The Thermoelectric Effect in Internal Combustion Engines

8/9/2019 The Thermoelectric Effect in Internal Combustion Engines

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Mazilu Adrian-Ștefan

AE 1721


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The Seebeck effect is the conversion of

temperature differences directly, when applied on a

thermocouple, into electricity.

The Peltier effect is the conversion of electricity

directly, when applied on a thermocouple, into

temperature differences.

The Thomson effect describes the heating or

cooling of a current-carrying conductor with a

temperature gradient.

*The Peltier and Seebeck effects are essentially the

inverses of one another, while thermoelectricity is a

wider definition that includes both.


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Thermoelectricity refers to a class

of phenomena in which a

temperature difference creates an

electric potential or an electricpotential creates a temperature

difference.

The thermoelectric effect is the

direct conversion of temperature

differences to electric voltage and

vice versa.

This effect can be used to generate

electricity, to measure

temperature, to cool objects, or to

heat them.

One of the most commonly usedmaterial in such application is

Bismuth telluride (Bi2Te3), a

chemical compound of bismuth

and tellurium.


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Electricity requirements in vehicles

is increasing due to the demands

of enhanced performance

To gain fuel efficiency, it may be

possible to shift energy draw from

the engine (in certain cases) to theelectrical load in the car

Thermoelectric devices are thus

being investigated to convert

waste-heat into usable energy

using the Seebeck Effect.


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Almost 70% of the energy released

from the fuel by a car engine is

lost, mostly in the form of heat

Assembled into so-called

thermoelectric generators, or

TEGs, they can soak up heat that

would otherwise be wasted andproduce an electrical current.

Without the requirement for any

moving parts!


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TEGs depend upon a temperature

difference to "drive" the device –

so one side needs to be hot and

the other side cold.

The electrons one the "hot" side

vibrate more vigorously so theytend to move towards the colder

side where the electrons are

moving more slowly.

This movement gives rise to a

current that can be tapped off as

electricity.


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After its nineteenth Century

discoverers, Jean Charles Athanase

Peltier and Thomas Johann

Seebeck

Seekbeck showed that linking up

two different conductors that areat different temperatures results in

a voltage being produced between

them

This voltage is related to the

difference between the two

temperatures.


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The trick with thermoelectrics is

that you want the heat to stay at

the hot end for as long as possible,

keeping the temperature gradient

in place, yet still allowing the

electrons to flow freely.

But because materials that allow

electricity to flow also generallyallow heat to flow. So finding a

material that does one but not the

other is a huge challenge.

That said, materials with high

electrical conductivity but low

thermal conductivity do exist. Infact, most commercial TEGs

contain bismuth telluride


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The rather exotic-sounding

bismuth telluride (Bi2Te3), which is

about 4% efficient at 250°C

For higher temperatures we needto use silicon and germanium.

These are more common materials

but are much less efficient at

turning heat into electricity.

Thankfully, scientists are confident

that, by resorting to

"nanosculpture" to craft the

structures of the materials in just

the right way, it is possible to

create substances that

simultaneously impede the flow ofheat but are very permissive for

the flow of electrons, and this will

dramatically improve the

efficiency.


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The Apollo astronauts relied on

these devices during their Moonmissions, and the Cassini and

Voyager spacecrafts are also

powered by on-board RTGs, which

work by converting the heat

released by the decay of a

radioactive source, such as

strontium-90 or plutonium-238,

into an electric current.

In space, the required "cold side"

for the device is also easy to supply

given that the average

temperature is just three degrees

above absolute zero


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Caterpillar is working on a thermo-electricity concept to reduce fuelconsumption on Diesel engines.They provide a cold side of the

thermo-electric element withliquid that is part of a secondarycooling system.


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BMW eventually limited the usage ofthe alternator in a test vehicle bysupplying power from a TEG deviceinstead.

BMW 530i is equipped with a thermo-electric generator in the exhaust.

The program goal is 10% fuel efficiencyimprovement


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Although thermoelectrics can only

capture only a small percentage of the

world’s “waste” energy, on a global scale

this amounts to a huge potential saving...


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The Promise and Problems of

Thermoelectric Generators

www.wikipedia.org

www.heat2power.net

www.thenakedscientists.com
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The Thermoelectric Effect in Internal Combustion Engines

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