TransForum Vol. 8, No. 1

The liquid breakup of a high-density stream from a fuel injector as imaged with ultrafast synchrotron x-ray full-field phase contrast imaging at Argonne’s X-ray Operations and Research beamline 32-ID. The internal structure of the nozzle is visible, as well as the liquid jets emanating from the two orifices.

New X-ray Technique May Lead to Better, Cleaner Fuel Injectors for Automobiles

Standard microscopy and visible light imaging techniques cannot peer into the dark centers of dense-liquid jets, which keep scientists from fully understanding liquid breakup in devices such as automobile fuel injectors.

Argonne physicist Kamel Fezzaa and his colleagues, along with collaborators from Visteon Corp., developed a new, ultrafast technique to look through high-speed dense liquids using high-energy X-rays from Argonne’s Advanced Photon Source (APS).

“Research in this area has been a predicament for some time, and there has been a great need for accurate experimental measurement,” Fezzaa said. “Now we can capture the internal structure of the jet and map its velocity with clarity and confidence, which wasn’t possible before.”

A key to the experiment was taking advantage of the special properties of the X-ray beam generated at the APS. Unlike hospital X-rays, APS X-rays are a trillion times brighter and come in very short pulses with durations as little as 0.1 nanoseconds. The new technique has the ability to examine the internal structure of materials at high speed, and is sensitive to boundaries. Multiphase flows, such as high-speed jets or bubbles in a stream of water, are ideal systems to study with this technique. Other applications include the dynamics of material failure under explosive or ballistic impact, which is of major importance to transportation safety and national security, and material diffusion under intense heat.

This work is highlighted in the Advance Online Publication of the journal Nature Physics (see http://www.nature.com/nphys/ journal/vaop/ncurrent/index.html).

Calculations proved that sprays from modern direct injectors are atomized only a few millimeters from the nozzle. As shown here, the breakup immediately at the nozzle exit is verified by the detailed 3-dimensional reconstruction of a fuel spray.

Earlier Fuel Spray Research

In earlier efforts, a number of “first ever” results occurred when Argonne researchers at the Advanced Photon Source, working with Visteon Corp. and Cornell University, used ultrafast monochromatic X-tomography to study the near-field, multi-orifice gasoline direct injection sprays. The effort yielded, for the first time ever, a highly quantitative characterization of the dynamic mass distribution in the spray with very precise time resolution.

Also, calculations proved that sprays from modern direct injectors are atomized only a few millimeters from the nozzle. As shown here, the breakup immediately at the nozzle exit is verified by the detailed 3-dimensional reconstruction of a fuel spray. However, a more thorough understanding of the fuel breakup and spray formation process required higher temporal and spatial resolutions in the X-ray images. This work is described in the accompanying article.

May 2008