Autoignition flame dynamics in sequential combustors

Schulz, O.; Noiray, Nicolas

doi:10.1016/j.combustflame.2018.01.046

Cited by 57 publications

(39 citation statements)

References 83 publications

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“…Therefore, we computed the ratio between the resolved part of the turbulent kinetic energy and the total kinetic energy a posteriori. Results in [18] show that more than 95% of the total kinetic energy was resolved for the atmospheric case (≈ 16 million cells). For the cases at 10 bar, the mesh was significantly refined to resolve at least 80% of the total kinetic energy (≈ 60 and ≈ 74 million cells; see Table 1).…”

Section: Configuration and Numerical Methodologymentioning

confidence: 99%

“…Another type of sequential combustor [1] features a flame that is stabilized substantially downstream of the fuel injector in order to ensure good mixing of the fuel with the vitiated flow before the former is consumed, and it falls into the category of partially-premixed combustion. The response of these flames to different types of perturbation, such as acoustic velocity [16,17] or temperature fluctuations [18][19][20] have been investigated numerically in the context of thermoacoustic instabilities in sequential combustors [21,22].…”

Section: Introductionmentioning

confidence: 99%

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Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Schulz

Noiray

2019

Combustion and Flame

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This numerical study investigates the combustion modes in the second stage of a sequential combustor at atmospheric and high pressure. The sequential burner (SB) features a mixing section with fuel injection into a hot vitiated crossflow. Depending on the dominant combustion mode, a recirculation zone assists flame anchoring in the combustion chamber. The flame is located sufficiently downstream of the injector resulting in partially premixed conditions. First, combustion regime maps are obtained from 0-D and 1-D simulations showing the co-existence of three combustion modes: autoignition, flame propagation and flame propagation assisted by autoignition. These regime maps can be used to understand the combustion modes at play in turbulent sequential combustors, as shown with 3-D large eddy simulations (LES) with semi-detailed chemistry. In addition to the simulation of steady-state combustion at three different operating conditions, transient simulations are performed: (i) ignition of the combustor with autoignition as the dominant mode, (ii) ignition that is initiated by autoignition and that is followed by a transition to a propagation stabilized flame, and (iii) a transient change of the inlet temperature (decrease by 150 K) resulting into a change of the combustion regime. These results show the importance of the recirculation zone for the ignition and the anchoring of a propagating type flame. On the contrary, the autoignition flame stabilizes due to continuous self-ignition of the mixture and the recirculation zone does not play an important role for the flame anchoring.

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Section: Configuration and Numerical Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Schulz

Noiray

2019

Combustion and Flame

Self Cite

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“…In the present DNS, chemistry was modelled using an ARC (Analytically Reduced Chemistry) scheme [26][27][28][29][30] adapted for ndodecane / air flames at 3.4 MPa.…”

Section: Introductionmentioning

confidence: 99%

A conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on direct numerical simulation and experiments

Tagliante

Poinsot

Pickett

et al. 2019

Combustion and Flame

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conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on direct numerical simulation and experiments Official URL:https://doi. ABSTRACT Keywords: ONS Lifr-off length Flame stabilization Auto-ignition Triple flame Diesel combustionThis work presents an analysis of the stabilization of diffusion flames created by the injection of fuel into hot air, as found in Diesel engines. lt is based on experimental observations and uses a dedicated Direct Numerical Simulation ( ONS) approach to construct a numerical setup, which reproduces the igni tion features obtained experimentally. The resulting ONS data are then used to classify and analyze the events that allow the flame to stabilize at a certain Lift-Off Length (LOL) from the fuel injector. Both ONS and experiments reveal that this stabilization is intermittent: flame elements first auto-ignite before being convected downstream until another sudden auto-ignition event occurs closer to the fuel injec tor. The flame topologies associated to such events are discussed in detail using the ONS results, and a conceptual mode( summarizing the observation made is proposed. Results show that the main flame sta bilization mechanism is auto-ignition. However, multiple reaction zone topologies, such as triple flames , are also observed at the periphery of the fuel jet helping the flame to stabilize by filling high-temperature burnt gases reservoirs localized at the periphery, which trigger auto-ignitions.

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“…Hence, they play a decisive role for the generation of noise and system stability. 21 Consequently, precise models for the prediction of hot spots emitted by the first stage are particularly desired for this type of combustion systems.…”

Section: Introductionmentioning

confidence: 99%

Modelling the generation of temperature inhomogeneities by a premixed flame

Steinbacher

Meindl

Polifke

2017

International Journal of Spray and Combustion Dynamics

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The response of a laminar, premixed flame to perturbations of upstream equivalence ratio is investigated and modelled, with emphasis on the generation of 'entropy waves', i.e. entropic inhomogeneities of downstream temperature. Transient computational fluid dynamics simulations of two adiabatic lean methane-air flames of different Péclet numbers provide guidance and validation data for subsequent modelling. The respective entropy transfer functions, which describe the production of temperature inhomogeneities, as well as transfer functions for the variation of the heat release, are determined from the computational fluid dynamics time series data by means of system identification. The processes governing the dynamics of the entropy transfer functions are segregated into two sub-problems: (1) heat release due to chemical reaction at the flame front and (2) advective and diffusive transport. By adopting a formulation in terms of a mixture fraction variable, these two sub-problems can be treated independently from each other. Models for both phenomena are derived and analysed using simple 0-and 1-dimensional configurations. The heat release process (1) is represented by a fast-reaction-zone model, which takes into account variations of the specific heat capacity with equivalence ratio in order to evaluate the magnitude of downstream temperature fluctuations with quantitative accuracy. For the transport processes (2), two types of models based on mean field data from the computational fluid dynamics simulation are proposed: A semi-analytical, low-order formulation based on stream lines, and a state-space formulation, which is constructed by Finite Elements discretisation of the transport equation for mixture fraction. Model predictions for the entropy transfer functions are found to agree well with the computational fluid dynamics reference data at very low computational costs.

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Autoignition flame dynamics in sequential combustors

Cited by 57 publications

References 83 publications

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

A conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on direct numerical simulation and experiments

Modelling the generation of temperature inhomogeneities by a premixed flame

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