Observation of Turbulent Mixing in Lean-Direct-Injection Combustion at Elevated Pressure

We report the first quantitative single-shot multiscalar data obtained from a realistic air-fed lean-direct-injection burner operating on gaseous methane (CH4) fuel at elevated pressure (5 atm) using single-shot spontaneous Raman spectroscopy. From a statistical analysis of the multiscalar data, we present spatially mapped probability density functions of the concentration of CH4 and O-2, and the instantaneous temperature. The measured three-scalar correlations and probability density functions provide insights into the nature and extent of the mixing process and its impact on the subsequent combustion process. The data will also be useful for comparison with the various turbulence-chemistry interaction models such as large-eddy simulation. The swirl-stabilized flame investigated in this paper was characterized as operating in a partially premixed combustion regime that was dominated by turbulent mixing provided by the lean-direct-injection configuration. Although a majority of the single-shot data indicated complete or near-complete reactions including stoichiometric combustion, a considerable number of the data points exhibited incomplete combustion characterized by a substantial amount of residual fuel at intermediate temperatures or were simply unreacted with little or no preheating of the mixture.