Reducing CO2 and NOx emissions: a regenerative hybrid engine system for trucks and buses that converts engines into an air pump during deceleration, so harvesting braking energy.


Brunel Air Hybrid, the Vulcanaer System for Buses and Trucks

A novel regenerative hybrid engine system that reduces CO2 and NOx emissions from diesel trucks and buses by converting the vehicle engine into an air pump during deceleration. 

While the all-electric transport revolution is awaited, Vulcanaer will enable existing bus and truck diesel vehicle fleets to meet emerging civic requirements for cleaner air in cities - and additionally provide cost savings.

In urban transport systems there is a significant waste of energy due to frequent acceleration and deceleration. There is an opportunity to modify existing diesel engines to harvest the energy ‘wasted’ through deceleration thereby reducing CO2 and NOx emissions and saving on fuel costs. Vulcanaer harvests the braking energy and stores it as compressed air for subsequent use.

In busy urban areas, where there is a requirement for buses to turn off their engines when stopped to reduce emissions from idling, there are issues with the need to then restart the engine. This uses the battery and an electrical starter both of which wear out quickly resulting in broken down buses requiring expensive replacements. Vulcanaer provides a solution to this problem using the harvested compressed air to restart the engine.

Vulcanaer also saves fuel as the harvested compressed air assists the normal engine-driven air compressor to augment other air systems on the vehicle. Furthermore it can enhance the turbo thus reducing black smoke during acceleration from stationary.

First generation system trials on a Yuchai bus in China showed fuel savings of 5% to 9% on an urban bus operating cycle. A second generation retrofit system has been demonstrated to be feasible on a 9.6L bus engine in the UK with no adverse effect on driveability.

Vulvanaer is protected by a family of patents with granted cases in multiple countries.

Key Benefits

Reduced CO2 and NOx emissions.
Fuel savings.
Reduced use of battery and starter motor on restarting engine from idle mode.
Mechanical system that is simple and fail safe.
Suitable for retrofit with conversion taking less than a day without the need to remove the engine.
Low cost (typically £4k) providing fleet operators with payback in less than 2 years.
Also suitable for original equipment manufacturers.


Diesel transport systems, particularly urban bus and delivery trucks, where there is frequent acceleration and deceleration and a need to reduce emissions.

Purchase a license for full unlimited access to all innovation profiles on LEO

  • Direct connection to thousands of more innovations
  • Access to market Experts and Universities
  • Filter relevant solutions into your own dedicated Network