Hybrid-electric plane that ‘scrubs’ exhaust before ejecting it into the atmosphere could reduce emissions of harmful nitrogen oxides by 95 percent, MIT engineers claim


Harmful emissions of nitrogen oxides from aircraft could be cut by up to 95 percent using a new hybrid-electric design that scrubs the exhaust clean, a study claimed. Nitrogen oxides, or 'NOx', linger in the air to produce ozone and fine particulates — and are associated with asthma, respiratory diseases and cardiovascular problems.

Experts have warned that NOx pollution from the global aviation industry is responsible for some 16,000 premature deaths each year. Inspired by the emissions scrub-bers used in diesel trucks, the aircraft concept from the Massachusetts Institute of Technology could cut these deaths by 92 percent.

The design would offer a less polluting alterative to larger aircraft which are too large, at present, to be completely electric powered, the team said. Like those of aeroplanes, the engines of trucks also produce NOx emissions — the release of which is limited by so-called post-combustion emissions-control systems which use catalysts to convert NOx in the exhaust into nitrogen and water.

In jet aircraft, however, the exhaust is what gives the plane thrust — with air sucked into the fro-nt of the engine being compressed by giant fan blades before fuel is injected into it and ignited, causing it to heat up, expand and shooting out the back.

On the way out of the engine, the hot exhaust drives a turbine which drives the compressor fans, allowing the process to continue. Given this configuration, any attempt to make use of an emissions-control device in a jet engine would interfere not only with the exhaust composition but also its role in propelling the aircraft forward and, by extension, keeping it aloft.

To get around this, aeronautics researcher Steven Barrett of the Mas-sachusetts Institute of Technology(MIT) and colleagues propose instead to relocate the gas turbine part of the engine into the fuselage, where its exhaust could be scrubbed. This would then drive a generator to supply power to electric propellers attached to the plane's wings — as to produce the necessary thrust to fly.'This would still be a tremendous engineering challenge, but there aren’t fundamental physics limitations,' said Professor Barrett.

If you want to get to a net-zero aviation sector,this is a potential way of solving the air pollution part of it, which is significant. The approach, he added, comes 'in a way that’s technologically quite viable.' According to the researcher's cal-culation, a hybrid-electric aeroplane on the scale of a Boeing 737 or an Airbus A320 would only require around 0.6 per cent more fuel to fly the plane, given the extra weight of the engine configuration.

'This would be many, many times more feasible than what has been proposed for all-electric aircraft,' explained Professor Barrett.'This design would add some hundreds of kilograms to a plane, as opposed to adding many tons of batteries, which would be over a magnitude of extra weight.''The research that’s been done in the last few years shows you could probably electrify smaller aircraft, but for big aircraft, it won’t happen anytime soon without pretty major breakthroughs in battery technology,' Professor Barrett said.

'So I thought, maybe we can take the electric propulsion part from electric aircraft, and the gas turbines that have been around for a long time and are super reliable and very efficient — and combine that with the emissions-control technology that’s used in automotive and ground power to at least enable semi-electrified planes.'The team imagines the emissio-nscontrol system using a catalyst with a pleated structure that would maximise the available surface area while taking up only a limited amount of space in the craft's fuselage. With their current study complete, the team are now working on designs for a 'zero-impact' airplane that could fly without emitting both nitrogen oxides and other climate-altering compounds like carbon dioxide.

We need to get to essentially zero net-climate impacts and zero deaths from air pollution,' said Professor Barrett.'This current design would effectively eliminate aviation’s air pollution problem. We’re now working on the climate impact part of it.'The full findings of the study were published in the journal Energy and Environmental Science.

Mail Online dissects the impact greenhouse gases have on the planet - and what is being done to stop air pollutionEmissionsCarbon dioxideCarbon dioxide (CO2) is one of the biggest contributors to global warming. After the gas is released into the atmosphere it stays there, making it difficult for heat to escape - and warming up the planet in the process.

It is primarily released from burning fossil fuels such as coal, oil and gas, as well as cement production. The average monthly concentra-tion of CO2 in the Earth's atmosp-here, as of April 2019, is 413 parts per million (ppm). Before the Industrial Revolution, the concentration was just 280 ppm. Nitrogen dioxide The gas nitrogen dioxide (NO2) comes from burning fossil fuels, car exhaust emissions and the use of nitrogen-based fertilisers used in agriculture.

Although there is far less NO2 in the atmosphere than CO2, it is between 200 and 300 times more effective at trapping heat.Sulfur dioxide Sulfur dioxide (SO2) also primarily comes from fossil fuel burning, but can also be released from car exhausts.SO2 can react with water, oxygen and other chemicals in the atmosp-here to cause acid rain. Carbon monoxide Carbon monoxide (CO) is an indirect greenhouse gas as it reacts with hydroxyl radicals, removing them. Hydroxyl radicals reduce the lifetime of carbon dioxide and other greenhouse gases.

Health impactWhat sort of health problems can pollution cause?According to the World Health Organization, a third of deaths from stroke, lung cancer and heart disease can be linked to air pollution. Some of the effects of air pollution on the body are not understood, but pollution may increase inflammation which narrows the arteries leading to heart attacks or strokes.

Particulates find their way into the lungs and get lodged there, causing inflammation and damage. As well as this, some chemicals in particulates that make their way into the body can cause cancer.

Deaths from pollution Around seven million people die prematurely because of air pollution every year. Pollution can cause a number of issues including asthma attacks, strokes, various cancers and cardiovascular problems.

Asthma triggersAir pollution can cause problems for asthma sufferers for a number of reasons. Pollutants in traffic fumes can irritate the airways, and particulates can get into your lungs and throat and make these areas inflamed.

Problems in pregnancy Women exposed to air pollution before getting pregnant are nearly 20 percent more likely to have babies with birth defects, research suggested in January 2018.Previous research suggests this causes birth defects as a result of women suffering inflammation and 'internal stress'.