Study on the Characteristics of Sprays,combustion and Mechanism of Soot Reduction for Hydrous Ethanol Emulsions

Author:Zhang Xiao Qing

Supervisor:li tie


Degree Year:2018





The key to sustainable development is the harmonious development of energy substitution,environmental pollution improvement and sustainable economic growth.To protect the social economic development from obstructing by energy shortages and ecological deterioration,it has received increasing attention for exploring the clean alternative energy sources,promoting the utilization of multiple renewable energy sources and changing the energy consumption structure from a single traditional fossil energy source.On the other hand,the exhaust emissions from marine engines and vehicle engines are the important sources of atmospheric pollution.Therefore,the International Maritime Organization(IMO)and the related government departments have issued very stringent emission regulations to force the development and improvement of engine clean combustion technology.In this situation,Bio-ethanol,as a renewable clean energy,carbon-neutral,extensive extraction sources,and mature technology,is considered to be the alternative fuel for traditional fossil energy in the future.While the Bioethanol can be used on the diesel engines and indicates a broad application prospect.With the oxygenated OH component,Bio-ethanol is oxygen-containing fuel and it can be used on diesel engines to reduce emissions.Usually,Bio-ethanol is used by blending with diesel fuel.Considering the energy consumption and stratification issues,hydrous ethanol with a 20% mass fraction of water can be blended with diesel fuel and developed into the hydrous ethanol emulsions.Experiments have been conducted and the results indicate that the emulsions can maintain a long stable time.With the experimental platform of constant volume vessel,a series of experimental research work focusing on the spray combustion and emissions of hydrous ethanol emulsions,have been conducted in this dissertation.The main research work includes the physicochemical properties of the emulsions,the characteristics of non-evaporating spray and the evaporating spray,spray flame temperature and soot concentration(KL)distributions measurement of hydrous ethanol emulsions by using the two-color method,and the micro-explosion of hydrous ethanol emulsion fuel.The main research work and conclusions of this dissertation can be summarized as follows:1)With the aim of obtaining the best energy balance in the whole life cycle for utilization of ethanol,the emulsions of HE10,HE20 and HE30 were developed by emulsifying the 0 # diesel fuel,hydrous ethanol with the 20% mass fraction of water,Span80 and n-butanol.These emulsions can keep a long stable time.2)The micro-structure and physicochemical properties of the hydrous ethanol emulsion were investigated.The results show that,compared with the diesel fuel,the hydrous ethanol emulsion has the higher oxygen content,kinematic viscosity and vaporization latent heat,while the lower surface tension,distillation temperature,cetane number and low heat value.These properties have important influence on the spray and combustion characteristics of the emulsions.3)The shade photograph method and Mie scattering method were employed to study the characteristics of non-evaporative spray and evaporative spray of hydrous ethanol emulsion.It is found that the differences of spray characteristics among diesel,HE10,HE20 and HE30 are not particularly obvious,while the spray penetration decreases with the increase of ambient density and increases with the increase of injection pressure;The maximum liquid phase penetration in the evaporating sprays decreases with the increase of the hydrous ethanol volume fraction or the ambient density.4)The spray flame temperature,KL distribution and lift-off length(LOL)of diesel and emulsions were measured by using two color method and schlieren method.The results show that,for the same ambient conditions,the average flame temperature and KL value of the spray combustion flame of the emulsions are lower than that of the diesel,and the lift-off length of the spray combustion flame of the emulsions is longer than that of the diesel fuel.5)The micro-explosion temperature boundary mathematical model of hydrous ethanol emulsion was proposed,and the boundary conditions of the micro-explosion temperature of the emulsified fuel were calculated.The micro-explosion of the hydrous ethanol emulsion was observed and investigated by using high speed micro-photography method.The results indicate that the temperature boundary condition for micro-explosion occurrence of hydrous ethanol emulsified fuel is about 453 K under atmospheric pressure,while it is 495K under the diesel engine sprays.The relationship between micro-explosion strength of hydrous ethanol emulsion fuel and the volume fraction of hydrous ethanol meets the parabolic law.The occurrence of micro-explosion was observed at the end stage of high speed spray under the diesel-like condition.6)It is concluded that soot reduction mechanism of hydrous ethanol emulsion fuel is as follows.Firstly,the hydrous ethanol emulsion is the oxygenated fuel,when the spray combustion,the oxygen element OH can improve the equivalent ratio in the local area,thus improving the combustion and reducing the formation of soot.Secondly,hydrous ethanol emulsion fuels have a lower cetane number and greater latent heat of vaporization,so that the emulsion fuels have a longer ignition delay and lift-off length(LOL)during spray combustion,which are advantageous for sprays to entrain more air and can achieve more thorough mixing of fuel and air before combustion,thereby improving combustion and reducing soot generation.At last,the theoretical model and experimental results show that micro-explosion can occur under the diesel-like condition.The occurrence of micro-explosion promotes the secondary atomization of sprays,obtains smaller droplet size and larger distribution space,which improves the mixing of the spray droplets and air,thereby improving the combustion performance and reducing soot.The experimental data of spray combustion characteristics of hydrous ethanol emulsion fuel were obtained,and the soot reduction mechanism of hydrous ethanol emulsion fuel was clarified.The research results of this dissertation can provide support for the design of high efficiency and clean combustion engine.The study work of this dissertation has significant research value for adjusting energy consumption structure and alleviating environmental pollution.