Effects Of Pressure Waves On Twi-injection Characteristics In High Pressure Common Rail Injection System

High pressure common-rail(HPCR)system aims at providing fuel with steady pressure to the injectors.However,it turns out that there will still be some pressure waves inside high pressure pipes which connect rail and injectors even the pressure inside the rail is rather steady.In order to research the pressure waves inside the pipes,the emergence and development of pressure waves,and the effects of pressure waves on injection characteristics under twi-injection were investigated.A pressure wave model was used to analyze the effects of system parameters on pressure wave.A HPCR test system with only one piezo-injector was designed and set up.A flow meter was used to study the relationship between pressure wave and injection characteristics,including injected fuel mass and injection rate.An optical test system was set up,among which a spray visualization system was used to study the effects of pressure waves on spray development.A Phase Doppler Anemometry(PDA)system was used to study the relationship between pressure waves and atomization characteristics,including particle size and velocity.The results show the followings.Parameters of pressure wave model will make some difference on pressure wave profiles.The compression and rarefaction waves generated during injection period will increase and decease the injection pressure.When the high pressure pipe is short,the frequency of pressure wave will increase.Variation of injection intervals only affect the phase and amplitude,but not the frequency.The value of rail pressure will not affect the phase and frequency but amplitude of pressure waves.The pressure wave will make difference on the spray shapes,such as the change of penetration lengths of pilot and main injection.After pilot injection and before main injection,pressure waves with different injection intervals will be overlapped to be a curve family.Once the main injection starts,the corresponding curve will be separated from the curve family.The pressure drop during main injection period will be compensated by the pressure rise caused by the pilot injection.The injection pressure will influence the needle lift to cause a throttling effect.Pressure wave may make the main injected fuel mass vibrates regularly,which owns to the pressure compensation and needle throttling effect.The spray atomization characteristics will be influenced by the needle throttling effect.When the injection pressure is high,needle throttling effect was obvious,and the spray particle velocity will decrease and particle size will increase.The injection pressure only provide the spray an initial velocity.When the spray is apart from the nozzle orifice,it will no longer be influenced by injection pressure,but determined by the air friction.