Combustion properties of glass fiber/phenolic resin at low ambient pressures

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.