## 2 Experimental Equipment Setup  
Single-droplet combustion is a type of diffusion combustion. The liquid fuel volatilizes into vapor and subsequently mixes with the surrounding air, constituting a pre-vaporized combustion mode [10]. Due to the constant temperature difference between the exposed heating wire and the surrounding air, natural convection driven by the temperature difference persists around the heating wire. This phenomenon not only significantly disturbs the temperature field in the vicinity of the heating wire, but also influences the distribution of the vapor mixture surrounding the droplet. In the microgravity environment, the buoyant lift caused by gravity is greatly reduced in fluids, resulting in convective effects being reduced to a negligible level [1; 2; 3; 4]. Consequently, it is necessary to establish a uniform-temperature static-air environment prior to conducting ignition experiments. The diagram of the facility is shown in Figure 3.  
The heating vessel was constructed from a high-borosilicate quartz glass cylinder with high temperature endurance, externally wrapped with a heat-resistant insulating material, as shown in Figure 4a. The heating device consists of two segments with a 0.5 mm diameter heating wire capable of reaching a maximum temperature of 1354 K. The heating wires were placed at the top and bottom of the heating vessel and connected in parallel to the temperature control module, which consists of three parts: a PID-based control panel, a solid-state relay, and a 400 W power supply, as shown in Figure 4b.  
After entering the set temperature on the control panel, the actual temperature detected by the K-type thermocouple inside the vessel was compared with the set value, and the solid-state relay dynamically regulated the power output to realize automatic temperature control. The thermocouple was aligned coaxially with a vertical support fiber at a 20 mm separation distance, as shown in Figure 5. This distance ensures that the thermocouple junction does not influence the droplet ignition process thro  
Figure 4: Partial experimental instruments. (**a**) Reaction vessel; (**b**) temperature control module.  
Figure 3: Diagram of experimental facility. 1. Temperature control module. 2. Thermocouple. 3. Heating wire. 4. Heating vessel. 5. Bracket for vertical support fiber. 6. Sliding guide. 7. High-speed camera.  
allows for the accurate measurement of the ambient temperature during droplet ignition. A viewing window is reserved to allow for the recording of the ignition process by a camera. The right endcap is equipped with a small orifice to enable the fiber with the droplet to enter the vessel interior. The droplet is suspended on a nichrome wire with a diameter of 0.2 mm. In a relatively static environment, heat conduction between the droplet and the nichrome wire can have a certain impact. However, studies have shown that as the ambient temperature increases, the influence of the support fiber on the experimental results diminishes [23]. Specifically, under high-temperature conditions exceeding 1000 K, the effect of the support fiber on the experimental outcomes becomes negligible. In the literature [24], it was found that the difference in droplet lifetime is no more than 2% when the diameters of the thermocouple and the support fiber are both 0.21 mm. In this study, a 0.2 mm diameter nichrome wire was employed to suspend the droplet, with experimental temperatures ranging from 750 K to 1250 K. Considering the findings from references [23; 24], the influence of the supporting fiber on the experimental results is deemed negligible. The high-speed camera is equipped with an infrared cut-off filter (IR-cut filter) on its photosensitive element that can minimize the impact of thermal radiation.