Effects Of Nozzle Geometry On Characteristics Of Spray And Combustion

The atomization effect of fuel has a very important influence on clean and efficient combustion.Results show that the internal structure parameters of nozzles affect the fuel atomization characteristics directly.In order to investigate the effects of nozzle structure parameters on characteristics of diesel spray and combustion characteristics under the condition of high injection pressure.This thesis respectively studies the effect of injection pressure,ambient pressure and the structure of nozzles on the fuel atomization and combustion characteristics based on a high pressure common rail injection system,a phase doppler particle analyzer system(PDPA),a spray bomb and a constant volume bomb.Through a large number of bench tests and data analysis,the following conclusions can be obtained:The increase of injection pressure can reduce the spray particle size obviously.It also increases the penetration distance and the cone angle.But the increase of ambient pressure has obvious effect on shortening the penetration distance.In addition,the peak cylinder pressure and heat release rate are increased while the injection pressure increased.Meanwhile the combustion duration is shortened,the brightness of flame is reduced and the soot is reduced.The decrease of nozzle diameter directly promoted the decrease of spray SMD.However,it also reduces the penetration distance and spray cone angle.With the decrease of pore size the brightness of spray combustion flame together with the time of combustion decreased.But the combustion heat release rate and cylinder pressure are slightly increased.The ratio of length to diameter of spray hole has complex influence on fuel spray characteristics.When the ratio is less than or equal to 5,the diameter of the spray increases obviously with the increase of the length diameter ratio.When the ratio is greater than 5,with the increase of ratio the overall SMD of spray decreases continuously.The brightness of spray combustion flame decreases with the increase of the ratio of length to diameter.But the duration of combustion the amount of soot is reduced.The K coefficient of nozzle has different effects on the spray and combustion characteristics of fuel.When K<0,the fuel spray cone angle increases with the increase of K coefficient,but the spray particle size decreases gradually.When K>0,the cone angle of spray decreases with the increase of K coefficient,while the SMD of spray increases continuously.The influence of K coefficient on the soot formation characteristics is consistent with the spray characteristics.So the reasonable selection of K coefficient can effectively reduce soot formation.As the space of group-hole increasing,SMD increased firstly and then decreased.The amount of soot formation also showed the same trend.Heat release rate reached a peak when the space of group-hole is 0.2mm.The peak value of the heat release rate between a single hole and the 0.4mm space of group-hole differs a little.