A new type of hybrid bus — CE Power — that runs on both diesel and liquid nitrogen has successfully completed a series of trials.

Built by engineers at Horiba Mira (www.horiba-mira.com) in Nuneaton as part of an Innovate UK consortium, the bus features a high-efficiency zero-emission Dearman engine that is powered by liquid nitrogen and runs alongside a conventional diesel engine.

The Innovate UK consortium comprised leading industry, academic, local organisations and national governmental organisations.

It was led by Dearman and included Air Products, Cenex, Coventry University, Horiba Mira, the Manufacturing Technology Centre, Productiv Ltd and the Transport Research Laboratory.

The bus uses its hybrid propulsion system to reduce emissions while accelerating after stopping — the part of a bus’s drive cycle that traditionally sees a diesel engine produce significant amounts of NOx and CO₂ emissions.

Because the Dearman engine produces none of these harmful emissions, the bus can make frequent stops and pull away without expelling the same level of damaging pollutants.

While driving below 20mph, the liquid nitrogen — stored in a low-pressure insulated cylinder — is warmed up to its boiling point, creating enough pressure to drive the multi-cylinder Dearman engine.

Once the bus reaches 20mph, the diesel engine kicks in (at this speed, the bus requires less effort from the engine to operate).

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

“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 that see their environmental performance often offset by complexity and cost.

“These successful trials could be the first step towards rolling out a British innovation to the streets of the UK and around the world.”