Could nitrogen fuel future mobility?
A breakthrough by British inventor in his garage opens way for zero-emissions engines made from plastic.
February 07, 2013
Article at a glance
- Boiling liquid nitrogen drives Dearman engine
- Engine produces no heat so could be plastic
- Potential challenge to hydrogen and electric vehicles
The race towards zero emissions motoring is getting more crowded. As electric and hydrogen-powered vehicles struggle to gain traction, they face new competition: from an engine that runs on liquid nitrogen.
Nitrogen makes up almost four-fifths of the air we breathe. Liquid nitrogen is a plentiful by-product of various industrial processes. It is used in cryogenics, refrigeration and as a smoky garnish for flashy cocktails. It is extremely cheap.
Liquid nitrogen boils at -196 degrees Celsius, releasing large amounts of energy as it turns back into a gas.
Peter Dearman, a British inventor working out of his garage, has found a way to harness that energy to power an engine.
The Dearman engine injects liquid nitrogen into a cylinder together with a mixture of water and antifreeze, which both introduce heat. Within microseconds, the nitrogen boils and expands by over 700 times, exerting enough pressure to drive a piston.
“It is simply expansion that drives the engine,” explains Toby Peters, CEO of the Dearman Engine Company. There is no combustion, nor emissions. The engine gives off cool not heat.
Liquid air, which is cheaper to produce, can also be used but liquid nitrogen’s lower boiling point and greater density give it more punch.
3D printed engines
The fact that the engine stays cool could be a game-changing advantage.
“You don’t have to build it from metal. You can build it from plastic or resin which allows you to think about using future techniques like 3D printing to make the engines,” says Peters.
That would significantly reduce weight, increase fuel efficiency and cut manufacturing costs.
Colin Garner, Professor of Applied Thermodynamics at Loughborough University and an advisor to Dearman Engine Company, estimates that a Dearman engine car could be built at lower cost than a diesel car and a fraction of the price of an electric car.
The Dearman engine is now being developed by engineering consultancy Ricardo, which expects it to “compete with hydrogen fuel cell and battery electric systems in zero emission applications”.
Longer term, the technology could also be suitable for small urban vehicles, the company forecasts. Why only small urban runabouts? Because the energy density of liquid nitrogen is comparatively low, so range will be limited.
Infrastructure in place
Print an engine and fill it up with liquid air? It sounds fanciful, but there are reasons why it might happen.
To begin with, many of the pieces necessary to develop the technology are already in place. The liquefaction plants are already there, supply chains are mature and relatively little new technology or upfront investment is required.
“This is a great innovation story of taking a technology that has been used for decades in one market and applying the thinking to a completely different market,” says Philippa Oldham, Head of Transport and Manufacturing at the UK’s Institution of Mechanical Engineers (IMechE).
Another advantage is that liquid nitrogen can be kept at normal pressure (unlike hydrogen) and can be transported and pumped into vehicles like conventional liquid fuels.
A tank of liquid nitrogen also doesn’t require extra energy to keep cool, just very good insulation.
In the long term, excess renewable energy that can’t be used by the grid, wind power generated at night for instance, could power nitrogen liquefaction plants. The plant would make liquid nitrogen through the night ready to fill up vehicles, at a bus depot for instance, in the morning.
Toby Peters highlights three areas which could benefit from liquid nitrogen or liquid air engines as precursors to the car market:
- Forklift trucks working indoors or in mines where zero combustion and zero emissions are mandatory
- Diesel-powered buses, which lose about half the available energy in waste heat from the radiator. A Dearman engine could capture that heat, converting hot air into power to run air conditioning or electrics
- Refrigerated vehicles, which could leverage the hybrid concept and also utilize the cold exhaust from a Dearman engine to assist with chilling, saving on diesel fuel
If these three prove fruitful, the hope is that carmakers will come calling.