Enhancement and Control of Turbulent Reactive Flows via Electrical Fields - A Mesoscopic Perspective

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Based on the UK and the world's energy structures for the foreseeable future, new combustion concepts and advanced engine technologies are required to drastically increase energy efficiency and reduce emissions in order to have the most direct and significant beneficial impact on the climate and human health. Electric field assisted combustion can be a viable option in the control of flames, leading to improved flame stability, higher efficiency and reduced pollutant emissions. Flames are under weakly ionized plasma states, since charged particles are generated in the reaction zones through chemi-ionization and subsequent ion chemistry. One promising technology is to utilize an electric field as an actuator for modulating a flame in order to achieve optimal burning and minimal emissions.Electric field assisted combustion is a multi-physical, multiscale, and nonequilibrium process. The direct action of the electric field is on charged particles (cations, anions and electrons), which happens at the atomic scale. Further up the scale, a drift of cations or an ionic wind is generated. At macroscales, flame propagation, structure and, in some cases, instability are observed. As turbulence spans a wide range from micro- to macroscales, numerous mesoscale interactions occur among the electric field, ionic wind, turbulence and flame. Existing studies have been focused on macro-phenomena, while crucial links between the atomic events and the macro-phenomena have rarely been investigated by either experimental or numerical methods. In addition, there is a wide range of time scales associated with the above phenomena, which causes hydrodynamic, thermodynamic and chemical nonequilibrium. Nonequilibrium effects have rarely been quantified if studied at all. With the availability of the national HEC platform such as ARCHER, it is now feasible and timely to tackle the complex interactions among the electric field, fuel chemistry, ion chemistry, flame and turbulence in order to further our understanding of the underlying mechanisms. Moreover, effects of the electric field on turbulent flames will be quantified by advanced simulation techniques.In this project, advanced numerical simulations will be further developed and employed to clarify the key physical mechanisms responsible for the electric field - flame interactions, ultimately leading to technologies for control and optimization of combustion using electric fields. Building on substantial in-house expertise and successful preliminary studies, direct numerical simulation (DNS) will be further developed to incorporate realistic ion chemistry to study the macro-behaviours such as turbulent flame structure, dynamics and instability in the presence of an externally applied electric field. In addition, our newly developed mesoscopic simulation approach, the discrete Boltzmann method (DBM) capable of simulating nonequilibrium combustion, will be applied to revealing the crucial interactions between the electric field and the flame at mesoscales. The study will answer many unanswered fundamental questions behind the "magic" effect of the electric field. For example, how are chemical pathways affected by the imposed electric field? How does turbulence affect momentum and energy transfer between the electric field and the flame? How are macro-properties of flames affected by mesoscopic and atomistic events? Answering these questions will help us to develop strategies for combustion control, leading to lower emissions and more efficient energy utilization.