Dieselgate inspires NOx-reducing plane design from MIT

What’s happening? Scientists at MIT have designed a system that could capture nitrogen oxide (NOx) emissions from aircraft, reducing them by 95%. The concept moves the gas turbines that usually drive the jet engines inside the plane’s cargo hold, enabling NOx to be captured in a separate system and releasing clean air back into the atmosphere. The turbines inside the hold power generators that then drive electric motors on the wings to provide propulsion. The team said their design would add “hundreds of kilograms” to a plane and would require just 0.6% in additional fuel, unlike electrification, which would add tonnes of weight from batteries.

Why does this matter? As well as producing CO2, which plane manufacturers are looking to tackle through electrification or using hydrogen, airplane engines also create NOx, which can create ozone in the upper troposphere and affect pollution at ground level and at airports. Aviation-related NOx emissions have been shown to result in 16,000 deaths a year.

Dieselgate inspired – The MIT system’s design was partly inspired by truck-based catalytic converters after the researchers investigated the health impacts of NOx emissions following Volkswagen’s dieselgate scandal.

It places the turbines in the central cargo hold as housing emissions-control devices on wing engines would limit aircraft thrust. The design, while an engineering challenge, is not limited by the laws of physics, according to the researchers. If it were implemented across the world they estimate 92% of aviation air pollution-related deaths would be avoided. The researchers are now looking at whether the design can be modified to also capture CO2.

Coasting on winds – There are other less-technical methods to reduce aviation’s environmental impact, such as flying more efficiently. Another academic study published this week shows that better satellite coverage over the North Atlantic will enable further optimisation of flight routes to exploit favourable winds, reducing fuel burn and lowering emissions. This could have a far greater short-term impact than technological-based fuel efficiency improvements, according to the researchers.

Is it as straightforward as just reducing NOx? In conventional aircraft, more fuel-efficient engines actually increase NOx pollution, while actions to tackle NOx emissions can increase CO2 emissions. A further recent study published in Nature looks at this trade-off and concludes that, from a climate perspective, promoting fuel efficiency at the expense of increased NOx emissions is a preferable strategy to limit global warming.