Title: Effect of fuel composition and differential diffusion on flame stabilization in reacting syngas jets in turbulent cross-flow

Abstract

Here, three-dimensional direct numerical simulation results of a transverse syngas fuel jet in turbulent cross-flow of air are analyzed to study the influence of varying volume fractions of CO relative to H₂ in the fuel composition on the near field flame stabilization. The mean flame stabilizes at a similar location for CO-lean and CO-rich cases despite the trend suggested by their laminar flame speed, which is higher for the CO-lean condition. To identify local mixtures having favorable mixture conditions for flame stabilization, explosive zones are defined using a chemical explosive mode timescale. The explosive zones related to flame stabilization are located in relatively low velocity regions. The explosive zones are characterized by excess hydrogen transported solely by differential diffusion, in the absence of intense turbulent mixing or scalar dissipation rate. The conditional averages show that differential diffusion is negatively correlated with turbulent mixing. Moreover, the local turbulent Reynolds number is insufficient to estimate the magnitude of the differential diffusion effect. Alternatively, the Karlovitz number provides a better indicator of the importance of differential diffusion. A comparison of the variations of differential diffusion, turbulent mixing, heat release rate and probability of encountering explosive zones demonstrates that differential diffusion predominantly plays anmore » important role for mixture preparation and initiation of chemical reactions, closely followed by intense chemical reactions sustained by sufficient downstream turbulent mixing. The mechanism by which differential diffusion contributes to mixture preparation is investigated using the Takeno Flame Index. The mean Flame Index, based on the combined fuel species, shows that the overall extent of premixing is not intense in the upstream regions. However, the Flame Index computed based on individual contribution of H₂ or CO species reveals that hydrogen contributes significantly to premixing, particularly in explosive zones in the upstream leeward region, i.e. at the preferred flame stabilization location. Therefore, a small amount of H₂ diffuses much faster than CO, creating relatively homogeneous mixture pockets depending on the competition with turbulent mixing. These pockets, together with high H₂ reactivity, contribute to stabilizing the flame at a consistent location regardless of the CO concentration in the fuel for the present range of DNS conditions.« less

Authors:

Minamoto, Yuki  ^[1];

• Search DOE PAGES for author "Minamoto, Yuki"
• Search DOE PAGES for ORCID "0000-0002-6157-8370"

Kolla, Hemanth ^[1]; Grout, Ray W. ^[2]; Gruber, Andrea ^[3]; Chen, Jacqueline H. ^[1]

---

+ Show Author Affiliations

1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
3. SINTEF Energy Research, Trondheim (Norway)

Publication Date:

Fri Jul 24 00:00:00 EDT 2015

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC); National Science Foundation (NSF)

OSTI Identifier:

1248620

Alternate Identifier(s):

OSTI ID: 1247757

Report Number(s):

SAND-2015-4736J
Journal ID: ISSN 0010-2180; PII: S0010218015001947

Grant/Contract Number:  

AC04-94AL85000; AC05-00OR22725; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Combustion and Flame

Additional Journal Information:

Journal Volume: 162; Journal Issue: 10; Journal ID: ISSN 0010-2180

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

10 SYNTHETIC FUELS; flame stabilization; transverse jet; syngas combustion; direct numerical simulation