Experimental Study On Characteristics Of Typical Fuel Under Sub-atmosphere Environment

The development of human technologies leads people to working and living in a broader space. It’s known that people are moving their work and living space towards high altitude areas. In this condition, the low atmospheric pressure related events have become one of the focus. this also makes the study of the fire characteristics under low pressure conditions particularly important.There have been a series of fire combustion phenomena studied and analyzed by many scholars. They found out the major factors under low pressure condition is the differences of the density of air (oxygen partial pressure). This leads to the differences combustion characteristics.This paper designed two low pressure cabinet of different size considering the scales of the fuels to simulate the low atmospheric pressure environment in the study of typical combustion characteristics. The including three main parts the flame shape, mass burning rate and carbon smoke characteristics are as follows:(1)In studying the flame shape, it is found that the small scale n-heptane flame turned stable under low pressure with water bath. The flame height of the same size is in direct proportion with pressure. The lower the pressure, the fire becomes wider. there are tow obvious parts for gas jet flame in this paper: The bottom of the flame is blue like a balloon, and the upper part of the flame is a yellow bright flame. with the decrease of pressure, the decreased air density may caused flame easier to be lifted up. The relationship between flame height and width with pressure followed the similar trendsfor two fuel used in this paper. With the decrease of the pressure, the height of the blue flame increased gradually, while the yellow flame height decreased gradually. Also the maximum cross-sectional area is proportional to the square of pressure.(2) A series of n-heptane pool fire experiments in low-pressure experimental cabinet with water bath was conducted to learn more about the relation between pressure and the mass burning rate. Water bath was used to prevent the fuel boiling. The experimental results show that the length of the quasi steady state is inversely proportional to the size of pool and pressure. At the same time, the average mass burning rate at the stable stage increases with increasing pressure and the increasing of pool size.(3) In order to learn the pressure effect on smoke point for acetylene,a series of experiments were conducted from 45 kPa to 101 kPa every 5 kPa interval. It is found that the flow rate and flame height of acetylene fuel at smoke point were recored at every pressure condition. The height of acetylene at smoke point follows exponential relationship with pressure, i.e. Hsp ∝ P0.75, meanwhile the flow flux at the smoke point follows msp ∝ P0.75.(4)The decreasing of the bright yellow parts indicates the decreasing production of soot under low pressure. A Semi-quantitative optical method named Laser induced incandscence method to study the soot production. It’s clear that soot volume fraction of the gas fuels (ethylene and propane) used here follows power law with pressure. the power exponent for ethylene is 3.0, while that for propane is 1.5.The data obtained in this paper is relatively limited, which indicates a further verification with more experiments in the future. At the same time, the laser diagnostic methods was only used to study gas fuel containing less carbon number. So it’s necessary to learn the rule of soot particle production with more carbons such as liquid fuel. What’s more, the laser diagnostic method is also needed to be optimized.