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Brunel University

1. Lee, Cho-Yu. Computational and experimental study of air hybrid engine concepts.

Degree: PhD, 2011, Brunel University

The air hybrid engine absorbs the vehicle kinetic energy during braking, stores it in an air tank in the form of compressed air, and reuses it to start the engine and to propel a vehicle during cruising and acceleration. Capturing, storing and reusing this braking energy to achieve stop-start operation and to give additional power can therefore improve fuel economy, particularly in cities and urban areas where the traffic conditions involve many stops and starts. In order to reuse the residual kinetic energy, the vehicle operation consists of 3 basic modes, i.e. Compression Mode (CM), Expander Mode (EM) and normal firing mode, as well as stop-start operation through an air starter. A four-cylinder 2 litre diesel engine has been modelled to operate in four air hybrid engine configurations so that the braking and motoring performance of each configuration could be studied. These air hybrid systems can be constructed with production technologies and incur minimum changes to the existing engine design. The regenerative engine braking and starting capability is realised through the employment of an innovative simple one-way intake system and a production cam profile switching (CPS) mechanism. The hybrid systems will allow the engine to be cranked by the compressed air at moderate pressure without using addition starters or dedicated valves in the cylinder head. Therefore, the proposed air hybrid engine systems can be considered as a cost-effective regenerative hybrid powertrain and can be implemented in vehicles using existing production technologies. A novel cost-effective pneumatic regenerative stop-start hybrid system, Regenerative Engine Braking Device (RegenEBD), for buses and commercial vehicles is presented. RegenEBD is capable of converting kinetic energy into pneumatic energy in the compressed air saved in an air tank using a production engine braking device and other production type automotive components and a proprietary intake system design. The compressed air is then used to drive an air starter to achieve regenerative stop-start operations. The proposed hybrid system can work with the existing vehicle transmission system and can be implemented with the retro-fitted valve actuation device and a sandwich block mounted between the cylinder head and the production intake manifold. Compression mode operation is achieved by keeping the intake valves from fully closed throughout the four-strokes through a production type variable valve exhaust brake (VVEB) device on the intake valves. As a result, the induced air could be compressed through the opening gap of intake valves into the air tank through the intake system of proprietary design. The compressed air can then be used to crank the engine directly through the air expander operation or indirectly through the action of an air starter in production. A single cylinder camless engine has been set up and operated to evaluate the compression mode performance of two air hybrid concepts. The experimental results are then compared with the computational output with…

Subjects/Keywords: 621.4; Air hybrid engine; Regenerative efficiency; Engine brake; Kinetic energy; Fuel consumption improvement

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APA (6th Edition):

Lee, C. (2011). Computational and experimental study of air hybrid engine concepts. (Doctoral Dissertation). Brunel University. Retrieved from ;

Chicago Manual of Style (16th Edition):

Lee, Cho-Yu. “Computational and experimental study of air hybrid engine concepts.” 2011. Doctoral Dissertation, Brunel University. Accessed July 20, 2018. ;

MLA Handbook (7th Edition):

Lee, Cho-Yu. “Computational and experimental study of air hybrid engine concepts.” 2011. Web. 20 Jul 2018.


Lee C. Computational and experimental study of air hybrid engine concepts. [Internet] [Doctoral dissertation]. Brunel University; 2011. [cited 2018 Jul 20]. Available from: ;

Council of Science Editors:

Lee C. Computational and experimental study of air hybrid engine concepts. [Doctoral Dissertation]. Brunel University; 2011. Available from: ;