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Topic Name: Scientists have Developed New X-ray Technique to Peer Through High-Speed Dense Liquids Using High-Energy X-rays

Category: Optical imaging

Research persons: Argonne National Laboratory Scientists

Location: Argonne National Laboratory, U.S. Department of Energy, United States

Details

Standard microscopy and visible light imaging techniques cannot peer into the dark and murky centers of dense-liquid jets, which has hindered scientists in their quest for a full understanding of liquid breakup in devices such as automobile fuel injectors.

Scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory have developed a technique to peer through high-speed dense liquids using high-energy X-rays from Argonne's Advanced Photon Source (APS).

“The imaging contrast is crisp and we can do it orders of magnitude faster than ever before,” Argonne X-ray Science Division physicist Kamel Fezzaa said.

Fuel injector efficiency and clean combustion is dependent on the best mixture of the fuel and air. To improve injector design, it is critical to understand how fuel is atomized as it is injected. However, standard laser characterization techniques have been unsuccessful due to the high density of the fuel jet near the injector opening. Scientists have been forced to study the fuel far away from the nozzle and extrapolate its dispersal pattern. The resulting models of breakup are highly speculative, oversimplified and often not validated by experiments.

“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.”

Fezzaa and his colleagues, along with collaborators from the Mayo Clinic and Visteon Corp. developed a new ultrafast synchrotron X-ray full-field phase contrast imaging technique and used it to reveal instantaneous velocity and internal structure of these optically dense sprays. This work is highlighted in the Advance Online Publication of the journal Nature Physics.

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, the synchrotron x-rays are a trillion times brighter and come in very short pulses with durations as little as 100 nanoseconds.

“The main challenge that our team had to overcome was to be able to isolate single x-ray pulses and use them to do experiments, and at the same time protect the experimental setup from being destroyed by the overwhelming power of the full x-ray beam,” Fezzaa said.

Their 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.

Note for Fuel Injection
A fuel injection system is designed and calibrated specifically for the type(s) of fuel it will handle: gasoline (petrol), Autogas (LPG, also known as propane), ethanol, methanol, methane (natural gas), hydrogen or diesel. The majority of fuel injection systems are for gasoline or diesel applications. With the advent of electronic fuel injection (EFI), the diesel and gasoline hardware has become similar. EFI's programmable firmware has permitted common hardware to be used with multiple different fuels. For gasoline engines, carburetors were the predominant method to meter fuel before the widespread use of fuel injection. However, a wide variety of injection systems have existed since the earliest usage of the internal combustion engine.
The primary functional difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on the vacuum created by intake air rushing through it to add the fuel to the airstream.
The fuel injector is only a nozzle and a valve: the power to inject the fuel comes from farther back in the fuel supply, from a pump or a pressure container.
The functional objectives for fuel injection systems can vary. All share the central task of supplying fuel to the combustion process, but it is a design decision how a particular system will be optimized. There are several competing objectives such as:
power output 
fuel efficiency 
emissions performance 
ability to accommodate alternative fuels 
reliability 
driveability and smooth operation 
initial cost 
maintenance cost 
diagnostic capability 
range of environmental operation 
Certain combinations of these goals are conflicting, and it is impractical for a single engine control system to fully optimize all criteria simultaneously. In practice, automotive engineers strive to best satisfy a customer's needs competitively. The modern digital electronic fuel injection system is far more capable at optimizing these competing objectives than a carburetor.

Note for High Energy X-rays
High Energy X-rays or HEX-rays are very hard X-rays, with 80 keV - 1000 keV typically one order of magnitude higher in energy than conventional X-rays. They are produced at modern synchrotron radiation sources such as the beamline ID15 at the ESRF. The main benefit is the deep penetration into matter which makes them a probe for bulk samples in physics and materials science and facilitates sample environment and operation in air. Scattering angles are small and diffraction directed forward allowing for simple detector setups.
High Energy X-Rays (HEX-rays) between 100 and 300 keV bear unique advantage over conventional hard X-rays, which lie in the range of 5-20 keV. They can be listed as follows:
High penetration into materials due to a strongly reduced photo absorption cross section. The photo-absorption strongly depends on the atomic number of the material and the X-ray energy. Several centimeter thick volumes can be accesses in steel and millimeters in lead containing samples. 
The Ewald sphere has a ten times smaller curvature than in the low energy case and allows to map whole regions in a reciprocal lattice, similar to electron diffraction. 
Access to diffuse scattering. This is absorption and not extinction limited at low energies while volume enhancement takes place at high energies. Complete 3D maps over several Brillouin zones can be easily obtained. 
High momentum transfers are naturally accessible due to the high momentum of the incident wave. This is of particular importance for studies of liquid, amorphous and nanocrystalline materials as well as PDF-analysis. 
Simple diffraction setups due to operation in air. 
Diffraction in forward direction for easy registration with a 2D detector. 
Negligible polarization effects due to relative small scattering angles. 
Special non-resonant magnetic scattering. 
LLL interferometry. 
Access to high-energy spectroscopic levels, both electronic and nuclear. 
Forward scattering and penetration make sample environments easy and straight forward. 
Neutron-like, but complementary studies combined with high precision spatial resolution. 
Cross sections for Compton scattering are similar to coherent scattering or absorption cross sections.

About Advanced Photon Source
The Advanced Photon Source (APS) at Argonne National Laboratory is a national synchrotron-radiation light source research facility funded by the United States Department of Energy, Office of Science, Office of Basic Energy Sciences. Argonne National Laboratory is managed by UChicago Argonne, LLC, which is composed of the University of Chicago, Jacobs Engineering Group Inc. and BWX Technologies, Inc. (BWXT).
Using high-brilliance X-ray beams from the APS, members of the international synchrotron-radiation research community conduct forefront basic and applied research in the fields of materials science, biological science, physics, chemistry, environmental, geophysical, planetary science, and innovative X-ray instrumentation.
Electrons are produced by a cathode that is heated to about 1,100°C (2,000°F). The electrons are accelerated to 99.999% of the speed of light in a linear accelerator. From the linear accelerator, the electrons are injected into the booster synchrotron. Here, the electrons are sent around an oval racetrack of electromagnets, providing further acceleration. Within one-half second, the electrons reach 99.999999% of the speed of light. Upon reaching this speed, the electrons are injected into the storage ring, a 1,104 meter (3 622 ft) circumference ring of more than 1,000 electromagnets.
Once in the storage ring, the electrons produce x-ray beams that are available for use in experimentation. Around the ring are 40 straight sections. One of these sections is used to inject electrons into the ring, and four are dedicated to replenishing the electron energy lost though x-ray emission by using 16 radio-frequency accelerating cavities. The remaining 35 straight sections can be equipped with insertion devices. Insertion devices, arrays of north-south permanent magnets usually called "undulators," cause the electrons to oscillate and emit light in the invisible part of the electromagnetic spectrum. Due to the relativistic velocities of the electrons, that light is Lorentz contracted into the x-ray band of the electromagnetic spectrum.

The research was funded by DOE's Office of Basic Energy Sciences as part of its mission to foster and support fundamental research to expand the scientific foundations for new and improved energy technologies and for understanding and mitigating the environmental impacts of energy use, and by a laboratory-directed research and development grant.

Argonne National Laboratory brings the world's brightest scientists and engineers together to find exciting and creative new solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America 's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

In figure 1, Advanced Photon Source facility

In figure 2, The liquid breakup of a high-density stream from a fuel injector can easily be seen using an X-ray technique developed at Argonne National Laboratory. The technique could lead to better and cleaner fuel injectors.