The leakage of liquid fuel onto high-temperature components, such as aircraft engine nozzles, poses an ignition hazard, particularly under sudden conditions arising from fuel system aging, mechanical impact, or structural damage. Given that it is a critical issue for aviation fire safety, this study investigates the ignition characteristics of fuel droplets on high-temperature surfaces. Titanium alloys, widely used in modern aircraft for their high strength-to-weight ratio and thermal stability, were selected as the substrate to systematically examine the effects of droplet diameter, surface temperature, and fuel composition on ignition probability and ignition delay time.

An experimental platform was established using a TC4 titanium alloy heating plate to simulate a high-temperature hot surface. RP-3 aviation kerosene and n-heptane droplets with diameters of 3.62-9.49 mm were generated using a precision pipette and released from a height of 30 mm onto the heated surface. Surface temperatures were controlled between 200 ℃ and 800 ℃ with a PID system, and ignition events were recorded with a high-speed camera. Ignition probability was defined as the ratio of successful ignitions to the total number of trials, while the ignition delay time was defined as the time interval from droplet contact to sustained flame appearance. A physics-based logistic model and an energy conservation-Arrhenius model were developed to predict ignition behavior and incorporate dimensionless parameters, such as the Bond and Weber numbers, to account for droplet impact dynamics.

The minimum ignition temperatures for RP-3 aviation kerosene and n-heptane droplets on titanium alloy surfaces are approximately 590 ℃ and 580 ℃, respectively. Ignition probability increased monotonically with surface temperature but displayed nonmonotonic variation with droplet diameter, peaking at a critical diameter of 7.26 mm. For smaller droplets, ignition probability increases with diameter because of enhanced heat transfer and vapor concentration, whereas larger droplets exhibit reduced ignition probability due to weaker internal thermal gradients and limited oxygen diffusion. Ignition delay time decreases with increasing surface temperature and is the shortest at the critical diameter. Under equivalent conditions, RP-3 droplets show a 5%-15% lower ignition probability and a 20%-30% longer ignition delay time than n-heptane. These changes are attributable to RP-3's complex composition, high boiling point, antioxidant additives, and smoke formation. Titanium alloys exhibit ignition temperatures 50-70 ℃ lower than stainless steel because of their lower thermal conductivity, diffusivity, and catalytic activity. The logistic model accurately predicted ignition probability with < 1% error, while the energy conservation-Arrhenius model predicted ignition delay with < 2 s error.

Droplet diameter and surface temperature are the principal factors controlling thermal surface ignition on titanium alloys. The identified critical diameter serves as a useful parameter for monitoring and mitigating fire risks. The developed models offer reliable predictive capability, supporting fire prevention design in aircraft engines. For risk reduction, monitoring droplets 5-9 mm in diameter is recommended, and surface temperatures should be maintained below 600 ℃. Future research should consider additional factors, such as low-oxygen conditions at high altitudes, droplet impact velocity, vibration frequency, and surface characteristics, to further optimize the model and enhance aviation fire safety.

In aviation transportation, which is characterized by low-pressure environments, aircraft fires pose an unpredictable threat. The interior wall materials of civil transport aircraft are predominantly composed of composite materials. The Federal Aviation Administration of the United States and the Civil Aviation Administration of China require experimental validation of their fire-resistant properties. This study aims to address the current research gap by investigating the development patterns of aircraft fires under low-pressure conditions. Specifically, this study examines the combustion rates of interior wall materials in civil aircraft in multiple-pressure environments. The goal is to detect and prevent aircraft fires under low-pressure conditions at the earliest opportunity.

This study investigates the sandwich structure panel material (Panel A) and the laminated panel material (Panel B) used in Airbus aircraft. Panel A comprises the upper and lower layers of resin-based substrates, an aramid honeycomb core intermediate layer, and an adhesive. Panel B is composed of resin-based glass fiber-reinforced laminate. The study is conducted using a low-pressure combustion chamber research facility in Guanghan, Sichuan (96 kPa), and Kangding, Sichuan (61 kPa). Combustion rates and flame phenomena of cabin wall panel materials are examined at 40, 50, 61, 70, 80, and 96 kPa pressure levels. A combustion rate model is applied to adjust the effect of pressure on the combustion rate of cabin wall panel materials. The heat release of the cabin wall panel materials is determined using a cone calorimeter, which enables the assessment of heat release in various pressure environments. Finally, following relevant regulations and standards, a fire penetration resistance test apparatus is constructed to investigate the fire penetration resistance characteristics of cabin wall panel materials under different pressure conditions.

The relationship between the combustion rate and pressure for glass fiber/phenolic resin sandwich panels and glass fiber/phenolic resin laminated panels is approximately and, respectively. According to the fire-base dimensions, the combustion rate-pressure models are and, respectively. The peak heat release rates of aircraft interior wall panels in low-pressure environments are lower than those in atmospheric-pressure environments. When the air pressure drops from 96 kPa to 40 kPa, the peak heat release rate of glass fiber/phenolic resin sandwich and glass fiber/phenolic resin sandwich decreased by about 40.97% and 43.85%, Similarly, compared with atmospheric-pressure environments total heat release significantly decreases under low pressure by 14.20% and 24.71%, respectively. The flame color of aircraft interior wall panel materials shifts from bright yellow at atmospheric pressure to a lower degree of brightness under low pressure. Additionally, the flame height significantly decreases under low pressure compared with the height under atmospheric pressure, with glass fiber/phenolic resin sandwich panels and glass fiber/phenolic resin laminated panels experiencing a reduction of approximately 10.9% and 11.6%, respectively, compared with atmospheric pressure. Research on the fire penetration resistance of aircraft cabin interior wall panels reveals that the char layer of sandwich panel materials becomes more pronounced under low pressure than under atmospheric pressure, indicating increased fire resistance. Conversely, laminated panel materials are minimally affected by pressure.

According to the above research findings, pressure significantly affects the fire characteristics of cabin wall panel materials. This study provides direct relevance to the practical needs of aircraft fire prevention and control, offering data support for aircraft fire prevention efforts.

The primary aim of this research is to address the critical issue of potential fires arising from fuel spillage on hot surfaces. This work is vital owing to the inherent risks associated with such scenarios, particularly in industrial environments where accidental contact between flammable liquids and hot surfaces can lead to disastrous outcomes. A comprehensive understanding of the evaporation patterns and heat transfer mechanisms of fuel droplets on heated surfaces is imperative for mitigating these fire hazards.

By undertaking this investigation, the goal is to provide valuable insights that can inform safety protocols, design considerations, and risk assessment strategies in various industries dealing with flammable substances. Glass heating substrates serve as the foundation for the investigations, allowing us to simulate real-world scenarios in which fuel droplets come into contact with hot surfaces. To maximize the infrared transmittance of the glass, we increase the transmittance film on the quartz glass to 93%-96%. This study encompasses a range of representative fuels, including acetic acid, ethanol, acetone, ethyl acetate, n-heptane, and cyclohexane, to ensure a comprehensive understanding of the diverse fuel properties. In experimental analysis, we employ state-of-the-art infrared imaging technology in conjunction with a robust volume estimation method. This combination of tools enables us to precisely observe and measure the evaporation behavior of the selected fuel droplets.

This study had yielded innovative and noteworthy results that significantly contributed to the current body of knowledge in this field. Unique thermal patterns on the surfaces of different fuel droplets were observed, providing a detailed understanding of the evaporation process. Hydrothermal waves (HTWs) and Bénard-Marangoni (B-M) cells were identified on acetic acid and ethanol droplets, representing a novel finding with implications for the broader understanding of thermal dynamics on liquid surfaces. A particular highlight was the identification of a previously unreported double-vortex thermal pattern on the surface of cyclohexane droplets. This discovery added a layer of complexity to the existing literature, highlighting the complexity and diversity of thermal behaviors in the context of fuel evaporation on heated surfaces. It founded that the contact angle exhibited minimal variation, generally staying within a range of 10 degrees for all six fuels. Consequently, when evaluating the droplet volume using the volume estimation method, it became clear that the liquid was not significantly influenced by changes in the contact angle, and such variations didn't affect the primary results.

In conclusion, this research illuminates the intricate interplay between fuel droplets and hot surfaces, providing crucial insights for fire prevention strategies and safety measures. The observed thermal patterns, including the novel double-vortex pattern, provide a deeper understanding of the underlying mechanisms governing fuel evaporation. This knowledge is instrumental in refining safety protocols, designing effective preventive measures, and informing future research in the broader field of fire safety and risk management. The findings of this investigation underscore the need to consider specific fuel properties and surface characteristics when developing targeted safety strategies for industries dealing with flammable substances. In the future, the goal is to integrate these insights into practical applications, potentially enhancing the safety and resilience of industrial processes involving flammable liquids.

Artificial oxygen enrichment devices are used in several situations to ensure the safety and health of workers and travelers in high-altitude regions, such as in high-altitude airport control command centers, VIP rooms, medical rooms, and luxury hotels. Indoor oxygen enrichment can meet the oxygen supplementation needs of people. However, the flammability of materials is affected in nonstandard atmospheric conditions such as low-pressure and oxygen-rich environments, resulting could cause additional fire hazards.

This study simulates the combustion of typical indoor fabrics in the Kangding Plateau (60.5 kPa) and Guanghan, Sichuan (95.8 kPa) inside a combustion chamber by adjusting the pressure and oxygen concentration. It explores changes in the core combustion parameters such as flame form, ignition time, mass loss rate, heat release rate, and total heat release amount of pure cotton and polyester at 60.5 kPa and various oxygen concentrations (21.0%, 27.0%, 33.0%, and 39.0%).

Fabric combustion at low pressure involved the stages of thermal decomposition, ignition, intense burning, and flame decay until extinction. In a low-pressure environment with normal oxygen content, complete cotton combustion was achieved, resulting in the formation of residual char that was loose and easily pulverized. In contrast, polyester combustion exhibited an efficiency of only 11.1%, producing a considerable amount of black and brittle residual char. The rates of mass loss and heat release decreased during the combustion of cotton and polyester, resulting in lower flame heights. The ignition time of cotton decreased by 3.6%, while the ignition time of polyester decreased by 7.8%. The duration of combustion increased by 46.8% for cotton and 197.0% for polyester. Additionally, the burning time of melted polyester droplets increased by 296.0%. With an increase in the oxygen concentration, the ignition time of pure cotton and polyester decreased by 19.1% and 25.7%, respectively. The time of peak rates of mass loss and heat release for pure cotton and polyester were reduced by 78.1% and 52.1%, respectively. The flame height of both materials increased, and the peak mass loss rate and heat release rate significantly rised. The combustion efficiency of polyester was improved by 68.1%, and the total heat release was increased by 1.2 times. Additionally, the burning time of melted droplets was increased by 3.1 times. In contrast, the changes in these parameters were not considerable for cotton combustion. The decrease in the partial pressure of nitrogen in a low-pressure environment decreased the flame-retardant effect of the inert nitrogen gas. Thus, if the peak rate of heat release was taken as the criterion for a fire hazard, the combustion fire hazard of fabrics at a pressure of 60.5 kPa and oxygen concentration of 30.0% was equivalent to that of combustion under normal pressure and normal oxygen conditions.

This study analyzes the effects of the changes in oxygen concentration at low air pressure on the combustion characteristics and reveals the fire behavior characteristics of typical combustible materials such as cotton and polyester in low-pressure oxygen-rich environments. It provides a basis for the fire safety design of artificial oxygen enrichment environments in high-altitude regions.

Accidental fires seriously threaten the safe operation of aircraft. Air transportation environments typically have low ambient pressures that can significantly influence the occurrence and spread of fire. The wallboards in civil aircraft are generally made of composite materials. The Federal Aviation Administration of the United States and the Civil Aviation Administration of China require that the fire resistance characteristics of these materials be experimentally verified. This study investigated a sandwich structure panel (panel A) and a laminated panel (panel B) of an Airbus aircraft to understand the influence of ambient pressure on aircraft fires and to enable the earliest possible detection, management, and prevention of aircraft fires at the low ambient pressures typically encountered in such situations. Panel A was composed of upper and lower resin base panels, with an aramid honeycomb core and adhesive middle layer, whereas panel B was a resin-based glass fiber-reinforced laminate.

The effects of ambient pressure on the thermal insulation, ignition time, mass loss, and smoke characteristics of the panels A and B were studied using self-built, low-pressure, oxygen-enriched combustors in Kangding, Sichuan Province (61 kPa) and Guanghan, Sichuan Province (96 kPa), respectively. The thermal insulation characteristics of the panels were studied by measuring the temperature on the back surface of the panel after heating the front surface for 60 s with a heating rod. The effect of pressure on the convective heat loss was studied using the ideal gas relation. The mass loss during the fire was recorded by an electronic balance, and the smoke generation was recorded in real time by a smoke analyzer.

The temperature of the back surface of panel A was 692.3 ℃ at atmospheric pressure and 512.4 ℃ at low pressure with a decrease of about 26.0%. The temperature of the back surface of panel B at normal and low pressures was 810.5 ℃ and 820.9 ℃, respectively. Furthermore, the temperature variation as a function of time was almost the same under either pressure condition for panel B, indicating that changes in the ambient pressure in the range studied had almost no impact on the insulation of panel B. The heating rate of panel B was higher than that of panel A, demonstrating the superior thermal insulation performance of panel A. Regarding the effect of pressure on the convective heat loss, the measured ignition times were in good agreement with the analytical model. The ignition time for panel A was reduced from 24.16 s to 20.34 s, i.e., reduced by 16%. Pressure variations had less influence on the ignition time for panel B. Variations in the pressure affected the rate of combustion; the mass loss for panel A decreased from 8.7% to 4.9%, and the peak mass loss rate decreased from 68.7×10^-3 g·s^-1 to 22.8×10^-3 g·s^-1, whereas the mass loss for panel B decreased from 5.8% to 4.8% and the peak mass loss rate decreased from 35.0×10^-3 g·s^-1 to 12.5×10^-3 g·s^-1. The time of the maximum O₂ consumption and the time of the CO and CO₂ production peaks of either kind of panels were almost the same under different pressure environments, whereas the maximum O₂ consumption and CO and CO₂ production peaks in the low-pressure environment were higher than those at atmospheric pressure.

This preliminary study on the effect of pressure on the combustion characteristics of aircraft panels finds that pressure has a significant impact on the occurrence and spread of aircraft fires. This study can provide theoretical support for cabin fire prevention and fire rescue under different pressure environments.