Exhaust heat recovery system

In transportation, an exhaust heat recovery system turns thermal losses in the exhaust pipe into energy. This technology seems to be more and more of interest by car and heavy-duty vehicle manufacturers as an efficient way to save fuel and reduce vehicles’ CO₂ emissions. This technology can be used either on a hybrid vehicle or a conventional one: it produces either electric energy for batteries or mechanical energy reintroduced on the crankshaft.

Even if current engines consume less fuel than they used to, the thermal efficiency of an internal combustion engine has not really increased since its creation. The peak efficiency reached by a 4-cycle Otto cycle engine is around 35%, which means that 65% of the energy contained in the fuel is lost as pumping losses, friction losses, cooling losses, exhaust losses and accessories. High speed Diesel cycle engines fare better with around 45% peak efficiency, but are still far from their Carnot efficiency, and hence 55% of the fuel energy content is lost.

Inside the exhaust pipe of an internal combustion engine, energy losses are various: thermal, kinetic, chemical and latent heat. Most important energy parts are located in the thermal and kinetic losses, the two others are negligible. Kinetic losses can be recovered through a turbocharger or a turbo-compound.

The 2016 Chevrolet Malibu Hybrid car features an Exhaust Gas Heat Recovery (EGHR) system to accelerate coolant heat up time. This gives faster heat up of the engine coolant which in turn heats up the engine faster. Less choke is used giving reduced emissions and fuel consumption. This will also quicken cabin heating warm up for passenger comfort and window defrosting. For hybrid applications it also can warm the battery pack. The cooling system is connected to a heat exchanger placed in the exhaust gas transferring the thermal energy from the exhaust gas to the cooling system. When the engine is warmed up the exhaust gas is diverted to a by-pass pipe. http://gmauthority.com/blog/2015/04/2016-chevrolet-malibu-hybrid-exhaust-gas-heat-recovery-feature-spotlight/

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