in expanding spherical flames. J Fluid Mech 2007; 583:1-26.

[24]	Ghajar A, Cengel Y. Heat and mass transfer:fundamentals and applications. 6th ed. New York City: Mcgraw-Hill Education; 2020.

[25]	Li J, Zhao Z, Kazakov A, Dryer FL. An updated comprehensive kinetic model of hydrogen combustion. Int J Chem Kinet 2004; 36(10):566-75.

[26]	Miller JA, Bowman CT. Mechanism and modeling of nitrogen chemistry in combustion. Pror Energy Combust Sci 1989; 15(4):287-338.

[27]	Konnov AA, Colson G, De Ruyck J. NO formation rates for hydrogen combustion in stirred reactors. Fuel 2001; 80(1):49-65.

[28]	Rutar T, Malte PC. NO x formation in high-pressure jet-stirred reactors with significance to lean-premixed combustion turbines. J Eng Gas Turbine Power 2002; 124(4):776-83.

[29]	Bozzelli J W, Dean AM. O + NNH: a possible new route for NO x formation in flames. Int J Chem Kinet 1995; 27(11):1097-109.

[30]	Hanson RK, Salimian S. Survey of rate constants in the N/H/O system. In: Gardiner WC, Combustion chemistry. New York City:Springer; 1984. p. 361-421.

[31]	Westenberg AA. Kinetics of NO and CO in lean, premixed hydrocarbon-air flames. Combust Sci Technol 1971; 4(1):59-64.

[32]	Yu T, Wang X, Zhang X, Zhou H, Ren Z. Numerical investigation of super-adiabatic flame temperature in multislot turbulent premixed hydrogen flames. J Propuls Power 2025; 41(6):742-35.

[33]	Babazzi G, Gauthier PQ, Agarwal P, McClure J, Sethi V. 2019 Jun 17-21; NO x emissions predictions for a hydrogen micromix combustion system. In: Proceedings of the ASME Turbo Expo 2019:Turbomachinery Technical Conference and Exposition; Phoenix, AZ, USA. New York City: ASME; 2019. p. V003T03A008.

[34]	Haj Ayed A, Kusterer K, Funke HHW, Keinz J, Striegan C, Bohn D. Improvement study for the dry-low-NO x hydrogen micromix combustion technology. Propuls Power Res 2015; 4(3):132-40.

[35]	Kuo KK. Principles of combustion. Hoboken: Wiley; 1986.

[36]	Merk HJ. The macroscopic equations for simultaneous heat and mass transfer in isotropic, continuous and closed systems. Appl Sci Res 1959; 8(1):73-99.