Investigation of Mode Shift Dynamics of Lean, Premixed Flames

Prakash, Shashvat; Neumeier, Yedidia; Zinn, B. T.

doi:10.2514/6.2006-961

Cited by 6 publications

(2 citation statements)

References 20 publications

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“…Characterizing "stage 2" in swirl flames is complicated by different degrees to which changes in the vortex breakdown process occur. Muruganandam [44] and Prakash et al [45] have observed that as the heat release decreases near blowout, due to local extinction and entrained reactants in the inner recirculation zone, the vortex breakdown mechanism changed from a bubble type to a spiral/helical type. Zhang [46] showed that these vortex breakdown changes are dependent on fuel composition, as this controls the amount of thermal expansion across the flame.…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

Near-lean blowoff dynamics in a liquid fueled combustor

Rock

Emerson

Seitzman

et al. 2020

Combustion and Flame

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“…In order to reduce pollutant emissions, one of the most commonly used combustion methods is central staged swirl lean fuel combustion, but lean fuel combustion will induce unstable combustion and, in serious cases, damage the overall structure of the combustor. Therefore, the research on the prevention and suppression of unstable combustion is of great significance to the normal operation of the engine [ 1 , 2 , 3 , 4 , 5 ]. As the most easily obtained unstable signal in engineering tests, the complex change of dynamic pressure (DP) is caused by the coupling of various physical processes in the combustor.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Pressure Fluctuation Characteristics of Central Swirl Combustors Based on Empirical Mode Decomposition

Wang

Zhang

Chen

et al. 2022

Sensors

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In order to study the characteristics of pressure fluctuation during unstable combustion, experimental studies had been conducted on the mechanism model of the swirl combustor and the industrial swirl combustor. The signal of dynamic pressure, heat release rate, and the high-speed flame image in the two combustors were synchronously collected by using dynamic pressure sensors, a photoelectric sensor, and a high-speed camera under normal temperature and pressure. After empirical mode decomposition of the dynamic pressure signal, several intrinsic mode functions were obtained. It was found that the pressure pulsation energy is concentrated in the first three order intrinsic mode function. Through fast Fourier transform spectrum calculation, it was found that the first three order intrinsic mode function pulsation can characterize the changes of heat release rate and air flow pulsation under cold state and flame instability. It showed that the decomposition of the dynamic pressure in the combustor by this method can obtain the main physical processes in its connotation, and provide data processing methods for the induction mechanism of oscillating combustion and combustion diagnosis in an industrial combustor test.

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