Chemistry and turbulence effects in bluff-body stabilized flames

Pan, J. C.; Ballal, D. R.

doi:10.2514/6.1992-771

Cited by 9 publications

(4 citation statements)

References 9 publications

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“…However, determination of what constitutes this critical level of flamelet disruption and extinction is unclear at this point and is, we suggest, a key unsolved problem remaining to understand the blowoff phenomenology. This ''critical extinction level'' must be strongly influenced by the entrainment of reactants into the recirculation zone, the cooling of regions of the recirculation zone, and the shrinking in size of the recirculation zone [105]. However, as noted in Section 4.1, as long as hot products of sufficiently high temperature are in contact with the reactants, they will autoignite and burn.…”

Section: Discussionmentioning

confidence: 98%

“…Finally, several studies have proposed a flamelet based description based upon local extinction by excessive flame stretch [68,105]. This description is considered extensively in Section 4.1.…”

Section: Discussionmentioning

confidence: 99%

“…Extinction of the flame sheet downstream of the recirculation zone will certainly lead to unsteadiness in heat release rate, but will exert a secondary influence upon the dynamics or composition of the recirculating wake. 10 Extinction of the flame sheet within a region entrained into the recirculation region, on the other hand, could lead to entrainment of these high density, ''cold'' reactants into the recirculating wake, as emphasized by Pan and Ballal [105]. Such occurrences disrupt the ''baseline'' wake/recirculation zone structure and dynamics.…”

Section: Isocontours Of Flame Strain Rate Pdfmentioning

confidence: 94%

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Lean blowoff of bluff body stabilized flames: Scaling and dynamics

Shanbhogue

Husain

Lieuwen

2009

Progress in Energy and Combustion Science

529

206

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Isocontours Of Flame Strain Rate Pdfmentioning

confidence: 94%

See 1 more Smart Citation

Lean blowoff of bluff body stabilized flames: Scaling and dynamics

Shanbhogue

Husain

Lieuwen

2009

Progress in Energy and Combustion Science

529

206

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“…Furthermore, as the equivalence ratio decreases towards its blowoff value, the flame speed decreases accordingly and the flame moves inward toward low velocity regions in the shear layers [33,[37][38][39]. Opposing sides of the flame move towards each other near the downstream end of the bluff-body recirculation zone, where it eventually extinguishes [6,[37][38][39][40][41], a point that will be revisited later.…”

Section: Introductionmentioning

confidence: 95%

Near-lean blowoff dynamics in a liquid fueled combustor

Rock

Emerson

Seitzman

et al. 2020

Combustion and Flame

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This paper describes an analysis of the near-lean blow off(LBO) dynamics of spray flames, including the influence of fuel composition upon these dynamics. It is motivated by the fact that, while reasonable correlations exist for predicting blowoffconditions, the fundamental reasons for why flames supported by flow recirculation actually blow offare not well understood. Prior work on gaseous systems has shown that the blowoffevent is a culmination of several intermediate processes, initiating with local extinction of reactions ("stage 1"), followed by large scale changes in flame and flow dynamics ("stage 2"), finally leading to blowoff. In this study, near-LBO dynamics were characterized for ten liquid fuels with widely varying kinetic and physical properties. Results were compared at two air inlet temperatures, 450 and 300 K, as this influences the relative importance of physical and kinetic properties in controlling LBO. Extinction, re-ignition, and recovery of the flame are evident from these data, and grow in frequency as blowoffis approached. Results show that after a near-blowoffevent, the flame can move upstream at velocities much faster than the flow velocity, corresponding to re-ignition. Nonetheless, the majority of the flame recovery events appear to be associated with convection of hot products back upstream, not re-ignition. In contrast, downstream motion of the flame faster than the flow, which would correspond to bulk flame extinction, was never observed. This indicates that "extinction events"actually correspond to convection of the flame downstream by the flow when it loses its stabilization point. The dependence of the equivalence ratio when these events appear, their frequency, and event duration were quantified as a function of fuel composition and air inlet temperature. For example, the data shows a higher percentage of recovery from near-blowoffevents through re-ignition for high DCN fuels at the 450 K air temperature condition. These extinction/re-ignition results suggest that high DCN fuels are harder to blow offthan low DCN fuels through two mechanisms: (1) by delaying the onset of LBO precursor events, and (2) because they are able to recover from these precursor events through re-ignition more often.

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