Yoshihiro Sukegawa

In-cylinder airflow of automotive engine by quasi-direct numerical simulation

Abstract A Computational Fluid Dynamics (CFD) program for in-cylinder airflow analysis has been developed by the authors. The feature of the developed program is that it treats turbulence flow with the quasi-direct numerical simulation (Quasi-DNS). So it is possible to present transient turbulence eddy motions in detail. For fast and high quality mesh generation, the Voxel method was employed. The computational domain is discretized by uniform cubic cells in this method. The simulation results were verified by two benchmark tests. One of them in common use is a backward step flow test, the other is an in-cylinder flow test that supposed the engine induction stroke. Good agreement was obtained between the simulation and the experimental results of these benchmark tests.

Numerical analysis for mixture formation in direct fuel injection spark ignition engines

Abstract Influences of fuel-spray specifications on mixture formation of direct fuel injection spark ignition engines were studied. Fuel-spray, mixture and combustion gas behavior was calculated by numerical simulation and the following results were obtained. The amount of attached fuel on a piston for the stratified charge mode is less using skewed type spray than for non-skewed type spray. This leads to faster flame propagation near the piston surface.

Applying Particle/Grid Hybrid Method to Fuel Spray With Collision Jet for Automobile Engines

A fuel spray contains multi-scale free surfaces: liquid films formed at the fuel-injector outlet, ligaments generated by the liquid-film breakup, and droplets generated from the ligaments within the air/fuel mixture region. To simulate multi-scale free surfaces, we previously developed a fuel spray simulation combining the liquid-film breakup with the air/fuel mixture. In this study, we modified a part of the liquid-film breakup simulation that uses a particle/grid hybrid method. The procedures combining a particle method and a grid method were changed to obtain more accurate prediction. First, a simple benchmark test, collapse of a water column as investigated by Martine and Moyce, was used to verify the modified simulation method; the behavior of the water column better agreed with measurements than that by the original method. Next, we applied the modified method to simulate the collision jets from three kinds of nozzles. The simulation results were verified by comparison with measurements; the predicted liquid-film breakup qualitatively agreed well with measurements. Furthermore, the errors of mean droplet-diameters between the simulations and the measurements were less than 12%. Therefore, we found that the modified method was effective for spray simulation.Copyright

Fuel Spray Simulation With Collision Jets for Automobile Engines

Fuel injectors for automobile engines atomize fuel into multi-scale free surfaces: liquid films formed at the fuel-injector outlet, ligaments generated by the liquid-film breakup, and droplets generated from the ligaments within the air/fuel mixture region. We previously developed a fuel spray simulation combining the liquid-film breakup near the injector outlet with the air/fuel mixture. The liquid-film breakup was simulated by a particle method. The fuel-droplet behavior in the air/fuel mixture region was simulated by a discrete droplet model (DDM). In this study, we applied our method to simulate fuel sprays from a fuel injector with collision jets. The simulation results were compared with the measurements—the mean diameter of droplet in spray, D32 , was 35 percent larger than measured D32 . We also studied the effects of DDM injection conditions on the spray distribution in the air/fuel mixture region—diameter distributions of injected DDM-droplets were given by the liquid-film breakup simulation, or by Nukiyama-Tanazawa’s theory. The diameter distribution of droplets near the injector outlet was found to affect the spray distribution within the air/fuel mixture region, mainly around the leading edge of spray.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