Behavior of preheated premixed flames at rich conditions

Gibson, Joseph Edward; Ayoobi, Mohsen; Schoegl, Ingmar

doi:10.1016/j.proci.2012.06.141

Cited by 8 publications

(6 citation statements)

References 25 publications

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“…Prior 1D investigations have shown that significant shifts in chemical reaction pathways occur at similar temperatures. 39–41 A major result of these studies was a relative insensitivity of temperature thresholds to stoichiometry, which is consistent with current observations.…”

Section: Resultssupporting

confidence: 89%

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Numerical analysis of flame instabilities in narrow channels: Laminar premixed methane/air combustion

Ayoobi

Schoegl

2017

International Journal of Spray and Combustion Dynamics

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Premixed flames propagating within small channels show complex combustion phenomena that differ from flame propagation at conventional scales. Available experimental and numerical studies have documented stationary, non-stationary, or asymmetric modes that depend on properties of the incoming reactant flow as well as channel geometry and wall temperatures. This work seeks to illuminate mechanisms leading to symmetry breaking and limit cycle behavior that are fundamental to these combustion modes. Specifically, four cases of lean premixed methane/air combustion—two equivalence ratios (0.53 and 0.7) and two channel widths (2 mm and 5 mm)—are investigated in a 2D configuration with constant channel length and bulk inlet velocity, where numerical simulations are performed using detailed chemistry. External wall heating is simulated by imposing a linear temperature gradient as a boundary condition on both walls. In the 2 mm channel, both equivalence ratios produce flames that stabilize with symmetric flame fronts after propagating upstream. In the 5 mm channel, flame fronts start symmetrically, although symmetry is broken almost immediately after ignition. Further, 5 mm channels produce non-stationary combustion modes with dramatically different limit cycles: in the leaner case ( φ = 0.53), the asymmetric flame front flops periodically, whereas in the richer case ( φ = 0.7), flames with repetitive extinctions and ignitions (FREI) are observed. To further understand the flame dynamics, reaction fronts and flame fronts are captured and differentiated. Results show that the loss of flame front symmetry originates in a region close to the flame cusp, where flow and chemical characteristics exhibit large gradients and curvatures. Limit cycle behavior is illuminated by investigating flame edges that are formed along the wall, and accompany local or global ignition and extinction processes. In the flopping mode ( φ = 0.53), local ignition and extinction in regions adjacent to the wall result in oblique fronts that advance and recede along the wall and redirect the flow ahead of the flame. In the FREI mode, asymmetric flames propagate much farther upstream, where they experience global extinction due to heat losses, and re-ignite far downstream with opposite flame front orientation. In both cases, an interaction of flow and chemical effects drives the asymmetric limit cycles. The lack of instabilities and asymmetries for the 2mm cases is attributed to insufficient wall separation, which is of the same order of magnitude as the flame thickness.

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Section: Resultssupporting

confidence: 89%

“…This behavior is not unexpected, as in the leaner case less chemical energy is released despite equal inlet velocities. To burn at the same rate, peak temperatures need to be similar, 39–41 which is consistent with numerical results: for φ = 0.7, the peak temperature at the flame front is 1884.2 K, whereas for φ = 0.53, it is 1814.1 K.…”

Section: Resultssupporting

confidence: 78%

Numerical analysis of flame instabilities in narrow channels: Laminar premixed methane/air combustion

Ayoobi

Schoegl

2017

International Journal of Spray and Combustion Dynamics

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“…In the range of inlet velocities tested, the model and experiment agreed very well in both trend and magnitude, and the analytical model fits the data very well. This trend has been observed by other researchers and is explained in detail in the literature [32,41]. We also compared the modeling predictions with the experimental measurements of standoff distance as a function of ϕ while V was held constant at 15 cm/s (Fig.…”

Section: Standoff Distancesupporting

confidence: 76%

“…Both butanol and jet fuel have been studied extensively at moderate equivalence ratios (ϕ). Studies on butanol include basic investigations on flames [28], kinetic modeling [29,30], combustion in engines [31], and catalytic combustion [32]. At rich conditions where the interest is on the production of syngas, butanol research has focused on equilibrium thermodynamic analysis [33][34][35][36], and conversion by catalytic methods [37][38][39].…”

Section: Effect Of Preheat On Premixed Methane/air Flamesmentioning

confidence: 99%

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Non-Catalytic Reforming with Applications to Portable Power

Ellzey¹,

Belmont²,

Smith³

2013

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Effects of Stratification and Preheat on Turbulent Flame Characteristics and Stabilization

Souflas

Koutmos

2021

Flow Turbulence Combust

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Behavior of preheated premixed flames at rich conditions

Cited by 8 publications

References 25 publications

Numerical analysis of flame instabilities in narrow channels: Laminar premixed methane/air combustion

Numerical analysis of flame instabilities in narrow channels: Laminar premixed methane/air combustion

Non-Catalytic Reforming with Applications to Portable Power

Effects of Stratification and Preheat on Turbulent Flame Characteristics and Stabilization

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