Characterisation of diesel engine mixture formation using laser-induced fluorescence imaging

该项目的目的是开发一种基于激光诱导荧光（LIF）的测量方法，用于同时测定燃料密度和温度，以表征跨临界喷涂过程，这在广泛的能源和工艺工程系统以及制药应用中高度相关。该技术目前正在进一步发展，用于液滴周围的测量。对于液相的识别，检测和评估概念将通过平面Mie散射和微观LIF设置进行扩展。由于目前的发展，重点将不再是集成电路发动机中的多次注入，而是更多地关注在测量单元中简化条件下跨临界注入过程的基本分析。该项目旨在有助于更好地理解跨临界注入过程中液滴蒸发或扩散混合以及混合物形成的物理行为。它还将为模型和数值模拟方法的开发和验证提供全面的参考数据，其中一些模型和数值模拟方法无法预测跨临界混合行为。使用模型燃料（如正庚烷、异辛烷）对跨临界注入进行了研究，这些燃料与广泛的技术过程有关。燃料也可以作为碰撞伙伴影响荧光信号。因此，我们还研究了其他与应用相关的燃料对LIF信号的影响，如乙醇或合成含氧燃料，如POMDME（聚甲醛二甲醚）。在这种情况下，还分析了甲烷混合物对LIF信号的影响，这对于精确研究双燃料发动机的混合物形成具有重要意义。在可变边界条件下，将进行燃料密度和气体温度的微观和宏观测量。作为一个子目标，将确定跨临界注射评价的特征。这包括识别喷雾中发生相变或向扩散混合过渡的区域。蒸发时间或达到超临界状态前的寿命将被确定，这方面迄今尚无定量研究。作为进一步的子目标，确定了评估混合物形成的数量，例如气相和液相的渗透深度和喷雾角度。此外，“气体夹带”将被量化。将数据与模型进行比较，并对模型进行相应的修改和扩展。所有的研究都是在为此目的而修改的校准池中进行的，它可以在精确可调的温度和示踪剂浓度下进行准确的测量。

The aim of the project is to develop a measurement method based on laser-induced fluorescence (LIF) for the simultaneous determination of fuel density and temperature to characterize transcritical spray processes, which are highly relevant in a wide range of energy and process engineering systems as well as in pharmaceutical applications. The technique is now being further developed for measurements in the droplet surrounding. For the identification of the liquid phase, the detection and evaluation concept will be extended by a setup for planar Mie scattering and a microscopic LIF setup. Due to current developments, the focus will be less on multiple injections in the IC engine and more on the fundamental analysis of the transcritical injection process under simplified conditions in a measuring cell. This project is intended to contribute to a better understanding of the physical behavior of droplet evaporation or diffusive mixing as well as mixture formation during transcritical injection. It will also provide comprehensive reference data for the development and validation of models and numerical simulation approaches, some of which fail to predict transcritical mixing behavior.Investigations of transcritical injections are carried out with model fuels (such as n-heptane, isooctane), which are relevant for a wide range of technical processes. The fuels can also affect the fluorescence signal as collision partners. Therefore, the influence of other application-relevant fuels on the LIF signal is also investigated, such as ethanol or synthetic oxygenated fuels like POMDME (polyoxymethylene dimethyl ether). In this context, the effect of methane admixture on the LIF signal is also analyzed, which is important for accurate mixture formation studies in dual-fuel engines. Microscopic and macroscopic measurements of fuel density and gas temperatures under variable boundary conditions will be performed. As a sub-objective, characteristics for the assessment of transcritical injection will be determined. This includes e.g. the identification of areas in the spray with phase change or the transition to diffusive mixing. Times for evaporation or lifetimes until the supercritical state is reached will be determined, for which no quantitative studies are available to date. As a further sub-objective, quantities for assessing the mixture formation are determined, such as the penetration depth and the spray angle of the gas and liquid phases. Furthermore, the "gas entrainment" will be quantified. The data will be compared with models, which will be modified and extended accordingly. All investigations are carried out in a calibration cell modified for this purpose, which enables accurate measurements at precisely adjustable temperatures and tracer concentrations.