The most commonly used form of regenerative braking is where a vehicle’s electric motor is used as an electric generator to capture the vehicle’s kinetic energy, which is otherwise lost as heat when braking.
The generator converts the kinetic energy into electricity that is then fed back into the vehicle’s battery pack where it is stored for later use. New research suggests that pneumatic or air hybrids that instead store the energy as compressed air would be much cheaper to produce than the current crop of EVs and battery-electric hybrids and could halve the fuel consumption of ICE powered vehicles.
Although converting kinetic energy to electricity is the system found in the majority of EV’s and hybrids on our roads, such as the Toyota Prius, there are also systems that allow the kinetic energy to be stored in other forms. Mechanical systems use a flywheel to store it as rotational energy, while hydraulic systems store the energy as pressurized fluid.
Pneumatic systems that store the energy as compressed air are yet another option and it is pneumatic or air hybrid systems that Sasa Trajkovic believes can be used to produce more fuel efficient vehicles. Trajkovic, a doctoral student in Combustion Engines at Lund University in Sweden, did his doctoral thesis on pneumatic hybrid vehicles and he says that compressed air could be used to provide extra power to the engine when starting up and save fuel by avoiding idle operation when the car is at standstill.
For the study the researchers converted heavy duty Scania engines converted to operate as pneumatic hybrid engines. 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. One of the engine inlet valves has been modified to work as a tank valve in order to control the pressurized air flow to and from the pressure tank.