Doing away with dirty diesel

There are approximately 8,700 buses operating in London and 47,000 public service buses around the UK. Buses, in fact, form the backbone of transport infrastructure networks in urban areas all over the world. However, their diesel engines are also responsible for emitting vast quantities of pollutants, such as carbon monoxide, nitrous oxide and particulate matter into the air.

While hybrid buses help to reduce emissions and cut fuel costs, currently the only way to get a hybrid bus is to buy a new one. With new hybrid buses costing at least 50% more than the diesel equivalent, this choice has not proven popular. This challenge was what inspired Alex Schey and Toby Schulz to develop a solution that ultimately led to Vantage Power being founded.

They understood that to have a significant but affordable impact on reducing bus emissions, they would need to develop a product which could be retrofitted to buses already on the road.

Schey and Schulz met while studying mechanical engineering at Imperial College, and both shared a keen desire to develop hybrid vehicle technology. After graduation they designed and built the world's longest range electric car and drove it from Alaska to the southernmost tip of Argentina. The success of this project inspired them to found Vantage Power and develop an energy efficient transport solution on a bigger scale.

Setting the wheels in motion

Vantage created the B320 System – a self-contained hybrid powertrain that is designed to retrofit the most common diesel-powered double-deckers on the road. Current focus is on the two most popular bus models - the Volvo B7/B9TL and ADL E400.

The system is designed to be robust and reliable while at the same time reducing fuel consumption and emissions by over 40%. "A bus powered by our B320 system can be thought of as an electric vehicle with on-board charging capabilities," said Schey, who is CEO of Vantage Power.

The hybrid technology is based on a series architecture. This means that the engine is mechanically decoupled from the wheels, which are instead powered by an electric motor. This motor is powered by a battery pack, which in turn is charged by an electric generator. This generator is turned by the diesel engine. Schey continued: "This overall architecture is well known in the industry, but it's the design and performance of the many subsystems that make it unique. Key technologies that have been developed in-house include the battery pack, control system and cooling system. This has all been designed from the ground up."

As well as being Euro 5 (and soon Euro 6) compliant, each B320-powered double-decker bus will save operators about £20,000 per year in fuel costs. Schey commented: "The cost of replacing a conventional powertrain with similar components is typically £20k-£40k depending on whether new or used components are used. Our B320 system compares very favourably with this considering that our product gives the operator a brand new warranty on the entire driveline alongside a suite of new technologies including zero-emissions geo-fencing and 24/7 live data monitoring and logging."

The existing engine and gearbox are removed, and the B320 is installed by connecting it into the existing body electronics, hydraulics, pneumatics and chassis mounting points, but designing for retrofit has its problems.

"The biggest challenges for our application was packaging all the components of the hybrid system into a standard engine bay," said Schey "We don't have the luxury of packaging our system around the bus as one would when building a new vehicle - we have to make do with the space we have. This influences the second challenge that relates to cooling of the engine, power electronics and battery. Unlike in cars where radiators can be positioned in line with high-speed airflow, the buses' engine bays are located at the rear of the vehicle without access to airflow. This makes cooling a particularly challenging problem given that engine bay temperatures can reach up to 90°C!"

Temperature control was a limiting factor in the battery design. Each of the 1,760 cells - each one slightly larger than a standard AA cell - within the battery must stay within 2°C of each other in order to promote the longevity of the pack and to reduce degradation. To do this Vantage designed a liquid cooling system to bring cool fluid to each of the cells, and to ensure that the temperature of the fluid was as uniform as possible. This is a demanding requirement, but made particularly challenging given that one side of the pack is located next to a hot engine, and the other side next to a fan drawing in cool air. Consequently, Vantage had to conduct detailed computational fluid dynamics calculations to visualise the fluid flow, and the cooling effect it would have on each cell.

Starting up with CAD

Although only founded in January 2011, the first design was complete by early 2013. Subsequently, the first prototype was ready by the end of 2013 and the first model was put to the test in early 2014. "We achieved our target fuel savings and also demonstrated technologies such as geo-fencing and cloud-based remote control and telemetry," observed Schey.

Right from the start the Autodesk Product Design Suite played an important role, as Schey explained: "When we were starting out we were very resource stretched. We found that one of the biggest expenses in starting up an engineering company was the CAD packages - up to £12,000 per person for all the required software. However, Autodesk was there to support small businesses like ours, and allowed us to purchase over £100,000 worth of professional CAD software for a few hundred pounds. This level of support is a true enabler, and gave us the resources to design our product and build our business much faster than alternative options."

Two systems have been built to date, and the manufacture of 6-10 pre-production units will be underway shortly now that the design is proven. Both prototypes were fully designed and FEA simulated on Autodesk's Inventor prior to any components being built or assembled.

"Simulation in such a diverse and multifaceted system is a big challenge, and typically can't be done with a single piece of software," added Schey. "Inventor is great for simulating mechanical components from a finite element point of view e.g. stress analysis, computational fluid dynamics and thermal simulation. However, for performance simulations software like MATLAB and LabVIEW needs to be used."

Vantage Power has now partnered with Ensignbus Company - the UK's largest used bus dealer. The company's 40 years of industry expertise is helping Vantage Power bring the concept of retrofitting buses with the B320 System to a global client base. The company's mission is to manufacture 1000+ units a year by 2018.Once the system has been rolled out to a range of bus operators, Vantage Power will also look to the rest of the heavy goods vehicles market.