Engineering news

Nitrogen-diesel hybrid bus finishes trials

Liz Wells

The world’s first hybrid bus to run on diesel and liquid nitrogen has moved a step closer to hitting the roads after completing trials.

The bus, called CE Power, was built by engineers at Horiba MIRA as part of an Innovate UK consortium led by Dearman and including Air Products, Cenex, Coventry University, Manufacturing Technology Centre (MTC), Productiv, and the Transport Research Laboratory.

The bus uses an alternative propulsion system to address air pollution and features a high-efficiency, zero-emission Dearman engine, powered by liquid nitrogen, alongside a conventional diesel engine.

When driving at 20mph or below, the liquid nitrogen – stored in a low-pressure insulated cylinder – is heated to boiling point, when it creates enough pressure to drive the multi-cylinder Dearman engine. Once the bus reaches 20mph, the diesel engine kicks in as at this speed the bus requires less effort from the engine to operate.

The benefits of using liquid nitrogen over an electric hybrid bus include a much longer life, local production and easy refuelling. Batteries, which power many of the UK’s electric hybrids, require changing several times over the course of a vehicle’s lifetime, whereas the liquid nitrogen system will last the lifetime of the bus.

Liquid nitrogen can be produced locally without the need for neodymium or lithium, which are both used by motors and batteries and sourced from overseas. In addition, refuelling liquid nitrogen can take a matter of minutes, enabling the bus to return to the road quickly.

“Our engineers worked to ensure the liquid nitrogen system operates seamlessly and safely with the diesel engine, in addition to carrying out the whole-vehicle thermodynamics modelling and the overall vehicle control and testing,” said Martin Watkinson, technical lead on the project at Horiba MIRA.

“The completion of these trials paves the way for the use of liquid nitrogen more widely in the automotive sector, and takes the UK one step closer to stamping out harmful emissions for good.”

The trials included components and full system testing along with an engineered drive cycle to simulate a standard bus route with a variety of stops.

Jonathan Reid, technical lead on the project at the MTC, said: “The project has enabled the consortium to begin the journey of advancing the UK cryogenic supply chain from a niche industry to one capable of mass manufacture.”

Mike Hawes, SMMT chief executive, told Professional Engineering: "The UK is home to a thriving engine design and manufacturing sector and, as a significant investor in R&D, is well placed to lead the charge toward ultra-low emission vehicle development – whether this be in the form of ever more efficient and low emission combustion engines or other propulsion systems.

"This progression will continue with ever greater diversity as manufacturers continue to create new innovations to suit different driving needs. The biggest change to air quality will be achieved by encouraging uptake of the latest, lowest emission technologies, regardless of vehicle or fuel type, and ensuring road transport can move smoothly.”

The first application of Dearman technology was a zero-emission transport refrigeration unit which started commercial trials last year. Other applications of Dearman technology include a back-up cold and power system for the built environment, and a waste-heat hybrid drive system for trucks and buses. 

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