Advanced modelling for two-phase reacting flows

燃烧以石油为基础的燃料占英国温室气体排放量的约31%，也是全国范围内有毒、刺激性和致癌污染物的主要罪魁祸首（www.naei.org.uk）。目前，几乎所有形式的运输都依赖于液体化石燃料，而且这种液体燃料的使用很可能会继续下去；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上所有能量密集的液体燃料的使用。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。发动机设计师希望计算机程序帮助他们发明使用更少燃料和产生更少污染的方法。但是目前可用的计算模型还不足以预测一些重要的影响：比如未来碳中性生物燃料的混合物将如何改变发动机的性能。当液体燃料注入发动机时，会发生三个相互作用的过程。首先，液体和气体表现出湍流，即它们旋转并混乱地混合。第二，液体燃料中的许多化合物蒸发成气态燃料蒸气。第三是燃烧，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、蒸发和燃烧基本上是难以计算的。其中一个原因是，它们发生在大范围的空间和时间尺度中，因此需要以非常精细的分辨率进行计算。另一个原因是有很多不同的化合物参与其中。因此，即使模拟几毫秒的高度湍流燃烧过程，也远远超过了世界上最大的超级计算机的资源。本研究计划旨在通过提供一个精确、实用和严谨的液体燃料混合物喷射和燃烧模型来解决这些问题。将分析高分辨率模拟数据，以提供气体和液体之间耦合的基本信息。所得数据将用于设计一个模型，该模型将湍流、蒸发和燃烧过程综合成一个统一的框架。这个新模型具有巨大的潜力，因为它可以详细地描述蒸发和混合过程，即使是在最小尺度的流动中发生的过程，并且计算成本可以接受。所提出的模型不仅对设计先进的燃烧系统有用。在喷雾燃烧中发现的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局部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影响重大的环境政策决定。拟议的模式将应用于这一领域，以帮助向决策者提供这种急需的信息，从而促进健全的环境政策。

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.