Study On The Influence Of Shock Wave And Soot Oxidation Process In Diesel High-pressure Spray

Shipping and Marine engineering account for up to 25% of the transport industry,and diesel engines are still the main source of power for ships,whose emissions have accelerated the melting of Arctic ice and caused a host of environmental problems.At present,there are many researches on soot emission from vehicle diesel engines,but few studies on soot generation and oxidation process under high background pressure and density in the cylinder of Marine diesel engines.IMO is developing regulations on soot emission from ocean-going ships,so it is necessary to study soot generation and oxidation process under high background pressure and density to provide reference for soot emission reduction technology.In this paper,aiming at the spray visualization experimental research of high background density in Marine diesel cylinder,an experimental platform with constant volume combustor as the core device is built.Based on Lab VIEW software of NI equipment,the control system of constant volume Combustor is designed,and the high temperature and high pressure working environment in the diesel cylinder is simulated with constant volume combustor.The oil injection rate was measured and analyzed based on Zeuch method,and the image of diesel spray was obtained and processed by single light Schlieren method.The spray and shock wave morphology under different working conditions were analyzed,and the macro characteristics such as spray penetration distance and spray cone Angle were studied.The CFD spray model was calibrated with the spray experimental data,and the effects of injection pressure and oxygen concentration on the formation and oxidation of carbon smoke in diesel jet were studied based on the constant-volume combustion bomb combined with PSM carbon smoke model.For the spray characteristics under the condition of high background density,it is found that the spray develops more rapidly with the increase of injection pressure,and the penetration distance of spray increases at the end of injection.With the increase of background gas density,the development of spray along the axis is slower,and the penetration distance of spray decreases,while the spray cone Angle has no obvious uniform law.With the increase of injection pressure and background density,the shock cone Angle increases.For the carbon fume formation and oxidation process of high pressure diesel jet simulated by CFD,it is found that diesel jet combustion has two stages: premixed combustion and diffusion combustion,and diffusion combustion is the main combustion.With the increase of background density,the larger the spray cone Angle,the larger the enrolling air volume,the lower the equivalent ratio,which is more conducive to combustion and soot oxidation,the ignition delay period and the overall combustion duration are shortened,and the carbon soot nucleation mass is increased.With the increase of oxygen concentration,the duration of fuel combustion is shortened,and the influence of background density on soot generation quality and soot generation quality is reduced.With the increase of injection pressure,the amount of air entrainment,momentum exchange and oil-gas mixing rate increases,and the generation of soot decreases at low oxygen concentration,while the generation of soot is basically unchanged at high oxygen concentration.The volume fraction of soot particles in 2-3 equivalent ratio interval and 1600-1800 K temperature interval is the largest,and the nucleation and surface reaction of soot particles are more likely to occur.The number density of soot particles in 1-2 equivalent ratio interval and2000-2400 K temperature interval is the largest,and the oxidation of soot is more likely to occur.Diesel combustion is more likely to generate soot particles in the range of 2-3 equivalent ratio and 1600-2400 K temperature.Therefore,the larger injection pressure,oxygen concentration and lower background gas density are conducive to the atomization and full combustion of diesel spray in the diesel cylinder,reduce the generation of soot,accelerate soot oxidation and improve emissions.