Design & Flow Field Simulation Of A Cyclone Electrostatic Air Filter

Air filters for vehicular engine in common uses at the present time areprimarily including centrifugal type, barrier type, viscous impingement type andinertia type. Because it usually can not satisfy the criterion of the engine intake airquality by only one means, the combination of the two or three of the 4 basalfiltration means mentioned above is often adopted.In recent years, some improved or new air filters, such as constanttemperature control air filter, electron oxygen enhancement air filter and noiseelimination air filter etc, are being studied and tested. However, there are stillproblems existing on the air filter used nowadays:1. The cycle of maintenance and replacing is short.2. The air intake loss is high.Those problems will become much more distinct when concern the vehicleswhich usually work in the dusty area including construction cars and chariot etc. Ifthe air filters can not be maintained and replaced in time, there might be lots of badinfluence, such as the air intake loss increasing sharply, the filtering net bursting,then:1. The dust particle enters the engine, which will damage the cylinder,piston and piston ring, and reduce the life of the engine.2. The air intake loss is high and the volumetric coefficient of the engine isdecreased, which may result in high air-fuel ratio and more fuel consumption,which will greatly affect the performance and fuel economy of the engine.As the vehicle engine is developing to be with high velocity, low weightand environment-protected, the air filter is developing to be low air intake loss,environment-protected and long life.As the research on the cyclone-electrostatic filtering technology is deeperday after day, many scholars have applied this technique on the filtering equipment.Although the frame model and corona electrode layout of the studying objects arenot same, the similar result that the electricity can enhance the general filteringefficiency of the cyclone, especially for the tiny dusts, is educed.However, research on the application of cyclone electrostatic technique tothe air intake and exhaust systems of the vehicle engine is few, nevertheless, thesame conclusion that application of the filtering style combinating the cyclone andelectrostatic filtering style together to the air filter for collecting dust is a better way,is got.If the cyclone electrostatic air filter is produced, it will be specialized withthese characteristics as following:1 the cyclone and electrostatic filtering styles acting on the dusts together inthe same space at the same time, so this air filter volume is relatively small;2 using the cyclone can filter the big dusts, and clean the electrodes, whichwill prolong the life of the air filter;3 the effect of the electrostatic can enhance the driving force of the dusts,and also can filtering the dusts with the diameter from 7 μm to 40 μm twicewhich make the most serious damage to engine;4 in this air filer, the electric force and centrifugal force act on the dustsdirectly rather than taking advantage of the dust gravity and fiber obstructing, so airintake loss is small and invariable.5 the oxygen in the intake air can produce ozone in the electrostatic field,which will decompose to be oxygen molecule and oxygen atom. This oxygen atomhas strong oxidation, and can accelerate the burning of the fuel.In a word, this cyclone electrostatic air filter has great research anddevelopment value.To the air filters' problems existed at present, a lot of information about thecharacters of dust property in the heavy dust area and the particle diameter whichhave a great influence on the life of the engine, is read, finding that in the conditionthe vehicles travel, the basic ingredient of the dust are SiO2, Al2O3, Fe2O3 as wellas a few calcium, magnesium, natrium and the compound of other elements, quartzis 65%~95% which is the most in the dust and the electronic resistivity of the dustis within the range of 3×107? ·cm to 1×1013? ·cm. it can be found from the dataof the makeup of the dust that there are 50%~60% of the dust radius between10 μm to 30 μm , and approximately 4%~10% particle is with the radius less than5 μm . Moreover, the particle with the radius around 7~40 μm makes the mostdamage to the engine, and should be completely filtered out.Though analyzing sorts of mechanisms and characteristics of dust filteringdevices in industry, the similar goal of using the dust filtering devices in industryand the air filter on the vehicle is found. Both of them could filter dust and clean air.Moreover, there are more filtering means in industry. In these means, theelectrostatic filtration could collect and filtrate the particle with the diameter morethan 0.05 μm and electric resistance in the range of 104~1013? ·cm, and is withlower air intake loss. However, it only fits for the airflow with particle less than60g/m3. Considering the dust property in the area the vehicles travel and thecharacters of so many kinds of filtering mechanism, the filtering means combiningcyclone with electrostatic is chosen for this new cyclone-electrostatic air filter. Inthis air filter, the cyclone dust filtering element could reduce the dust thickness andmake the collecting electrostatic electrodes keep clean, and the electrostaticelement could filter the small dust.For the sake of the limited fixing space on the vehicles, Buell structuredesign scale is chosen for the structure design, which has the smaller whole volume.According to the intake air requirement of the Dragoon 300 Wheeled ArmoredVehicle's 6V-53T engine, the air filter whose vent-pipe's inserting depth is 80mm isdesigned. However, taking accounting of the vent-pipe insert depth's influence tothe efficiency of the air filter and the corona electrode layout, the flow fields in thethree kinds of air filter are modeled and simulated respectively, whose insertingdepths are 80mm, 120mm and 200mm, obtaining the pressure distribution, velocityvector, and particle movement tracks of the two kinds of particles whose diametersare 20 μm and 2 μm as well. Through analyzing the results of the simulation, it isfound that, without taking the effect of the electricity wind into account, the airintake loss in this air filter is much lower than the air intake loss criterion, and thestructure, whose vent-pipe's inserting depth is 120mm, is adopted as the basalframe of the two filtering elements in this paper.Based on the fixed frame of this air filter, the corona electrode, collectingelectrode and the power system are designed. It can be known from the dustmoving track figure that, although the dusts with the diameter 2 μm are forced intothe collecting box, they may be out. Consequently, the scheme that the coronaelectrode extends into the collecting box is brought forward, which is used forrestraining the dust to raises again. The dimension, material and initial voltage ofthe corona electrode is given. Meanwhile, the structure figure of power system andoverall frame drawing of the air filter are provided. Through electric fieldsimulating, the electric field intensity and voltage distribution figure is obtained. Itis indicated that, when calculating the air intake loss of the cyclone electrostatic airfilter, neglecting the effect of the electric wind is reasonable.Finally, the approach to calculating the filtering efficiency of the cyclonicand electrostatic elements is introduced, and qualitative analysis of thiscyclone-electrostatic air filter' filtering efficiency is made, which indicates that thefiltering efficiency of this cyclone electrostatic air filter is higher than theconventional cyclone air filter.