| With the increasingly prominent environmental problems and energy crisis,the internal combustion engine as the main source of air pollutants and the major consumer of oil resources,its emissions and performance have been more and more concerned by the relevant agencies around the world.At the same time,with the rise of China and other developing countries,human demand for large construction machinery is increasing.China has the largest plateau area in the world,and the plateau area is one of the areas where construction machinery driven by internal combustion engine works most frequently.Its special environmental conditions put forward higher requirements for the normal operation of internal combustion engines.In recent years,partly due to the influence of the plateau environment on the fuel and air mixing in the engine cylinders,problems such as emission deterioration,power performance decline and difficulty in starting often occur during the operation of internal combustion engines in plateau region.Therefore,in order to further investigate the reasons for the deterioration of the working performance of the internal combustion engine in the plateau environment,the spray characteristics of different fuels at high-altitude conditions are tested in this study.Based on the self-built spray visualization experiment platform,four kinds of fuel spray experiments under different working conditions are carried out by direct photography and shadowgraphy.The vapor and liquid phase images of the spray are processed by the MATLAB program,and the specific values of the spray penetration length,cone angle and projection area are obtained.The influence of fuel quality,ambient conditions(ambient pressure and temperature)and fuel injection conditions(injection pressure and pulse width)on fuel spray characteristics are investigated.The experimental results show that at non-evaporative conditions,the influence of fuel quality on spray characteristics mainly depends on the physical and chemical properties of the fuel.If the fuel qualities are not significantly different,the spray characteristics are not significantly different.At evaporative conditions,even a small difference of fuel qualities will have a significant impact on the spray characteristics.In this study,the liquid phase penetration length of No.1 and No.2 fuel is about 10 mm longer than that of No.3 and No.4 fuel when it reaches a steady state;At non-evaporative conditions,when the ambient pressure is increased,the spray penetration length and area both decrease,and the spray cone angle increases.At evaporative conditions,the vapor and liquid phase penetration length and area both decrease when the ambient pressure is increased,and the vapor and liquid phase cone angle does not change much.Increasing the ambient pressure in a small range has a more significant effect on the penetration length of the vapor phase than the liquid phase;Increasing the ambient temperature can promote the evaporation and atomization of fuel droplets,so that the liquid phase penetration length and area reach a steady state in advance.At a lower ambient temperature,the liquid phase penetration length is too long,which is likely to cause “wet wall” phenomenon;At non-evaporative conditions,the spray penetration length and area increase with the increase of fuel injection pressure.At evaporative conditions,the vapor phase penetration length and area increase when the fuel injection pressure is increased,but the liquid phase penetration length and area does not change significantly after reaching a steady state.Increasing the fuel injection pressure can greatly enhance the atomization of fuel and the mixture of fuel and air;At both non-evaporative and evaporative conditions,changing the fuel injection pulse width only affects the duration of fuel spray,without any significant effect on its spray characteristics. |
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