## 2 Experimental Equipment and Methods
### Experimental Setup
It should be noted that this work did not analyze the influence of the excess air coefficient on the fuel combustion characteristics. The video recording system (Figure 1) consisted of a Phantom V411 color high-speed video camera (Vision Research, Wayne, NJ, USA) and a laptop computer with the Tema Automotive software (Image Systems AB, Linkoping, Sweden). The shooting speed was at least 2000 fps at a resolution of 600 \(\times\) 480 pixels. To enhance the image contrast of a fuel droplet and its fragments formed after dispersion, a MultiLed QT LED spotlight (GS Vitec GmbH, Bad Soden-Salmunster, Germany) with a 15\({}^{\circ}\) lens (luminous flux 12,000 Lumen (white), power 150 W) was installed at the opposite side of the muffle furnace (Figure 1) relative to the video camera location. Light intensity (0-100%) was controlled by a MultiLed G8 controller. Ignition delay times \(t_{d}\) and burnout times \(t_{\text{burn}}\) were determined from video recordings using original software developed in the Wolfram Mathematica programming envelope (Wolfram Research, Champaign, IL, USA). The ignition delay time of the composite fuel corresponded to the duration of the time period between two recorded events. The first event was the beginning of the induction period, which was controlled by the moment when the fuel particle was introduced into the muffle furnace (\(t=0\)). The second event was the vapor-gas mixture ignition in the vicinity of the composite fuel droplet (\(t=t_{d}\)). The onset of this event corresponded to the moment when the first peak value of the controlled glow intensity in the video recording area was reached (Figure 2). The developed processing algorithm controlled the values of visible light emission intensity frame by frame in the entire video recording area. The ignition moment was determined automatically by a sharp jump in the luminosity intensity in the controlled vicinity of the fuel droplet (Figure 2). The burnout time of a fuel droplet (\(t_{\text{burn}}\)) was recorded from the ignition moment to the end of combustion, which was characterized by a decrease in the glow intensity to the initial level--the luminosity value before fuel ignition (Figure 2). The systematic and random uncertainties of \(t_{d}\) and \(t_{\text{burn}}\) connected with the video recording speed and the scatter of experimental data did not exceed 0.5% and 10%, respectively. The size of the region where fine fragments and combustible gases burn out (\(d_{\text{burn}}\)) after fuel droplet dispersion was calculated by averaging four values \(d_{\text{burn}}\) = (\(d_{1}\) + \(d_{2}\) + \(d_{3}\) + \(d_{4}\))/4 [34] measured in different sections at the time when the projection area of the corresponding region on the focal plane was maximum (Figure 3). The systematic uncertainty of \(d_{\text{burn}}\) connected with the lens features and the video camera settings (video recording resolution parameters) did not exceed 3%. The random uncertainty for a series of experiments performed under identical initial conditions was no more than 30%. Figure 3: Visualization of the video frame processing for determining the size of the burnout region of fuel components without dispersion (**a**) and with dispersion (**b**). Figure 2: Visualization of the video frame processing for determining the fuel ignition delay times.