Rising sustainable awareness and regulatory requirements are the main drivers for continuous progress towards more efficient and environmentally friendly solutions in the marine industry. Fossil fuels have to be substituted with alternative fuels such as ammonia, hydrogen, or synthetic fuels in the future. This development poses technological challenges to creating efficient and reliable marine engines, especially for key components such as fuel injectors. Over the past decade, there has been an exponential growth of applications in Additive Manufacturing (AM), also known as 3D printing. AM technologies widen the possible design space and radically change the philosophy of how advanced products are created.
This dissertation aims to unravel the opportunities offered by AM for fuel injectors, exemplified in applications for large marine engines. Fuel injectors are operating at the heart of entire propulsion systems. Changes to their design or properties cause cascades of implications but can also create numerous chances. A novel framework combining Quality Function Deployment and Design for AM is applied to enable a value-driven implementation of AM amidst an encircled, complex, and matured system. This interdisciplinary approach necessitates the indispensable interplay between design, processes, and materials for AM.
The present work includes the conceptualization, embodiment, manufacturing, and testing of novel design ideas focusing on flow-related and thermo-structural features. Moreover, the AM process capabilities for fuel injectors are elucidated through a cross-technological benchmark study featuring state-of-the-art Laser Powder Bed Fusion (LPBF) and Binder Jetting (BJ) systems. The general dimensional accuracy and surface texture of different AM process chains are assessed, focusing on the characterization of AM channels via X-ray CT scanning and image analysis. Additionally, the properties of LPBF- and BJ-manufactured maraging steels and nickelbased superalloys are investigated, and their enhancements via post-processing routes are explored. The featured AM materials include M300, IN718, 17-4PH, and MAR-M247, with a focus on the latter two. Their characterization encompasses Hot-Isostatic-Pressing (HIP) and subsequent heat treatments. Lastly, holistic considerations of LPBF and BJ for the series production of AM fuel injectors are discussed.
AM for fuel injectors can increase the energy efficiency of marine engines by reducing pressure losses through improved in-nozzle flow due to curved flow paths. The consequential enhancement of mass flow, velocity, and homogenous spreading of discharged fuel aids the combustion efficiency and may reduce emissions after further combustion tuning. 3D flow features such as in-channel micro-features and non-circular outlet geometries can enhance the propagating jets' properties. Passive thermo-structural features such as conformal isolation and monolithic shielding are introduced to enhance the lifetime of fuel injectors without introducing further complexity to the system.
LPBF and BJ are both promising AM processes for manufacturing fuel injectors with the potential to meet specifications regarding dimensional accuracy. LPBF is evaluated as more suitable for implementing thermo-structural features, whereas BJ is considered predestined for injectionrelated features. For the first time, it is shown that BJ can achieve similar mechanical properties as LPBF if the HIP treatment is appropriately included in the process chain. Additionally, it is shown that extremely heat-resistant materials and materials considered unweldable, such as the MAR-M247 alloy, can be manufactured via the BJ route with desirable properties.
Finally, this work includes full-scale fired testing of AM fuel injectors on a large two-stroke marine engine, demonstrating the matureness of the applied designs, process chains, and materials. Thus, this work lays the foundation for a broader implementation of AM fuel injectors in the marine landscape and for advanced applications facing similar requirements.