EMPI - Reactive Fluids

Multi-line laser-induced fluorescence (LIF) spectroscopy is a powerful non-invasive optical diagnostic technique used to measure gas-phase species concentrations and temperature in reactive media. This method is essential for understanding reaction and transport processes in environments such as flames and chemically reacting flows. Our team has developed LIFSim 4.0, a modular software for simulating and analyzing LIF spectra of diatomic molecules like NO, SiO, OH, and O₂, accessible at http://lifsim.com/.

LIF involves exciting molecules with a laser at specific wavelengths, causing them to fluoresce. By analyzing the emitted fluorescence spectra, we can determine gas concentration and temperature. Multi-line LIF enhances this technique by using multiple excitation wavelengths to capture the temperature-dependent population distribution of quantum states. This method is particularly useful for species such as NO, OH, O₂, and SiO, which are prevalent in reactive flows and indicative of pollutant formation and reaction zones.

LIFSim 4.0, an open-source MATLAB-based tool, simulates absorption, excitation, and emission spectra of diatomic molecules, incorporating effects such as line broadening and quenching based on spectroscopic data. It supports temperature sensitivity analysis to identify optimal spectral regions for temperature measurements and performs multi-line thermometry, deriving temperature from the shape of LIF excitation spectra. This minimizes background signal interference and enhances measurement accuracy even in challenging conditions.

Applications of multi-line LIF thermometry include measuring temperature fields in combustion environments. For instance, NO LIF has been used in low-pressure premixed flames to obtain precise temperature profiles essential for understanding flame dynamics and pollutant formation. SiO LIF is applied in nanoparticle synthesis to optimize conditions for SiO₂ production by analyzing temperature and reaction kinetics. OH-LIF thermometry is widely used in hydrocarbon combustion to study temperature distribution, aiding in improving combustion efficiency and reducing emissions.

LIFSim 4.0 also determines relative mole fractions of target species by analyzing LIF signals at various wavelengths, crucial for studying pollutant formation and reactive intermediates.

In summary, multi-line LIF and LIFSim 4.0 provide a comprehensive, accurate, and efficient approach to characterizing reactive flows. These tools support advanced research in combustion, environmental monitoring, and nanoparticle synthesis, fostering collaboration and innovation within the diagnostics community.