Advanced modelling for two-phase reacting flows

燃烧油基燃料约占英国温室气体排放量的31%，也是全国范围内有毒、刺激性和致癌污染物的罪魁祸首（www.naei.org.uk）。目前几乎所有形式的运输都依赖液体化石燃料，而且这种液体燃料的使用可能会继续下去;电力和氢气的储存技术还不足以完全取代重型货车和飞机中所有高能量液体燃料的使用。因此，有必要探索减少排放和提高液体燃料燃烧效率的方法。发动机设计人员需要计算机程序来帮助他们发明使用更少燃料和产生更少污染的方法。但目前可用的计算模型不足以预测一些重要的影响：例如未来碳中性生物燃料的混合物将如何改变发动机性能。当液体燃料注入发动机时，发生三个相互作用的过程。首先，液体和气体显示湍流，即它们涡旋并混乱地混合。第二，液体燃料中的许多化合物蒸发成气体燃料蒸气。第三，燃烧，即燃料与氧气结合形成数百种不同的中间和最终燃烧产物。湍流、蒸发和燃烧从根本上说是难以计算的。一个原因是它们发生在广泛的空间和时间尺度上，因此需要以非常精细的分辨率进行计算。另一个原因是涉及到许多不同的化合物。因此，模拟哪怕是几毫秒的高度湍流燃烧过程，也远远超过世界上最大的超级计算机的资源。本研究提案旨在通过为液体燃料混合物的喷射和燃烧提供准确、实用和严格的模型来解决这些问题。高分辨率的模拟数据将进行分析，以提供气体和液体之间的耦合的基本信息。由此产生的数据将被用来设计一个模型，综合湍流，蒸发和燃烧过程到一个统一的框架。这种新的模型具有很大的潜力，因为它可以描述蒸发和混合过程，即使是那些发生在最小尺度的流动，在一个可接受的计算成本，所提出的模型不仅是有用的设计先进的燃烧系统。喷雾燃烧中具有挑战性的物理组合也存在于许多工业过程中，包括食品和化学工业中的喷雾干燥，喷漆和金属部件的喷雾成型。这项研究还将展示如何使用新的模型来改进更有效的工业过程的设计。最后，一些在湍流喷雾燃烧中起作用的过程在影响当地空气质量和全球气候变化的环境过程中也起着关键作用。目前，环境监管机构往往不得不在没有准确预测后果的情况下做出高影响力的环境政策决定。拟议的模式将应用于这一竞技场，以帮助向决策者提供这一迫切需要的信息，从而有助于制定健全的环境政策。

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.