A Cost-Effective Regenerative Air Hybrid Powertrain for Low Carbon Buses and Delivery Vehicles

Lead Research Organisation: Brunel University
Department Name: Mech. Engineering, Aerospace & Civil Eng


The hybrid powertrain with regenerative energy recovery is recognised as one of the most effective means to low carbon vehicles in short to medium term. It can significantly improve the fuel economy, particularly for buses and delivery vehicles in cities and urban areas where the traffic conditions involve a lot of stops and starts. 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 deceleration. Capturing, storing and reusing this braking energy can therefore improve fuel efficiency, and this can be achieved by using the momentum of the vehicle during coasting and deceleration to top up an energy storage device and later releasing the energy to propel the vehicle during cruising and acceleration. The most researched and developed hybrid vehicles are electric based. The application of electric hybrid powertrain to buses and delivery vehicles is severely limited by the huge additional cost associated with the engineering complexities of the combined electric and mechanical powertrain and transmission systems. Currently, the electric hybrid buses are heavily subsidised and will not be suitable for commercially viable large volume production. Unlike the electric and hydraulic hybrids, air hybrids can be implemented without adding an additional propulsion system to the vehicle when it is applied to a reciprocating internal combustion engine. In this case, the engine itself can be used as a compressor during braking/deceleration or an expander for starting/ acceleration, transmitting power through the pistons and the crankshaft of the engine thus braking or propelling the vehicle using the existing drivetrain of the vehicle. For buses and delivery vehicles, air energy will be stored at moderate pressure (less than 15 bar) in a compressed air storage tank already available on such vehicles. Similar to its electric cousins, the air hybrid will be able to recover the braking energy and store it for later use to start the engine and help the vehicle to accelerate, allowing significant improvement in fuel economy without adding the large weight and complexity of the electric hybrid. In addition, the stored high pressure air is available readily on demand for other uses to improve driveability and reduce emissions, such as briefly boosting the engine to eliminate turbo-lag in a turbo-charged engine resulting in better response and removal of the black smoke typically seen from accelerating diesel vehicles. For buses and commercial vehicles, compressed air is required for air assisted braking and the operation of pneumatic equipment (e.g. door opening and closing) and is currently produced by an engine driven compressor. Air hybrid powertrain technology will enable further and readily achievable fuel savings to be realized by providing the service compressed air from the regenerative engine braking in place of the engine driven compressor. These are exciting synergies enhancing many attributes of the engine at minimum cost and are immediately available, not possible with the other hybrid energy types and unique only with the air hybrid because of the readily available air supply. Therefore, the exploitation of such synergies will result in an air hybrid powertrain system with significant and concurrent improvements in fuel consumption, emission, and performance.The aim of this proposal is to carry out research and development of suh a novel air hybrid powertrain system for urban buses and commercial vehicles with significant and concurrent improvements in fuel economy, emissions, and performance over the current IC engines.

Planned Impact

Based on 10% reduction in fuel consumption which can be achieved by the proposed powertrain technology, for the typical mileage of 45000 km/year per vehicle, it can reduce CO2 emission by 7.2 tons as well as a fuel saving of 2250litres per year per vehicle. Taking the UK fleet as 50,000 city buses this would equate to 360000 tons of CO2 per annum and or 25 million gallons of diesel over the bus fleet per year, a not inconsiderable amount of savings. The adoption of the proposed powertrain technology in other countries, such as China and India, will lead to significant economic and environmental benefits. In addition, Brunel University and UK in general will benefit directly from the royalties and commissions that will arise from any licensing agreement with engine manufacturers worldwide. The IPR is protected by international patents and assisted by the technical knowhow developed through previous research and the proposed project. Bus engine manufacturers will benefit by offering to the bus builders a new engine with regenerative compressed air capability and at small additional cost. The indirect clients will be bus builders taking advantage of the new engine and offering to the bus operators additional fuel savings from self-sustaining stop/start, supplementary air for onboard pneumatic equipment, better driving response, lower emissions and meeting global targets for CO2 reduction. The project will provide an excellent training opportunity for a young postdoctoral RA and a PhD student. The RA will gain valuable experience and skills in the engine experimentation, data analysis, presentation and project management. The PhD student will have the opportunity to develop and apply advanced control theories and vehicle drive cycle simulation programmes for the optimisation of the proposed powertrain system and its components. The project will involve substantial technical support by Guanxi Yuchai Machinery Ltd. (Yuchai) to equip a bus diesel engine with their VVEB devices. Yuchai is the largest diesel engine manufacturer in China and enjoys 80% of the domestic market. Alexander Dennis, a bus/coach builder based on UK, will contribute to the project by providing technical information required for control and drive cycle simulations. There is a limited research activity in the UK in the engineering of buses. However there is a huge user community and a very significant maintenance activity. Yuchai's pledge of support will led to widespread application of the arising technology in China. At the same time, the opportunity of a retro-fit programme to UK buses is substantial. Yuchai will lead the development of new build in China and across the developing world. At the same time, working with indigenous manufacturers and fleet operators a retro-fit programme can be initiated. Targets include, TfL and Stagecoach where an initial presentation of results is expected to lead to the formulation of a follow up development and application project. The successful outcome of the proposed project will also serve to demonstrate the capability of the proposed technology to European Manufacturers and those in Japan and US for its adoption to these developed countries. Prof Zhao and Dr Ma at Brunel University will be in charge of the implementing the impact activities. Brunel University's Commercialisation Office will assist in the new patent applications and the licensing of patented technologies. It is our intention to bid for an EPSRC follow-up funding to place the RA in the industry for technology transfer after the successfuel completion of the project. In addition, the web-based diseemination activity will be supported by the newly appointed webmaster within the School of Engineering and Design at Brunel Univerisity. The results from the study will be presented at UnICEG meetings, SAE Congress, UKACC's meeting and SAE Commercial Vehicle conference, as well as publication at international journals.


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Cho_yu Lee (Author) (2011) Pneumatic Regenerative Engine Braking Technology for Buses and Commercial Vehicles in SAE International Journal of Engines

Description Air hybrid engine and vehicle simulation programmes were developed and validated for different bus driving cycles. The simulation predicted 7% reduction in fuel consumption for a double decker bus on a London bus route. A demonstration bus built by Yuchai in China demonstrated 5-9% reduction in fuel consumption through the regenerative stop-start operations in a Chinese city driving cycle.
Exploitation Route An commercial license agreement was signed between Brunel University London and Yuchai, the largest diesel engine manufacturer in China. Prototype air hybrid engine accessories have been undergone systematic design improvement for durability and better performance through joint effort between Yuchai and Brunel. In the meantime, Brunel is working with PTech, a UK based company to develop new retrofit air hybrid engine systems for a Volvo engine that is used in many Buses in UK. The air hybrid Volvo engine is expected to be operational in the second quarter of 2016 and installed for bus trials in the third quarter of 2016. After the bus trail, commercial operations of the new air hybrid engine technologies will be discussed with the relevant users in UK and other countries.
Sectors Construction,Transport

Description Two designs were implemented on a bus diesel engine in Brunel and another one in Yuchai, the largest diesel engine manufacturer in china. Both engines have demonstrated the functionality of air hybrid engines . Yuchai has been conducted durability tests on one of the air hybrid designs and is in the process to prepare the air hybrid engine for a bus in China. In the meantime, Brunel is working with Ptech to implement a retrofit air hybrid system on a diesel engine and the demonstration of the air hybrid engine technology on a London Double deck bus in late 2016. The technology has been further developed and being implemented on a bus through the support of Innovate UK in UK.
Sector Transport
Impact Types Economic

Description IDP13, Innovate UK
Amount £302,420 (GBP)
Organisation TSB Bank plc 
Sector Private
Country United Kingdom
Start 04/2017 
End 03/2018