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Geyer, Dirk

Publications and source records attributed to Geyer, Dirk.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Assessing an experimental approach for chemical explosive mode and heat release rate using DNS data

Obtaining information about burning characteristics and flame structures by analyzing experimental data is an important issue for understanding combustion processes and pursuing combustion modeling approaches. It has been shown that Raman/Rayleigh measurements of major species and temperature can be used to approximate the local heat release rate and the chemical explosive mode, and that these results are sufficiently accurate for a qualitative assessment of the relative importance of different heat release zones within the same overall flame structure in laminar and mildly turbulent partially premixed flames. The present study uses data from direct numerical simulation (DNS) to extend and quantify the understanding of the approximation method with respect to premixed and stratified-premixed flames with significant turbulence–chemistry interaction (high Karlovitz number). Here, the accuracy of the approximation procedure is assessed as previously applied, using just major species and temperature, as well as with the OH radical included as an additional experimentally accessible species. The accuracy of the local chemical explosive mode and the local heat release rate results from the approximation are significantly improved with OH included, yielding quantitative agreement with the DNS results. Further, a global sensitivity analysis is applied to identify the sensitivity of the heat release rate and chemical explosive mode to experimental uncertainties imprinted upon the DNS data prior to the approximation procedure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Modeling stratified flames with and without shear using multiple mapping conditioning

A stochastic sparse particle approach is coupled with an artificial thickening flame (ATF) model for large eddy simulations (LES) to predict a series of turbulent premixed-stratified flames with and without shear and stratification. The thickened reaction progress variable serves as reference variable for the multiple mapping conditioning (MMC) mixing model which emulates turbulent mixing of the stochastic particles. The key feature of MMC is to enforce localness in this reference space when particle pairs are mixed and prevents unphysical mixing of burnt and unburnt fluid across the flame front. We apply MMC-ATF to three flames of a series of turbulent stratified flames and validate the method by comparison with experimental data. The new measurements feature increased accuracy in comparison to previously published data of the same flames due to a better signal-to-noise ratio and a setup which is less prone to beam steering. All flame locations are well predicted by the LES-ATF approach and an analysis of the MMC particle statistics demonstrates that MMC preserves the flamelet-like behaviour in regions where the experiments show low scatter around the flamelet solution. Predicted (local) deviations from the flamelet-solution are comparable to deviations observed in the measurements and variations in the flame structure due to differences in stratification and shear are reasonably well captured by the method.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Structure of a stratified CH 4 flame with H 2 addition

To explore the effect of H 2 addition (20 percent by volume) on stratified-premixed methane combustion in a turbulent flow, an experimental investigation on a new flame configuration of the Darmstadt stratified burner is conducted here. Major species concentrations and temperature are measured with high spatial resolution by 1D Raman-Rayleigh scattering. A conditioning on local equivalence ratio (range from φ = 0.45 to φ = 1.25) and local stratification is applied to the large dataset and allows to analyze the impact of H 2 addition on the flame structure. The local stratification level is determined as Δφ/ΔT at the location of maximum CO mass fraction for each instantaneous flame realization. Due to the H 2 addition, preferential diffusion of H 2 is different than in pure methane flames. In addition to diffusing out of the reaction zone where it is formed, particularly in rich conditions, H 2 also diffuses from the cold reactant mixture into the flame front. For rich conditions (φ = 1.05 to φ = 1.15) H 2 mass fractions are significantly elevated within the intermediate temperature range compared to fully-premixed laminar flame simulations. This elevation is attributed to preferential transport of H 2 into the rich flame front from adjacent even richer regions of the flow. Additionally, when the local stratification across the flame front is taken into account, it is revealed that the state-space relation of H 2 is not only a function of the local stoichiometry but also the local stratification level. In these flames H 2 is the only major species showing sensitivity of the state-space relation to an equivalence ratio gradient across the flame front.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗