Energy drive

As the search continues for more renewable energy sources, scientists at Queen Mary, University of London are investigating whether nanofuels could be future energy vectors.

A team backed by Shell Researchand led by Dr Dongsheng Wen, a specialist in nanoparticles research at Queen Mary, is exploring the potential of silicon, aluminium and iron as nanofuels by assessing their combustion process in internal combustion engines (ICEs).

The materials will be tested as wet fuel, where nanoparticles are introduced into a conventional liquid fuel such as diesel or petrol, and then as pure metal nanoparticles (dry fuel).

They will undergo three processes — oxidation, ignition, and combustion — and researchers will assess how each affects the nanofuels’ energy release.

’The chemistry behind this project is pretty simple,’ said Wen. ’When a metal reacts with oxygen, you get metal oxides. This is an exothermic reaction, which means you release heat during the reaction process and then you utilise the heat to do the work.

’Fossil fuels also use heat to do the work, but the heat comes from the combustion of fossil fuels, whereas here the heat comes from the oxidation process.’

This concept means any oxidation experiments or reactions that produce heat can be used as secondary energy carriers, and Wen identified silicon, iron and aluminium as possibilities. ’We think these three are likely candidates because they are abundantly available in the earth. We do not want to have a heavy or precious metal because these are too costly and resources are quite limited,’ said Wen.

’Another factor is the energy density, which is how much energy an energy carrier can carry. We want high energy-intensity materials, and these three have reasonable energy density — slightly lower than fossil fuels at this stage.’ According to Wen, the metal with the highest energy density is beryllium, but this was not considered because of its limited availability.

The first stage of the study will involve burning the wet fuel in the ICEs. By adjusting the concentration of nanoparticles in the conventional fuel the scientists will be able to test how effective the nanofuels are by comparing the known performance of the engine when it is operating solely on fossil fuels with how well it operates on the new fuels.

The second stage will involve the combustion of pure nanoparticles, and will depend on the results of the first.

In addition to assessing the engine performance by analysing the in-cylinder pressure, the temperature and the work output from the cylinders, the scientists also want to assess the nanofuels’ emissions.

’The engine performance will not only be assessed against energy efficiency, it also needs to be assessed by its exhausts and emissions,’ said Wen. ’Carbon dioxide and soot are two problems with using fossil fuels. For nanofuels you do not have these problems, but you do have some others that need to be investigated. One is how can you be 100 per cent sure you can capture all these particles, especially at the nanoparticle range?

’If you cannot capture these particles one consequence is that you lose your energy materials. Another one is that you introduce particle matter, which is another emission problem.’

Wen added: ’Another possible emission is nitric oxide, which will be inevitable, either when you are using fossil fuels or nanoparticle fuels, because it is a reaction of oxygen and nitrogen in the air. So as long as you introduce it into the air you will generate nitric oxide under combustion conditions.’

Different combustion scenarios, however, will have a different impact on the generation of nitric oxide, and Wen said it is not known how the nitric oxide will be generated under particle fuel conditions.

’The project is risky because no one else has proposed such a concept and, from a research point of view, the ignition and combustion of these nanoparticles is not well established,’ he said.

While the Queen Mary team will provide the nanoparticles, Shell Research is to supply specialised fuels for the project.