|TIGERS. The switched reluctance generator is in yellow.|
British engineers have developed a simple mechanism for recovering energy from engine exhaust gases that could potentially reduce vehicle fuel consumption by up to 10%.
The TIGERS—Turbo-generator Integrated Gas Energy Recovery System—consortium (a Foresight vehicle project) diverts exhaust gases to drive a small switched reluctance generator to create enough electricity to power a car’s electrical system.
The small turbo-generator is installed in a by-pass waste pipe fitted just below the engine exhaust manifold. A valve linked to the engine’s management control system allows some of the high-energy exhaust gases to pass through a turbine to drive the generator, depending on engine load conditions.
Typically the 800º C gases have a velocity of 60m/s and a mass flow rate of 0.05 kg/s, providing enough energy to spin the generator at up to 80,000 rpm and create electrical power of up to 6kW—sufficient to handle the car’s electrical systems.
An energy management system will ensure optimal utilization of the available energy. During highway driving, when the available exhaust energy is high, the energy will be captured and the excess power will be stored in a battery. However, at engine idle the penalty for recovery is high and so the vehicle will be operated in battery only mode.
The researchers have looked at placing the new generator at various locations along the exhaust system. Placed too far away from the engine, the waste gases start to lose energy, so in the development stage the generator has been placed just beneath the exhaust manifold to maximize energy recovered. The gases then pass through the catalytic converter after the turbine, to ensure that the gases can still be conventionally cleaned.
By placing it close to the manifold the energy available is optimized. This also allows for shorter runs for control leads and coolant pipes and provides greater protection to the unit. Disadvantages are that the high temperatures mean the generator has to be water-cooled and totally sealed. However, the researchers are convinced that they can fully develop the system and plan to have a fully operating prototype ready for bench testing within a few months.
Because the system is fairly simple and partly based on existing technology, it could be fully developed for all car, van, bus and truck engines within a few years.
The simple design of the switched reluctance generator enables a low cost and easy to manufacture unit to be built that can run reliably at high speeds. It gives the TIGERS device a power density of approximately three times that of a typical alternator. An efficiency in excess of 80% can be achieved compared with 60% for traditional technology.
Dr Richard Quinn, one of the engineers leading the TIGERS project, says the system could be developed to produce anything from 12v to 600v.
The recovered energy could power all of a car’s heating, lighting, air conditioning and in-car entertainment systems. Longer term, the cam belt, drive belts and alternator could be scrapped with the TIGERS-recovered power providing electrical drive instead for further potential for gains in engine efficiency.
The additional electrical energy could be used to power more advanced engine technologies, such as electro-magnetic valve actuation, electric intake charge cooling, electric-powered super-charging or electrical exhaust after-treatment.
Parasitic losses from mechanical support systems (i.e., belt-driven) can normally be as high as 6kW or 8hp in a family sedan but can be significantly higher in larger capacity cars and trucks. Moving from those mechanical systems to electrical removes those loses, and fuel consumption could be reduced from between 5%–10%.
In a hybrid electric car the TIGERS system could feed the extra power directly to the drive motors or back to the battery to increase the range of the vehicle.
On commercial vehicles the extra electricity could be used to power electrical systems to run refrigeration units for chilled food, turn the motors on cement mixers or power pumps on fuel tankers.
The TIGERS group comprises researchers from Visteon UK Ltd in Coventry, Switched Reluctance Drives of Harrogate and The University of Sheffield Electrical Machines & Drives Research Group.
Switched Reluctance Drives is a leader in switched reluctance technology and is developing a high-speed generator to work in this demanding environment. The University of Sheffield research group is applying its knowledge of electrical system modelling and design to optimise the control and energy storage system.
Visteon is the lead partner in the project and is one of the world’s leading Tier 1 automotive suppliers. It is responsible for the system design, testing and implementation.