Getting from A to B by most means of transport is polluting; incomplete combustion of fuels releases soot and unburned fuel into the atmosphere, along with greenhouse gases such as carbon monoxide and nitrogen oxide, which is contributing significantly to climate change. Whilst much research is focused on alternatives to replace petrol and diesel, other studies are finding ways to improve the fuels we currently use.
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Nanotechnology has improved - even revolutionized - several technology and industry sectors including information technology, security, medicine, energy, and food safety. It also has a role to play in transport and fuel and has expanded the toolbox at researchers’ disposal, allowing them to create novel additives to help fuels burn more completely. In turn, this reduces the volume of greenhouse emissions released.
Nanoparticles have a relatively large surface-area-to-volume ratio, making them ideal catalysts. The nanoparticles disperse throughout the fuel and encourage better air-to-fuel mixing and enhance chemical reactivity during combustion, leading to better performance, combustion, and quality of emissions. And because they are so small – less than 100 nanometers in length - they are also needed in smaller quantities.
Cerium oxide (CeO2) is proving to be a popular additive. Its lattice structure donates an oxygen molecule to carbon at a lower temperature and pressure than normal combustion. This oxidation reaction allows for the decomposition of unburned hydrocarbons and soot, thereby reducing the volume of pollutants released and the amount of fuel used. The lower pressure in the combustion chamber also reduces the production of nitrogen oxides (NOx) and makes combustion more efficient.
CeO2 is also used as a short-term treatment for particulate filters in diesel engines. These filters can become clogged with soot, which is cleared away by the nanoparticles, thus improving the performance of the filter and the cleanliness of the exhaust emissions.
Aluminum’s high combustion energy is known to increase the power output of engines. Nano-aluminum in suspension encourages microexplosions during combustion that leads to better air-to-fuel mixing and therefore a cleaner, more efficient combustion. Aluminum is sometimes combined with magnesium, and this compound demonstrates the same characteristics.
Both nanoaluminum and magnesium-aluminum have been shown to work better in ethanol-based fuels, so they could also be effective additive packs in bioethanol fuels. Not only do they improve performance, but alumina nanoparticles also produce fewer emissions; the nano-spiked fuels produce significantly lower quantities of NOx and CO while also producing less soot.
Platinum might be the catalyst of choice because it works fast and it's stable, but it is also expensive. Cobalt has shown itself to be an excellent alternative to platinum because it is more durable, less expensive and readily available.
Like nanoaluminum, cobalt oxide had been added to biodiesel fuels; it’s oxygen can encourage combustion much like cerium’s, making the process cleaner by reducing the amount of carbon monoxide and unburned hydrocarbons released in emissions.
Cobalt oxide has also been shown to reduce NOx, especially significant is the vehicle is fueled by biodiesel, which is known to release higher volumes of the gases than petrochemical diesel.
However, there are concerns about the environmental impact of using nanoparticles as additives: yes, they can improve fuel efficiency and the quality of exhaust emissions, but are they going to present another problem? The issue is that nanoparticles could be released in emissions. Cerium oxide, for example, has been shown to make its way into exhaust fumes: it could accumulate in the environment, especially in roadside areas. Its potential effects are not well understood, but it is possible that nanoparticles will make their way into the body since they are much smaller than particles such as soot where they could cause damage.
Nanoparticles could potentially be utilized in fuel cells to replace combustion engines; again, they act as a catalyst for chemical reactions that produce electricity. These nanoengineered, high-powered rechargeable battery systems will charge quicker, are lightweight and have a greater power density with the ability to hold charge for longer. The use of nanoparticles in fuel cells is likely to make electric vehicles a common sight on the roads.
The use of nanoparticles has been shown to encourage cleaner combustion; fuels mix better with air in the combustion engine burn better and more completely, leading to fewer polluting emissions. They also enhance the efficiency, meaning the engine requires less fuel and reducing running costs. The environmental impact, however, is a huge stumbling block which needs to be overcome before the sector can move forward.
References and further reading
Nanoparticles as Fuel Additives
Could nanoparticles change fuel production?
Nanoparticles as an additive in biodiesel on the working characteristics of a DI diesel engine
Nanoparticles increase biofuel performance, lower emissions
Investigation of Nanoparticle Additives to Biodiesel for Improvement of the Performance and Exhaust Emissions in a Compression Ignition Engine