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DDFlyTrain flywheel hybrid technology to deliver around 10% fuel savings, rapid ROI

The DDFlyTrain research project, conducted by Ricardo, Artemis Intelligent Power (a group company of Mitsubishi Heavy) and Bombardier Transportation, (earlier post) has projects a fuel savings of around 10% based on the use of high speed flywheel brake recovery technology retrofitted to Diesel Multiple Unit (DMU) rolling stock. This order of saving means that the technology has a potential return on investment (ROI) of inside five years.

The DDFlyTrain hybrid solution—designed for integration onto a Bombardier Turbostar DMU—is based on Ricardo’s TorqStor high-speed flywheel energy storage technology and the high efficiency Artemis Digital Displacement hydraulic pump-motor transmission. (Earlier post.) The project has also produced a proof of concept test rig used to demonstrate the technology to rail industry stakeholders and a concept for integration onto a Bombardier Turbostar DMU.

220 kJ TorqStor. Click to enlarge.

The project set out to demonstrate—using simulation and rig testing—the practical feasibility; operational fuel and energy savings; and the economic investment case for the use of high speed flywheel energy storage technology on DMU trains.

The research project, which started in 2013 and was led by Artemis, was co-funded by Innovate UK and the Rail Safety and Standards Board. It included extensive simulation work based on field service data, which was used in the optimal sizing and design of a practical installation high speed flywheel brake energy system for rail-based application, and the construction and commissioning of a test rig for demonstration purposes.

The project has also completed an initial integration exercise to incorporate the hardware and software onto a Turbostar DMU. Significant effort has been focused on identification and management of the key operational concerns of such a solution.

Even before the project completion and current delivery of the results, the project and its constituent technologies had been widely recognized. In late 2014 the DDFlyTrain project received a Rail Exec award in the safety and sustainability category and the Ricardo TorqStor flywheel technology on which it is based received the 2014 SAE Tech Award, as one of the top five technologies to be on display at the SAE World Congress.

Although it has previously been used exclusively on electric rolling stock, regenerative braking represents a particularly attractive fuel-saving proposition for DMUs. The launch phase efficiency of conventional diesel rail vehicle transmissions, which typically use a torque converter on starting from rest, can be as low as 30%. By capturing and storing energy otherwise dissipated during braking, a significant improvement in fuel consumption is possible if this energy is subsequently reused to augment acceleration from rest during the period of poor transmission efficiency.

Other associated benefits can also be realized: improved longevity of braking system components as retardation is applied through absorbing energy into the flywheel, less noise and vibration from the engine during launch, and reduced exhaust emissions produced in the vicinity of stations.

In addition to its very promising application on DMU rolling stock, the high speed flywheel technology demonstrated in the DDFlyTrain project is also extremely attractive for electric multiple units operating on DC conductor rail networks such as the London DC electrified lines region. Network power capacity issues can place a significant restriction on the number of trains allowed to operate in some sectors, given the high current demand during launch. By applying high speed flywheel technology a significant element of this launch requirement can be eliminated, thus increasing effective capacity.

Scaled-down test rig based on a single 220kJ TorqStor
Scaled-down test rig based on a single 220kJ TorqStor. Click to enlarge.

How the DDFlyTrain hybrid system works. Ricardo’s TorqStor is connected to the DMU driveline via Artemis Digital Displacement hydraulic pump-motors in which computer-controlled solenoid valves coordinate the responses of individual pistons to the overall power and torque requirements. Compared with conventional hydraulics, Digital Displacement pump-motors have inherently high part-load efficiencies and controllability and this makes it economically feasible to use hydraulics in energy sensitive applications such as DMU regenerative braking.

Ricardo’s TorqStor differentiates itself from other flywheel designs with its unique permanent vacuum. This is made possible by its advanced magnetic gear system that enables the transmission of torque across a vacuum without the limitation of rotating seals or necessity for vacuum pumps.

It provides an industrial design for deployment in real-world applications where durability and ease of serviceability are of paramount importance. It is also highly scalable depending on the requirements of each application.

In the DDFlyTrain project, the optimal configuration for a DMU was found to be two 4.5MJ capacity TorqStor units with a maximum speed of 45,000 rev/min. The proof of concept demonstration test rig was a scaled-down version of the DMU architecture, based on a single 220kJ TorqStor.


Thomas Pedersen

It works! Just ask the Audi Le Mans Racing Team.

Henry Gibson

Artemis systems can eliminate the need for bio-fuels and the accompanied present destruction of rain-forests throughout the world.

Parry People Movers, two rail-cars, in-revenue-service, have demonstrated already, for years, the economy of similar systems.

New York City had electric flywheels on some of its vehicles for energy recovery, and modern technology makes it possible to place electric versions of the Ricardo flywheels in the vehicles as well as at the stations or anywhere along the track as URENCO tried to do.

In the vehicle flywheels with or without companion DURATHON batteries might be the best choice to eliminate power failures when vehicles cross third rail gaps just like the ancient London flywheel locomotives for freight trains in third rail districts. The present electro-diesels on the same lines now should have Ricardo electro-flywheels added immediately for both electric and diesel operation.

The ARTEMIS technology is not sufficiently appreciated. It is very lightweight compared to electrical systems of the same power and much less expensive and more efficient at regeneration and can bring the vehicle to a full stop to recover more energy and save on brake wear. Vehicles on long down grades can dissipate energy in fluid cooling coils with no brake wear or over-heating if necessary. Artemis motor-electric-generators could also charge batteries on these hills.

Using only compressed Nitrogen filled hydraulic bladder tanks for storing energy, it can save half the fuel for vehicles operated within cities and at least one third the fuel for vehicles operated on motorways without a change in engine size. With just smaller engines more fuel is saved but equal performance is available for most uses. A dual internal-combustion free piston hydraulic pump similar to the INNAS-CATERPILLAR Chiron design would make vehicles even more efficient and reliable. The Chiron engine also demonstrated the use of complicated electronic controlled timing of hydraulic valves for its operation similar to Artemis. A modification of it would be the best way to burn natural gas to pump water for reverse osmosis purification.

The use of Artemis systems eliminates complicated, expensive transmission systems and can be used to drive four or more wheels on a vehicle with little more cost or complexity and even more energy can be regenerated for improved acceleration upon start-out. The Artemis pump-motors have very simple mechanics and can run at high speeds, but not the unreduced speeds of small flywheels. ARTEMIS systems are torque multipliers, and a single one-horse-power engine pump can move a filled rail-car at low speed. Using a large model-airplane engine with Ricardo's magnetic gear and hydraulic pump could do the same.

The Ricardo flywheels, with magnetic gearing, add an extra dimension to the energy storage available and the possible regenerative breaking energy, because flywheels can deliver one of the highest peak powers available along with Nitrogen tanks, but with a great deal more energy storage with multiple small units. Carbon-Graphite fibers can be used to make flywheels or pressure tanks and their best use can be engineered. Through the vacuum tight wall magnetic gearing or electrical generation has a very small cost and the flywheel part can have an infinite life.

A much smaller system could be added to every automobile with a non-automatic transmission and rear wheel drive at much lower cost than electric hybrid. Front wheel drive cars could have rear wheel drive and regeneration added with small lightweight modifications.

It would be interesting to see an engine crankshaft pulley replaced with a compact Artemis pump pulley or the starting motor replaced with a same sized or smaller but continuously engaged Artemis pump-motor with or without flywheel ring gear enhancements. With the Ricardo-flywheel-Artemis-pump-motor and perhaps air tanks no other modifications would be needed to make many existing vehicles into hybrids. Many standard transmission automobiles would never have to shift from high except to reverse, occasionally to start or idle to speed up the flywheel when starting a trip. Pressure tanks can keep pressure for years for starting. Years ago a method of starting engines with fuel injector and spark timing by computer was invented.

The FORD model T with batteries for vibrator spark coils would rarely crank itself to a start when the ignition was turned on in a similar way. Perhaps instructions could have been designed to move the crank shaft to a certain position and then turn on the spark coils to start the engine. Hand operated starter fluid injectors would make the operation more certain. Compressed air injection is still used to start some engines. Airplane engines were sometimes started with gun powder charges.

The high economy of Artemis automobile experiments relied upon stopping the engine when the vehicle was stopped or when energy was available in pressure Nitrogen tanks.

Pressurized Nitrogen in an air bladder tank could not only start an engine but also move the vehicle, and it could be moved many feet by an up to speed flywheel. ..HG..

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