| Because GDI gasoline engine (gasoline direct injection) has obvious advantages in terms of energy saving and emissions than traditional PFI engine (port fuel injection), GDI gasoline engine has become mainstream of gasoline engine technology. Spray characteristics has a very direct impact on combustion and emissions performance of GDI gasoline engine, and the deposit produced in high-temperature environment will affect the engine’s spray characteristics. Therefore, the study of the influence of deposit on GDI gasoline engine’s spray characteristics has great significance for guiding the development of the GDI engine’s combustion system.A set of experiment equipment had been designed and made which including constant volume combustion bomb, optical platform, high pressure oil supply system, high pressure nitrogen gas system, heating and temperature control system, circuit control system and high-speed photography system and so on. MATLAB software had been used to write the program which is used to process the spray image of the test. The process mainly includes:import the image, remove the background of the image, display image, image segmentation, image edge and corrosion, the refining of image edge, extract the image edge, calculate the spray cone angle and penetration, analyzed and summarized the influence of the injector deposit on the spray characteristics.This study researched the influence of the injector deposit on the spray characteristics with a high pressure (2MPa) constant volume combustion bomb by four kinds of different deposit levels of gasoline injectors, and four different injection pressure which are 4MPa,5MPa,6MPa,and7MPa respectively. Experimental results show that:1. While the injection pressure is low, the injector without deposit or the injector with a little deposit had a better degree of atomization than the other two. When the injection pressure gets higher, all the injectors has a better degree of atomization, the injector with middle deposit and the injector with much deposit improve significantly.2. Compared with the injector of no deposit, the injector with lots deposit is more prone to splitting mist in the process of spray development. There is a large gap between the oil beam and the uniformity of spray is poor.3. With the deepening of the carbon deposit of fuel injectors, the initial spray cone angle shows an increasing trend. But when the deepening of the carbon deposit comes to a certain extent, the spray cone angle will become smaller. A fuel injector with higher injection pressure will corresponding to have a larger spray cone angle.4. While the injection pressure is under 5MPa, the spray penetration of the four injectors from small to large in the order:the injector without deposit< the injector with middle deposit≤ the injector with much deposit< the injector with a little deposit.When the injection pressure gets higher, the injector without deposit and the injector with the most deposit had larger spray penetration than other two injectors.5. At the injection pressure during 4 to 7MPa, all of the spray penetration of the injector is increasing rapidly before 2000us, but this trends becomes slowly after 2000us. When the injection pressure increases sequentially from 4MPa to 7MPa, the trends of moderate carbon injector spray penetration showing increases and then decreases again after the first increase. The values of the spray penetration that severe carbon injectors spray fuel at initial stage (1000us) for different injection pressure is scattered, while the other three injectors are more concentrated distribution.The curve of the spray penetration of severe carbon injector fuel injection pressure in 4MPa is similar to the curve in 5MPa, the curves show a similar trends for 6MPa and 7MPa, but when the injection pressure rises from 5MPa to 6MPa, the spray penetration improves significantly. |
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