World's first liquid nitrogen hybrid bus makes breakthrough

The world's first hybrid bus to run on both liquid nitrogen and diesel has moved one step closer to being rolled out across the streets of the UK after completing a series of rigorous trials.

A concept artwork of HORIBA MIRA's liquid nitrogen hybrid bus

A concept artwork of HORIBA MIRA's liquid nitrogen hybrid bus

The CE Power bus was built by engineers at HORIBA Mira as part of an Innovate UK consortium. It features a zero-emission engine - made by cooling technology specialists Dearman - which is powered by liquid nitrogen during acceleration to improve air quality.  

The liquid nitrogen - stored in a low pressure insulated cylinder - is warmed up to the point of boiling, at which time it creates enough pressure to drive the multi-cylinder Dearman engine. A diesel engine then kicks in when the bus hits 20mph, the speed at which the bus requires less effort from the engine to operate.

“As the UK wrestles with dangerous levels of urban air pollution, a bus that runs on ‘thin air’ represents a significant breakthrough,” said Dearman commercial director David Sanders.

“The Dearman engine has the potential to significantly improve the efficiency of both buses and HGVs, reducing fuel consumption and cutting pollution. Crucially it can provide a cost-effective alternative to other emerging zero-emission technologies, whose environmental performance if often offset by complexity and cost. This successful trial could be the first step towards rolling out a British innovation to the streets of the UK and around the world.”

Paving the way

The CE Power bus trials were completed at HORIBA MIRA’s engineering facilities in Nuneaton and included components and full system testing along with an engineered drive cycle to simulate a standard bus route with a variety of stops.

The developers stressed the numerous advantages of liquid nitrogen over an electric hybrid bus, such easy refuelling, local production and longer life than batteries.

HORIBA MIRA project technical lead Martin Watkinson said: “The hybrid nature of CE Power demanded a sleek systems integration process. 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.

“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.” 

Fuel-efficient fleets

The adoption of liquid nitrogen to reduce noxious tail-pipe emissions has been trialled by businesses on previous occasions. British supermarket chain Sainsbury's, for instance, last year became the first company in the world to trial a refrigerated delivery truck cooled by a liquid nitrogen powered engine, which was supplied by Dearman.

British retail chain Waitrose, meanwhile, aims to have 50 100% biomethane gas-fuelled trucks operating in its fleet by the end of year, in an effort to lower emissions from its distribution fleet. CNG Fuels, a UK supplier, originally launched the biomethane fuel in December 2016. The fuel is derived from food waste, and Waitrose were joined by John Lewis and Argos in trialling the fuel upon its announcement.

George Ogleby


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