Yoshihito Yasukawa

Quick Response Fuel Injector for Direct-Injection Gasoline Engines

We developed a new injector for direct injection gasoline engines that reduce the exhaust emissions and help to reduce fuel consumption. The newly developed actuator in this injector has two features. One is a bounce-less valve closing mechanism, and the second is quick-response moving parts. The first feature, the bounce-less valve closing mechanism, can prevent ejecting a coarse droplet, which causes unburned gas emission. The new actuation mechanism realizes the bounce-less valve closing. We analyzed the valve motion and injection behavior. The second feature, the quick response actuator, achieves a smaller minimum injection quantity. This feature assists in reducing the fuel consumption under low load engine conditions. The closing delay time of the needle valve is the dominant factor of the minimum injection quantity because the injection quantity is controlled by the duration time of the valve opening. The new actuator movements can be operated with a shorter closing delay time. The closing delay time is caused by a magnetic delay and kinematic delay. A compact magnetic circuit of the actuator reduces the closing delay time by 26%. In addition, the kinematic delay was improved when the hydraulic resistance was reduced by 9%. As a result, the new injector realizes reduction of the minimum injection quantity by 25% compared to a conventional injector.Copyright

Fuel Spray Analysis Near Nozzle Outlet of Fuel Injector During Valve Movement

Reducing the exhaust emissions of gasoline engines is important for the global environment. Coarse droplets during valve moving, late fuel during valve closing of a fuel injector, and fuel films stuck on the wall around the nozzle outlets are all sources of particulate matter (PM). In this work, we analyze these fuel sprays during valve moving timing by means of fuel spray simulation and direct measurement of valve movement. We developed a fuel spray simulation near the nozzle outlets of a fuel injector during valve opening and closing and simulated fuel flow within the flow paths of the fuel injector by a front capturing method while the fuel breakups near the nozzle outlets were mainly simulated by a particle method. The inlet boundary of the fuel injector was controlled to affect the valve motions on the fuel behavior. We developed a technique for directly measuring the valve movement by measuring the valve lift using a thin diameter Doppler laser method and an optical window with high pressure resistance. The simulation results were validated by comparing the simulated fuel breakup near the nozzle outlets with the measured ones, revealing a good agreement between them. By using the valve movement measurement and fuel spray simulation, we found that fuel spray at the valve opening/closing timing had coarse droplets. Moreover, we found that the late fuel had several types of fuel spray that were generated by low speed fuel flow through the nozzles during the bounds of the valve. The effect of the bounds of the valve on the fuel around the nozzle outlets was also clarified by means of experimental results showing the decreasing bounds of the valve. The late fuel of the nozzle outlets decreased with the decreasing bounds of the valve.

Late-Fuel Simulation Near Nozzle Outlet of Fuel Injector During Closing Valve

Late fuel during closing of the valve of a fuel-injector and fuel films stuck on the wall around the nozzle outlets are sources of PM. In this study, we focused on effects of the valve motions on the late fuel and the fuel films stuck on the walls around the nozzle outlets. We previously developed a particle/grid hybrid method: fuel flows within the flow paths of fuel injectors were simulated by a front capturing method, and liquid-column breakup at the nozzle outlets was mainly simulated by a particle method. The velocity at the inlet boundary of a fuel injector was controlled in order to affect the valve motions on the late-fuel behavior. The simulated late fuel broke up with surface-tension around the time of zero-stroke position of the valve, then liquid columns and coarse droplets formed after the bounds of the valve, and finally only coarse droplets were left. We found that the late fuel was generated by low-speed fuel-flows through the nozzles during the bounds of the valve. The effect of the bounds of the valve on the fuel films stuck on the wall around the nozzle outlets was also studied with a simulation that removed the bounds of the valve. The volume of the fuel films stuck on the wall of the nozzle outlets decreased without the bounds of the valve.Copyright

Advanced Numerical Approach to Simulate GDI Sprays Under Engine-Like Conditions

Gasoline direct-injection (GDI) engines provide both higher engine power and better fuel efficiency than port-injection gasoline engines. However, they emit more particulate matter (PM) than the latter engines. Fuel stuck on walls of pistons and combustion chambers forms a high-density region of fuel in the air/fuel mixture, which becomes a source of PM. To decrease the amount of PM, fuel injectors with short length of spray-penetration are required. A fuel-spray simulation was previously developed; that is, the air/fuel-mixture simulation was integrated with the liquid-column-breakup simulation. The developed fuel-spray simulation was used to optimize the nozzle shapes of fuel injectors for gasoline direct-injection engines.In the present study, the factors that influence spray-penetration length were identified by the numerical simulation. The simulation results were validated by comparing the simulated spray-penetration length with the measured ones and revealing good agreement between them. Angle α was defined as that formed between the direction of flow entering the nozzle inlet and the direction of flow leaving the nozzle outlet; in other words, a indicates a change of flow direction. It was found that α and spray-penetration length was closely related. Velocity that are accelerated with a were studied, and it was found that the velocity within a plane perpendicular to the center axis of the nozzle increases with increasing α.Copyright

A Fuel-Spray Simulation Considering Fuel-Jet Breakup Near Fuel Injector and Composition of Air/Fuel Mixture

To simulate multi-scale free surfaces in the fuel spray of an injector for automobile engine, we combined a liquid-film-breakup simulation and an air/fuel-mixture simulation. The liquid-film breakup near the injector outlet was simulated by using a particle method, and the air/fuel mixture after the liquid-film breakup was simulated by using a “discrete droplet model” (DDM). Distributions of droplet diameters and velocities, calculated in the liquid-film breakup simulation, were used as the injection condition of DDM. We applied our new method to simulate the spray from a collision fuel injector. The simulation results were verified by comparing them with measurements. The liquid-film breakup near the injector outlet and the behavior of the air/fuel mixture qualitatively agreed with the measurements. We found that out new method was useful to the fuel-spray simulation for automobile engines.Copyright

Fine Atomization and Low Penetration Fuel Spray by Using a Multi-Swirl Nozzle for Automobile Engines

Improving fuel economy and reducing exhaust emissions of automobile engines have become very important. The direct injection gasoline engine has the advantage of reduced fuel consumption, but it also has disadvantages related to exhaust emissions. Weak mixing of fuel with air due to short mixing time and fuel liquid-film adhering to the engine cylinder walls cause emission problems. To reduce these emissions, injectors need to provide fine atomization, low fuel penetration (length of fuel spray), and spray formation control. In this study, we developed a multi-swirl nozzle that forms a thin liquid-film at the nozzle outlet for fine atomization; the thin liquid-film easily breaks up into small droplets. We investigated the fuel spray characteristics of these nozzles experimentally and numerically. Using a long-distance microscope, we found that a liquid-film formed at the nozzle outlet even if its diameter was small. This is an effect of the centrifugal force from the swirl flow. Experimental results also showed that the multi-swirl nozzle reduced the size of coarse droplets (irregular, large droplets) and shortened fuel penetration. We also simulated numerically the fuel flow of the multi-swirl nozzle. Numerical analysis described the swirling flow that the multi-swirl nozzle generated above the nozzle inlet and the thin liquid-film at the nozzle outlet.Copyright