Waste Heat Energy Harvesting for Improving Vehicle Efficiency 2011-01-1167

Currently, in the typical internal combustion engine, approximately one third of fossil fuel combustion by-product is wasted heat. In the continued effort to improve fuel economy, one area that is being researched today is the harvesting of wasted energy to increase vehicle efficiency.

This paper will address how heat emitted by exhaust systems can be captured and used to increase vehicle efficiency. Overall we will compare energy content in the exhaust manifold and exhaust underfloor mid-vehicle position, where potential exhaust heat exchanger concepts can reside. These heat exchanger concepts are designed primarily to capture heat from these locations and transfer the energy for increased passenger heating and comfort during cold conditions and/or supplement other improvements in power train efficiencies. An analysis of the energy exchange to the heated fluid is compared in the exhaust manifold and underfloor position respectively. Issues associated with heat energy harvesting from a typical exhaust system will be presented in detail, with suggestions for improving future systems.

The innovation behind the Faurecia Exhaust Heat Recovery System (EHRS) performance will be presented in detail for exhaust underfloor installation. Rather than throw off the heat emitted by exhaust systems, this innovation uses a gas/water heat exchanger to supplement the heating up the engine coolant. As a result, exhaust heat helps the vehicle interior to warm up in 25 percent less time than with conventional systems. This process can provide a shorter heating time for the powertrain as well. When the powertrain temperature increases more rapidly after start-up, fuel consumption improves.

Adaptation of this technology is also under development to boost the fuel savings of hybrid vehicles by increasing the duration of all-electric driving in the winter. More rapid warming decreases power demand and enables vehicles to travel farther on their electric motors. This system offers the potential of an 8 to 10 percent improvement in fuel economy for hybrid vehicles, with an environmentally friendly solution that replaces auxiliary heating systems.