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

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.

The proposed research has the potential to contribute to more efficient, cleaner and greener engine and power generation technologies. The outcomes will thus benefit the aerospace, automotive and energy sectors, which are vital to the UK economy and society in general. The UK has the second largest aerospace sector in the world, employing 230,000 people across the UK and generating about £30 billion worth of exports annually. More importantly, aerospace is a fast growing industry with demand for aircraft worth over $5.5 trillion in the next 20 years. In the meantime, the automotive industry in the UK accounts for more than £77.5 billion turnover and £18.9 billion value added annually. The sector accounts for 12.0% of total UK export of goods and invests £4 billion each year in automotive R&D. Finally, the energy sector is a large contributor to the UK economy, creating £24 billion in gross value added (GVA) and delivering further £88 billion in associated economic activities.

More efficient and cleaner energy and power systems will also be beneficial to the climate, the environment and human health through reduced CO2, soot, NOx, CO, UHCs, etc. To combat climate change, the UK government has set the overall targets to cut the GHG emissions by 34% by 2020, 50% by 2025 and 80% by 2050, compared to 1990 levels. As it stands, UK electricity generation from non-combustion means (nuclear, wind, solar and hydroelectric) is around 35% (in 2016). The energy from non-combustion means is about 10% of the total UK energy consumption. Therefore, continued efforts are required to increase the share of energy from non-combustion sources while great efforts should be devoted to improving efficiency and reducing emissions from combustion that still provides 90% of the UK energy mix. Air pollution from combustion is a major problem for big cities throughout the world including London. As London Mayor Khan said in 2017: "It's sickening to know that not a single area of London meets World Health Organisation health [air quality] standards, but even worse than that, nearly 95% of the capital is exceeding these guidelines by at least 50%." The problem is not limited to London, as 37 out of 43 zones across the UK are in breach of pollution limits. Air pollution causes diseases like asthma, strokes, heart disease, lung cancer. Even worse, air pollution kills up to 9,000 people in London and around 7 million worldwide each year. Such massive losses easily dwarf any price to pay to fight pollution.

In order to realise the above potential, we will firstly collaborate with Jeely Auto Group and Dassault Systèmes Simulia. Jeely is a global private company with a strong presence in the UK through its ownership of Volvo Cars and London Electric Vehicle Company (LEVC), and majority ownership of Lotus. Geely has invested heavily into its R & D, with a globalised network consisting of four R & D Centres in Coventry (UK), Gothenburg (Sweden), Hangzhou and Ningbo (China). To facilitate collaboration, detailed plans for mutual visits, data sharing and dissemination of results are in place. Meanwhile, Dassault is a global software giant, which has 64 R & D laboratories, 210,000 enterprise customers and 25 million users. It has a particular focus on serving the global aerospace industry. Through our associated project "HiLeMMS: High-Level Mesoscale Modelling System" (EPSRC grant No. EP/P022243/1, 08/2017 - 08/2020) as well as UKCOMES, we have been collaborating with Next Limit Dynamics (NLD), now part of Dassault, on the development of the lattice Boltzmann method (LBM). In addition to collaboration with specific companies, the project will produce new models and simulation methods, which will be implemented into the open-source code DL_MESO under the management of UKCOMES and Daresbury Laboratory, which will benefit a wide range of industrial sectors.