# Overview of Clean Automotive Thermal Propulsion Options for India to 2030
## 2 The Current and Future Technological State-of-the-Art
### Advanced Internal Combustion Engine Solutions for Near Zero Emissions
#### 2.4.4 Advanced Boosting  
Several boosting solutions have been developed over the last decade. One notable such technology is the electrically-assisted turbocharger [33], where a device based on variable turbine geometry turbocharger can be coupled with a Switched Reluctance (SR) electrical machine. This was accommodated in the bearing housing of the turbocharger and coupled with the turbocharger shaft.  
Such devices are well known as hybrid turbochargers. This device was evaluated based on transient and steady-state engine conditions with the turbocharger providing electric assist/electric generation, of which the response matched a stock 2-stage turbocharger on the same engine. Electric modification of the turbocharger can be applied to both fixed geometry or variable geometry turbines. The SR motor was designed to provide a peak power in excess of 5 kW equally in motoring or generating the electricity. The stator in this device was cooled with engine coolant and not oil cooled that allowed greater output while maintaining temperatures not beyond the limit of winding material withstanding temperature.  
In a similar case an electric turbocharger was tested in the project 'Hybrid Petrol advance Combustion Engine' (HyPACE) [34], where efforts were made to develop an engine with advanced electric boosting (e-boosting). These efforts are made to meet the CO2 emissions that need to be realized by 2025 to meet the requirements whilst at the same time satisfying the stricter forthcoming Euro7 emissions regulations. Real Driving Emissions (RDE) have been adopted in Europe since September 2017. This was mandated to make a correlation of emissions between the real driving conditions and the ones achieved under the controlled laboratory test conditions mandated to that point in time. In order to meet future CO2 requirements, it is required that the engines get improved technology with electric hybridisation in combination with additional measures and changes to the vehicle. The turbocharger used in this engine was a BorgWarner 48V eTurbo. This hybrid turbocharger improves boost response while allowing pre-turbine pressures at peak power and exhaust energy recovery with the turbocharger mounted on the integrated exhaust manifold. The eTurbo has a permanent magnet electric machine coupled with the turbine shaft in the turbocharger and is located inside the bearing housing as described earlier. This system of the hybrid turbocharger has two modes of operations (1) Electrical assist and (2) Electrical Regeneration modes. These can be used to recover the waste energy of the exhaust by generating electricity from the excess turbine power available. A 48V battery supplies the electricity to this turbocharger as well as to store the electricity when generated. The use of this hybrid turbocharger gives us the freedom to match the turbine size which enables a big sized turbine selection for ideal efficiency at high speed and load. This successively benefits a reduced rate of over-fuelling and improves the operation area achieved at stoichiometric air-fuel mixtures. The negative effects are usually linked to an oversized turbine in terms of reduced transient response and run-up line performance, which can be balanced using electrical assistance. This eTurbo has a built-in variable geometry turbine mechanism which has various advantages when compared with the conventional turbocharger. This turbocharger was claimed to be having a potential of maximum fuel saving of between 2 to 3%. As described by the authors [35], one of the main advantages of a VGT is that the area to radius ratio can be rapidly varied to obtain ideal turbine efficiency over the range of engine operation. E-turbos have been successfully introduced into production in the last few years.