Simulation of OH-PLIF spectra based on rate equations and application in flame temperature measurement

The present study introduces a comprehensive model for simulating OH-LIF spectra based on rate equations, designed to enhance the accuracy of flame temperature measurements in combustion diagnostics. The model integrates a detailed representation of the LIF process, encompassing 240 energy levels across two electronic states, each with four vibrational levels and 30 rotational levels, accounting for laser absorption, stimulated emission, spontaneous emission, and quenching. It also considers vibrational and rotational energy transfers, resulting in a system of 240 differential equations that describe the population dynamics over time. By incorporating environmental factors such as temperature, pressure, and composition, the model provides a robust framework for simulating OHLIF spectra under various combustion conditions. The study demonstrates that the fluorescence intensity ratio from two vibrational bands serves as a reliable indicator for temperature measurement, independent of pressure and laser energy. Experimental validation confirms that the simulated fluorescence ratio-temperature curve aligns well with empirical data, offering a significant advancement in the field of OH-LIF spectroscopy for combustion diagnostics.