Feature Sidebars: Transportation Research

Yang Shao-Horn: Lightweight Lithium-Air Batteries
Professor Yang Shao-Horn leads the Electrochemical Energy Lab (EEL), which, among other things, is working to develop efficient lithium-air (Li-O2) batteries for electric cars. Because Li-O2 batteries utilize oxygen for energy storage instead of the heavier transition metal-based materials in today’s batteries, they represent the potential to create a lightweight battery with up to three times the energy density of standard lithium-ion batteries. Professor Shao-Horn’s research group has pursued a strategy that combines fundamental characterization and electrode materials design to help address the efficiency challenges. In one project, the group developed a vertical carbon-fiber-based electrode, increasing the amount of void space – essential for maximizing the amount of discharge product and energy that can be stored – up to roughly 90% compared with approximately 60% in more conventional electrodes. The electrode structure enabled one of the highest gravimetric energy densities, 2400 Wh/kg electrode, to be realized to date.

Pedro Reis: Wrinkling for Drag Reduction
Associate Professor Pedro Reis and his team have studied how wrinkling occurs on curved surfaces and found regular dimpled patterns similar to the topography on golf balls. Their rough surface allows them to fly farther compared to a ball with a smooth surface. This occurs because the dimpled pattern holds the airflow close to the ball for longer, thus reducing the size of the downstream turbulent wake that is the major source of aerodynamic drag. The advantage of the mechanism developed by Professor Reis’s group is that the depth of the dimples of their morphable surfaces – and consequently the effect for reducing the aerodynamic drag – can be switched and tuned on-demand by reducing the pressure of inner cavities. This discovery could be used to reduce drag on automobiles at certain speeds and improve fuel efficiency.

Ken Kamrin: Driving on Sand
Assistant Professor Ken Kamrin has been working on large-scale models of sand flow for most of his career. Granular materials, which have the odd characteristic of behaving like a solid and a liquid without actually changing phase, have not been understood to nearly the same extent as water or elastic solids. When he and graduate student Jake Slonaker ‘15 looked at a recent empirical model that was able to predict the resistive force of sand against arbitrarily shaped objects, they found to their surprise an invariance in the system that tipped them off to the idea that a general scaling law could exist that relates different granular locomotion problems to each other. Scaling relations are commonly used in fluids contexts such as aerodynamics and ocean engineering but have not been available for granular materials due to their complexity. Along with undergraduate student Carrington Motley (read more about Carrington here), and with aid of equipment in MIT’s Robotic Motility Group, Professor Kamrin’s team has verified their scaling relation in many experiments that used their newly created scaling law to successfully relate the performance of different wheels. They are now developing models that can optimize tire designs for ideal driving in sand. Their scaling relation, through an ability to scale gravity, could potentially allow NASA to simulate how a tire will behave on Mars and then optimize a design specifically for that environment.

Amos Winter: A Clutchless, Hybrid Supercar
Last year, Assistant Professor Amos Winter and MIT alum Franco Cimatti SM ’82, Technical Director of Vehicle Concepts and Predevelopment Manager at Ferrari, partnered up around an idea that could have a profound effect on the engineering of supercars: What if you could decrease their weight and increase their performance by hybridizing the vehicle and packaging the electric drivetrain components directly into the transmission? Professor Winter posed the question to his students in 2.76: Global Engineering, with the following requirements: Maintain the weight and size of the existing transmission and take advantage of the functionality of two electric motors in as many ways as possible. The students proposed an innovative concept that no one, especially Ferrari, had expected: Remove the clutch from the transmission entirely by using the electric motors to control the engagement of the engine to the drivetrain instead. The students built a prototype that demonstrated all the core functionality and showed through simulation that the concept could maintain all the features consumers want from a hybrid supercar – a quick launch, stationary charging, mobile charging, and an option to switch to electric only. PhD candidate Daniel Dorsch, SB ’12, SM ’14, who has mentored the Ferrari team in 2.76 for the past two years, is continuing the project for his PhD research.