Experimental And Computational Study On The Effects Of Low Atmospheric Pressure On The Gas Fuel Combustion Characteristics And Smoke Properties Under High Altitudes

China is a long-history country and has a large number of cultural heritages. Especially in the Tibetan Autonomous Region on the Qinghai-Tibet Plateau, there are many ancient temple buildings of Tibetan Buddhist. Most of these ancient buildings are wood structures or wood-stone hybrid structures, which lead to the very heavy fire load and low fire resistance rating, and even there are large quantities of flammable materials inside, thus the fire safety situation of these ancient buildings is very serious. However, there has been no specialized investigation on the application of exiting fire safety techniques for the special plateau environment. Therefore, the fire protection research for the plateau environment is very urgent, and the studies of combustion characteristics and smoke properties under low atmospheric pressure&low oxygen concentration conditions are important, as the basis of building fire protection design and fire detection.As the altitude increases or atmospheric pressure decreases, air density, oxygen concentration, molar diffusivity, etc. would change, which will inevitably generate some influence on the combustion reaction process, smoke movement and so on. For solid and liquid fuel, the effects of pressure on the combustion are very complex, which can be probably attributed to two aspects. firstly, the atmospheric pressure can affect the burning rate of combustion itself, slow burning rate with increasing altitude. Secondly, changed pressure would cause changes in the oxygen mass concentration in air, in the mass flow rate of air entrainment into plumes, thus affecting other related phenomena (such as flame height, flame and plume temperatures, soot smoke concentration, etc.), meanwhile, these parameters are also controlled by burning rate (or heat release rate). Since these parameters are double effect by pressure, it is difficult to analyze their dependences on pressure directly. Hence, gas fuel combustion was selected as the main target in this paper, so to eliminate the difference in burning rate with pressure by controlling the gas mass flow rate to ensure a constant burning rate, and so to facilitate experimental measurements and simplify the analysis.The effect of atmospheric pressure on the combustion can be generally attributed to the effect of physical and/or chemical mechanisms. At first, based on the classical combustion and fire science theories combined with some semi-theoretical or empirical model, qualitative analysis of the effect mechanisms of atmospheric pressure on combustion characteristics and smoke properties was completed, and then the variation trends of related fire parameters (such as flame height, flame and plume temperatures, species concentrations of soot and smoke, flame thermal radiation, etc.) with pressure were derived. These semi-theoretical or empirical analysis provide guidance for the following studies.In order to study the combustion characteristics and smoke properties under low atmospheric&low oxygen mass concentration conditions, a series of comparative fire experiments were conducted at two places in China, namely Lhasa and Hefei with altitudes of3650and50m respectively. A range of parameters were measured using various measuring instruments, including flame height recorded by digital video camera, flame and plume temperature by thermocouples and infrared thermal imager, transmittance through smoke and irradiance by laser kapnometer, carbon monoxide volume fraction by integrated gas analyzer, flame thermal radiation by radiant flux sensor. Through the comparative analysis of experimental results, some semi-quantitative rules were concluded. In addition to field experiments, we also designed a small-scale experimental platform with adjustable inner ambient pressure to simulate the plateau environment of low pressure in the plains. With this experimental platform, more fire experiments under a wide range of ambient pressures can be carried out to obtain more experimental results.The numerical simulations of laminar diffusion combustion under low pressure condition wire also conducted in this paper. The results from theoretical analysis, experiment measurements and numerical calculations were compared and validated among each other. In the numerical simulations, a simplified multi-step finite rate reaction model was adopted and appropriate boundary conditions and physical parameters were established to present the effect of atmospheric pressure on flame and smoke characteristics. In the last, some preliminary discussions, in terms of mathematical models and variables modeling, were made on the applicability of common fire simulation programs for simulating fires under low pressure condition.