Hybrid powertrains that use compressed air to help power a vehicle could dramatically improve the fuel economy, particularly in cities and urban areas where the traffic conditions involve a lot of starts and stops. In such conditions, a large amount of fuel is needed to accelerate the vehicle, and much of this is converted to heat in brake friction during decelerations. Capturing, storing and reusing this braking energy to produce additional power can therefore improve fuel efficiency. In this study, three approaches towards air hybrid powertrains are proposed and analyzed. In the first approach, an energy recovery valve or two shut-off valves connected to a convenient access hole on the engine cylinder is proposed to enable the cylinder to operate as a regenerative compressor and/or expander when required. In the second approach, one of the exhaust valves in an engine equipped with a Fully Variable Valve Actuation (FVVA) system is pneumatically or hydraulically operated as a dedicated gas transfer valve connected to an air reservoir. The third approach combines the advantages of the conventional valvetrain’s simplicity with emerging production technologies. In order to achieve this, two well established technologies are used in addition to valve deactivation; Variable Valve Timing (VVT) and/or Cam Profile Switching (CPS). Provided that a conventional, camshaft-operated variable valvetrain is used, the need of adopting fully variable valve actuation is eliminated and thus only minor modifications to the engine architecture are required. The aforementioned concepts are described in details. Some basic principles of their operation are also discussed in order to provide a better understanding on how fuel economy is achieved by means of engine hybridization and regenerative braking. Both experimental and computational results are presented and compared. Finally, a vehicle and driveline model, which simulates the operation of a typical passenger vehicle in urban driving conditions and predicts the efficiency of the energy regeneration, has been set up and used to study the effects of the application of each air hybrid concept on the vehicle’s energy usage throughout the New European Driving Cycle (NEDC) and the 10-15 driving cycle. The results have shown that each concept involves the optimization of valve timing for the best regenerative energy recovery and its subsequent usage. For the modelled vehicle, it has been shown that any of the three concept engines is capable of providing more braking power than needed during every deceleration and braking process, especially throughout the urban driving part of each cycle. The recovered braking energy in the form of compressed air has proved to be always sufficient to start the engine, if stop-and-start engine operation strategy is to be adopted.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:557678 |
| Date | January 2007 |
| Creators | Psanis, Christodoulos |
| Contributors | Zhao, H. |
| Publisher | Brunel University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://bura.brunel.ac.uk/handle/2438/3218 |
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