Experimental Study On The Performance Of Combustors With Single Or Double Meshes Using Electrospray Technique

MEMS(Micro-electromechanical Systems)have received a rapid development with the development of manufacture technique.Miniaturized equipment plays an important role in many aspects.More severe requirements were put forward due to the reduction of equipment size.The energy densities of chemical batteries used for MEMS were too low.Micro energy supply systems based on micro combustion were promising alternatives for high energy density and long duration.The investigation and design of micro combustors was one of the hot pots.Liquid fuels had the advantages of high heating value and easy for storage.Electrospray technique can produce quasi-monodispersed droplets especially for small flow rate.The motion of droplets can be controlled by changing the electric field.The electrospray based on the nozzle-ring electrode-grounded mesh configuration under cone-jet mode,skewed cone-jet mode and multi-jet mode by adjusting the voltage of ring electrode(4.80 kV,5.00 kV and 6.00 kV)with ethanol flow rate of 3.5 ml/h was experimentally studied.Based on the study of electrospray,the combustion characteristics of two different combustors were then investigated.The droplets sizes and velocities were measured by PDA.The diameters of droplets were 13.33 ?m,7.48 ?m and 4.46 ?m respectively under different electrospray modes.The droplets sizes had a homogeneous distribution.The evaporation time was calculated based on the droplets sizes and the residence time was solved according to the droplets velocities.The residence time was always larger than evaporation time under all conditions.The flame was anchored near the mesh in the single mesh combustor,the flame diameter decreased from 12 mm to 6 mm with the increasing ?.The flammability limit was 0.8~1.6.Under the identical electrospray mode,flame temperatures,heat losses and combustion efficiencies both increased firstly and then decreased with the increasing ?,and reached their maximums at ?=1.Thermal efficiencies decreased with the increasing ? in a whole view.At the identical ?,flame temperatures,heat losses and combustion efficiencies under cone-jet mode were higher than other two electrospray modes,the highest combustion efficiency was 92.53% and the thermal efficiencies were similar in the single mesh combustor.Two flames patterns(single flame and double flame,critical ?=1.3)were found in the double meshes combustor.The diameter of the flame was approximately 12 mm and remained unchanged with changing equivalence ratios.The flammability limit was 0.7~1.6.Under the identical electrospray mode,flame temperatures,heat losses and combustion efficiencies both increased firstly and then decreased with the increasing ?,and reached their maximums at ?=1 in the single flame condition.Combustion efficiencies and thermal efficiencies increased sharply and the decreased slowly when shifted to double flame mode.At the identical ?,combustion efficiencies under cone-jet mode were higher than other two electrospray modes,the highest combustion efficiency was 93.58%.The heat loss ratios in the two small scale combustors were in the range of 30%~50%,which were much higher than that in the macro scale combustors.Radiation heat loss was dominant of heat losses.The small scale combustor using electrospray technique with single or double meshes can realize fine atomization,evaporation and combustion of liquid ethanol.The droplets diameters and velocities shared the highest homogeneity under cone-jet mode.Cone-jet mode was suitable for the two combustors.The adding of another mesh improved the flammability,combustion efficiency and flame stability.The combustor with double meshes had a better performance than the combustor with single mesh.