Effects of Opening and Closing Fuel-Injector Valve on Air/Fuel Mixture

Abstract

Lower engine emissions and improved fuel efficiency have recently become more necessary in automobile engines. Fuel injectors need to be designed to decrease late fuel during valve closing and to deal with multiple injections. Fuel-spray behaviors are controlled by the valve-lifts of fuel injectors; therefore, air/fuel mixture simulations that integrate with inner flow simulations in fuel injectors during the opening and closing of valves are essential for studying the effects of valve motions on air/fuel mixtures. We previously developed a late-fuel simulation near the nozzle outlets of a fuel injector during valve closing; fuel flows within the flow paths of the fuel injector were simulated by a front capturing method, and fuel breakups near the nozzle outlets were mainly simulated by a particle method. The inlet boundary of the fuel injector was controlled in order to affect the valve motions on the late-fuel behavior. In this study, we improved the late-fuel simulation by adding a valve opening function. The motion of droplets within the air/fuel mixture region was calculated by using a discrete droplet model (DDM). The injection conditions for the DDM were defined with the results of the improved late-fuel simulation; positions and velocities of droplets at the injection point were defined by using the results of the late-fuel simulation. The simulation results were validated by comparing the simulated fuel breakup near the nozzle outlets and the air/fuel mixtures in the air region with the measured ones, revealing good agreement between them. The effects of opening and closing the valve on the air/fuel mixtures were also studied; the opening and closing of the valve affected the front and rear behaviors of the air/fuel mixture and also affected spray penetrations. The developed simulation was found to be an effective tool for studying the effects of valve motions on the air/fuel mixtures.