Abstract
As recent vehicle industry has focused on global warming and air pollution, high thermal efficiency and eco-friendly engines with low CO2 emission levels have become more attractive. To meet strict future emission regulations, diesel engines are increasing interests due to its high efficiency. Higher injection pressure and multiple injections enable an improvement of air-fuel mixing characteristics and it makes increase of thermal efficiency and reduction of vehicle emissions. Therefore in these days, a piezo type injector with common-rail which has fast response and possibilities of multiple injections in shorter time is adopted for diesel engines instead of solenoid type injector. More powerful performance and accurate engine control are predicted with using piezo injector. Therefore in this paper, injection rate and spray image of multiple injections which are important design parameters for a piezo type injector have been investigated. Interval of injections and a number of injections in multiple injection strategy has been controlled to verify interaction of each injection. Characteristics of multiple injections have been researched through optical process with a high speed camera in a high pressure chamber. Also a method of RMS(Root Mean Square) process has been used for comprehending the distribution of injection easily. As a result, in case of piezo type injector, rapid response of injection was confirmed and spray characteristics of multiple injections were improved; multiple injections were possible in a shorter time interval between each injection. Penetration lengths become shorter and characteristics of evaporation get better.
