Rocket man

In a single hand, William Sirignano can hold his newly created combustor, the fuel-burning component of a jet engine.

It’s not with exceptional physical strength but with his extraordinary knowledge of jet and rocket engine fuels that he has devised a mini-combustor that fits in a cylinder less than a centimeter in diameter.

His palm-size combustor can produce anywhere from 10 watts to 10 kilowatts of energy. Connected to the appropriate turbine engine, the device could meet the mobile energy needs for anyone from a camper to a soldier in the field.

Sirignano, professor of mechanical and aerospace engineering, and chemical engineering and materials science in The Henry Samueli School of Engineering, managed a feat that has defied the efforts of many other engineers. It is a considerable breakthrough, but with his recent election to the elite National Academy of Engineering, perhaps not so surprising.

After decades of studying liquid fuels, with a particular interest in their function in space rockets and jet engines, Sirignano collected his first patent with the mini-combustor.

While his research may be complex, the reason for holding this single patent over his distinguished career, he says, is relatively simple. “Most of my work is theoretical and computational rather than experimental. Basically, I model systems with a combination of mathematical methods and large-scale computing.”

In essence, Sirignano provides the framework that other engineers utilize to build everything from better fighter jets to space rockets. But for once, Sirignano, along with his colleague, engineering professor Derek Dunn-Rankin, can claim the invention rather than supplying the shoulders upon which others could stand.

Earlier attempts to develop small combustors failed because, as the combustors tested got smaller, they became less efficient, losing a greater degree of energy through their walls. Rather than concentrate on the containment structure, Sirignano decided to work on how the fuel functioned inside the device.

“The new patent we have says how you should apply the liquid and therefore avoid those energy losses and maintain the efficiency,” he says.

William Sirignano started studying engineering during the Sputnik era of the 1950s, when rocket science was taking off. In keeping with his times, Sirignano decided to devote himself to rockets and jet engines, which led him to study propulsion.

“I became interested in combustion and fluid mechanics and their underlying science. I’ve been largely in this field ever since.”

An engine operates by mixing fuel with air and allowing the mixture to burn. The combustion drives an engine, which in turn creates the propulsion that puts a vehicle in motion.

But Sirignano sees much more.

“In the combustors of jet engines and liquid-propellant rocket engines, the machines are literally spraying millions of droplets of fuel that are very small. The droplets go into the combustor and are vaporized. The action going on in and around these droplets significantly influences engine performance.

“Trying to model these actions computationally is difficult because there is so much information. The data has to be reduced to a simpler, mathematical form that can still capture the phenomena, which is one major thing I’ve done.

“Others have worked on this issue, either by studying a particular droplet and how it works or by looking at a flow field of spray and how that works on a larger scale. I’ve tried to connect the larger-scale phenomena with the smaller-scale in a physically meaningful, yet computationally feasible way.”