Chemiluminescence-based multivariate sensing of local equivalence ratios in premixed atmospheric methane-air flames

► Partial Least Squares-Regression (PLS-R) model to estimate equivalence ratios. ► PLS-R uses raw spectral intensities negating CO2∗ nonlinear background subtraction. ► Premixed methane-air flame equivalence ratios predicted with PLS-R. ► Equivalence ratios from PLS-R compared to those from OH/CH intensity calibrations. ► PLS-R equivalence ratio predictions were within 7% of measured values.