The presented experimental investigation aims at providing a microscopic insight into the flame char-acteristics of the conventional (light/heavy diesel), a renewable fuel (waste cooking oil), and its blends with light/heavy diesel oils. A hyperspectral camera is used to provide detailed information on fuel reactivity and radiation intensities within the flame zones via the analysis of the C2 and CH radiation emissions. The experiments cover four equivalence ratios (F) of 0.63, 0.75, 0.96, and 1.1. A coaxial disc stabilized burner having a twin air jet atomizer is employed. The flame images are taken in the open atmosphere and the assessment of the combustion efficiency is obtained through the measurements of the cooling load inside a cylindrical combustor. The calculated values of the spatial cross-sectional average flame temperatures along the different flames are compared with the corresponding values obtained by a type S thermocouple. The processing of the hyperspectral flame images proves to be an extremely useful tool to define the location, size, and characteristics of the flame zones. The burning of HDO/WCO blend at near stoichio-metric conditions appears to be a viable renewable alternative to burning standalone HDO. The burning of a standalone waste cooking oil must be avoided. (C) 2020 Elsevier Ltd. All rights reserved.