Studies On Flame Of Aviation Fuel

With the rapid development of economy, the process of manufacture in petrochemical industries and transportation of hazardous materials with airplane or watercraft often occur fuel spills, which frequently incur severe fires and result in catastrophic consequence. Aviation fuel, with high combustion heat and large risk, is the risk source in the fuel-spilled-fires. Research on basic principles and processes of aviation fuel flame spreading has significance to understand the occurrence and development of such types of accidents, and so as to reduce the occurrence of such types of fire.There is great difference between the characteristic of aviation fuel spreading and that of elemental low flash point fuel as alcohol. Aviation fuel is high flash point multi-component mixed fuel with high flash point of 66℃, and research on which has not been reported before. The initial process of fire flame spreading is mainly liquid-control flame spreading and it's necessary to carry out the research on liquid-control flame spreading of aviation fuel of China in order to support the research on the aviation fuel fire control and fire-extinguishing mechanism of China.The experimental system of aviation fuel flame spreading has been developed to simulate the process of liquid-control flame spreading of aviation fuel of China in this paper. The behavior of liquid-control flame spreading of aviation fuel has been analyzed, and the flame structure, spreading rate and oscillation process have been paid great attention to in the study. Fuel surface temperature distribution and heating process during flame spreading has been discussed. The characteristics of surface flow velocity and temperature distribution has been probed based on the mathematical model of surface flow, and the aviation fuel flame oscillation process and the ignition mode of flammable vapor on fuel Surface have been analyzed after the establishment of mathematical model of aviation fuel flame oscillation. Content in this paper is summarized below.Firstly, the experimental system of aviation fuel flame spreading has been developed. the position and rate of spread of the flames have been studied using CCD camera considering the size of the fuel oil pool which is 1m×0.04m×0.10m. Temperature measurement on the surface and under the liquid surface has been carried out during flame spreading with infrared cameras, and micro-thermocouple. The liquid surface flow in front of the flame had been studied by the use of schlieren.Secondly, aviation fluid fire spread processes under different initial temperature conditions have been studied experimentally. The main flame spread rate gradually increased from 0.6cm/s at the temperature of 16℃to 2cm/s at the temperature of 70℃with the increase of initial temperature of fuel. At the temperature of 73℃liquid-control mode changed into vapor-control mode, and the main flame spread rate jumped to 1m/s. Aviation fuel flame consists of the main flame and the flash combustion flame. Aviation fuel flame at different initial temperature spread forward by oscillating before and after in the liquid-control mode. It's the fundamental wave with large oscillating amplitude that pushed forward the main flame spreading, and the frequency of which increased from 2Hz at the temperature of 16℃to 5.4Hz at the temperature of 70℃.The flash combustion flame has the characteristic of intermittent oscillating at low frequency of 0.2Hz—1Hz.Thirdly, fuel surface temperature distribution and heating process before the flame front have been studied experimentally. It's revealed that fuel surface heating area consists of preheating heating area, flash combustion heating area and main flame heating area. Preheating heating area disappears when the initial fuel temperature is higher than the open-cup flash temperature of 66℃, and 66℃is the value of the temperature which means flash combustion probably appear. The temperature at the root of the main flame is 107℃. The highest temperature at fuel surface in this paper ranges from 115℃to 145℃.When the initial fuel temperature is below 66℃, the temperature at surface rises slowly, and a specific heating stability stage appears. When the initial fuel temperature is higher than 66℃, the temperature has a linear rapid growth. Surface flow before the flame front consists of weak disturbance zone and strong disturbance zone, and with the initial fuel temperature increase, both zones decrease gradually in length, and the proportion of weak disturbance increases until the surface flow totally acts as weak disturbance when the initial fuel temperature is higher than 65℃. In strong disturbance zone, surface temperature of aviation fuel is relatively stable. Surface flow with high temperature at the root of the main flame undergoes oscillating cooling process during the transition to the strong disturbance. Buoyancy is the main driving force of surface flow during aviation fuel flame spreading.Fourthly, a steady-state model of surface flow during aviation fuel flame spreading has been established to analyze temperature and velocity distribution of surface flow. It's proved that surface flow transits from the weak disturbance state to the strong disturbance state because of viscous shear flow disturbance increasing gradually with the decreasing temperature during the fuel flame spreading, and at the same time, the temperature distribution transits from linear decrease at the weak state to uniform at the strong disturbance state. The Width and thickness of strong disturbance zone of surface flow gradually increase with the initial temperature decreasing. The separation and transition Reynolds number when weak disturbance state transits to strong disturbance state increase with the initial temperature increase. Some low-temperature fuel was involved in the upper surface flow at the recycling process of surface flow, and that is the main reason for cold flow appearing in the surface flow.Finally, a model for flammable vapor movement before the flame front has been proposed to analyze the flame oscillation and ignition mode during flame spreading. It's indicated that a maximum chemical reaction rate of greater than 0.077kg/m3·s is the ignition condition for aviation fuel. The aviation fuel flame oscillation consists of development stage and decay stage. Flash combustion flames always appear in front of the main flame front, and which has the lowest fuel evaporation rate in flame oscillation region. The main flame region consists of diffusion combustion and premixed combustion, and the flash combustion zone is premixed combustion.