Turbulent Combustion

Multiscalar Measurements in the Turbulent Combustion Laboratory

Much of the experimental reacting flow research at the CRF is aimed at gaining a better fundamental understanding of interactions between turbulent fluid dynamics and chemical kinetics in nonpremixed, partially premixed, and premixed flames of gaseous fuels. These turbulence-chemistry interactions can have significant effects on flame stability and pollutant formation in practical combustion systems.

Line-imaged Raman scattering, Rayleigh scattering, and laser-induced fluorescence (LIF) of carbon monoxide (CO) are combined in the Turbulent Combustion Laboratory (TCL) to obtain simultaneous, single-shot measurements of temperature and major species (i.e., N2, O2, CH4, CO2, H2O, CO, and H2). From these, we calculate important derived scalars, including mixture fraction, reaction progress variable, and parameters quantifying differential diffusion. Crossed planar imaging of either hydroxyl (OH) LIF or Rayleigh scattering (355 nm) is also applied simultaneously with the line measurements to determine instantaneous 3D flame orientation. This unique combination of laser diagnostics allows CRF researchers to determine 3D scalar gradients and scalar dissipation from the 1D measurement. Scalar dissipation is a quantity of central importance in the theory and modeling of turbulent combustion.

Diagram of the new Raman/Rayleigh/CO-LIF detection system and table of representative signal-to-noise ratios, comparing the point measurement system (1995-2001) with the current system. The last column shows further improvements using a method of spatial oversampling and wavelet denoising.

Measuring scalar dissipation in flames presents significant challenges for laser diagnostics, requiring a combination of high precision and spatial resolution approaching the smallest scales of turbulence at the measurement location. By developing customized detection hardware and innovative methods for data analysis, CRF researchers have achieved significant advances in multiscalar diagnostics. Beyond the fundamental insights that these experiments provide, the multiscalar data form an important basis for validating combustion models and especially submodels for turbulence-chemistry interaction. This is a central theme of the TNF Workshop series, and much of the experimental work is done in collaboration with visiting researchers who are workshop participants.