Determination of the biodiesel content in diesel/biodiesel blends by using the near-near-infrared thermal lens spectroscopy

[Display omitted] •N-NIR spectral region for low absorption of CH third overtone.•Thermal diffusivity to determine biodiesel content in diesel.•Photothermal signal for diesel/biodiesel characterization. A dual-beam mode-mismatched configuration of the Thermal Lens (TL) technique was applied to characterize biodiesel, diesel and diesel/biodiesel blends. The excitation was performed using a tunable laser in the near-near infrared region in order to assess overtones and combination bands of the vibration modes. The thermo-optical properties of the fuels were also determined. The results showed that the biodiesel contents in diesel/biodiesel blends can be monitored with this technique, by excitation the third overtone of the C–H (4ν(C–H)) bond stretching vibration at 916 nm. Both the amplitude of the photothermal signal and thermal diffusivity are important parameters to quantify the biodiesel content in diesel/biodiesel blends.