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ENERGY ANALYSIS OF DROPLET IMPINGEMENT ON AN INCLINED WALL UNDER DIFFERENT TEMPERATURE ENVIRONMENTS
Date of Award
Campus Access Dissertation
Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)
Administrative Home Department
Department of Mechanical Engineering-Engineering Mechanics
Committee Member 1
Committee Member 2
Jeffrey D. Naber
Committee Member 3
The study of spray-wall interaction is of great importance to understand the dynamics that occur during fuel impingement onto surfaces in internal combustion engines. Basic droplet-wall interaction is imperative as well since it can quantitatively provide an estimation of energy transformation in spray-wall interaction. Furthermore, it can also influence the air-fuel mixing and hydrocarbon and particle emissions at combusting conditions.
Firstly, a theoretical model which considers energy conservation before and after impingement was developed in terms of βm (the ratio of maximum spreading length to initial droplet diameter) under different temperature environments. Then, experimental work of droplet impinging on an inclined wall was performed at a certain range of the Weber number (20 to 800) with various impact angles (45° to 90°), as well as droplet-wall temperature configurations (25°C to 150°C). The analytical model was validated and evaluated with experimental results. The validated model can be employed to predict maximum spreading length of the droplet. It can also be further utilized to determine the transition from capillary regime to viscous regime at different impact angles.
Simulations of single droplet impinging on an inclined wall under isothermal and non-isothermal conditions were performed with OpenFOAM by means of the volume of fluid (VOF) technique. An additional vapor phase is introduced apart from the liquid and gas phases in evaporation sub-model to understand the mixing and diffusion of vapor phase. The transient transformation of kinetic energy, gravitational energy, viscous dissipation energy, adhesion energy, deformation energy, and transferred heat energy under different impinging Weber number and wall temperatures were analyzed parametrically.
Water injection has been used to reduce the charge temperature and mitigate knocking. Thus, experimental and computational studies of water spray in constant volume combustion chamber (CVCC) under gasoline conditions were conducted. With the aid of Mie-scattering and schlieren techniques, spray study was firstly conducted using a multi hole injector by injecting pure water and water-methanol mixtures into CVCC at naturally aspirated and boosted engine conditions. Simulations of water spray injection were also performed under the framework of CONVERGE© using the Eulerian-Lagrangian modeling approach. The amount of vaporized water, evaporation rate, and saturation ratio before and after wall impingement were analyzed and compared.
Moreover, a data-driven approach utilizing Machine Learning (ML) classification models was proposed for the identification of droplet-wall post-impingement patterns. A data pool with 1093 observations of single droplet impinging on a dry wall was established. Sixteen input features describing liquid properties and wall characteristics were firstly determined. Feature engineering methods were adopted to investigate the most informative and influential features of the splash phenomenon. Selected feature subsets/spaces were then fed into six well-known classifiers individually for the model tuning. The performance of the classifiers was evaluated by metrics such as accuracy, precision, recall, and F1 score, and compared with previous empirical criterion-based models.
To summarize, the main objective of this dissertation is going to benefit the understanding of the fundamental droplet impingement which will assist in studying impinged spray in reacting engine conditions. An analytical view of energy transformation is analyzed and further revealed by the CFD simulations.
Zhai, Jiachen, "ENERGY ANALYSIS OF DROPLET IMPINGEMENT ON AN INCLINED WALL UNDER DIFFERENT TEMPERATURE ENVIRONMENTS", Campus Access Dissertation, Michigan Technological University, 2023.