Development of Efficient and Clean Turbulent Stratied Mixture Combustion Technologies for Future Combustors using High-Fidelity Simulations

根据美国能源部的数据，化石燃料的燃烧占世界能源使用量的80%，他们的预测显示，到2050年，这一比例将减少到只有68%。燃烧产生的排放会导致气候变化，导致人口稠密城市的空气质量变差。因此，污染控制法规变得越来越严格，这对工程师设计具有可接受发动机效率的环境友好型内燃机提出了重大挑战。在一些工程应用中，燃烧发生在燃料和氧化剂在燃烧之前既不均匀混合也不完全分离的充气环境中。这种燃烧通常被称为分层充填燃烧或部分预混燃烧。这种不均匀的混合气允许使用更稀薄的总体燃料/空气比，这有可能显著减少污染物排放，同时提高发动机效率。该技术目前正被用于现代车辆的直接喷射和均质充气压缩点火发动机，以及飞机的稀薄预混合预混燃气涡轮发动机以及许多其他应用。在大多数情况下，这种发动机仍处于初级阶段。与预混和非预混对应物相比，燃烧行为的不确定性阻碍了它们的广泛采用。以汽车发动机为例，如果混合气准备不当，可能会因压力过大而导致预燃，或者由于火焰没有消耗所有可用反应物而导致发动机爆燃。这两者都大大降低了发动机的效率。因此，需要进一步研究合理的混合气制备方法，以实现可靠、清洁和高效的分层混合气燃烧。在本研究项目中，将在国家高性能计算设备上进行湍流分层混合气燃烧的直接数值模拟。与预混和非预混情况相比，分层混合气燃烧的研究很少。直接数值模拟完全解决了湍流反应流，不需要湍流模型(即近似)。模拟数据可以作为实验数据，具有很高的分辨率。作为本项目的第一步，将使用简单的化学方法进行三维直接数值模拟，以提高对分层装药燃烧过程的热方面的基本理解。简化的化学减少了要求解的方程式的数量，从而使模拟时间更快。基于这一认识，将进行详细的化学3D模拟。这些模拟将提供重要的物理洞察，以了解尚未被很好地理解的湍流混合物理，并将进一步了解清洁、高效燃烧的最佳混合物和湍流特性。由于这些模拟具有如此高的计算成本，它们不能用于常规工程计算。因此，从这个模拟数据库中获得的物理洞察力将被转化为基于雷诺平均Navier-Stokes和大涡模拟框架的工业求解器的精确湍流模型。这项工作的主要好处是工业部门致力于开发低污染、高效的汽车发动机和燃气轮机的新概念。这些应用中的设计过程取决于工程计算的预测能力。

According to the U.S. Department of Energy, the combustion of fossil fuels accounts for 80% of the worlds energy usage, and their projections show this gure reducing to only 68% in 2050. The emissions resulting from combustion lead to climate change and poor air quality in densely populated cities. Consequently, pollution control regulations are becoming ever stricter, posing a major challenge for engineers to design an environmentally friendly combustion engine withacceptable engine efficiency.In some engineering applications, combustion takes place in a conguration where the fuel and oxidiser are neither homogeneously mixed nor completely separated from each other prior to combustion. This kind of combustion is often referred to as stratified charge combustion or partially premixed combustion. This inhomogeneous mixture allows a leaner overall fuel-air ratio to be used, which has the potential to signicantly reduce pollutant emissions while increasingengine efficiency. The technology is currently being used in direct injection and homogeneous charge compression ignition engines in modern vehicles, and in lean premixed prevapourised gas turbine engines in aircraft as well as many other applications. Such engines are still in their infancy in most cases. Uncertainties regarding combustion behaviour, when compared with premixed and non-premixed counterparts, is impeding their widespread adoption. Taking automotive engines as an example, improper mixture preparation and can lead to pre-ignition caused by excessive pressure, or engine knocking due to the flame not consuming all of the available reactants. Both of these drastically reduce engine efficiency. Thus, further research is required into proper mixture preparation for reliable, clean and efficient stratified mixture combustion.In this research project, Direct Numerical Simulations of turbulent stratied mixture combustion will be performed on national high-performance computing facilities. The number of such studies of stratified mixture combustion is scarce when compared with premixed and non-premixed cases. Direct Numerical Simulations resolve the turbulent reacting flow entirely, without the need for turbulence models (i.e. approximations). The simulation data can be treated as experimental data with a very high resolution. As the first step of this project, three-dimensional Direct Numerical Simulations will be performed with simplied chemistry to improve the fundamental understanding of the thermal aspect of the stratified charge combustion process. Simplified chemistry reduces the number of equations to be solved resulting in much quicker simulation times. Based on this understanding, detailed chemistry 3D simulations will be carried out. These simulations will provide important physical insight into the not-well-understood physics of turbulent mixing and will further knowledge regarding optimal mixture and turbulence properties for clean, efficient combustion. As these simulations are of such high computational cost, they cannot be afforded for routine engineering calculations. Therefore, the physical insight obtained from this simulation database will be transferred into accurate turbulence models for industrial solvers based on the Reynolds Averaged Navier-Stokes and Large Eddy Simulation frameworks.The major beneciaries of this work are the industrial sectors engaged in developing new concepts for designing low-pollution high-efficiency automotive engines and gas turbines. The design process in these applications depends on the predictive capability of engineering calculations.