Before embarking on a transcontinental journey, jet airplanes fill up with tens of thousands of gallons of fuel. In the event of a crash, such large quantities of fuel increase the severity of an explosion upon impact. Researchers at Caltech and JPL have discovered a polymeric fuel additive that can reduce the intensity of postimpact explosions that occur during accidents and terrorist acts. Furthermore, preliminary results show that the additive can provide this benefit without adversely affecting fuel performance.
The work is published in the October 2 issue of the journal Science.
Jet engines compress air and combine it with a fine spray of jet fuel. Ignition of the mixture of air and jet fuel by an electric spark triggers a controlled explosion that thrusts the plane forward. Jet airplanes are powered by thousands of these tiny explosions. However, the process that distributes the spray of fuel for ignition—known as misting—also causes fuel to rapidly disperse and easily catch fire in the event of an impact.
The additive, created in the laboratory of Julia Kornfield (BS '83), professor of chemical engineering, is a type of polymer—a long molecule made up of many repeating subunits—capped at each end by units that act like Velcro. The individual polymers spontaneously link into ultralong chains called "megasupramolecules."
Megasupramolecules, Kornfield says, have an unprecedented combination of properties that allows them to control fuel misting, improve the flow of fuel through pipelines, and reduce soot formation. Megasupramolecules inhibit misting under crash conditions and permit misting during fuel injection in the engine.
Other polymers have shown these benefits, but have deficiencies that limit their usefulness. For example, ultralong polymers tend to break irreversibly when passing through pumps, pipelines, and filters. As a result, they lose their useful properties. This is not an issue with megasupramolecules, however. Although supramolecules also detach into smaller parts as they pass through a pump, the process is reversible. The Velcro-like units at the ends of the individual chains simply reconnect when they meet, effectively "healing" the megasupramolecules.
High-speed video showing untreated jet fuel (upper half) and jet fuel treated with 0.3% Caltech polymer (lower half) after a 140 mph projectile impact disperses fuel mist over continuously burning propane torches. The fireball formed by jet fuel is absent for fuel treated with Caltech polymer. Credit: Caltech/JPL
When added to fuel, megasupramolecules dramatically affect the flow behavior even when the polymer concentration is too low to influence other properties of the liquid. For example, the additive does not change the energy content, surface tension, or density of the fuel. In addition, the power and efficiency of engines that use fuel with the additive is unchanged—at least in the diesel engines that have been tested so far.
When an impact occurs, the supramolecules spring into action. The supramolecules spend most of their time coiled up in a compact conformation. When there is a sudden elongation of the fluid, however, the polymer molecules stretch out and resist further elongation. This stretching allows them to inhibit the breakup of droplets under impact conditions—thus reducing the size of explosions—as well as to reduce turbulence in pipelines.
"The idea of megasupramolecules grew out of ultralong polymers," says research scientist and co–first author Ming-Hsin "Jeremy" Wei (PhD '14). "In the late 1970s and early 1980s, polymer scientists were very enthusiastic about adding ultralong polymers to fuel in order to make postimpact explosions of aircrafts less intense." The concept was tested in a full-scale crash test of an airplane in 1984. The plane was briefly engulfed in a fireball, generating negative headlines and causing ultralong polymers to quickly fall out of favor, Wei says.
In 2002, Virendra Sarohia (PhD '75) at JPL sought to revive research on mist control in hopes of preventing another attack like that of 9-11. "He reached out to me and convinced me to design a new polymer for mist control of jet fuel," says Kornfield, the corresponding author on the new paper. The first breakthrough came in 2006 with the theoretical prediction of megasupramolecules by Ameri David (PhD '08), then a graduate student in her lab. David designed individual chains that are small enough to eliminate prior problems and that dynamically associate together into megasupramolecules, even at low concentrations. He suggested that these assemblies might provide the benefits of ultralong polymers, with the new feature that they could pass through pumps and filters unharmed.
When Wei joined the project in 2007, he set out to create these theoretical molecules. Producing polymers of the desired length with sufficiently strong "molecular Velcro" on both ends proved to be a challenge. With the help of a catalyst developed by Robert Grubbs, the Victor and Elizabeth Atkins Professor of Chemistry and winner of the 2005 Nobel Prize in Chemistry, Wei developed a method to precisely control the structure of the molecular Velcro and put it in the right place on the polymer chains.
Integration of science and engineering was the key to success. Simon Jones, an industrial chemist now at JPL, helped Wei develop practical methods to produce longer and longer chains with the Velcro-like end groups. Co–first author and Caltech graduate student Boyu Li helped Wei explore the physics behind the exciting behavior of these new polymers. Joel Schmitigal, a scientist at the U.S. Army Tank Automotive Research Development and Engineering Center (TARDEC) in Warren, Michigan, performed essential tests that put the polymer on the path toward approval as a new fuel additive.
"Looking to the future, if you want to use this additive in thousands of gallons of jet fuel, diesel, or oil, you need a process to mass-produce it," Wei says. "That is why my goal is to develop a reactor that will continuously produce the polymer—and I plan to achieve it less than a year from now."
"Above all," Kornfield says, "we hope these new polymers will save lives and minimize burns that result from postimpact fuel fires."
These gifts are the latest in a decades-long association between the foundation and Caltech that has advanced research and education in fields including sustainable energy, materials science, and applied physics.
"The industrial-academic partnership between Dow and Caltech exemplifies our two institutions' commitment to addressing urgent problems that confront the world," says Thomas F. Rosenbaum, Caltech's president, holder of the Sonja and William Davidow Presidential Chair, and professor of physics. "We are grateful to The Dow Chemical Company Foundation for enabling chemists and chemical engineers to pursue their best ideas in defining areas such as materials chemistry and renewable energy."
One grant will underwrite start-up costs for new faculty members, giving CCE a key advantage in attracting creative, original thinkers. This is especially important funding for CCE—an academic program that has pushed the frontiers of discovery and trained generations of scientific leaders by making every recruitment count. This approach has helped the division build an active faculty that includes three Nobel laureates, four National Medal of Science recipients, one recipient of the National Medal of Technology and Innovation, and 20 members of the National Academies.
The second commitment will help CCE update and maintain equipment shared by all of its scholars—facilities for nuclear magnetic resonance, electron paramagnetic resonance, and mass spectrometry. The funds also will support the cost of teaching graduate students how to use these instruments.
"Dow and Caltech have built a robust relationship, with a history of advancing research that addresses some of society's toughest challenges. These latest grants from the foundation will expand research opportunities, delivering benefits to engineering, the science community, the Institute, and ultimately society," says A.N. Sreeram, Dow's corporate vice president for research and development.
The link between the Institute and Dow stretches back more than 30 years and includes numerous joint research projects as well as steady foundation support for Caltech's Dow Travel Fellowship and Dow's Seminar Series in Organic and Organometallic Chemistry.
In 2009, Dow and Caltech initiated a $4.2 million partnership that fueled investigations aimed at creating solar cells from inexpensive, abundant materials. That same year, Dow's Graduate Fellowship in Chemical Sciences and Engineering was endowed with help from the Gordon and Betty Moore Matching Program.
A $10 million collaboration followed in 2011, providing resources for the Resnick Sustainability Institute at Caltech as well as endowing five graduate fellowships in chemistry and chemical engineering and another five fellowships in energy science. The agreement made Dow a member of Caltech's Corporate Partners Program, which provides a gateway for exchange and productive collaborations between industry and the Institute.
"Caltech's leadership in science education and sustainability research make these grants a perfect fit in advancing innovation and building the workforce of tomorrow," says Rob Vallentine, president and executive director of The Dow Chemical Company Foundation and global director of corporate citizenship at The Dow Chemical Company. "We are pleased to provide resources that enable Caltech faculty and students to advance science and invent important technologies."
Established in 1979, The Dow Chemical Company Foundation contributes to sustainable communities by supporting strategic philanthropic investments to build the workforce of tomorrow and drive innovative global solutions to address the world's most pressing challenges. The foundation is a separately governed private foundation designed to carry out the charitable efforts of Dow.
Caltech undergraduate students returned to campus this week, many after spending the summer working at companies in biotechnology, technology, and finance, among other fields. These students have had the opportunity to learn firsthand about the career opportunities and paths that may be available to them after graduation. They also had the chance to put Caltech's rigorous academic and problem-solving training to the test.
In the summer of 2015, nearly a third of returning sophomores, juniors, and seniors were placed in an internship position through Caltech's Summer Undergraduate Internship Program (SUIP). The program, run through the Institute's Career Development Center (CDC), helps connect current undergraduate students with a wide range of companies and businesses that can provide practical skills and work experiences that give the students an edge in the future job market.
Many undergraduates find paid summer internships through the CDC, says Lauren Stolper, the director of fellowships, advising, study abroad, and the CDC. The center organizes fall and winter career fairs and offers workshops related to finding internships; provides individual advising on internship options and conducting a job hunt for an internship; organizes interviews for students through its on-campus recruiting program; and provides web-based internship listings and company information through Techerlink, its online job-posting system.
Through the formal establishment of SUIP two years ago—thanks, in part, to the initiative of Craig SanPietro (BS '68, engineering; MS '69, mechanical engineering) and with seed money provided by him and three of his alumni friends and former Dabney House roommates, Peter Cross (BS '68, engineering), Eric Garen (BS '68, engineering), and Charles Zeller (BS '68, engineering)—the CDC has been able to dedicate even more time and attention to helping undergraduates secure these important positions, Stolper says.
"Through internships, students have the opportunity to learn more about the practical applications of their knowledge by contributing to ongoing projects under the guidance of professionals," says Aneesha Akram, a career counselor for internship development/advising, who oversees SUIP.
"Completing summer internships help undergraduates become competitive candidates for full-time positions," says Akram. "When it comes to recruiting for full-time positions, companies seek out candidates with previous internship experience. We have found that many large companies extend return offers and full-time conversions to students who previously interned with them."
The infographic at the above right provides a snapshot of Caltech undergraduate internships over this past summer. Students seeking internships for next summer can contact Akram or look at the CDC website for more information.