Ethanol turbulent spray flame response to gas velocity modulation
| Autor: | Virginia Fratalocchi, Jim B. W. Kok |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2018 |
| Předmět: |
Materials science
Laminar flames General Chemical Engineering Mass flow UT-Hybrid-D General Physics and Astronomy Energy Engineering and Power Technology Computational fluid dynamics Combustion 01 natural sciences 7. Clean energy 010305 fluids & plasmas Physics::Fluid Dynamics Turbulent premixed combustion 0103 physical sciences Physics::Chemical Physics Premixed flame Ethanol blends geography geography.geographical_feature_category 010304 chemical physics business.industry Turbulence General Chemistry Mechanics Acoustic wave Flame speed Inlet Tabulated chemistry Fuel Technology Modeling and Simulation business |
| Zdroj: | Combustion Theory and Modelling, 22(1), 91-109. Taylor & Francis |
| ISSN: | 1364-7830 |
| Popis: | A numerical investigation of the interaction between a spray flame and an acoustic forcing of the velocity field is presented in this paper. In combustion systems, a thermoacoustic instability is the result of a process of coupling between oscillations in heat released and acoustic waves. When liquid fuels are used, the atomisation and the evaporation process also undergo the effects of such instabilities, and the computational fluid dynamics of these complex phenomena becomes a challenging task. In this paper, an acoustic perturbation is applied to the mass flow of the gas phase at the inlet and its effect on the evaporating fuel spray and on the flame front is investigated with unsteady Reynolds averaged Navier-Stokes numerical simulations. Two flames are simulated: a partially premixed ethanol/air spray flame and a premixed pre-vaporised ethanol/air flame, with and without acoustic forcing. The frequencies used to perturb the flames are 200 and 2500 Hz, which are representative for two different regimes. Those regimes are classified based on the Strouhal number St = (D/U)ff: at 200 Hz, St = 0.07, and at 2500 Hz, St = 0.8. The exposure of the flame to a 200 Hz signal results in a stretching of the flame which causes gas field fluctuations, a delay of the evaporation and an increase of the reaction rate. The coupling between the flame and the flow excitation is such that the flame breaks up periodically. At 2500 Hz, the evaporation rate increases but the response of the gas field is weak and the flame is more stable. The presence of droplets does not play a crucial role at 2500 Hz, as shown by a comparison of the discrete flame function in the case of spray and pre-vaporised flame. At low Strouhal number, the forced response of the pre-vaporised flame is much higher compared to that of the spray flame. |
| Databáze: | OpenAIRE |
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