Prediction of autoignition in a lifted methane/air flame using an unsteady flamelet/progress variable model
- Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109 (United States)
An unsteady flamelet/progress variable (UFPV) model has been developed for the prediction of autoignition in turbulent lifted flames. The model is a consistent extension to the steady flamelet/progress variable (SFPV) approach, and employs an unsteady flamelet formulation to describe the transient evolution of all thermochemical quantities during the flame ignition process. In this UFPV model, all thermochemical quantities are parameterized by mixture fraction, reaction progress parameter, and stoichiometric scalar dissipation rate, eliminating the explicit dependence on a flamelet time scale. An a priori study is performed to analyze critical modeling assumptions that are associated with the population of the flamelet state space. For application to LES, the UFPV model is combined with a presumed PDF closure to account for subgrid contributions of mixture fraction and reaction progress variable. The model was applied in LES of a lifted methane/air flame. Additional calculations were performed to quantify the interaction between turbulence and chemistry a posteriori. Simulation results obtained from these calculations are compared with experimental data. Compared to the SFPV results, the unsteady flamelet/progress variable model captures the autoignition process, and good agreement with measurements is obtained for mixture fraction, temperature, and species mass fractions. From the analysis of scatter data and mixture fraction-conditional results it is shown that the turbulence/chemistry interaction delays the ignition process towards lower values of scalar dissipation rate, and a significantly larger region in the flamelet state space is occupied during the ignition process. (author)
- OSTI ID:
- 21350364
- Journal Information:
- Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 10 Vol. 157; ISSN CBFMAO; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AIR
AUTOIGNITION
CHEMICAL REACTIONS
COMBUSTION
EXPERIMENTAL DATA
FLAMES
FORECASTING
LARGE-EDDY SIMULATION
Lifted flames
MASS
MATHEMATICAL MODELS
METHANE
MIXTURES
Non-premixed combustion
SCALARS
TEMPERATURE RANGE 1000-4000 K
TIME DEPENDENCE
TRANSIENTS
TURBULENCE
Turbulent combustion
Unsteady flamelet modeling