Large Eddy Simulation of n-dodecane spray flames using Flamelet Generated Manifolds

Wehrfritz, Armin; Kaario, Ossi; Vuorinen, Ville; Somers, Lmt Bart

doi:10.1016/j.combustflame.2016.02.019

Cited by 131 publications

(96 citation statements)

References 72 publications

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“…As shown in Figure 5, the model shows fairly good qualitative agreement, but underpredicts the fuel mass fraction on the spray centerline. Similar results have been reported by Wehrfritz et al [12,15] for comparable grid resolutions using Lagrangian spray models that rely on parameter tuning. In reference [15], the mixture field prediction could be improved by increasing the spatial resolution, which has not been targeted in this study due to the high computational cost.…”

Section: Inert Casesupporting

confidence: 78%

“…Those detached flame spots are mainly causing the underprediction of the flame lift-off length, while the main flame seems to be in better agreement with the experimental value. It should be noted that only a single realization was performed in the present work and ignition delay time scattered up to 0.05 ms in LES studies of the Spray A case with multiple realizations [10,12]. Overall, the simulation seems to capture the underlying physical processes well, since all quantities are in good agreement with the experimental findings.…”

Section: Ignition Delay and Flame Lift-offsupporting

confidence: 75%

“…Even though the ignition delay was only marginally affected by turbulence effects, the laminar chemistry model failed to predict other flame characteristics like flame lift-off and heat-release, while the MRIF model showed overall good agreement with experimental results. Recently, a few LES studies of the Spray A case have been published [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

“…While the state of high-temperature ignition can be well characterized by the major combustion products, the low temperature combustion is rather denoted by intermediate species. Thus, Wehrfritz et al [12] used a linear combination of CO, CO 2 , and CH 2 O, where CH 2 O can be attributed to the first stage and CO and CO 2 to the second stage of ignition, respectively. Since the chemistry is computed under constant strain rate, the effect of its temporal evolution is not captured correctly in this model.…”

Section: Introductionmentioning

confidence: 99%

“…While flame structures, ignition delays, and flame lift-off could be well predicted by both turbulence models, the LES captured the mixing field more accurately and showed more distinct combustion recession compared to RANS. Wehrfritz et al [12] used the Flamelet Generated Manifold (FGM) model, which has been applied successfully to n-heptane spray LES before [13], and compared the performance of different chemical n-dodecane mechanisms. Besides the overprediction of the flame lift-off length for high ambient oxygen concentrations, the model showed overall good agreement with experimental data.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

Davidovic

Falkenstein

Bode

et al. 2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-A single-hole n-dodecane spray flame is studied in a Large-Eddy Simulation (LES) framework under Diesel-relevant conditions using a Multiple Representative Interactive Flamelets (MRIF) combustion model. Diesel spray combustion is strongly affected by the mixture formation process, which is dominated by several physical processes such as the flow within the injector, break-up of the liquid fuel jet, evaporation and turbulent mixing with the surrounding gas. While the effects of nozzle-internal flow and primary breakup are captured within tuned model parameters in traditional Lagrangian spray models, an alternative approach is applied in this study, where the initial droplet conditions and primary fuel jet breakup are modeled based on results from highly resolved multiphase simulations with resolved interface. A highly reduced chemical mechanism consisting of 57 species and 217 reactions has been developed for n-dodecane achiving a good computational performance at solving the chemical reactions. The MRIF model, which has demonstrated its capability of capturing combustion and pollutant formation under typical Diesel conditions in Reynolds-Averaged Navier-Stokes (RANS) simulations is extended for the application in LES. In the standard RIF combustion model, representative chemistry conditioned on mixture fraction is solved interactively with the flow. Subfilter-scale mixing is modeled by the scalar dissipation rate. While the standard RIF model only includes temporal changes of the scalar dissipation rate, the spatial distribution can be accounted for by extending the model to multiple flamelets, which also enables the possibility of capturing different fuel residence times. Overall, the model shows good agreement with experimental data regarding both, low and high temperature combustion characteristics. It is shown that the ignition process and pollutant formation are affected by turbulent mixing. First, a cool flame is initiated at approximately stoichiometric mixture and propagates towards the rich side. Hence, heat and radicals are transported away from the most reactive mixture and thus the ignition is delayed. At the same time, the transported heat and radicals increase the reactivity of rich mixtures, which strongly affects the CO formation. NO was found to increase compared to the no transport case due to enhanced mixing, which is related to a broader high-temperature zone and the additional transport of oxygen from lean into high-temperature regions.

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Section: Inert Casesupporting

confidence: 78%

Section: Ignition Delay and Flame Lift-offsupporting

confidence: 75%