Primary and Secondary Aerosol Formation in Low-Temperature Combustion of Alcohol Biofuels

A desire for environmentally cleaner automobiles has led to the idea of using biologically derived fuels in engines that operate at lower temperatures. Such systems would minimize exhaust emissions that contribute to photochemical smog. Next-generation passenger vehicles equipped with low-temperature combustion engines are expected to appear in larger numbers soon.

However, the environmental impacts associated with these vehicles have not yet been completely assessed. This research project combines techniques from atmospheric and combustion sciences to determine the air-quality and climate impacts of pollutants emitted from the low-temperature combustion of advanced biofuels. Results from this research will be valuable for designing efficient emission-control strategies for these vehicles in advance of their deployment in the market.

The project will afford education-through-research opportunities for undergraduates and high-school summer interns, and the research team will develop lesson plans on biofuels, renewable energy, and air quality to be implemented in high-school STEM curricula. By working with schools in Athens Clarke County that have high enrollments of minorities and economically disadvantaged students, these educational programs will increase the inclusion of such groups in STEM education.

Low-temperature combustion reduces the production of two key pollutants compared to conventional diesel combustion: Nitrogen oxides (NOx) and black carbon. However, it is not clear how low-temperature combustion, especially when utilizing alcohol biofuels, affects the formation of primary and secondary organic aerosol – both important pollutants in terms of their effect on air quality and the climate system.

This research will utilize controlled combustion experiments that will elucidate the connections between the molecular structure of biofuels and the gas-phase reactions leading to aerosol formation within the ranges of temperatures, pressures, and equivalence ratios encountered in low-temperature combustion engines. To isolate the effects of fuel structure on aerosol formation and properties, the investigation will involve three alcohol biofuels and their hydrocarbon analogues: 1-butanol and n-butane, iso-pentanol and iso-pentane, and cyclopentanol and cyclopentane.

The aerosol emissions will be characterized for their properties that dictate their air-quality and climate impacts, including chemical composition as well as microphysical and optical properties. Furthermore, the emissions will be sent through an oxidation flow reactor that simulates atmospheric oxidation, and the secondary organic aerosol formed will be characterized.

In parallel, the gaseous emissions will be speciated to identify intermediates implicated in primary organic aerosol formation as well as prominent secondary organic aerosol precursors, which will shed light on the connections between gas-phase combustion chemistry and aerosol formation.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.