## 1 Introduction  
The Combustion Science Experimental System (CSES) in the China Space Station serves as an experimental platform for research on fundamental combustion science in a microgravity environment. The CSES provides a comprehensive experimental platform capable of supporting combustion studies with gaseous, liquid, and solid fuels [1, 2, 3, 4, 5, 6]; the structure is shown in Figure 1. Since its commissioning, multiple series of microgravity gaseous combustion experiments have been successfully conducted through this system, yielding significant experimental results that advance fundamental combustion theory. According to the CSES construction plan, in the next stage, microgravity liquid combustion experimental modules will be designed and developed based on the structural framework of the existing gaseous combustion experimental modules. Three experimental modules capable of performing single-droplet combustion, droplet array combustion, and droplet atomization combustion functions, respectively, will be designed and installed into the combustion chamber on the CSES through an interchangeable modular framework. The gaseous combustion experimental module employs a 10 W heating wire as the igniter, as shown in Figure 2. However, experimental observations revealed that this igniter struggles to achieve stable ignition for liquid fuels with slow vaporization rates, such as n-dodecane. Understanding ignition limits helps in the design of combustion systems with reliable and controllable igniters [7]. Therefore, prior to optimizing the ignition scheme, it is essential to analyze the ignition characteristics of single fuel droplets, establish a single-droplet ignition model, determine the required ignition temperature range for combustion experiments, and provide theoretical guidance for the design and optimization of ignition solutions in the single-droplet combustion experimental module. Figure 1: Spatial layout of the Combustion Science Experimental System [4]. Figure 2: (**a**) Heating wire igniter on the gas combustion experiment plugin; (**b**) unsatisfactory ignition performance. The classical theory of single-droplet combustion is the \(D^{2}\) law [8], which states that the square of the droplet diameter changes proportionally to time during the combustion process. However, compared to studies on the combustion characteristics of single droplets, there is relatively limited research on droplet ignition processes and the criteria for determining ignition. Based on the assumptions of quasi-steady-state and single-step overall chemistry, [PERSON] [9] developed the droplet group combustion theory and derived a dimensionless number that can predict the combustion modes of droplet groups: individual droplet combustion, internal group combustion, external group combustion, and enveloping combustion. However, this droplet group combustion theory, based on the quasi-steady-state assumption, was later found to be incapable of accurately predicting the transient ignition behavior of droplets. The classical Frank-Kamenetskii method analyzed the ignition conditions of homogeneous gas mixtures [10]. [PERSON] and [PERSON] conducted an experimental investigation into the ignition of Unsymmetrical Dimethylhydrazine (UDMH) liquid droplets, proposing both steady-state analysis theory and steady-state simplified model theory [11]. The researchers proposed the correlation between the ignition characteristics of droplets and parameters such as temperature, pressure, boundary layer thickness, and droplet radius, predicting that the droplet autoignition temperature exhibits a negative correlation with droplet radius. However, studies on droplet ignition behavior in microgravity environments remain limited and predominantly qualitative. Although foundational research has explored aspects such as droplet evaporation and combustion in microgravity, comprehensive quantitative analyses of transient ignition phenomena are scarce [12; 13; 14; 15; 16]. This necessitates further experimental and theoretical investigations.