Advancing predictive models for particulate formation in turbulent flames via massively parallel direct numerical simulations

Abstract

Combustion of fossil fuels is likely to continue for the near future due to the growing trends in energy consumption worldwide. The increase in efficiency and the reduction of pollutant emissions from combustion devices are pivotal to achieving meaningful levels of carbon abatement as part of the ongoing climate change efforts. Computational fluid dynamics featuring adequate combustion models will play an increasingly important role in the design of more efficient and cleaner industrial burners, internal combustion engines, and combustors for stationary power generation and aircraft propulsion. Today, turbulent combustion modelling is hindered severely by the lack of data that are accurate and sufficiently complete to assess and remedy model deficiencies effectively. In particular, the formation of pollutants is a complex, nonlinear and multi-scale process characterized by the interaction of molecular and turbulent mixing with a multitude of chemical reactions with disparate time scales. The use of direct numerical simulation (DNS) featuring a state of the art description of the underlying chemistry and physical processes has contributed greatly to combustion model development in recent years. In this paper, the analysis of the intricate evolution of soot formation in turbulent flames demonstrates how DNS databases are used to illuminate relevant physico-chemical mechanisms and to identify modelling needs.

Modeling of Fine-Particle Formation in Turbulent Flames

“…(This aspect is further discussed in Section 4.2.) Attili et al (2014Attili et al ( , 2015 and Bisetti et al (2014) also determined that turbulent motions cause soot to be predominantly transported to richer mixture fractions, whereas only a small fraction is transported toward the lean side at which oxidation removes soot mass.…”

“…Recently, DNS using detailed precursor chemistry has been conducted (Attili et al , 2015Bisetti et al 2012Bisetti et al , 2014. A particular focus of these studies is the role of gas-phase precursors on the soot-formation process.…”

“…The highest soot mass fraction occurs in regions in which the number density is relatively low, indicating that the soot particles in these regions are large and hence more difficult to eliminate through surface oxidation. Figure adapted with permission fromBisetti et al (2014).…”

Aerodynamics, computers and the environment

“…In relation to aeroengines, Bistetti et al 's [5] paper shows how direct numerical simulation can enhance our understanding of the science of pollution generation. The focus is very much on soot, which is of critical environmental importance but not what one immediately expects when considering environmental issues.…”

Simulation of aerosol nucleation and growth in a turbulent mixing layer

“…The small scale statistics of turbulent mixing affect this process strongly, thereby influencing the growth rates of droplets. This and related issues are well-known to the combustion research community interested in sooting flames, 35,37,38,68,69 but remain largely overlooked in the literature on aerosol condensation in inhomogeneous flows. This important mechanism is discussed in detail using Lagrangian statistics.…”