Hybrid Turbocharger
Encyclopedia
A hybrid turbocharger is an electric turbocharger
consisting of an ultra high speed turbine
-generator and an ultra high speed electric air compressor
. The turbine and compressor are high-speed aeromachines, as in a conventional turbocharger. The electrical motors run at speeds in excess of 120,000 rpm and when used as generators, generate electricity at 98.5% electrical efficiency. High electrical efficiency is paramount, because there is no mechanical link between the turbine and compressor. In other words, hybrid turbocharger refers to a series hybrid setup, in which compressor speed and power are independent from turbine speed and power. This design flexibility leads to further improvements in turbine and compressor efficiency, beyond a conventional turbocharger.
The designers claim that hybrid turbocharger technology (HTT) virtually eliminates turbo lag and enables engine downsizing without compromising engine performance. This means that a HTT equipped engine can save up to 30% on CO2 emissions and fuel economy compared to an equivalent naturally aspirated engine.
HTT has currently been developed and tested to proof of concept stage by UK based company, Aeristech Ltd who also hold the patents for the design.
The HTT motor will accelerate from 40,000 to 120,000 rpm in less than 450 ms. The HTT motor control therefore requires a fast acting CPU to match the magnetic field of the stator to the changing position of the rotor.
. The compressor motor is powered from the energy storage medium allowing it to accelerate to full operating speed in <500 ms. This rate of acceleration eliminates the turbo lag which is a major limiting factor on the performance of standard turbocharged engines.
During this transient stage, the engine control unit
(ECU) on a standard turbocharged engine uses a combination of sensors such as lambda sensors and air mass flow sensors to regulate the fuel flow rate. In an HTT equipped engine the ECU can deliver the precise fuel flow rate for complete combustion more accurately. This is achieved by directly controlling the air flow rate and boost pressure via control of the compressor speed.
Aeristech's prototype motor delivers 26 kW at 120,000 rpm, weighs under 3.5 kg (8 lb) and is approximately 10 centimetres (4 in) in length.
When combined with a variable geometry turbine, the back pressure on the engine can be varied according to the electrical demands of the vehicle and charge state of the energy storage medium.
Development is underway for replacing battery energy storage with a super capacitor which can be charged and discharged very quickly.
The HTT generator will generate around 7 kW in a standard 2 liter engine and in excess of 26 kW in larger applications.
.
Here the hybrid turbocharger efficiently transfers the electricity between the turbine and compressor. Aeristech's latest test program has proven the efficiency of the hybrid turbocharger to be equivalent to (if not better than) that of an ordinary mechanical turbocharger.
Other types of electric turbochargers and electric superchargers are under development with varying degrees of success:
Here they use an electrically coupled compressor and turbine in an engine directly and not to assist a piston engine.
The engine compresses the fuel to be burned in a combustion chamber which is ejected via the turbine.
Its claimed this engine overcomes the inefficiencies in small scale gas-turbine engines.
These brushless motors do not use permanent magnets, in fact the rotor is just 2 laminated plates.
This means the motors can withstand the massive centripetal forces at 200,000 rpm and above required for the gas-turbines operation.
Development is underway for a single-stage range extender model at around 5 kW and also a two-stage 150 kW engine, two of which are going to be used in the Impulse-EV hydrogen powered supercar.
The designers claim the Impulse-EV will be capable of maintaining speeds in excess of 200 mi/h.
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
consisting of an ultra high speed turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
-generator and an ultra high speed electric air compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
. The turbine and compressor are high-speed aeromachines, as in a conventional turbocharger. The electrical motors run at speeds in excess of 120,000 rpm and when used as generators, generate electricity at 98.5% electrical efficiency. High electrical efficiency is paramount, because there is no mechanical link between the turbine and compressor. In other words, hybrid turbocharger refers to a series hybrid setup, in which compressor speed and power are independent from turbine speed and power. This design flexibility leads to further improvements in turbine and compressor efficiency, beyond a conventional turbocharger.
The designers claim that hybrid turbocharger technology (HTT) virtually eliminates turbo lag and enables engine downsizing without compromising engine performance. This means that a HTT equipped engine can save up to 30% on CO2 emissions and fuel economy compared to an equivalent naturally aspirated engine.
HTT has currently been developed and tested to proof of concept stage by UK based company, Aeristech Ltd who also hold the patents for the design.
Physical arrangement
The electric motors utilize permanent magnets which have a higher efficiency than standard high speed induction motors. Induction motors induce an electro-magnetic field into a solid rotor core. The induction motor is much simpler to control, but there are substantial losses involved in generating the magnetic field in the rotor.The HTT motor will accelerate from 40,000 to 120,000 rpm in less than 450 ms. The HTT motor control therefore requires a fast acting CPU to match the magnetic field of the stator to the changing position of the rotor.
Operating modes
Acceleration
When the driver depresses the throttle, the HTT initially acts like an electric superchargerSupercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
. The compressor motor is powered from the energy storage medium allowing it to accelerate to full operating speed in <500 ms. This rate of acceleration eliminates the turbo lag which is a major limiting factor on the performance of standard turbocharged engines.
During this transient stage, the engine control unit
Engine control unit
An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...
(ECU) on a standard turbocharged engine uses a combination of sensors such as lambda sensors and air mass flow sensors to regulate the fuel flow rate. In an HTT equipped engine the ECU can deliver the precise fuel flow rate for complete combustion more accurately. This is achieved by directly controlling the air flow rate and boost pressure via control of the compressor speed.
Aeristech's prototype motor delivers 26 kW at 120,000 rpm, weighs under 3.5 kg (8 lb) and is approximately 10 centimetres (4 in) in length.
Charging
At high engine speeds there is more energy generated by the turbine than is required by the compressor. Under these conditions, the excess energy can be used to recharge the energy storage for the next acceleration phase or used to power some of the auxiliary loads such as an electric air conditioning system.When combined with a variable geometry turbine, the back pressure on the engine can be varied according to the electrical demands of the vehicle and charge state of the energy storage medium.
Development is underway for replacing battery energy storage with a super capacitor which can be charged and discharged very quickly.
The HTT generator will generate around 7 kW in a standard 2 liter engine and in excess of 26 kW in larger applications.
Steady state
For the majority of the time the hybrid turbocharger is operating, the compressor and turbine power (not necessarily speed) will be matched. This gives an extra degree of freedom to the designer of a turbocharger impellerImpeller
An impeller is a rotor inside a tube or conduit used to increase the pressure and flow of a fluid.- Impellers in pumps :...
.
Here the hybrid turbocharger efficiently transfers the electricity between the turbine and compressor. Aeristech's latest test program has proven the efficiency of the hybrid turbocharger to be equivalent to (if not better than) that of an ordinary mechanical turbocharger.
System benefits
Aeristech claim many other benefits to running a hybrid turbocharged engine:- Improved packaging by enabling the turbine and compressor to be placed in separate parts of the engine bay.
- Higher density charge air by reducing the length of intake ducts and increasing the size of the compressor wheel.
- ECU controlled boost levels will enable tighter predictive control of in-cylinder combustion.
- Similar engine downsizing benefits to a hybrid vehicle, but with far less (approx 1/7th) energy storage capacity to achieve the same level of downsizing.
Other types of electric turbochargers and electric superchargers are under development with varying degrees of success:
- eBooster by BorgWarner - a small auxiliary electric compressor powered by the vehicle's electric system.
- TurboPac by TurboDyne - Electric supercharger
- Garrett electrically-assisted turbo
Future production
Aeristech is currently in discussion with a number of major vehicle manufacturers and tier 1 suppliers to develop an HTT equipped engine for mass manufacture.Decoupled Gas Turbine Generator
This is a similar technology but applied to micro gas-turbine engines.Here they use an electrically coupled compressor and turbine in an engine directly and not to assist a piston engine.
The engine compresses the fuel to be burned in a combustion chamber which is ejected via the turbine.
Its claimed this engine overcomes the inefficiencies in small scale gas-turbine engines.
Special very high speed brushless DC motor/generators
The motors used in the design are also designed by Turbo Electric Ltd, who hold patents for the micro gas-turbine and the special brushless DC motor/generators used.These brushless motors do not use permanent magnets, in fact the rotor is just 2 laminated plates.
This means the motors can withstand the massive centripetal forces at 200,000 rpm and above required for the gas-turbines operation.
Development is underway for a single-stage range extender model at around 5 kW and also a two-stage 150 kW engine, two of which are going to be used in the Impulse-EV hydrogen powered supercar.
The designers claim the Impulse-EV will be capable of maintaining speeds in excess of 200 mi/h.