# Conditions for and Characteristics of the Dispersion of Gel Fuel Droplets during Ignition
## 2 Materials and Methods
### Experimental Setup for Creating the Conditions for High-Temperature Heating of Liquid Mixtures  
Based on an analysis of well-known works [6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20] devoted to the study of dispersion (secondary atomization) of multicomponent droplets, the following main conditions for high-temperature heating of droplets were chosen:  
1. The heat supply mechanism was mixed (conductive, convective, and radiation);
2. The temperature of the heating medium was 900 \({}^{\circ}\)C;
3. The number of components in the composition of the droplet and their concentration were two components with a concentration of 50% \(\times\) 50% (vol.);
4. The droplet formation conditions were intensive mixing of the components at a temperature corresponding to laboratory conditions (from 20 to 24 \({}^{\circ}\)C) for at least 20 min with a magnetic armature rotation speed of at least 1200 rpm;
5. The droplet location was on a holder.  
The above conditions for conducting the experimental studies of the dispersion of mixture droplets were implemented by using the experimental setup presented in Figure 2.  
Figure 1: Experimental setup for measuring the static contact angles formed by liquid droplets and solid surfaces (AMG-6, PTFE): 1—liquid droplet; 2—AMG-6 or PTFE discs; 3—electronic dispenser; 4—goniometer; 5—camera; 6—light source; 7—fiber optic cable; 8—telecentric tube.  
Binary liquid mixtures were obtained by mixing two of the components listed in Table 1 in a ratio of 50% to 50% (by volume) by using an AIBOTE ZNCLBS-2500 magnetic stirrer (Aibote Henan Science and Technology Development Company, Zhengzhou, China) under laboratory conditions. Stirring was conducted for 20 min at a magnetic armature rotation speed of 1200 rpm. A 10 \(\upmu\)L droplet of a binary mixture (1) then was formed on a holder (2) by using a Lennipet Stepper high-precision electronic dispenser (Thermo Scientific, Waltham, MA, USA). The holder was made of heat-resistant, high-temperature steel wire with a diameter of 500 \(\upmu\)m. The holder is fixed on a tube (3) made of steel. A high-precision coordinate mechanism (4) (ZAO Mechatronic Products Plant, Solnechnogorsk, Russia) controlled by an electronic unit (5) was used to move the tube with a holder and a droplet to the center of a tubular muffle furnace (6) (Nabertherm GmbH, Lilienthal, Germany). A temperature of 900 \({}^{\circ}\)C inside the ceramic tube (7) was kept constant during the experiments, and it was set and controlled by the built-in controller of the furnace. The high-temperature heating of the droplet was recorded according to a well-tested method [38] by using a V411 high-speed video camera (Vision Research, Wayne, NJ, USA) placed on the coordinate mechanism. A 5-inch LED lamp (9) (Edmund Optics, Barrington, IL, USA) was used to provide the required level of illumination and create a contrast image of the process under study. The video recording was conducted at a speed of at least 2000 fps at a resolution of 800 \(\times\) 600 pixels. The resulting video files were processed using the Tema Automotive (Image Systems AB, Linkoping, Sweden) and Phantom Camera Control (Vision Research, Wayne, NJ, USA) software according to a well-tested technique [38]. The criterion for the onset of one of the four possible mechanisms (evaporation, boiling, puffing, or microexplosion) during the high-temperature heating of the binary liquid droplets was its steady repetition in at least 70% of the experiments in a series performed under identical conditions. Each series of experiments consisted of 10 repetitions under identical and well-reproducible conditions.