In this installment of a 13-part series of monthly articles, The Combustion Institute recognizes the 2019 Distinguished Papers selected from among the scientific papers presented during the 37th International Symposium on Combustion. Congratulations to Zhenghong Zhou, Siena S. Applebaum, and Paul D. Ronney for winning the DPA in the Laminar Flames colloquium.

The authoritative paper, Effect of stoichiometric mixture fraction on nonpremixed H2–O2–N2 edge-flames, has significantly advanced the knowledge of edge-flames in fuels with very high diffusivity, specifically hydrogen.  Edge-flames form the boundary between burning and non-burning regions of a flame sheet, and characterizing their properties is critical to understanding the behavior of flames in highly turbulent flows such as those occurring in both piston/cylinder and gas turbine (jet) engines.

Previous edge-flame research performed by Prof. Ronney’s group showed that for hydrocarbon-oxygen-inert mixtures, edge-flame behavior was affected by both the unusual chemistry of hydrocarbon-oxygen combustion and the diffusivity of the fuel molecule. The team wanted to determine if this knowledge could be applied to hydrogen in an attempt to understand the behavior of this clean-burning fuel. Their study delved into the factors that affect flame structure when using hydrogen fuel.

To carry out their study, the researchers modified a previously-constructed apparatus that provides a simple paradigm for the processes that occur inside an engine combustion chamber. Because of the different chemistry and high diffusivity of hydrogen, as well as the fact that hydrogen flames are not visible to the naked eye or standard cameras, the team had to alter the approach they took in their previous research. They used a different type of flame imaging system and carefully controlled the amount of nitrogen dilution supplied separately to the fuel and oxidizer flow streams.

The edge-flames in hydrogen fuel behaved very differently from that in hydrocarbon fuels. In particular, when the fuel stream was diluted, the flames became unstable and broke into multiple fragments; no such behavior had been found in hydrocarbon fuels. Moreover, even when the flames were continuous rather than broken, their response to dilution was very different from that previously observed in hydrocarbon fuels.  Their findings could be applied to the modeling of combustion in hydrogen-fueled engines, resulting in lower emission alternatives to the standard hydrocarbon-fueled engines. Ultimately, this could lead to the design of more efficient emission-free engines for ground and air vehicles.

The scientific team’s work was conducted entirely in their lab at the University of Southern California (USC), USA. Their work was also featured on the USC Viterbi School of Engineering news page, “Making a zero-emissions fuel even more effective”.

Over 1,600 papers were submitted to the 37th Symposium in 13 combustion science colloquia. Those papers were categorized by teams of colloquium coordinators and co-chairs, and then distributed to approximately 1,000 scientific reviewers. One paper in each discipline was awarded the recognition of Distinguished Paper.

The 13 Distinguished Papers undergo committee review for consideration to receive the Silver Combustion Medal that will be awarded during the 38th International Symposium in Adelaide, Australia. A paper selected for this honor exemplifies quality, achievement, and significance to advance a field of combustion science. Distinguished papers are selected biennially from among the scientific papers presented during the International Symposium on Combustion and accepted for publication in the Proceedings of The Combustion Institute.