Diesel exhaust is the main source of air pollution in cities
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Liquid nitrogen used to run engine as part of efforts to cut toxic air

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Commercial director of firm spearheading technology says it can compete against diesel

A company is using “zero-emission” liquid nitrogen to run an ancillary engine powering a transport refrigeration unit in an innovation that could slash some types of road traffic pollution.

The move comes as politicians in London are known to be examining whether there is any way of regulating so-called ancillary exhausts serving engines used to run the refrigeration systems of lorries making deliveries to supermarkets.

Many of these are currently far more polluting than the exhaust serving the vehicle itself.

David Sanders, the commercial director of Croydon-based firm Dearman, which has developed the new engine, said: “We think we can compete against diesel on an equal footing. We can easily, we believe, beat all the other zero-emissions solutions, whether you’re using hydrogen fuel cells, batteries or whatever.

“The [supermarket] fleets are going to have to move to zero emissions technologies because of NOx and particulate matter pollution.”

Regenerative braking and particle capture could also help combat the air pollution menace, technical specialists say.

Amid growing alarm about pollution in cities, academics and industry figures have told E&T how they believe the problem could be tackled via engineering fixes unleashed en masse onto vehicles on our roads.

The move to electric cars, often championed as a clean, green alternative, could even worsen it because such vehicles are typically heavier than their fossil-fuelled counterparts.

“When you put a brand new tyre on a car it’s perhaps got 10-15mm of tread on it,” said Tim Barlow, an emissions specialist from the Transport Research Laboratory. “That wears down to about 2mm, and then you’ve got to replace the tyre. All that wear, that’s all gone into the air.”

The heavier a vehicle, the more wear there will be. Drum brakes allow for particles from this part of the car to be relatively safely stored and disposed of, but disc brakes throw up harmful emissions into the atmosphere.

To mitigate this, wheel arches could be enclosed and capture technology deployed.

The type of pollutant known as particulate matter (PM) often contains metals which, when inhaled, can enter the lungs and bloodstream.

“The future is to go with regenerative brakes,” Barlow added. “Hybrid and electric vehicles use the energy from the vehicle to actually drive it. They’re absorbing the energy from the wheels and braking the wheels.

“With regenerative brakes you are not using friction to slow the vehicle down. It’s like engine braking, so you’re winning on both sides. You’re getting energy back and are also not producing wear on your friction brakes.”

Switching to carbon fibre to make vehicles lighter could also help.

“There’s also driver behaviour,” said Barlow. “If you stick to a nice constant speed, you don’t have the acceleration where you wear your tyres out, and you don’t have the braking that wears your tyres and brake pads out.”

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