Partially Premixed and Premixed Aero Engine Combustors

Hassa, Christoph

doi:10.1017/cbo9781139015462.014

Cited by 3 publications

(5 citation statements)

References 41 publications

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“…Fuel lean combustion is of interest for power generation as it can deliver both high efficiency and low emissions [1], but the ignition and combustion stability of lean mixtures present challenges for its practical use. The potential risks including flashback and structural damage due to thermoacoustics are overcome by careful design of combustor aerodynamics and using active or passive control strategies for fuel injection.…”

mentioning

confidence: 99%

Large-Eddy Simulation of Reacting Flows in Industrial Gas Turbine Combustor

Langella

Chen

Swaminathan

et al. 2018

Journal of Propulsion and Power

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The turbulent reacting flow in an industrial gas turbine combustor operating at 3 bar is computed using LES paradigm. The subgrid scale (SGS) combustion is modelled using a collection of unstrained premixed flamelets including mixture stratification.The non-premixed combustion mode is also included using a simple closure involving the scalar dissipation rate of the mixture fraction. A close attention is paid to maintain physical consistencies among sub-closure models for combustion and these consistencies are discussed on a physical basis. The importance of non-premixed mode and SGS mixture fraction fluctuations are investigated systematically. The results show that the SGS mixture fraction variance plays an important role and comparisons to measurements improve when contributions from the premixed and non-premixed modes are included. These numerical results and observations are discussed on a physical basis along with potential avenues for further improvements. a Research Associate, il246@cam.ac.uk b Research Associate, zc252@cam.ac.uk c Professor, ns341@cam.ac.uk d Engineer, suresh.sadasivuni@siemens.com 4 combustors. Thus, the ability of reacting flow CFD (Computational Fluid Dynamics) to capture these phenomena is crucial for their use in the design of next-generation combustors [2].Past studies have demonstrated that Large Eddy Simulation (LES) is suitable to capture aerodynamics of swirling flows, and the continuous increase of computing power allows application of LES-based models to practical burners [3][4][5][6][7]. Combustion requires modelling as it is a subgrid phenomenon in LES. Closures developed for the subgrid scale (SGS) reaction rate include: dynamic thickened flame model [8,9], linear eddy model [10], fractal flame-wrinkling model [11], partiallystirred reactor model [12], and Eulerian stochastic fields [13]. Another recently developed flamelet model for LES uses Scalar Dissipation Rate (SDR) closure [14,15], which is shown to be successful in RANS studies of industrial gas turbine combustors [16,17], but this approach has not been tested for LES of reacting flows in these combustors. This provides the motivation for this work.Due to large costs for experiments at realistic operating conditions of gas turbines (i.e. with optical access, high pressure, and preheated air), high quality validation data is rare [18]. One widely studied database is the set of laser-diagnostics obtained for Siemens SGT-100 combustor at 3 bar [19]. Analyses of these measurements and past LES results suggest that the combustion has flamelet-like properties despite the highly turbulent flow [5-7, 20, 21]. Flamelet models assume that the combustion time scale, τ c = s L /δ is shorter than the smallest turbulent scales (this also applies for length scales) implying that the flamelet structure is undisturbed by the turbulence. Thus, the SGS reaction rate can be calculated a priori using laminar flamelets. Hence, this methodology is also known as tabulated chemistry approach.Turbulent eddies can penetrate the flame-front di...

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mentioning

confidence: 99%

Large-Eddy Simulation of Reacting Flows in Industrial Gas Turbine Combustor

Langella

Chen

Swaminathan

et al. 2018

Journal of Propulsion and Power

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“…Interestingly, the characteristics of the curves in Figure 13 resemble those of fixed geometry partially premixed combustors with ascending mixture homogeneity from M to P [2]. For unstaged combustors, the maximum of those curves would be at stoichiometry.…”

Section: Idle Condition Resultsmentioning

confidence: 89%

“…Similar to the soot results, heterogeneous combustion with single droplet burning in the stoichiometric range may be one reason for the remaining NOx production at the lean end. Interestingly, the characteristics of the curves in Figure 13 resemble those of fixed geometry partially premixed combustors with ascending mixture homogeneity from M to P [2]. For unstaged combustors, the maximum of those curves would be at stoichiometry.…”

Section: Idle Condition Resultsmentioning

confidence: 89%

“…However, its inherently narrow range of stable combustion is a key problem, with a large propensity for combustion oscillations at the limits of this stability range [1]. For small engines of regional aircraft, lower combustor temperatures during cruise conditions exacerbate this problem [2]. To obtain a lean combustor with the necessary turn-down ratio for gas turbine operation, fuel staging is used as a standard solution.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Fluidic Control in a Staged Lean Jet Engine Burner on Combustor Performance

Yoshida

Hassa

Yamamoto

et al. 2019

Fluids

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To improve the turn-down ratio of a lean combustor, which has the greatest potential for reducing NOx emissions from jet engines, fuel staging is commonly employed. To further extend the stable operation range, air staging with a fluidic element is also considered. The influence of fluidic control on combustion was analyzed to better understand fluidic element-burner interactions. The pressure loss of each fluidic element was determined by measuring the pressure at the element exits. The effect of fluidic control on the atomization, fuel distribution, and flow field was investigated using optical, noninvasive techniques. The combustion performance of the burner with the fluidic element was evaluated using exhaust gas analyses. The pressure losses of the swirlers and fuel mixers were varied depending on the bleed air from the fluidic element. Under the idle condition, the reduction of pressure loss in the pilot fuel mixer resulted in inferior atomization due to the reduced gas velocity around the fuel film, which had a positive effect on lean blowout. Under the cruise condition and the staged mode, the reduction of the pilot air flow increased the equivalence ratio of the lean pilot stage and resulted in higher combustion efficiency.

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“…Heat release measurements are made more challenging due to the need to study relevant flames. For example, operating under partially premixed combustion [20] instead of perfectly premixed combustion will result in spatially distributed equivalence ratios/heat release rates within the combustor. For laminar, perfectly premixed flames, OH * , or CH * radical emission are proportional to heat release [21].…”

Section: Introductionmentioning

confidence: 99%

Dynamics of Thermoacoustic Oscillations in Swirl Stabilized Combustor without and with Porous Inert Media

Dowd

Meadows

2022

Journal of Combustion

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Lean premixed (LPM) combustion processes are of increased interest to the gas turbine industry due to their reduction in harmful emissions. These processes are susceptible to thermoacoustic instabilities, which are produced when energy added by an in-phase relationship between unsteady heat release and acoustic pressure is greater than energy dissipated by loss mechanisms. To better study these instabilities, quantitative experimental resolution of heat release is necessary, but it presents a significant challenge. Most combustion systems are partially premixed and therefore will have spatially varying equivalence ratios, resulting in spatially variant heat release rates. For laminar premixed flames, optical diagnostics, such as OH chemiluminescence, are proportionally related to heat release. This is not true for turbulent and partially premixed flames, which are common in commercial combustors. Turbulent eddies effect the strain on flame sheets which alter light emission, such that there is no longer a proportional relationship. In this study, phased, averaged, and spatially varying heat release measurements are performed during a self-excited thermoacoustic instability without and with porous inert media (PIM). Previous studies have shown that PIM can passively mitigate thermoacoustic instabilities, and to the best of the authors’ knowledge, this is the first-time that heat release rates have been quantified for investigating the mechanisms responsible for mitigating instabilities using PIM. Heat release is determined from high-speed PIV and Abel inverted chemiluminescence emission. OH ∗ chemiluminescence is used with a correction factor, computed from a chemical kinetics solver, to calculate heat release. The results and discussion show that along with significant acoustic damping, PIM eliminates the direct path in which heat release regions can be influenced by incoming perturbations, through disruption of the higher energy containing flow structures and improved mixing.

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Partially Premixed and Premixed Aero Engine Combustors

Cited by 3 publications

References 41 publications

Large-Eddy Simulation of Reacting Flows in Industrial Gas Turbine Combustor

Large-Eddy Simulation of Reacting Flows in Industrial Gas Turbine Combustor

Influence of Fluidic Control in a Staged Lean Jet Engine Burner on Combustor Performance

Dynamics of Thermoacoustic Oscillations in Swirl Stabilized Combustor without and with Porous Inert Media

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