Biofuel combustion chemistry more complex than petroleum-based fuels

LIVERMORE, Calif. — Understanding the key elements of biofuel combustion is an important step toward insightful selection of next-generation alternative fuels.

In a new paper on the cover of the May 10 edition of the journal Angewandte Chemie , Sandia researcher Nils Hansen and Lawrence Livermore scientist Charles Westbrook take a look at the vastly diverse and complex chemical reaction networks of biofuel combustion. 

The paper, "Biofuel Combustion Chemistry: From Ethanol to Biodiesel," examines the combustion chemistry of those compounds that constitute typical biofuels, including alcohols, ethers and esters.

Biofuels such as bioethanol, biobutanol and biodiesel are of increasing interest as alternatives to petroleum-based transportation fuels. According to Hansen and Westbrook, however, little research has been done on the vastly diverse and complex chemical reaction networks of biofuel combustion.

In general, the term biofuel is associated with only a few select chemical compounds, especially ethanol (used exclusively as a gasoline replacement in spark-ignition engines) and very large methyl esters in biodiesel (used as a diesel fuel replacement in diesel engines). The biofuels are oxygenated fuels, which distinguishes them from hydrocarbons in conventional petroleum-based fuels.

While much discussion surrounding biofuels has emphasized the process to make these alternative fuels and fuel additives, Hansen and Westbrook for the first time examined the characteristic aspects of the chemical pathways in the combustion of potential biofuels.

In collaboration with an international research team representing Germany, China and the United States, Westbrook, Hansen and former Sandia post-doctoral student Tina Kasper used a unique combination of laser spectroscopy, mass spectrometry and flame chemistry modeling to explore the decomposition and oxidation mechanisms of certain biofuels and the formation of harmful or toxic emissions.

"To understand the associated combustion reactions and to identify recurring reaction patterns, it is important to study prototypical variants of potential biofuels," Westbrook said.

The work leading to the paper was funded in part by the Department of Energy’s Office of Science, which supports fundamental research, including research aimed at understanding, predicting and ultimately controlling matter and energy at the electronic, atomic and molecular levels in order to provide the foundations for new energy technologies and to support DOE missions in energy, environment and national security. 

Angewandte Chemie is the weekly, peer-reviewed scientific journal of the German Chemical Society.