A detailed knowledge of the fuel injection process is recognized as a key to the design of clean-burning and efficient combustion engines. As standards for pollutant emissions are tightened worldwide, such knowledge becomes more critical. Computer modeling of the combustion process relies on accurate measurements of the spray throughout its lifetime, and in particular knowledge of the near-nozzle region of the spray is of great importance.

A number of techniques have been developed to study the properties of fuel sprays. However, all of these techniques are significantly limited in the region near the nozzle of high-pressure sprays. No mechanical or visible light probe is able to make non-intrusive and quantitative measurements of the spray in this region.

We have been developing techniques to study sprays using synchrotron x-rays from the Advanced Photon Source at Argonne National Laboratory. We are using an intense, monochromatic x-ray beam as a probe to make time-resolved, quantitative measurements, of intermittent fuel sprays. These experiments have demonstrated that x-rays overcome many of the limitations of other techniques, allowing quantitative characterization of the spray with high time and position resolution. The x-ray technique enables us to make a time-resolved mapping of the mass distribution near the spray nozzle, even immediately adjacent to the orifice. With such a mapping of the mass a number of spray characteristics can be determined, such as the fuel volume fraction, the injection rate and total mass, the speed of the leading and trailing edges of the spray, etc. These quantitative measurements should allow more realistic computational modeling of sprays with better predictive power.

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