Experimental And Numerical Study On Combustion Of Diesel Oil In An Electrically Preheated Porous Medium Burner

Reducing combustion emission and increasing combustion efficiency have become two hot topics in the international combustion community.In recent years,the porous media combustion technology has attracted much attention of scholars at home and abroad.,due to its obvious advantages in improving the combustion efficiency,expanding the lean-burn limit,reducing emissions and so on.In this work,the combustion characteristics of diesel in an electricly preheated porous medium burner are studied by experiment and simulation,which will provide some theoretical and practical guidance for the application of the liquid fuel porous burner.In this paper,experimental systems of porous medium burner with electric preheating is developed to realize a self-sustaining combustion of liquid fuel without second ignition.Based on the stability analysis of preheating temperature field,the characteristics of the flame and the distribution of temperature are discussed,and the influences of equivalence ratio and air mass flow on the combustion characteristics are analyzed.It is found that the electric heating systems has a strong stability,and the minimum preheating temperature for stable combustion is 750°C.Two type of flame,the stable flame and the filtration flame,are found during the process of liquid pre-evaporation combustion.The maximum temperature of the stable flame,similar to the premixed filtration combustion,is 1140.2°C.The propagated velocity of the filtration flame is on the order of 1m/s,while it is 0.1mm/s for the stable flame.As the gas mass flow increases,the stable flame moves downstream and the combustion becomes more complete.The equivalence ratio has more significant effects on the temperature distribution than that on the flame propagation.Based on the experiment data,a two-dimensional model of diesel combustion in porous medium burner is established on the platform of the software Fluent 18.0.The standard k-? turbulent model,dual temperature model and DO radiation model are considered,and the validity of the model is verified against experimental data.The results show that porous medium can effectively preheat the unburned fuel upstream of the flame and recycle the heat from the gas upstream of the flame.The combustion flame propagates downstream steadily with velocity on the order of 0.1mm/s,which belongs to a low-speed filtration combustion.The temperature of the solid sphere downstream the flame is lower than that of surrounding gas,and heat is transferred from gas to solid.On the contrary,the temperature of solid upstream the flame is higher than gas,and the solid spheres preheat the fresh air and unburned fuel.On the basis of the former two-dimensions numerical simulation,the effects of several important parameters on the combustion characteristics of diesel are discussed,such as fuel injection angle,inlet velocity,equivalence ratio and particle diameter.The results show that with increasing the inlet velocity and the sphere diameter,the propagation velocity of the flame increases.The maximum temperature in the combustion chamber inreases as the angle of injection drops or the equivalence ratio increases.The pressure loss between the inlet and outlet increases with the increase of the inlet velocity or the decrease of the sphere diameter.The mass fraction of the fuel vapor is mainly influenced by the flow field in the combustion chamber and the injection angle of liquid fuel.