Direct Numerical Simulation and Advanced Modelling of Turbulent Flame Kernels for High-Efficiency Low-Emission Spark Ignition Engine

道路运输加剧了碳排放和气候紧急情况。向电动汽车的过渡将需要中间解决方案，尤其是重型货车。开发高效率、低排放的新型发动机既昂贵又费时，因此需要快速、准确的计算模型。在实践中，快速工业软件牺牲了许多详细的小规模物理，而这些物理必须被工程模型所取代。开发这样的模型是具有挑战性的，并且依赖于高保真的模拟，包括基于第一原理的基本物理；这在工业环境中是做不到的里卡多以发动机效率方面的专业知识为基础，一直是提高汽油、柴油、新兴生物燃料和燃气发动机效率和减少排放的发动机技术的先驱。目前最先进的应用火花点火发动机建模经常依赖于紊流火焰速度的经验闭包。这受到与发动机运行参数范围内的有效性和适用性以及模型固有调谐系数影响相关的大量不确定性的影响。目前，可用的实验数据（大多数集中在平面火焰上）并没有提供足够的信息来减少这种不确定性。该项目将使用典型发动机条件下火焰核的高保真度模拟，以提高我们的基本理解，提高准确性和鲁棒性，并减少与湍流火焰速度预测相关的不确定性本项目的目的是提高紊流火焰模型在工程应用中的预测能力。该项目由Ricardo UK赞助，其软件将为模型开发和评估提供测试平台。*使用PeleLM创建一个高细节和高精度的直接数值模拟数据库，包括湍流火焰核和火焰壁相互作用。*利用数据库发展湍流燃烧行为的基本理解，以及IC发动机的设计如何影响火焰行为，从而影响发动机性能。*使用数据库，比较Vectis使用的湍流火焰模型的性能和准确性，并根据需要开发和实施修改项目计划将建立一个火焰核高保真模拟数据库，涵盖与SI发动机相关的一系列条件；里卡多将根据可用于DNS初始化的经过调整的RANS模拟，提供代表天然气和汽油发动机的流动和湍流现场条件。通过对湍流火焰响应的详细分析和对湍流动能和能量耗散率输运方程中单个项的评估，将发展基本的理解。这种分析是一个独特的优势，只有通过分析DNS才能实现，并将使开发湍流火焰模型的重要术语得到识别，这些模型包括积分长度尺度、热量释放和曲率等影响。由此产生的湍流火焰模型可以在VECTIS CFD套件中实现，并在真实的发动机模拟中进行评估，作为学生在里卡多英国学习时间的一部分。DNS计算将使用PeleLM进行，PeleLM是由劳伦斯伯克利国家实验室计算科学与工程中心开发的。模拟规模将分阶段进行，从高规格工作站开始，通过纽卡斯尔的高性能计算设备“火箭”，直到国家超级计算机“射手”（计算时间应用于UKCTRF）。

1 IntroductionRoad transportation contributes to carbon emissions and the climate emergency. The transition to electrified vehicles will require intermediate solutions, especially for heavy goods vehicles. Developing new engines with high efficiency and low emissions is expensive and time intensive, hence fast and accurate computational modelling is necessary. In practise, fast industrial software sacrifices much of the detailed small-scale physics, which has to be replaced by engineering models. Developing such models is challenging and relies upon high-fidelity simulations that include fundamental physics based on first principles; this cannot be done in an industrial setting.2 OverviewRicardo was founded on expertise in engine efficiency, and remains a pioneer in engine technology for improving efficiency and reducing emissions from gasoline, diesel, emerging bio-fuel and gas engines. Current state-of-the-art applied spark-ignition engine modelling frequently relies upon empirical closures for turbulent flame speed. This suffers from substantial uncertainties associated with validity and applicability across the range of the engine operation parameters and the effect of the tuning coefficients inherent in the model. At the moment, available experimental data (with the majority focusing on planar flames) does not provide sufficient information to reduce this uncertainty. This project will use high-fidelity simulation of flame kernels under typical engine conditions to improve our fundamental understanding, enhance accuracy and robustness, and to reduce uncertainty associated with turbulent flame speed prediction.3 Research QuestionThe aim of this project is to improve predictive capabilities of turbulent flame models for engineering applications. The project is sponsored by Ricardo UK, whose software will provide the test bed for model development and evaluation.Objectives:* Create a high detail and high accuracy direct numerical simulation database using PeleLM consisting of turbulent flame kernels and flame wall interactions.* Exploit the database to develop fundamental understanding of the behaviour of turbulent combustion and how the design of an IC engine can affect the flame behaviour, and therefore engine performance.* Using the database, compare the performance and accuracy of the turbulent-flame models used by Vectis, and develop and implement modifications as necessary.4 Project PlanA database of flame kernel high-fidelity simulations will be constructed that span a range of conditions relevant to SI engines; Ricardo will supply flow and turbulent field conditions representative for natural gas and gasoline engines, based on tuned RANS simulations that can be used for DNS initialisation. Fundamental understanding will be developed through detailed analysis of turbulent flame response and assessment of individual terms in the transport equations for turbulent kinetic energy and energy dissipation rate. Such analysis is a distinct advantage only possible through analysis of DNS, and will enable identification of important terms for developing turbulent flame models that incorporate effects such as integral length scale, heat release and curvature.The resulting turbulent flame models can then be implemented in the VECTIS CFD suite and evaluated in real engine simulations, as a part of the student's time at Ricardo UK. The DNS calculations will be carried out using PeleLM, which was developed at the Center for Computational Sciences and Engineering at the Lawrence Berkeley National Laboratory. Simulations increasing in size will be carried out in stages, starting from a high-specification workstation, through Newcastle's HPC facility "Rocket", up to the national supercomputer "Archer" (compute time application to UKCTRF).