At cruising altitude, planes constantly emit a stream of nitrogen oxides (NOx), gaseous chemical compounds that remain in the atmosphere and produce ozone and fine particles, aerosols, which cause air quality degradation and climate change.
In a study published late last year in the journal Energy & Environmental Science, Massachusetts Institute of Technology (MIT) scientists are proposing the use of an ammonia-based selective catalytic reduction (SCR) system, which can result in an approximately 95% reduction in NOx emissions.
The new concept, which, according to the authors, is capable of eliminating “the problem of air pollution in aviation”, is inspired by the emission control systems already used in trucks and other diesel land transport vehicles. These devices have an after-burn emission control system to reduce the NOx generated by the engines.
The operation of airplanes without pollutant emissions
Current aircraft designs place jet engines mounted below each wing. Each engine receives a turbine that, in turn, drives a propeller to move the plane through the air, while the exhaust flows through the rear, which prevents the use of emission control devices, which could interfere with the thrust of the engines.
In the hybrid-electric, or turbo-electric design, proposed by MIT scientists, the aircraft’s power source remains a conventional gas turbine, but integrated into the cargo hold. This turbine drives an electrical generator (also in the hold) to drive the propellers or fans mounted on the plane’s wing.
SCR was previously unfeasible when core mass flow rates were an order of magnitude higher than diesel engines in trucks, but the current technology trend produces smaller engine cores with lower mass flow rates in the truck. core flow, presents new opportunities for emission control.