Characterization of Reactor-Assisted Burner Flames using Ultrafast Infrared Spectroscopy

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Many practical transportation fuels often undergo a two-stage ignition process under the so-called low-temperature combustion conditions. This feature can accelerate flame propagation which could be exploited to develop smaller, more efficient, and cleaner burning engines for automobiles and aircrafts. However, the low-temperature combustion physics governing flame propagation in these systems is poorly understood. Thus, a primary goal of this project is to improve our understanding of low-temperature combustion. New laser diagnostics will be developed to quantify the specific molecules that are formed during low-temperature combustion of transportation fuels and to determine how these molecules accelerate flame propagation at conditions relevant to modern engines. This project will provide new laser diagnostics, capable of characterizing combustion chemistry, and fundamental data, describing how the extent of low-temperature combustion alters the propagation of flames. The resulting knowledge can help engineers design clean and efficient combustion systems for propulsion and power generation.It is not well understood how the extent of low-temperature combustion alters the turbulent burning velocity and structure of turbulent flames fueled by heavy hydrocarbons (e.g., Jet-A, diesel). This issue is complicated by the large number of hydrocarbon species found in practical fuels and the fact that low-temperature ignition reforms the initial reactant stream into a complex mixture with a time-varying composition. Further, understanding the physicochemical processes governing the behavior of these flames is impeded by the lack of non-intrusive diagnostics. This research program will fill these gaps through: 1) the development of novel ultrafast mid- to far-infrared laser diagnostics with sub-picosecond resolution and 2) their application to characterizing reactor-assisted burner flames fueled by n-dodecane and Jet-A. The use of ultrafast pulses will enable large portions of the mid- to far-infrared spectrum to be interrogated on sub-picosecond timescales, while also enabling collision-free measurements of molecular spectra to be acquired. These attributes will be exploited to provide simplified multi-parameter characterization of the reactant stream and turbulent flames produced by a novel reactor-assisted burner. This approach will provide new fundamental data and insight regarding how the temperature and composition of the reactant stream alters turbulent flame propagation at conditions relevant to modern propulsion engines.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.