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Potential Fuel Additives Promote Cleaner and More Efficient Combustion

An additive for conventional fuel made up of oxygenated organic compounds could help in reducing the discharge of pollutants into the atmosphere during the combustion of fossil fuels. The aspect of how these potential additives decompose under combustion-relevant conditions has recently been established by KAUST Researchers.

The decomposition of DEC was evaluated using a laser beam that passed through a complicated system of mirrors and lenses (bottom) before reaching the shock tube (upper left). (© 2017 KAUST)

Selecting a perfect additive for a fuel blend is based on a better understanding of its kinetic behavior under combustion conditions. Organic compounds that comprise of more than 33% of oxygen by mass have recently developed as prospective additives for conventional fuel blends because of their potential to burn cleanly.

Diethyl carbonate (DEC), comprising of 40.6% of oxygen by mass, is specifically expected to facilitate the clean combustion of diesel fuels. Additionally, due to its high boiling point, it can further decrease the volatility of blended fuels, which is desirable in warm weather in order to minimize vapor buildup that blocks fuel lines. Its thermal decomposition however remains poorly understood.

Binod Raj Giri and Co-workers are presently evaluating the effects of temperature and pressure on the decomposition of DEC in order to fill this gap.

The Researchers, along with collaborators from the University of Miskolc, studied the decomposition kinetics of DEC by observing the evolution of ethylene, considered to be one of the reaction products, in real time by using a tunable CO2 gas laser. “We carefully selected the laser wavelength to minimize interferences from other reaction intermediates,” says PhD student, Muhammad AlAbbad, who carried out these experiments at the University’s low-pressure shock-tube facility.

The Researchers incorporated experiments with theoretical calculations in order to, “provide a detailed and reliable kinetic picture for the decomposition and its products,” says Giri.

Earlier, Giri’s team discovered that the carboxylate functional group had a minor effect on the decomposition of organic esters known as ethyl levulinate and ethyl propionate.

This motivated us to find out whether the same phenomenon would happen for DEC, which bears one more oxygen atom in its carbon skeleton than esters.

Binod Raj Giri, King Abdullah University of Science and Technology

The Researchers discovered that the additional oxygen atom destabilized the carbonate by majorly lowering the reaction energy barrier, thus increasing reactivity.

Giri explains that these findings will throw light on the applicability of biodiesel fuels, which comprise of different ethyl and methyl esters, to modern engine hybrids and diesel engines. These findings will also help simplify the blending effect of carbonates and esters with conventional fuels.

Presently, Giri’s team is exploring decomposition pathways for glycerol carbonate, which has greater oxygen content than DEC.

This molecule might be even more attractive than DEC regarding soot reduction and environmental impact.

Binod Raj Giri, King Abdullah University of Science and Technology

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