Study On Burning Behaviour Of Heptane Pool Fire With Various Lip Heights

Fossil fuels are essential to the development of human civilization.As the most important fossil fuel,crude oil is connected to every aspect of people's life.However,crude oil and relevant liquid fuels have the properties of combustible,explosive,etc..Meanwhile,the storage tanks of liquid fuel are often with large capacity and density,which enlarges the fire risk.The flame of liquid fuel fire has high temperature and irradiance intensity,leading to high risk of fire spread,high difficulty of firefighting and severe aftermath of disaster.In order to enlarge the capacity,storage tanks usually have high side walls,resulting in the impact on burning behaviors of liquid tank fire(pool fire).It is able to provide theoretical basis for preventing and fighting storage tank fire.This thesis studies the lip height effect on burning behavior of pool fire by combining experimental investigation and numerical simulation with Fire Dynamics Simulator(FDS).Main focuses are burning rate,flame geometry and irradiance properties of n-heptane pool fire with various lip heights.The experiments were conducted in a large space building to ensure quiescent ambient environment.Pool fire diameters were set as 5 cm,10 cm,15 cm and 20 cm,and lip heights were set as 0.25,0.5,1,1.5 and 2 times of pool diameter.During the experiments,fuel layer thickness was maintained at 3 cm using a fuel layer maintaining device,employing an electronic balance to record mass loss.Flame geometry was recorded by a CCD camera and processed into flame probability distribution contour,then choose the height of 50%to be the flame height.It was found that burning rate for all pool fires employed shows similar increase-decrease-increase trend,with the heat feedback mechanisms analyzed.As for flame height,most pool fires showed similar exponential decrease trend with lip height,while the 5 cm ones decrease firstly then increase.Radiation flux and radiation fraction of all pool fires tent to increase firstly then decrease,with the inflection point of h*=0.5.Numerical simulation was conducted using same fire source HRR and pool scale.Open space of 3D×3D×4D was set up above pool rim to ensure free air entrainment.The simulation part mainly focused on the evolution of flame heights(actual flame height ltotal and down-reaching flame height ldown)with lip height and thermal properties of inside space of pool.When D=5-10 cm,ltotai showed decrease-increase-decrease trend with lip height,while ldown increased linearly.When D=15-20 cm,ltotal decreased firstly then increased,while ldown increased then decreased.The ldown/ltotal ratio showed good linear relationship with lip height.This section also analyzed the thermal properties of vapor region above fuel surface by analyzing distributions of temperature,velocity and fuel vapor concentration.