The problem of global climate change is becoming increasingly serious, drawing worldwide attention to the need for carbon emissions reduction. As a primary mode of transport, maritime shipping accounts for 2% of global carbon emissions. Therefore, researchers have turned their attention to marine carbon emissions. Specifically, lifecycle assessment (LCA) has attracted wide attention due to its comprehensiveness and objectivity. This article reviews alternate fuels like biodiesel, liquefied natural gas (LNG), methanol, ammonia, and hydrogen. These fuels generate fewer Tank-to-Wake (TTW) carbon emissions than conventional diesel but higher emissions in the Well-to-Tank (WTT) stage owing to production-related emissions, resulting in varying overall carbon footprints. Most carbon emissions in marine transportation come from fuel consumption. Selecting the shortest route can cut fuel use and emissions. Port greening and electrification are vital for emission cuts. Current marine LCA research exhibits key gaps, including fragmented case studies, a lack of methodological standardization, and insufficient dynamic predictive capacity, severely constraining its guiding value for industry decarbonization pathways. This study systematically reviews and categorizes marine LCA research from the past decade in both Chinese and English from the Web of Science and CNKI databases through a Ship-Route-Port framework. Specifically, 34 papers underwent quantitative or qualitative analysis, comprehensively comparing the full lifecycles of six mainstream marine alternative fuels: biodiesel, LNG, methanol, ammonia, hydrogen, and electricity. This study also underscores the need for unified standards to boost low-carbon fuel use and explores the unique challenges and uncertainties involved in applying LCA to the marine sector. LCA applied to the maritime sector shows promise as a valuable tool for guiding low-carbon transition strategies.

Increasing the injection pressure has a significant impact on atomization and combustion characteristics. Spray tip penetration serves as a vital parameter for fuel injection control and engine structure design. However, a reliable spray tip penetration model for ultra-high-pressure injection is currently lacking. To address this gap, this study establishes a theoretical 0-dimensional model for spray tip penetration under ultra-high pressure (300 MPa) conditions. The model is based on the conservation of momentum and phenomenological models. The new model divides spray tip penetration into two stages: Pre-breakup and post-breakup, with fuel injection rate and spray cone angle used as model inputs. To validate the model, high-speed camera observations and constant-volume chamber experiments are conducted to investigate the spray characteristics. The results indicate that the new spray tip penetration model demonstrates improved predictive accuracy across all experimental conditions.

Amid the ongoing decarbonization of the international shipping industry, methanol has emerged as a promising alternative fuel for marine auxiliary boilers owing to its environmental advantages and engineering feasibility. However, its low viscosity and surface tension make the atomization process highly sensitive to operating conditions, posing challenges to stable and efficient burner operation. Existing studies have predominantly focused on engine applications, whereas systematic investigations into the atomization characteristics and operating-parameter matching of primary-air swirl-cup nozzles for marine auxiliary boilers remain limited. To address this gap, the present study combines experimental measurements and numerical simulations to investigate the effects of fuel flow rate, atomizing-cup rotational speed, and primary-air damper opening on spray characteristics. Spray imaging was employed to characterize the spray cone angle and macroscopic morphology, while PIV and PDA were used to measure the outer-flow-field velocity and droplet-size characteristics, respectively. Numerical simulations of liquid-film formation and breakup were performed using a coupled VOF-DPM framework. The predicted spray angle and outer-flow-field velocity showed good agreement with the experimental measurements, with overall deviations within 3–12%. Increasing the atomizing-cup speed generally promoted droplet refinement, while adjustment of the primary-air supply further influenced the droplet-size distribution. Under high-speed operating conditions, the atomized droplet size was generally maintained below 100 μm, and the SMD in the investigated near-field region was approximately 60–80 μm. Based on the multi-load experimental results, primary-air parameter-matching relationships were established for fuel flow rates ranging from 100 to 500 kg/h, providing guidance for maintaining stable atomization performance over a wide operating-load range. This study provides a quantitative basis for the operating-parameter design and stable operation of primary-air swirl-cup nozzles in marine methanol-fired auxiliary boilers and offers useful guidance for their engineering application.