US scientists master control of hypersonic jet engine with light-based tech

A new NASA-funded study has revealed for the first time that the airflow in supersonic combusting jet engines can be controlled by an optical sensor.

The finding can lead to more efficient stabilization of hypersonic jet aircraft, according to the study carried out by the researchers at the University of Virginia, School of Engineering and Applied Science.

The research allows operators to control airflow at the speed of light when a ‘shock train’ occurs. A shock train is a condition that precedes engine failure within a scramjet engine.

The earlier approach relied on monitoring airflow through a supersonic combusting jet engine using a pressure sensor, while the new breakthrough allows doing the same using an optical sensor.

NASA-funded research

NASA ’s hypersonic jet plane ‘Hyper-X set a record for flying faster than any other aircraft in 2004.

The final X-43A unmanned prototype had set the record in the last test held in November 2004, by clocking a world-record speed of Mach 10, which is 10 times the speed of sound. This type of speed had only been achieved by a rocket previously.

This breakthrough had led to a major shift in jet development – by allowing the leap from ramjets to more efficient scramjets. Although the hypersonic proof of concept was successful, the main challenge was achieving engine control, because the tech relied on old sensor approaches.

However, this new breakthrough by UVA brings some hope for the future X-plane series which can travel at hypersonic speeds.

Apart from showing that airflow in supersonic combusting jet engines can be controlled by an optical sensor, the NASA-funded study also achieved adaptive control of a scramjet engine.

According to the researchers, adaptive engine control systems respond to changes in dynamics to keep the system’s overall performance optimal.

Professor Christopher Goyne, director of the UVA Aerospace Research Laboratory,  said that the country’s aerospace priorities since the 1960s has been to build single-stage-to-orbit aircraft that fly into space from horizontal takeoff like a traditional aircraft and land on the ground like a traditional aircraft.

“Currently, the most state-of-the-art craft is the SpaceX Starship. It has two stages, with vertical launch and landing. But to optimize safety, convenience and reusability, the aerospace community would like to build something more like a 737,” Goyne said .

Optical sensors could be crucial for hypersonic aircraft

“It seemed logical to us that if an aircraft operates at hypersonic speeds of Mach 5 and higher, that it might be preferable to embed sensors that work closer to the speed of light than the speed of sound,” Goyne said.

UVA has several supersonic wind tunnels that can simulate engine conditions for a hypersonic vehicle traveling at five times the speed of sound.

Goyne explained that “scramjets,” short for supersonic combustion ramjets, build on ramjet technology that has been in common use for years.

Currently, like ramjets, scramjet engines need a step-up to get them to a speed where they can intake enough oxygen to operate.

The latest innovation is a dual-mode scramjet combustor, which was the type of engine the UVA-led project tested. The dual engine starts in ramjet mode at lower Mach numbers, then shifts into receiving full supersonic airflow in the combustion chamber at speeds exceeding Mach 5.

No longer limited to information obtained at the engine’s walls, as pressure sensors are, the optical sensor can identify subtle changes both inside the engine and within the flow path.

The tool analyzes the amount of light emitted by a source — in this case, the reacting gases within the scramjet combustor — as well as other factors, such as the flame’s location and spectral content.

First proof of adaptive control

According to a release by the UVA, the wind tunnel demonstration showed that the engine control can be both predictive and adaptive, smoothly transitioning between scramjet and ramjet functioning.

The wind tunnel test, in fact, was the world’s first proof that adaptive control in these types of dual-function engines can be achieved with optical sensors, the release stated.

The team believes optical sensors may be a component of the future plane-like travel to space and back.

This could help in making an all-in-one aircraft that could glide back to Earth like the space shuttles once did.

“I think it’s possible, yeah,” Goyne said. “While the commercial space industry has been able to lower costs through some reusability, they haven’t yet captured the aircraft-like operations. Our findings could potentially build on the storied history of Hyper-X and make its space access safer than current rocket-based technology.”