| Marine diesel engine has become the main propulsion device for marine ships because of its high power,good economy and high durability.The process of fuel fragmentation and evaporation directly determines the quality of combustion process,which has an important impact on power performance and emission performance,especially in the face of more and more stringent emission regulations of marine diesel engine.Compared with vehicle diesel engine,the injector of marine low-speed diesel engine usually has a larger orifice and a large pressure chamber structure to achieve higher fuel injection rate,The different nozzle structure will inevitably affect the spray phenomenon.However,the experimental research on the spray characteristics of marine diesel engine is still scarce.In addition,the atomization characteristic parameters are an important reference for the design and development of low-speed engine combustion system,and can also calibrate and verify the effectiveness of the calculation model.In addition,the intersecting hole nozzle with small diameter has been proved to be an effective structure to improve the atomization effect,while the research on the intersecting hole nozzle with large diameter has not been carried out.In this paper,a spray visualization experimental platform for marine fuel injectors was built.Direct photography and shadowgraphy were used to carry out spray experiments on four different diameter nozzles and six intersecting hole nozzles with different intersecting angles and sub apertures under different environmental conditions(ambient temperature,ambient pressure)and injection conditions(injection pressure and injection pulse width).A MATLAB program was used to process images,and the spray characteristics such as spray tip penetration and spray cone angle were obtained,and the influence rules of various factors were compared and analyzed.The results show that the nozzle has a small pressure coefficient and the injection duration is longer than the injection pulse width due to the large pressure chamber structure.Under non-evaporating condition,with the increase of injection pressure,the spray penetration distance and spray area increase,the fuel break-up time becomes shorter and the break-up distance remains constant.Under evaporating condition,with the increase of injection pressure,the time and distance of fuel break-up increase,the spray cone angle decreases,and the evaporation rate increases.Higher ambient pressure results in shorter spray tip penetration,larger spray cone angle and faster evaporation rate.Higher ambient temperature indicates a faster evaporation rate;For the straight hole nozzles,the initial velocity of the fuel injected by the nozzles with different apertures is equal;With the increase of nozzle diameter,the time and distance of spray break-up increase,and the spray tip penetration is longer after breaking up.Under evaporating condition,the evaporation phenomenon of smaller aperture orifice is much more intense.The time and distance of liquid spray reaching quasi-steady state are shorter,while the evaporation phenomenon of larger aperture nozzle is weaker. |
