Boundary Layer Ingestion: Environmentally Friendly Aviation?

Developed as a way to improve the fuel efficiency of passenger aircraft, could Boundary Layer Ingestion herald a more environmentally friendly air travel industry?

By: Ringo Bones

During the past few years, various aerospace research labs around the world, like NASA’s Glenn Research Center and the University of Cambridge’s Whittle Laboratory, are working on propulsion technology to increase the fuel efficiency of future aircraft and reducing the overall operating cost to consumers and also reducing the overall impact on the environment. Boundary Layer Ingestion (BLI) is a way of improving aircraft efficiency by reducing drag on the aircraft using the aircraft’s own engines. Analytical studies done since 2017 shows that this new technology has the potential to reduce aircraft fuel burn by as much as 8.5-percent compared to aircraft currently flown today. Boundary Layer Ingestion (BLI) could reduce aircraft fuel burn by up to 15-percent but it requires robust fan systems that can operate efficiently with high levels of inlet distortion or turbulence.

With the jet aircraft we are currently using, the engines are typically located away from the aircraft’s fuselage to avoid ingesting the layer of slower flowing air that develops along the aircraft’s surfaces called the boundary layer. The new propulsion system design – i.e. the inlet and the fan – is embedded in the aircraft’s body at the back of the fuselage in order to ingest the slower boundary layer airflow, using it to generate thrust needed to propel the aircraft. Using the slower boundary layer air means the engines do not have to work as hard, so their fuel consumption goes down. At the same time, the drag on the aircraft is reduced, since the engines are now “ingesting” part of that drag, so the overall aircraft fuel efficiency is improved and less thrust is needed by the aircraft to fly at the same speed. This means that the overall aircraft efficiency is higher and less fuel is needed to complete the flight.

According to NASA and the other teams involved in developing this newfangled propulsion concept, the design change is not as simple as it seems, but is actually quite challenging. Boundary layer airflow is highly distorted – as in turbulent – and that turbulence affects the way the fan performs and operates. These new designs require a stronger fan than the ones currently being manufactured by leading plane-makers. The new fan-blade assembly designs require a specialized inlet to help straighten out the turbulent airflow before it gets to the fan and a stronger, more durable fan to resist the constant pounding being applied by the turbulent airflow. As current problems will eventually be overcome, Boundary Layer Ingestion could herald a more environmentally friendly era of aviation before the end of the 2020s.