| Diesel engines are still widely used in agricultural production,vehicle transportation,engineering machinery,and military power because of their advantages such as high horsepower,high fuel efficiency,and good reliability.Compared with the compression ignition type,the ignition type has the advantage of large power-to-weight ratio in the application of small displacement engines.However,with the increasing pollution of the environment and the stricter emission regulations of various countries,achieving clean combustion of diesel is the only way out for the development of diesel engines.In order to improve the economy and emissions of small diesel engines,air-assisted injection has attracted much attention because of its advantages of reducing charge loss caused by scavenging,reducing hydrocarbon emissions and improving fuel consumption.Although air-assisted diesel injection undergoes secondary atomization and evaporation,it is unknown whether the fuel can be atomized well because the ambient temperature and pressure are not high;and because of the low-pressure injection,the spray and combustion performance of the fuel are more sensitive to environmental parameters and injection control parameters.Therefore,exploring the spray and combustion characteristics of air-assisted injection under different conditions is of great significance to the optimization and matching of engines with large changes in the working environmentThis thesis focuses on the ignition air-assisted injection technology,and studies the spray and combustion characteristics of diesel fuel under different operating parametersThe thesis used high-speed imaging technology to observe the macroscopic characteristics of the spray,and found that increasing environmental pressure,increasing the injection pulse width or increasing the oil pressure difference can reduce the spray penetration distance and increase the spray cone angle,and the impact of increased environmental pressure is more obvious.Changing the air pulse width has no significant effect on spray morphology.Increasing the interval of oil and air has little effect on the spray penetration distance,but it is more likely to generate turbulent vortex clusters,causing a sharp increase in the cone angle during the spray process,which is the result of the premixed diesel fuel causing turbulent movement of air in the spray and the constant volume bomb.The thesis used high-speed schlieren photography method to observe its combustion characteristics,record pressure changes.It was found that the larger the injection pulse width,the faster the instantaneous pressure rise of the constant volume bomb-holding,the higher the pressure peak,the higher final exposure area.Under the test conditions in this thesis,compared with the ignition delay of 4ms,diesel combustion occurs faster in 1ms,but the former has a higher-pressure peak,indicating that diesel combustion is more adequate.The thesis provides basic experimental research on spray and combustion of air-assisted injection system,and provides positive guidance for the calibration of air-assisted injection system,in-cylinder mixed air organization,and reliable lean combustion. |
