Researchers from Trinity College Dublin’s and TOTAL have designed, synthesized and tested new additives that increase fuel efficiency. Led by Professor Stephen Dooley in Trinity’s School of Physics, the Trinity researchers undertook the project as a result of an open competition by TOTAL, where their proposal welcomed several applications from research teams across the globe.

The research was funded by TOTAL Marketing Services and supported by MaREI, the Science Foundation Ireland Research Centre for Energy, Climate and Marine. While the specifics of the work are proprietary to TOTAL and can’t be disclosed, the research team published an open-access paper in the journal Energies on some of the thinking that lead to the design of the molecules.

The scientific work carried out by Trinity was focused on determining systematically what makes some molecular structures better octane boosters that others. By modifying these structures and adding molecular components as if they were LEGO pieces, the researchers were able to calculate if a given structure met the theoretical principles to become an efficient octane booster.

Ure et al.

Current market research indicates that internal combustion engine sales peaked in 2018 and that from now on sales of electric cars will slowly overtake cars running on fossil fuels. In recent years, many car manufacturers have announced ambitious plans to electrify their offering—mostly by hybridization with internal combustion engines.

However, there are still some technological and affordability risks to this transition. More than 90% of new car sales are still based on internal combustion engines as the prime mover. Although electrification is taking place it is unlikely to make significant impacts on emissions over the coming decade.

In addition, there are other transportation modes, such as aviation or maritime, where electrification is simply not yet an option. However, using additives within ubiquitous, affordable liquid fuels can make a difference. Fuel additives may become particularly important if applied to biofuels, which already have low greenhouse gas potential.

We risk missing important emissions targets if we do not explore further solutions which may allow vehicles to become more efficient and less environmentally harmful. Considering that liquid fuels are used for almost all vehicle transportation worldwide, even small improvements in efficiencies will have significant global impacts, especially in poorer countries where electric mobility is not an option.

Particularly, this last point is important if we are serious about CO₂ mitigation and climate justice. Additives of this type, and the methods we developed in discovering them, will be important tools as we transition to the large-scale use of low CO₂ biofuels.

—Stephen Dooley, Principal Investigator in Energy Science at Trinity and senior author

Fuel additives. Fuel additives are used extensively to improve the technical properties of fuels, allowing them to be environmentally safe and perform well in the engine. Typical additives range from simple dyes, to distinguish different types of fuels, to antioxidants to prevent degradation, and to octane boosters to make them more efficient.

Of these, octane-boosting additives are the most sought after as they allow the vehicle to go further on the same volume of gasoline by better controlling how the engine burns the fuel.

Although octane boosters are used extensively there is currently no complete understanding on their molecular mechanism of action. Innovation in this space tends to be identified by blind trial and error, rather than systematic scientific study.

The Trinity team (Professor Stephen Dooley, Dr Andrew Ure, Dr Manik Ghosh, Dr John O Brien), adapted pre-existing theories of chemical reaction kinetics and molecular thermodynamics for use with more modern machine learning techniques, making use of the super-computing facilities of the Irish Center for High End Computing (ICHEC).

This allowed them to identify many potential additives, but only those which the theory calculations suggested had the best attributes were chosen for the risky and difficult experimental studies.

An innovative and informed methodology for the rational design and testing of anti-knock additives is reported. Interaction of the additives with OH^● and HO₂^● is identified as the key reaction pathway by which non-metallic anti-knock additives are proposed to operate. Based on this mechanism, a set of generic design criteria for anti-knock additives is outlined.

It is suggested that these additives should contain a weak X-H bond and form stable radical species after hydrogen atom abstraction. A set of molecular structural, thermodynamic, and kinetic quantities that pertain to the propensity of the additive to inhibit knock by this mechanism are identified and determined for a set of 12 phenolic model compounds.

The series of structural analogues was carefully selected such that the physical thermodynamic and kinetic quantities could be systematically varied. The efficacy of these molecules as anti-knock additives was demonstrated through the determination of the research octane number (RON) and the derived cetane number(DCN), measured using an ignition quality tester (IQT), of a RON 95 gasoline treated with 1 mole % of the additive.

The use of the IQT allows the anti-knock properties of potential additives to be studied on one tenth of the scale, compared to the analogous RON measurement. Using multiple linear regression, the relationship between DCN/RON and the theoretically determined quantities is studied. The overall methodology reported is proposed as an informed alternative to the non-directed experimental screening approach typically adopted in the development of fuel additives.

—Ure et al.

Resources

• Ure, A.D.; Ghosh, M.K.; Rappo, M.; Dauphin, R.; Dooley, S. (2020) “Rational Design and Testing of Anti-Knock Additives.” Energies 13, 4923 doi: 10.3390/en13184923