High-Speed Imaging of Transient Diesel Spray Behavior during High-Pressure Injection of a Multi-Hole Fuel Injector

摘要

Reliable prediction of spray penetration and spray break-up is required to achieve increases in fuel efficiency and reduction of emissions in diesel engines. Of particular interest is the early transient-flow regime. In the current work, diesel fuel spray development was studied using high-speed imaging of a high-pressure diesel common-rail fuel injector mounted in a spherical constant volume combustion chamber. The fuel injector nozzle had four holes aligned on a radial plane with diameters of 90, 110, 130, and 150 μm. Fuel was injected into a room temperature T = 298 K (±1.5%), nitrogen environment at chamber densities of 17.5, 24.2, and 32.7 kg/m~3 (±3%) and for fuel-rail pressures of 1000, 1500, and 2000 bar (±1.5%). Images of the backlit fuel injection were captured at 100,000 frames per second. Image processing algorithms were used to determine fuel spray penetration distance and maximum penetration rate as a function of time. The experimental results for maximum penetration rate and transition time are compared with various quasi-one-dimensional fuel-spray models. The experimental results show departure from the model predictions at higher chamber densities and injection pressures at early times in the spray development. Furthermore, the spray penetration data show 2-dimensional spray geometry changes at early times. A fuel spray tip tracking algorithm was developed to show the maximum penetration distance does not occur along the jet center-line during the transient period of injection and to quantify the angular location of the maximum penetration distance. The data provide valuable insights into transient fuel spray behavior and guide the development of the next generation of spray theory and models.