In this third installment of a 14-part series of monthly articles, The Combustion Institute recognizes the 2017 Distinguished Papers selected from among the scientific papers presented during the 36th International Symposium on Combustion. Congratulations to Jeffrey O’Brien, Colin A.Z. Towery, Peter E. Hamlington, Matthias Ihme, Alexei Y. Poludnenko, and Javier Urzay for winning the DPA in the Turbulent Flames colloquium.

The authoritative paper, The cross-scale physical-space transfer of kinetic energy in turbulent premixed flames, has expanded fundamental understanding of how chemical energy is released by combustion chemical reactions and then transferred into kinetic energy of a gaseous environment. The scientific team performed their research within combustion environments that can be found in internal combustion engines, where premixed flames propagate in the cylinder upon igniting the fuel and air mixture, or in gas turbine combustors, where a continuous flow of fuel and oxidizer burns in a similar fashion.

The scientific team researched the problem of how premixed flames propagate in turbulent gas environments. Turbulence in fluids is manifested as a myriad of eddies of vastly different sizes that move around and create velocity fluctuations. These velocity fluctuations influence the propagation of flames by distorting, broadening and wrinkling the flame front, and in most cases, increasing the flame propagation speed. However, little is known about the inverse problem: how the flame front influences those eddies and their velocity fluctuations as they propagate through the gas.

The question of how the combustion energy released in the flame is transferred to the gas is complicated, in that the excess energy created by combustion has to be repartitioned in a nontrivial manner among all the different eddy sizes. In the paper, the authors precisely described the energy transfer landscape, and for that purpose they used massively parallel numerical simulations of turbulent deflagrations performed using thousands of CPUs simultaneously in the most advanced supercomputer clusters in the United States.

In the short term, the paper’s results will be used to improve physical subgrid-scale models of turbulent transport and turbulent combustion in numerical simulations. For instance, it is unclear whether current turbulent transport models can handle flows where there is an intense release of chemical heat in the subgrid scales of the turbulence. The results are also relevant from an engineering standpoint, in that the fundamental understanding of the propagation of turbulent premixed flames in engines is important for increasing combustion stability and efficiency, and for reducing pollutant emissions and decreasing fuel consumption.

In the future, the scientific team hopes to use this research to better command ignition and flame propagation processes in combustors for hypersonic aircrafts, where flame stabilization is an issue. For instance, as research progresses, it becomes possible to choose a point in space and time to ignite a flammable mixture in a combustor, such that the combustion energy would be most efficiently funneled across eddy scales in the turbulence cascade. The authors are also interested in unveiling the role of this energy transfer in processes related to deflagration to detonation transition, whereby slow moving flames are transformed into fast and large-amplitude reacting supersonic pressure waves as a result of the interaction of the flame with the fluctuations of velocity and pressure in the ambient gas. These waves cause extensive damage in accidental explosions and could be harvested as a source of extra thrust and power in supersonic combustion engines of hypersonic aircrafts or in rotating detonation engines for next-generation rocket propulsion systems.

The scientific team’s work was started at Stanford University, United States in 2014, during the Center for Turbulence Research (CTR) Summer Program. The authors kept sharpening their results and conclusions thereafter until the scope of research was completed in 2016 for the paper’s submission to the 36th Symposium.

About 1,300 papers were submitted to the 36th Symposium in 14 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 14 Distinguished Papers undergo committee review for consideration to receive the Silver Combustion Medal that will be awarded during the 37th Symposium in Dublin, Ireland. 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.