Wasted heat is wasted fuel consumption that increases CO2 emissions and contributes to global warming. The average efficiency of an internal combustion engine used in cars, aircraft and boats is about 30% to 40%. The majority of the energy used is emitted as heat with approximately half of that being carried away by the exhaust gas.

Thermo-electric generators are devices that can capture or harvest heat energy from, for example, exhaust gas and turn it into electricity. But, when used in engine exhausts, these generators are square pegs in round holes. They are flat, which makes it a challenge to fit them to existing cylindrical exhaust pipes because large chunks of metal are required – increasing vehicle weight and decreasing fuel efficiency.

To address these shortfalls, we propose to build the harvester directly into the exhaust pipe, but this requires a complex-shaped part.

The conventional processes of manufacturing complex parts are like chipping an ice sculpture from a block of ice: a lot of material is wasted and a lot of energy is used in the “chipping” process.

Methods of additive manufacturing – which involves the process of joining materials to make objects from 3D-model data – make the “sculpture” by building up the “ice” layer by layer. Existing additive-manufacturing methods for metal parts involve melting powder to add a thin layer on top of previous layers. This process has to be performed in a controlled environment as powder particles are explosive and can be a serious human health risk. It takes a lot of energy both to produce the powder and then to melt it. Worse, excess powder is often degraded making reuse or recycling difficult. The aim of this project is to introduce a new, low-energy way of making stronger, lightweight parts with high thermal conductivity, by growing material atom-by-atom in a cold liquid. This is much safer as it completely avoids both making and using nanoparticles. The growth process is also reversible, allowing easier recycling of old parts.

Products made by this process will be nanostructured to withstand high forces and temperatures, and deposited in the right shape to be light in order to optimise harvesting of waste heat energy from an engine. This will improve efficiency and enhance environmental sustainability.