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

• Applicant: Professor Dr.-Ing. Lars Zigan
• Subject Area: Hydraulic and Turbo Engines and Piston Engines
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 315067718

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.

• DFG Programme: Research Grants