Analysis of a novel mild air hybrid engine technology, RegenEBD, for buses and commercial vehicles

In this paper, a novel cost-effective mild air hybrid engine concept for buses and commercial vehicles, RegenEBD, is presented. This air hybrid technology is designed to convert kinetic energy into pneumatic energy of the compressed air stored in the air tank normally installed on such vehicles. The compressed air can then be used to drive an air starter to achieve regenerative stop-start operations for buses and delivery vehicles with frequent stop-start operations. For other commercial vehicles, it can provide service air required for braking and pneumatic operations and reduce the usage of the engine driven compressor. Furthermore, the availability of the free compressed air can be used to provide instant boost to a turbocharged engine at start-up and during acceleration for better performance and improved fuel economy. A six-cylinder diesel engine has been modelled to operate as a mild air hybrid engine and analysed using an engine simulation programme. In addition, a newly developed air hybrid vehicle driving cycle simulation programme has been applied to analyse the charging and discharging processes during a typical London Bus route and a German Braunschweig city cycle. The analysis shows that with the RegenEBD, almost all the idling periods can be eliminated through regenerative stop-start operations, resulting in a fuel saving of 6.5-7.2%.