Welch, Cooper Haddad (2024)
The Influence of In-Cylinder Flows on Spark-Ignition Engine Combustion.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00026340
Dissertation, Erstveröffentlichung, Verlagsversion

Kurzbeschreibung (Abstract)

The urgent need for a global energy transition from traditional fossil fuels to renewable sources has been underscored by the alarming rise in global temperatures and growing concerns about air pollution. Light-duty internal combustion engines, despite years of technological advances, continue to contribute significantly to greenhouse gas emissions and harmful pollutants, necessitating further progress in engine technologies for a multi-faceted solution to combat climate change and improve air quality. This cumulative dissertation addresses the critical challenge of understanding and controlling the cycle-to-cycle variability in engine combustion that directly impacts emissions. It extensively investigates the influence of in-cylinder flows on combustion phenomena in an optically accessible spark-ignition engine with the overarching goal of reducing cycle-to-cycle variations. The study includes five peer-reviewed articles and unpublished work, providing a comprehensive analysis of the relationship between engine flows and combustion processes from simplified to realistic engine configurations.

High-speed diagnostics and robust analysis techniques are employed to advance the development of predictive combustion models that contribute to improved engine design. This work extends existing measurement techniques by combining cutting-edge equipment with novel analysis approaches, culminating in the development of phenomenological models. In addition, it provides a vast database of accurate boundary conditions and multi-parameter vector and scalar data to benefit the engine research community and improve numerical simulations and models.

The thesis is structured in two parts, with each publication building on the previous one and increasing in complexity. The first part focuses on the fundamental processes of intake flows and their interaction with direct injection sprays. A designed flow bench integrated into the engine test cell is used to study turbulent intake flows of the spray-guided cylinder geometry, providing valuable validation data and controlled flow conditions for spray analysis. Building on the flow bench study, the investigation of backflow-induced pressure oscillations in the intake manifold during part-load motored operation reveals their significant impact on intake flow and tumble development, emphasizing the need to consider acoustics and accompanying physics in engine simulations. Finally, the relationship between in-cylinder flows and direct injection sprays is investigated by analyzing the influence of flow on spray morphology under different conditions, providing essential boundary conditions and multi-parameter data for validation.

The second part builds on the knowledge and techniques developed in the first part to explore cyclic variations in engine performance under diluted fired conditions. The use of different levels of external exhaust gas recirculation to alter flame speed, enhances the effects of flow on the combustion process, particularly ignition and flame development. Analysis of the influence of flow on ignition using measured voltage and current of the ignition coil, combined with flow fields, spark plasma images, and flame visualizations, sheds light on the significance of horizontal flow across the spark plug in promoting more stable and faster combustion. Multivariate and conditioned statistical analysis techniques are used to develop flow-flame and flow-misfire combustion models that describe cycle-to-cycle variations under diluted conditions, offering further promise for optimized design and control.

This dissertation makes substantial contributions to the engine research community by emphasizing the pivotal role of in-cylinder flows in the combustion processes of spark-ignition engines. Furthermore, the availability of a comprehensive database of controlled boundary conditions and well-documented multi-parameter data facilitates the further development of phenomenological models and computational fluid dynamics simulations, thereby promoting continued advances in engine technology for a sustainable future.

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