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TIGERS: Exhaust Gas to Electricity for Reductions in Fuel Consumption

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.




6 kW is way above the non-AC accessory load of passenger vehicles.  A couple hundred watts for lamps, another hundred for the audio, 100 for the computer and EFI and 50 for the instrument clusters and you're up to a whole 450.

The only way this works is with an integrated starter-generator or IMA to convert the excess power into motion.  This also works well with an energy-recovery turbine as a replacement for the throttle plate; the more the engine is throttled back, the more energy/stroke is available from the pressure drop across the intake.


80% efficiency? What kind of efficiency do they mean? The theroetical max mechanical efficiency of turbines is only 69%. It couldn't be thermal efficiency. That would leave the gases way too cool for the catalytic converter.


Bill's great grampa Hank sold flex fuel Model Ts. There was an adjustable fuel jet so farmers could enrich the mixture to run on home brew. Then Prohibition came along and ended that idea. So what else is new?


80% efficieny is for converting mechanical to electric energy in the SR machine. Better than today's alternator but far from the efficiency of a high speed PM motor.


Nice to see switched reluctance technology appearing in the real world.

SR motors/generators are cheap to produce (no expensive materials like in a PM motor), lightweight, robust and can have efficiencies in excess of 90%. The thing that has traditionally held them back is that controlling them requires microchip controlled power electronics, but with modern semiconductor tech that is not much of a problem anymore.


Would this system work on an engine that has a turbocharger on it?


On a turbocharger?  Certainly; I believe something of the sort is in the works, though it may not use switched reluctance motors.


Turbo-compounding was used in some of the last large piston engined aircraft 50 years ago.
I would have thought that placing the turbo downstream of the catalytic converter would make the heat generated there available for conversion.


Interesting that you would mention the large aircraft engines of the 1950's. These engines had a mechanical supercharger, the turbo-compounding was done through three exaust turbines linked to the chrankshaft through fluid drives. It gave them very good fuel economy with their 3350 cubic in engines, rated at 3400 hp for take off. The secret to their success is that an aircraft engine usually runs at 75% of its rated horsepower. This gave the turbine plenty of gas flow to draw power from. They were very complicated and suffered from reliabilty problems. The situation is different for an automobile where the engine is running at more like 15% of it's rated hp.


Exactly! Thats mean we can all use 1000cc engines instead of 5000cc fuel drinking engines and still serve us more then enough. If we add hybrid technology to the 1000cc engines, and here comes efficiency.


Yay! Where do I go to buy one? I've wanted something like this since I bought my Honda Insight, 2 1/2 years ago, but don't have the workshop facilities to try building my own.


Yay! Where do I go to buy one? I've wanted something like this since I bought my Honda Insight, 2 1/2 years ago, but don't have the workshop facilities to try building my own.


Why does this use an exhaust bypass? Why not use the entire exhaust on the turbine? Or possibly a recycle of catalytically rehabilitated exhaust reformed as a hydrogen-hydrocarbon mixture,to boost electrical generation during idling? No mention is made of catalytic treatment of exhaust before feed into the TIGER, or the possibility of an air intake, which would turn this device into a kind of air brake, or even a transmission flywheel. That makes it appropriate for trucks, which are big enough to justify this kind of capital addition.


Turbines like a certain flow rate through them; too low and the pressure ratio and energy recovery drop through the floor, too much and the back pressure goes through the roof.  A turbine which works well at cruise flow-rates will be seriously backed up with the engine at maximum power.  There are two ways to deal with this:  variable nozzles and waste gates.  Waste gates are simpler and more reliable than variable nozzles; the designers appear to have selected a waste gate.


So basically if they were to put a turbocharger on the exhaust manifold the traditional way, then adapt one of these Tigers to fit to the air side of the turbo then basically the heat the turbo generates will be converted into electricity and the vehicle will make lots of horsepower because it's turbo and have increased fuel efficiency because it's hybrid. Think of a 96 turbo mitsubishi eclipse only hybrid with multiple collection techniques. This would be even better if the power collected was sent to a battery that was also getting power from the brakes and flywheel. Is this theoretically possible?

Ayappa Reddy


I have read youer article on TIGERS. I am very much interested in marketing the product in Hyderabad, India. At first I would like to fit it on my car for demonstartion. Could you forward the information of how I could acquire one unit for myself.



sir i would like to know more about tiger concept. C ould you please send me the detailed working principle of TIGER.

bobby  r

i have been looling for a device like this to power a hydrogen generating cell for extended milage. catapillar diesel is introducing something similar for appox 3400 $.is this generator on the market yet?? thanks bob r.

bob reidel

please advise if this unit is currently available@ price the electric current generated would be great for hydrogen on demand systems . thank you bob reidel


i read your article. it's really informative. i want to know how the reluctance generator works.

ven katesh

i wish to know about how SRD helps in this project as a generator. please send me more details.

Arnold Liu

Please send further details on TIGERs. Is TIGERS driven using axial or radial turbine?


A charger takes several hp's from the crank, so that turbo has potential and doesn't obstruct the delicate power composition.

The stabilisation and storage possibly demand new-generation electrical installations.


what is the pressure of an exhaust gas ?


I am a mechanical engg student .I read about TIGERS
that was a innovative thing ,I want to present a paper
on TIGERS in technical paper presentation so please send me more detailed information about TIGERS

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