Air/pneumatic hybrids work by using vehicle braking energy to compress air and charging a high pressure air tank, which can then be used to drive the engine. This is a great technology that can be easily applied with conventional internal combustion engines running on gasoline, alcohol, diesel or propane/natural gas bringing about improved fuel efficiency. The above article describes experimental research being carried out at Lund Univeristy in southern Sweden, where the research team adapted some Scania truck engines for the study.
Here is a link to the PhD thesis of Sasa Trajkovic on the subject which he defended in January 2011, entitled “The Pneumatic Hybrid Vehicle – A New Concept for Fuel Consumption Reduction“.
Sasa Trajkovic also calculated that 48 per cent of the brake energy, which is compressed and saved in a small air tank connected to the engine, could be reused later. This means that the degree of reuse for air hybrids could match that of today’s electric hybrids. The engine does not require any expensive materials and is therefore cheap to manufacture. What is more, it takes up much less space than an electric hybrid engine.
Research on air hybrid IC engines are also being carried out at other universities including ETH in Switzerland (Swiss Federal Institute of Technology Zurich), Orléans in France and the Scuderi Engine company.
The success of this technology will come from its low cost and largely mechanical implementation. It does not require high technology computer control or electronic parts or batteries which are expensive and cause damage to the environment during manufacture or disposal. Batteries and the associated electrical equipment tend to be heavy.
According to the abstract of Trajkovic’s thesis
During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration (compressor mode) and during vehicle acceleration the engine can be operated as an air-motor driven by the previously stored pressurized air (air-motor mode). The compressed air is stored in a pressure tank connected to one of the inlet ports.
Vehicle drive cycle simulations showed that the fuel consumption of a conventional bus could be reduced by up to 58% when converted to a pneumatic hybrid bus.
The air hybrid technology is ideal for vehicles that make frequent stops, such as buses, postal vehicles, and generally all vehicles that are driven around in cities.