Study Of The Ignition And Combustion Intensification Of Liquid Fuels In Reduced Pressure At High Altitudes

Combustion is an extremely complex physical and chemical process controlled by flow,heat and mass transfer and chemical reactions.The combustion process will be affected by external environmental conditions,especially the external environmental conditions,such as ambient pressure and oxygen concentration,which have a significant influence on the combustion.In China's vast plateau region,especially the Qinghai-Tibet plateau areas,the high altitudes lead to the unique environment with low pressure and low oxygen concentration,which will definitely lead to the unique ignition and combustion properties of liquid fuels used in these areas.However,the burner currently used in the plateau areas of our country takes no consideration of the effect of the unique environment on the combustion,so there are lots of problems existing in the practical application,which includes the difficulty of ignition,the low burning efficiency,the high generation of soot and the unstable combustion.These problems seriously constrain the efficiency of energy use in the plateau,causing serious waste of resources and technical problems in many aspects of military and civilian use.Therefore,the correlational investigation not only matters the prevention and protection of fire safety but also of great significance to the energy utilization at high altitudes.The-35#diesel(which is widely used in plateau areas and is a representation of multi-component complicate fuel)are selected as the experimental materials.This project combines the foundational researches of ignition and combustion properties of liquid fuels with the optimization design of plateau burner.The details are summarized as follows:Field ignition and combustion experiments were performed at six different altitudes:Hefei(50m),Xining(2270m),Golmud(2830m),Lhasa(3650m),Yangbajing(4300 m),Tuotuohe(4780 m).The study is mainly divided into two parts:the first part is the study of the ignition characteristics of the fuel at high altitudes;the second part is the study on the combustion characteristics and combustion intensification at high altitudes.The research on ignition characteristics is divided into two steps.First,we focus on the variation of flash point of liquid fuels with reduced pressure and its prediction model.The flash point of the experimental material(-35#diesel)at different altitudes was measured using the automatic closed cup flash point tester.According to the experimental results,combined with Clausius-Clapeyron equation,the mathematic model of the variation of flash point with reduced pressure was established.Then,based on the flash point data of alkane fuels,a reasonable combination of Le Chatelier's flammability rule and Antoine equation is used to establish the flash point prediction model of the multi-component complex fuels(such as gasoline,aviation kerosene,diesel oil,etc.),and the model is verified to agree well with the experimental results of-35#diesel.At last,the surface temperature,ignition time,convective heat loss,gas diffusion coefficient,pyrolysis gas layer thickness and pyrolysis gas concentration gradient at different pressures were studied using FDS 6.0.The gas-phase ignition process of fuel were investigated to have a better understanding of the influence mechanism of pressure on fuel ignition and combustion.In the aspect of combustion characteristics and combustion intensification,the attenuation of reduced pressure on combustion was mainly focused on,and two possible combustion enhancement methods were put forward:first,fire whirl is proposed as a novel combustion intensification method to improve the combustion attenuation of liquid fuels in reduced pressure at high altitudes.Comparing the combustion characteristics of fire whirl with that of pool fire,such as burning rate,heat release rate,combustion efficiency and flame temperature,the intensification of fire whirl on pool fire in reduced pressure at high altitudes was quantified.The effect of peroxide additives on combustion intensification was studied by comparing the experimental results.The experimental data can provide the theoretical basis for the design and manufacture of the new plateau burner.Through field testing and improvement,the existing problems of plateau burner in practical application,such as ignition difficulty,low combustion efficiency,low energy utilization efficiency,high soot generation,combustion instability,equipment failure rate and other issues,can be solved.