Dearman hybrid bus completes trials

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Running on diesel and liquid nitrogen, the Dearman hybrid bus has successfully completed rigorous trials.

Team CV

A revolutionary hybrid bus that runs on both diesel and liquid nitrogen, powered by the UK-developed Dearman engine, has completed rigorous trials, bringing it one-step closer to the road. Expected to accelerate the use of liquid nitrogen for primary power, the hybrid bus – CE Power – has turned out to be the world’s first commercial vehicle of its kind to be powered by liquid nitrogen. Built by engineers at Horiba Mira as part of an Innovate UK consortium, the bus utilises alternative propulsion to address urban air pollution challenges and features a high-efficiency, zero emission Dearman engine, powered by liquid nitrogen, alongside a conventional diesel engine. The hybrid system enables the bus to reduce noxious tail-pipe emissions, improving local air quality. With the Innovate UK consortium comprising of leading leading industry, academic and local and national governmental organisations like Dearman, Air Products, Cenex, Coventry University, Horiba Mira, Manufacturing Technology Centre, Productiv Ltd, and TRL (Transport Research Laboratory), the CE Power uses a hybrid propulsion system to reduce emissions during acceleration.

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As part of a bus’ drive cycle, acceleration traditionally has a heavy impact on the diesel engine as it moves away from standstill. The engine can produce vast amounts of nitrogen oxide and carbon dioxide emissions, which are harmful. As the Dearman engine produces none of these harmful emissions, it will enable the bus to continue to frequently stop to unload and pull away from a bus stop without expelling the same level of damaging pollutants. Whilst driving at 20 mph or below, 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. Once the bus reaches 20 mph, the diesel engine will kick in. It is at this speed that the bus requires less effort from the engine to operate.

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Completed at Horiba Mira’s engineering facilities and Proving Ground in Nuneaton, UK, recently, 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. Expressed Martin Watkinson, Technical Lead on the project at Horiba Mira, “The hybrid nature of CE Power demanded a sleek systems integration process. Our engineers worked to ensure the liquid nitrogen system operated 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 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,” he averred.

The Dearman engine at Dearman in Croydon. 20th July 2015.

The Dearman engine at Dearman in Croydon. 20th July 2015.

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 bus’ 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. Refuelling liquid nitrogen can take a matter of minutes, and enables the bus to return to the road in a short timeframe. Mentioned David Sanders, Commercial Director at Dearman, “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, 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.”