A hybrid bus, called CE Power, running on both diesel fuel and liquid nitrogen has completed a series of trials. The bus is the first to be powered by liquid nitrogen and was built by engineers at HORIBA MIRA as part of a consortium in the United Kingdom.
The CE Power features a nitrogen-powered Dearman Engine alongside a conventional diesel engine.
The bus uses a hybrid propulsion system to reduce emissions during acceleration after stopping. This portion of the bus’ drive cycle traditionally has a heavy impact on the diesel engine and can produce large amounts of NOx and CO2 emissions. As the Dearman Engine produces none of these harmful emissions, it will enable the bus to continue to stop frequently to unload and pull away from a bus stop without expelling the same level of damaging pollutants.
While driving at 20 mph or below, the liquid nitrogen—stored in a low pressure insulated cylinder—s 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 as at this speed the bus requires less effort from the engine to operate.
The Innovate UK consortium comprised industry, academic and local and national governmental organisations. It was led by Dearman and included Air Products, Cenex, Coventry University, HORIBA MIRA, Manufacturing Technology Centre, Productiv Ltd, and TRL (the Transport Research Laboratory).
The benefits of using liquid nitrogen over an electric hybrid bus include a much longer life, local production and easy refueling. Batteries, which power many of the UK’s electric hybrids, require changing several times over the course of a bus’s lifetime, whereas the liquid nitrogen system will last the lifetime of the bus, Dearman said. 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. Furthermore, refueling liquid nitrogen can take a matter of minutes, enabling the bus to return to the road in a short timeframe.