Visible Research On Diesel Spray Field And Numerical Simulation

Diesel engine is used widely for its potential of promotion of power and lowing fuel cost. Facing gradually strict emission standard and energy crisis, in order to achieve clean and effective combustion in diesel engine, the diffuse combustion model of diesel must be deeply grasped due to characteristics of power, fuel consumption and emission affected by combustion process. However fuel injection, atomization and mixture formation process are the important aspect of impact on combustion process.It is unavoidable for present-day diesel that spray impinges on the chamber wall. After impinging a portion of fuel would stick on the surface and causes lower diffusivity and emission deterioration, so some researchers avoid spray impinging on the wall in during design, however, others consider impinging can enhance mixture formation ratio, improve fuel distribution in the chamber and accelerate combustion process.Based on the theoretical analysis, visualization experiment and simulation are adopted as research approach, main contents are listed below.On the one hand, visualization test system is established and spray field characteristics are obtained by the test system. Spray cone, penetration and concentration are analyzed by program which is designed by author. Free spray without obstacle, spray impinging on wall and chamber surface is observed, the result show that after injection timing 0.5ms, the much thicker film and richer mixture are formed after fuel impinging on the wall and the thick of oil film is 2.0mm, which will deteriorate the combustion. On the other hand, fuel impingement is beneficial to droplet breakup and vapor. Oriented arc changes the flow field in the cylinder. The air movement near the wall is enhanced and eddy distribution is more reasonable, improving mixture formationOn the other hand, combined with experiment data, spray and mixture process are simulated by STAR-CD software. Results show that contracted chamber and sharp convexity should be adopted to enhance air flow and promote mixture. Fuel impingement is used to accelerate fuel atomization. The film thickness should be reduced and have a thin distribution widely.