Utilizing crude vegetable oils in all types of heat engines can be a part of a sustainable economy in the future. Focusing on their local usage, they can possibly compete with fossil fuels. Furthermore, to keep the pollutant emissions at the lowest possible level, the feedback control of the equivalence ratio is essential. Regarding the harsh environment of the combustion chambers, optical flame diagnostics is a potential tool. Therefore, in order to examine its feasibility, the comparison of flame emission spectroscopy (FES) of rapeseed oil with standard diesel oil was carried out at atmospheric conditions in a lean premixed prevaporized (LPP) burner at 15 kW of firing power. The well-known chemiluminescence intensity ratios of OH*, CH*, and C-2* at 516 nm (C-2,C- 516*) were investigated. A further significant peak was found at 554 nm in case of rapeseed oil firing, which probably corresponds to C-2* (C-2,C- 554*). The corrected chemiluminescence intensity ratios as a function of air-fuel equivalence ratio are shown in the current work. It was found that these ratios involving C-2* at either 516 or 554 nm show less sensitivity to the pressure of atomizing air than OH*/CH*, therefore they are more suitable for diagnostics and for the control of the equivalence ratio of liquid fired burners. (C) 2015 Elsevier B.V. All rights reserved.