## 2 Materials and Methods  
The experimental investigation of the fuel atomization was done using the setup presented in Figure 1a. Portion of the composite fuel (200 mL) was placed into the reservoir (2) and follow injected into the rectangular chamber (\(75\times 75\times 110\) cm) through the nozzle (3) under the static 2 bar pressure made by the compressor (1). The flow of the aerosol particles was observed by the high-speed video camera Photron SA1 (4) equipped by the macro optics. The camera and light-source (5 W LED-projector (6) with 5\({}^{\circ}\) divergence of a light beam) can move along the axis of the cone of spray flow pattern. Therefore, one can see the evolution of the aerosol with propagation distance. The more details about the used experimental technique are shown in [16]. The essential difference from the previous experiments is usage of the nozzle with wider inner channels (diameter is about 1.5 mm). The scheme of the inner design of the nozzle is shown in Figure 1b. Such nozzle can atomize the liquids with kinematic viscosity below \(3\times 10^{-5}\) m\({}^{2}\)/s. In contrary to the case described in [16], the nozzle used in this work can atomize the CWS with concentration of solid part more than 50 wt.%. Wider channels of nozzle leads to production of bigger aerosol droplets. The nozzle used in this work allows the mean size of the aerosol about 500 \(\upmu\)m that is just 1.5-2 times bigger than used in [16]. There were two fuel compositions used:1. The coal-water slurry (CWS) consisting of the filter cake of the low-caking coal from the South-East Siberian region and water (40 wt.%);
2. The coal-water slurry consisting of the same filter cake and water (30 wt.%) with addition of the 10 wt.% of waste motor oil (CWSP). The dry filter cake was milled by the rotary mill to the powder state and further sifted through a sieve with hole size about 160 \(\upmu\)m. Therefore, the obtained powder has a mean particle size about 120 \(\upmu\)m with the FWHM of size distribution about 80 \(\upmu\)m. Before the experiments the powder was mixed with water during the 20 min by the mechanical mixer that produces the uniform slurry. The slurry keeps uniform state for more than two hours and, thus, it does not change the rheological properties much enough during the experiments. Preparation of the CWSP was done by the same way but the oil was mixed with water before the addition of coal. The stability of the CWSP mixture is even better than for CWS because the oil serves as plasticizer. An additional details about the physical properties of used filter-cake and petrochemicals are available in [25]. The main component of the used synthetic oil is a is polyalkylene glycol (PAG, takes about 70 wt. % or even more). The mechanical and main thermal properties of this are available from the oil manufacturer specifications but the exact chemical content is a commercial secret. For a simulation of ignition of CWSP we have assumed that oil totally consists of PAG [26; 27]. The flying aerosol particles around the central part of the ejection cone were observed by the video camera where the video frames were captured with frame-rate about 5000 fps. It corresponds to inter-frame shift of the droplets for approx. 2 mm when droplet velocity is 10 m/s. The transversal field of view of used macro-optics was about 15 mm that allows maximal measurable velocity more than 50 m/s. The physical size of video frame together with used optics allow the spatial resolution about 12 \(\upmu\)m/px. The recorded video was analyzed using the Particle Tracking Velocimetry (PTV) technique that allows measurement of velocities of each detected aerosol particle [28; 29]. The sizes of them were analysed using the shadow photography approach within the chosen depth of field around the focal plane of macro objective. The additional details about post-processing of the recorded video are available in [16].