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Open research questions in Combustion and flame dynamics

189 gap statements mined from Combustion and flame dynamics papers in our 7.9M-paper local library, which holds 2,391 papers on the topic — drawn mostly from each paper's own stated research gap, future-work, challenge and limitation notes, and its abstract. The ones listed below are a selection still marked open; each names the study that raised it, with a DOI link where the paper has one.

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What the literature leaves open

  • While U-bend micro-burner configurations have been shown to improve heat recirculation, the influence of channel asymmetry on catalytic combustion behavior has not been systematically addressed.

    Numerical Investigation of Catalytic Propane Combustion in Micro-Burners: A Comparison of Straight-Channel, Symmetric U-Bend, and Asymmetric U-Bend Designs · 2026 · DOI

  • However, the asymptotic consistency of models incorporating cubic terms remains a largely unexplored open question in flame theory that deserves further attention.

    Hydrodynamic theory of premixed flames under Darcy”s law: Interfacial conditions and effects of nonunity Lewis number and heat loss · 2026 · DOI

  • Recent studies have sought to leverage the operational flexibility of fuel staging to mitigate instabilities; however, its potential in systems with interacting flames remains unexplored.

    Self-excited thermoacoustic instabilities and flame dynamics in an H2-fueled trapped vortex combustor · 2026 · DOI

  • Novelty and significance statement: NRPDs can be used to alter the thermoacoustic stability of combustors, but the effect of actuation parameters on the linear flame response remains poorly quantified.

    Flame transfer functions and interference analysis under nanosecond repetitively pulsed discharge actuation · 2026 · DOI

  • Yet, experimental validation remains limited by the extreme thermodynamic conditions, particularly for propellant injection under transcritical conditions.

    Assessment of flamelet-based modeling for large eddy simulations of doubly transcritical methane/oxygen flames · 2026 · DOI

  • This addresses an “open question” in combustion modeling: annihilation events are a principal mechanism of local extinction but have lacked explicit representation in manifold-based paradigms.

    Manifold modeling of flame–flame interactions in turbulent premixed combustion · 2026 · DOI

  • Whether premixed flame annihilation interactions can be captured by a manifold model for premixed combustion is an open question since flame–flame interactions give rise to local extrema in progress variable dissipation rate ( ⇾ χ ΛΛ ⇾ 0) at non-zero/-unity progress variable.

    Manifold modeling of flame–flame interactions in turbulent premixed combustion · 2026 · DOI

  • While this approach is effective for kinetic studies, its validity under low-pressure conditions remains uncertain due to enhanced transport effects.

    On the importance of 2D modeling for quantitative species measurements in burner-stabilized ammonia flames · 2026 · DOI

  • Still, the role of thermodiffusive instabilities on the acoustic radiation associated with these quenching events in lean premixed hydrogen flames remains insufficiently investigated.

    Quenching mechanisms and their generated sound in thermodiffusively unstable laminar lean premixed hydrogen–air flames · 2026 · DOI

  • Although ammonia-induced surface nitriding has been studied at low and moderate temperatures, its behavior at temperatures above 1200 K in flames remains unexplored.

    Surface nitridation of nickel by NH3/H2 rich flames at elevated temperature · 2026 · DOI

  • Novelty and significance statement: High-frequency thermoacoustic instabilities remain poorly understood, despite increasing evidence of their occurrence in hydrogen jet flames.

    Suppression of high-frequency thermoacoustic oscillations in a hydrogen jet flame via impinging jets · 2026 · DOI

  • Conventional approaches to identifying the transition between the linear and non-linear development regimes of intrinsic flame instabilities rely on amplitude evolution or Fourier-mode analysis and are limited by ambiguities in flame-front definitions and non-unique, wavelength-dependent transition times.

    Entropy generation rates in acoustically perturbed hydrogen flames · 2026 · DOI

  • While both effects enhance burning rates, their mutual interaction and formation remain insufficiently understood.

    Interplay of strain and thermodiffusive instabilities in lean premixed hydrogen flames · 2026 · DOI

  • However, the interplay of heat recirculation, ammonia dehydrogenation, and pollutant formation at the pore scale has not yet been investigated.

    Numerical analysis of ammonia dehydrogenation in porous media combustion · 2026 · DOI

  • Inside combustion devices, such as internal combustion engines (ICEs), the role of crevices on emissions is not fully understood.

    A numerical study of ammonia-hydrogen flames: Propagation and emission formation in crevices · 2026 · DOI

  • Although significant progress has been made in studying single-particle ignition, limited data exist on how the ignition dynamics are affected in a turbulent flow.

    On the role of oxide layer thickness in iron particle cloud ignition: A carrier-phase DNS study · 2026 · DOI

  • Novelty and significance statement The secondary combustion stage in staged burners, such as the Rich-Relaxation-Quench-Lean (RRQL) system, remains poorly understood for high-efficiency ammonia (NH 3)-fueled gas turbines.

    Chemiluminescence signature of NH3-doped H2 inverse-diffusion flames · 2026 · DOI

  • However, the secondary combustion stage remains poorly understood for NH 3 –staged combustion systems.

    Double flame zone in laminar non-premixed counterflow H2–NH3 flames · 2026 · DOI

  • Despite its importance in high-speed combustion, flame physics in such environments is not well understood.

    Flame-turbulence interaction and vorticity generation in a confined high-speed premixed flow · 2026 · DOI

  • Novelty and significance statement: Previous studies have examined the effects of blend ratio and humidity on the laminar flame speed of hydrofluorocarbon (HFC) refrigerant blends, but their coupled influence under realistic conditions with radiation and buoyancy remains unclear, which is addressed in this study through DNS.

    Analysis of buoyant flame propagation and curvature-strain coupling in humid hydrofluorocarbon refrigerant mixtures · 2026 · DOI

  • Novelty and significance statement: While several studies exist on dual swirl hydrogen or methane combustion, the flame structure of dual swirl ammonia/hydrogen flames has not yet been characterized in detail.

    On the structure of dual swirl ammonia/hydrogen flames using time-resolved simultaneous OH–NH PLIF · 2026 · DOI

  • Novelty and significance statement: Premixed flames stabilized around a centrally-located mixture source have received little attention beyond constant-density model studies, and have not been investigated experimentally.

    Numerical investigation of stabilized inward propagating lean hydrogen-air flames · 2026 · DOI

  • Simulations of one-dimensional laminar flames with detailed kinetic mechanisms are often limited by the high computational cost of large and stiff chemical systems.

    Accelerating 1D laminar flame simulations with detailed chemistry using operator splitting · 2026 · DOI

  • It shows that both effects are significant, and that the widely used flashback criterion fails for lean hydrogen/air mixtures since it does not account for them.

    Effects of differential diffusion on the critical velocity gradient for boundary layer flashback of laminar hydrogen–air flames · 2026 · DOI

  • Novelty and significance statement: Flame annihilation is a critical process for flame surface area destruction in turbulent flames, but its local propagation speed is poorly understood.

    Propagation and corner dynamics of colliding and annihilating premixed flames · 2026 · DOI

Most-cited papers in Combustion and flame dynamics

Most recent work

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Open questions raised by papers listed on this page include: (1) The asymptotic consistency of models incorporating cubic terms remains a largely unexplored open question in flame theory that deserves further attention (“Hydrodynamic theory of premixed flames under Darcy”s law: Interfacial…”, 2026); (2) Recent studies have sought to leverage the operational flexibility of fuel staging to mitigate instabilities; however, its potential in systems with interacting flames remains unexplored (“Self-excited thermoacoustic instabilities and flame dynamics in an H2-fueled…”, 2026); (3) Experimental validation remains limited by the extreme thermodynamic conditions, particularly for propellant injection under transcritical conditions (“Assessment of flamelet-based modeling for large eddy simulations of doubly…”, 2026); (4) This addresses an “open question” in combustion modeling: annihilation events are a principal mechanism of local extinction but have lacked explicit representation in manifold-based paradigms (“Manifold modeling of flame–flame interactions in turbulent premixed combustion”, 2026); (5) Although ammonia-induced surface nitriding has been studied at low and moderate temperatures, its behavior at temperatures above 1200 K in flames remains unexplored (“Surface nitridation of nickel by NH3/H2 rich flames at elevated temperature”, 2026). 189 gap statements have been mined from Combustion and flame dynamics papers in our 7.9M-paper local library, which holds 2,391 papers on the topic; the gaps come from whichever of those papers state one. They are mostly the research gaps the authors state and the papers' abstracts, plus future-work, limitations and challenges passages. The ones listed below are a selection still marked open; each names the study that raised it, with a DOI link where the paper has one, so you can read the original claim in context.

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