RESEARCHERS are working on a thermoelectric generator that converts the heat from car exhaust fumes into electricity. The module feeds the energy into the car’s electronic systems.
In a nutshell, the process cuts fuel consumption and helps reduce the CO emissions from motor vehicles.
In an age of dwindling natural resources, energy saving is the order of the day, or at least it should be. And yet, many technical processes use less than one-third of the energy they employ.
This is particularly true of cars, where two-thirds of the fuel is emitted unused in the form of heat. About 30% is lost through the engine block and a further 30-35% as exhaust fumes.
It is a serious issue and scientists worldwide are at last looking to harness the unused waste heat, not just from cars, but from machines and power stations, in order to lower their fuel consumption.
One way of recovering some of the energy lost through heat is to use a device known as a thermoelectric generator (TEG).
A TEG converts heat into electrical energy by making use of a temperature gradient. The greater the temperature difference, the more current TEGs can produce.
Researchers at the Fraunhofer Institute for Physical Measurement Techniques in Germany are developing thermoelectric materials, modules and systems to harness the heat lost from vehicle engines.
“The temperatures in the exhaust pipe can reach 700 degrees Celsius or more,” says Dr Harald Böttner, head of the thermoelectric systems department.
“The temperature difference between the exhaust pipe and a pipe carrying engine cooling fluid can thus be several hundred degrees.”
A thermoelectric converter makes use of this huge differential: driven by the flow of heat between the hot exhaust fumes and the cold side of a coolant pipe, the charge carriers pass through special semiconductors, thus producing an electric current similar to a battery.
The long-term objective is to make obsolete the alternator, which routinely generates electricity (and eats some of the power output of a vehicle engine) and to supply energy to the constantly rising number of power consumers in the car, such as air-conditioning.
TEGs could cover a significant proportion of a car’s power requirements and, at the same time, cut petrol/diesel consumption by 5-7%. The researchers are still in the experimentation phase and haven’t yet built a prototype to test the claim.
A simple calculation will illustrate how important it is to increase the energy efficiency of cars: there are about 28million licensed motor vehicles in Britain, each of which is – as a basis for an estimation – on the road for an average of 200 hours a year. If their waste heat was utilised by TEGs during that time with an output of one kilowatt, sufficient to power parts of vehicle electronics, this would add up to about seven terawatt hours of energy a year. That equals a huge amount of energy.
