Advanced modelling for two-phase reacting flows

Burning oil-based fuels accounts for approximately 31% of UK greenhouse gas emission as well as being a major culprit in toxic, irritant and carcinogenic pollutants on a national scale (www.naei.org.uk). Nearly all forms of transport currently rely on liquid fossil fuels, and this use of liquid fuel is likely to continue; the storage technology for electricity and hydrogen is not good enough completely to replace all use of energy-dense liquid fuels in heavy goods vehicles and aircrafts. It is necessary, therefore, to explore ways of reducing emissions and raising efficiency in the combustion of liquid fuel.Engine designers want computer programs to help them invent ways to use less fuel and produce less pollution. But the computational models currently available are not adequate to predict some important effects: such as how blends of future carbon-neutral bio-fuels will change engine performance.When a liquid fuel is injected in an engine, three interacting processes take place. First the liquid and gas display turbulence, i.e. they swirl and mix chaotically. Second, there is evaporation of the many compounds in the liquid fuel into gaseous fuel vapour. Third, there is combustion, i.e. the fuel combines with oxygen to form hundreds of different intermediate and final combustion products. Turbulence, evaporation and combustion are fundamentally difficult to compute. One reason is that they happen among a wide range of spatial and temporal scales and therefore need to be calculated with a very fine resolution. Another is that so many different chemical compounds are involved. As a result, simulating even a few milliseconds of a highly turbulent combustion process far exceeds the resources of the largest supercomputers in the world.This research proposal aims to solve these problems by providing an accurate, practical and rigorous model for the injection and combustion of liquid fuel blends. High-resolution simulation data will be analysed to provide fundamental information on the coupling among gasses and liquids. The resultant data will be used to devise a model that synthesises turbulence, evaporation and combustion processes into a unifying framework. This new model has great potential because it can describe evaporation and mixing processes, even those occurring at the smallest scales of the flow, in detail and at an acceptable computational cost.The proposed model will not only be useful for designing advanced combustion systems. The challenging combination of physics found in spray combustion is also found in a number of industrial processes, including spray-drying in food and chemical industries, spray-painting, and spray-forming of metal components. This research will also demonstrate how the new modelling can be used to improve design of more efficient industrial processes.Finally some processes that play a role in turbulent spray combustion also play a critical role in environmental processes affecting local air quality and global climate change. Environmental regulators at present often have to make high-impact environmental policy decisions without an accurate way to predict the consequences. The proposed model will be applied in this arena to help to provide this badly needed information to policy-makers, thus contributing to sound environmental policy.

The engineering methods developed in this project will result in better tools to predict engine performance, assist engine design, and model other industrial spray processes. This will result in substantial economic and environmental improvements. Economic impact: In the first instance the proposed modelling will be developed in close collaboration with Rolls-Royce plc, with whom the research fellow has previously successfully collaborated. Regular communication with Rolls Royce will keep the academic objectives of the research aligned with real industrial requirements and simulation of appropriate test cases in collaboration with Rolls-Royce engineers will demonstrate the advantages of the methods and give Rolls-Royce expertise in their application (knowledge transfer). This aspect of the proposed research will result in an immediate business advantage for UK-based Rolls Royce, due to reduced development costs and timescales, and subsequent competitive advantage as improved combustor designs come to market (5-15 years). Beyond aerospace propulsion several other industrial applications can benefit from the proposed model. Examples of relevant technologies are spray-drying in food and chemical industries, spray-painting, and spray-forming of metal components. The research fellow will seek suitable partners for these activities through the Cambridge University departments for Manufacturing and Chemical Engineering. Improvement in these industrial applications will result in short and medium-term economic competitive advantage. Developing innovative high-impact engineers: The research programme will enable the training of two post-graduate engineers up to the degree of doctor. The design of the programme provides the students with the opportunity both to contribute fundamental engineering science and to participate in its industrial application, which means these students will graduate with an exceptional skill-set in theoretical analysis and computational simulation. These attributes are highly prized across science, engineering and finance, and the engineers will thus have excellent potential to continue their positive contribution to UK industry over the course of their careers. The Ph.D. students will start in the second year of the research programme, and it will take them 3.5 years to graduate. Environmental impact: All of society is affected by harmful pollutant emissions and anthropogenic climate change that is caused by modern industry. The proposed research will contribute to abatement of these processes in two ways. First, the research will facilitate reduction in carbon dioxide and pollutant emission through contributing to improved design of engines and other industrial applications as discussed above. Second, air quality and climate policy can benefit from the improved models developed in this project. Because of similarities between physical processes in spray combustion and atmospheric flows (turbulence, chemical reaction, evaporation and condensation), the proposed improvements to modelling can be applied to the modelling of atmospheric processes. Examples are cloud formation, or the dispersion and evolution of reactive, two-phase pollutants such as aerosols in the atmosphere. Improved atmospheric modelling will improve predictive tools that can help environmental regulators make high-impact environmental policy decisions. For the new technology in this proposal to impact policy makers it must be accepted and adopted by air quality engineers and climate scientists for their studies. This impact is to be achieved by dedicating a portion of the research programme to demonstrating the improvement the new modelling provides over the state of the art in environmental modelling, the results of which will be publicised strategically in appropriate publications and at conferences. Results of applicable modelling studies will hopefully start to become available in 5-10 years.