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High-speed imaging study provides insights into diesel fuel spray behavior
3 September 2013
Researchers at the University of Michigan have used high-speed imaging of diesel injection spray to provide insights into transient fuel spray behavior and to guide the development of the next generation of spray theory and models.
In the study reported in the journal Fuel, they used 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, nitrogen environment at chamber densities of 17.5, 24.2, and 32.7 kg/m3 (±3%) and for fuel-rail pressures of 1,000, 1,500, and 2000 bar (±1.5%). High-speed images of the backlit fuel injection were captured at 100,000 frames per second.
They then used image processing algorithms to determine fuel spray penetration distance and maximum penetration rate as a function of time.
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.
...The early time history of the spray penetration was not sensitive to orifice size, orifice location or chamber density at the conditions studied. However, fuel injection pressure significantly affected the spray-tip penetration and time to spray break-up.—Eagle et al.
The team compared the experimental results for maximum penetration rate and transition time with various quasi-one-dimensional fuel-spray models. The experimental data indicated a power law relationship for the spray-tip penetration at early times in the spray development; however, the experimental results for time to spray break up departed from the model predictions at most of the conditions studied, with the model significantly under-predicting the time for spray transition.
Furthermore, the spray penetration data showed significant fluctuations in the spray geometry at early times. A fuel spray-tip tracking algorithm was developed and the results showed the maximum penetration distance did not occur along the spray center-line during the transient period of injection and the results quantified the angular location of the maximum penetration distance.—Eagle et al.
These data provide valuable new insights into transient fuel spray behavior and will guide the development of the next generation of spray theory and models.
Ethan W. Eagle, Steven B. Morris, Margaret S. Wooldridge (2013) High-speed imaging of transient diesel spray behavior during high pressure injection of a multi-hole fuel injector, Fuel, Volume 116, Pages 299-309, ISSN 0016-2361, doi: 10.1016/j.fuel.2013.07.120
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