# 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
#### Waste Heat Recovery  
Waste heat recovery is being investigated in the automotive industry to increase the efficiency of ICEs, as well as to reduce CO\({}_{2}\) emissions by converting the thermal energy to electrical energy by using either thermal fluid systems via Organic Rankine Cycle (ORC) or Thermoelectric Generators (TEG). [PERSON] [26] observed that the conversion of 20% of exhaust waste heat into electricity might increase fuel efficiency up to 10%. It was then showcased that the use of exhaust heat recovery by replacing the conventional alternator was a cost-effective way to reduce the greenhouse gases in the heavy-duty vehicles.  
As observed in a [PERSON]'s energy flow diagram barely 25% of the fuel energy is used in the vehicle operation and the remaining 75% of energy is dissipated to the atmosphere. The other half is rejected by the coolant, lubrication and by the means of the charge-air heat exchangers [27]. It is also notable that even though it had been said that approximately 2/3 of the fuel energy is transformed into the waste heat, almost all this emitted thermal energy is an outcome of the limitation of the thermodynamic cycle of an engine. And hence, as a result, it is not feasible to reclaim all the thermal energy for the useful work without the laws of thermodynamics being violated. Some of the WHR options are discussed below.  
Electric Turbocompounding: As the name suggests this technology helps in generating electricity from the energy extracted from the residual kinetic energy of the exhaust gases downstream the turbocharger typically in Diesel engines, by coupling an electric generator to a turbine. An additional electricity-generating turbine is installed downstream of the main turbocharger turbine as suggested by [27], however, due to low pressure gas at the end of the exhaust, the second (power) turbine has to recover relatively efficiently at low-pressure. Therefore, the residual amount of pressure is used to generate electricity. The power turbine then generates electricity to be used by the vehicle components or to be stored directly to the battery of the vehicle.  
The electric turbo-compounding technology exhibited results of fuel economy gains between 3-10% depending upon the application. This system is typically installed on heavy duty diesel engines although increasingly electrified powertrains of any size can use this technology.  
Thermo Electric Generators: As discussed earlier TEGs were used to generate the electricity required in vehicle components by the means of temperature difference. The technology can be implemented for Waste Heat Recovery systems where the generators convert exhaust heat energy directly to electric energy using the Seebeck principle in electronics in which electricity is generated between two semiconductors because of temperature difference. As suggested by [28], the implementation of TEGs in ICEs shows good results in reducing fuel consumption. However, this technology is still under research and development and is expensive compared to other technologies. The research in this technology so far has yielded up to 2% of the fuel efficiency improvement.  
In a very special case of a hybridised boosted optimised system with turbo-compounding (HyBoost project [27]), a 1.0 L, four-cylinder downsized direct-injection gasoline engine was developed to deliver 116 kW and 240 Nm, offering 35% reduction in fuel consumption and CO2 emissions. The system was able to reduce carbon emissions from 169 g/km to 99.7 g/km on the new European Driving Cycle matching the 2.0 L engine performance, i.e., 50% downsizing was demonstrated. It was equipped with an electric supercharger for transient lag mitigation, electric turbocompound, efficient liquid charged air cooler and advanced knock mitigation technologies.