Nanoparticles as Fuel Additives

Topics Covered

Introduction
Cerium Oxide Nanoparticles
Aluminium Nanoparticles
Magnesium-Aluminium and Cobalt Oxide Nanoparticles
Toxicity and Environmental Impact of Nanoadditives
Conclusion
References and Further Reading

Introduction

Transportation is one of the biggest sources of greenhouse gas emissions - second only to electricity production in the USA. Many people have advocated a change in consumer behaviour as the best way to reduce consumption in this area.

This often proves difficult, however, and an approach which has seen more activity is on the fuel production side. Fuel formulations and additive packs are now being designed to improve fuel consumption and reduce harmful emissions.

In particular, soot emissions, caused by incomplete combustion, contribute significantly to the greenhouse effect. these can be reduced much more easily than carbon dioxide emissions, by using additives which help to promote more complete combustion. Cleaner combustion also produces less carbon monoxide and NOx emissions, which have a detrimental effect on air quality in areas with large amounts of road traffic.

The expanded set of tools which has been made available to researchers through advances in nanotechnology is being used to create novel fuel additives which aim to improve combustion cleanliness in engines. This article will explore a few examples of nanoadditives for fuel and their potential benefits.

Figure 1. Transport fuels are one of the largest contributors to global greenhouse gas emissions. Fuel producers are working to improve their environmental footprint by enhancing fuel economy and emissions using tailored additive packages. Image source: EPA.

Cerium Oxide Nanoparticles

Cerium oxide has the ability to catalyse combustion reactions, by donating oxygen atoms from it's lattice structure. This catalytic activity is dependent on surface area, amongst other things, so using nanoparticles can offer distinct advantages over bulk material or larger particles.

Adding cerium oxide nanoparticles to fuel can help decomposition of unburnt hydrocarbons and soot, reducing the amount of these pollutants emitted in the exhaust and reducing the amount of fuel used. It has also been shown that cerium oxide decreases the pressure in the combustion chamber, which reduces the production of NOx and makes combustion reactions more efficient.

Cerium oxide nanoparticles can also be used as a short-term treatment for particulate filters in diesel engines. The nanoparticles help to clear away soot which clogs up the filters, which can drastically improve the performance of the filters and the cleanliness of the exhaust emissions.

Aluminium Nanoparticles

Nanoparticles and microparticles of aluminium have also been investigated as a potential fuel additive. Aluminium is known to increase the power output of engines, due to its high combustion energy. Recent advances in fabrication and characterization of nanoparticles have allowed more detailed research into the relationship of particle size and structure with performance benefit.

A study carried out by researchers at Purdue University, Indiana, found that nano-sized particles or aluminium give a greater performance benefit than microparticles. The characteristics of nanoaluminium in suspension are more conducive to the formation of microexplosions during combustion, which assists the air-fuel mixing and leads to cleaner, more efficient combustion.

In addition, the nanoparticle suspensions in ethanol-based fuels were much better than those in model hydrocarbons, suggesting that nanoaluminium could be effective in additive packs for bio-ethanol fuels.

Figure 2. More and more public transport vehicles are being run on biofuels, to improve their environmental profile. Although the carbon may be from a renewable source, inefficient combustion of biodiesel could lead to an overall increase in the output of pollutants and greenhouse gases. Additives are needed to ensure the fuel burns cleanly and does not produce large amounts of soot. Image source: senate.iowa.gov.

Magnesium-Aluminium and Cobalt Oxide Nanoparticles

In a study published in 2011, researchers from Anna University, India, investigated the potential of cobalt oxide (Co3O4) and magnesium-aluminium (magnalium) nanoparticles as additives for biodiesel fuels.

The oxygen atoms in cobalt oxide particles can moderate the combustion reactions, much like cerium oxide. As a result, the combustion was cleaner when using the cobalt oxide additive, and emission of carbon monoxide and unburnt hydrocarbons were reduced.

The cobalt nanoadditives were also shown to reduce NOx production. This is especially significant with biodiesel combustion, as it is known that biodiesel fuels are prone to high NOx emissions compared to regular petrochemical diesel.

Magnalium nanoparticles serve a similar role to aluminium - high energy combustion produces microexplosions which improve combustion efficiency, helping to improve fuel efficiency or increase power output.

In this study, it was also noted that the magnalium particles acted as a heat sink within the combustion chamber - reducing the overall temperature, helping to avoid hotspots and reducing NOx production.

Toxicity and Environmental Impact of Nanoadditives

As with many nanomaterials, the main concern which will have to be dealt with before full commercial deployment of nanoadditives is their environmental impact.

Whilst nanoadditives have demonstrated the potential to improve fuel efficiency and the quality of exhaust emissions, they may also cause environmental issues if they are carried into the exhaust gases themselves.

Studies have shown that addition of cerium oxide nanoparticles to fuel results in emission of small amounts of the particles. These particles are likely to accumulate in the environment, in particular in roadside areas.

The potential effects of this are not fully understood, although it is very likely that the overall toxicity of the emissions will be reduced, thanks to the reduction of particulate emissions. Combustion-derived nanoparticles, which are generally particles of soot and other residues from incomplete combustion, have been shown to be a major contributor to the toxicity of diesel fumes.

Conclusion

The ability to explore the effect of additive particle size on performance has opened up a new range of potential to improve the performance of internal combustion engines, reduce fuel consumptions, and counteract some of the performance compromises currently associated with using biofuels.

The main challenge moving forward will be to fully assess the potential environmental impacts of releasing these nanoadditives into the environment, and comparing the results with the potential improvements to emissions.

References and Further Reading

Comments

  1. Tero Kallioinen Tero Kallioinen Finland says:

    You guys have gone off your rockers. Didn't we learn anything about fuel additives with lead already?

  2. Prashant Akerkar Prashant Akerkar India says:

    Can nanotechnology help in identifying new fuels other than Gasoline and CNG?

    Thanks & Regards,
    Prashant S Akerkar

  3. Dion Trevarthen Dion Trevarthen United Kingdom says:

    As a non scientist, I am concerned as to whether aluminium additives could contribute any kind of flammable residue given the scale of air traffic and the well documented rise in global temperatures.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoNano.com.

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