Chemical effects of hydrogen addition on soot formation in counterflow diffusion flames: Dependence on fuel type and oxidizer composition

Xu, Lei; Yan, Fuwu; Wang, Yu; Chung, Suk Ho

Chemical effects of hydrogen addition on soot formation in counterflow diffusion flames: Dependence on fuel type and oxidizer composition

Files

Hydrogen_soot_Revised version R2_2.2_NoMarks.pdf (3.21 MB)

Type

Article

Authors

Xu, Lei
Yan, Fuwu
Wang, Yu
Chung, Suk Ho

KAUST Department

Combustion and Laser Diagnostics Laboratory
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division

Online Publication Date

2019-12-02

Print Publication Date

2020-03

Date

2019-12-02

Abstract

We experimentally studied and kinetically modeled the effects of hydrogen addition on soot formation in methane and ethylene counterflow diffusion flames (CDFs). To isolate the chemical effects of hydrogen in such flames, we also ran a set of experiments on flames of the same base fuels but with the addition of helium. Specifically, we measured the soot volume fractions of the flames using the planar laser-induced incandescence technique. We simulated detailed sooting structures by coupling the gas-phase chemistry with the polycyclic aromatic hydrocarbon (PAH)-based soot model, using a sectional method to resolve the soot particle dynamics. Our experimental and numerical results show that hydrogen chemically inhibits soot formation in ethylene CDFs. While in methane flames, it is interesting to observe that the difference in soot production between the hydrogen- and helium-doped cases became much smaller when the oxygen concentration in the oxidizer stream (XO) was reduced. This suggests that for methane CDFs the chemical soot-inhibiting effects of hydrogen was highly dependent on oxidizer composition (i.e., XO). Explanations are provided through detailed kinetic analysis concerning the effects of hydrogen addition on the growth of PAH, soot inception, and soot surface growth processes. Our results suggest that hydrogen's chemical role in soot formation not only depends on fuel type (ethylene or methane), it also may be sensitive to oxidizer composition.

Citation

Xu, L., Yan, F., Wang, Y., & Chung, S. H. (2020). Chemical effects of hydrogen addition on soot formation in counterflow diffusion flames: Dependence on fuel type and oxidizer composition. Combustion and Flame, 213, 14–25. doi:10.1016/j.combustflame.2019.11.011

Acknowledgements

This work was supported by the National Key R&D Program of China (2017YFC0211201), National Natural Science Foundation of China (51976142 and 51606136), the National Engineering Laboratory for Mobile Source Emission Control Technology (NELM2018A11) and Fundamental Research Funds for the Central Universities (WUT: 2017YB024). SHC was supported by King Abdullah University of Science and Technology.