Shen Wu

The instability of marine low-sulfur fuel oil caused by asphaltene precipitation poses significant operational challenges in the shipping industry. This study systematically investigates the dispersing effects of biodiesel derived from three different feedstocks—palm oil, waste cooking oil (WCO), and microalgae oil—and their individual fatty acid methyl ester components on asphaltenes extracted from VLSFO. Biodiesel was selected as a dispersant due to its renewable nature, polar ester functional groups, and variable unsaturation levels, which enable favorable interactions with asphaltene molecules through hydrogen bonding and π-π stacking. Using UV–Visible spectrophotometry, the dispersion performance was quantitatively evaluated under various conditions including dispersant concentration, temperature, storage time, and molecular structural characteristics. The results demonstrate that microalgae oil biodiesel exhibits the most superior asphaltene dispersion capability among the three biodiesels, with a dispersion improvement index of 35% at 12 g/L, compared to 28% and 22% for waste cooking and palm oil biodiesels. Optimal performance is achieved at 80 °C, where the asphaltene concentration increases by 68% relative to the control, and remains stable within the first 10 days of storage but deteriorates significantly after 30 days due to oxidative degradation. Among individual FAME components, the dispersion effectiveness increases with alkyl chain length from C10 to C20, with the latter reaching a 30% improvement index. Functional group polarity plays a critical role, with carboxylic acid exhibiting a 45% improvement at 14 g/L, substantially outperforming alcohol at 32% and ester at 28%. The degree of unsaturation further enhances dispersion, as the improvement index rises progressively from 20% for saturated methyl stearate to 42% for tri-unsaturated methyl linolenate, representing a 2.1-fold increase. Dynamic light scattering (DLS) measurements confirm that biodiesel addition reduces asphaltene particle size from the micrometer range of 2 to 5 μm down to submicron levels of 200 to 500 nm, while microscopic observations reveal inhibited aggregation. These findings provide theoretical foundations for biodiesel application in marine fuel systems.

Developing an efficient power system is an important way for icebreakers to respond to high maneuverability and strong fluctuation loads under icebreaking conditions. The performance of power systems under short-period, regularly fluctuating load-sea conditions has been intensively studied. However, the performance of the power system in the face of a long-period, stochastic multi-frequency fluctuation icebreaking process has not been fully explored, especially the parameter uncertainty and battery cycle life. In this study, an integrated electric propulsion system with an optimal control strategy is suggested for improving the power system’s dynamic performance and battery cycle life. First, an energy flow model with a diesel–electric unit as the main body and coupled energy storage system/hybrid energy storage system has been constructed. A comparative analysis of rule-based and optimization-based energy management strategies has been performed, and an optimized strategy with dynamic programming as global regulation at the upper level and model predictive control at the lower level is suggested to integrate the slow and fast dynamic powers and achieve adaptability to strong fluctuation loads. In this control strategy, the uncertainties of energy storage system/hybrid energy storage system parameters have been introduced to eliminate their impact on the system performance. Then, the icebreaking process with multi-frequency fluctuation has been simulated, and the hybrid energy storage system with battery and supercapacitor is recommended to reach multi-objective with the lowest power fluctuation of diesel–electric unit, highest efficiency, and the minimum battery degradation. Finally, the fuel oil consumption and emissions of the hybrid energy storage system have been discussed, and the optimized strategy can save fuel oil by up to 5.33% and reduce the CO₂ emission by 22% during the icebreaking process, exhibiting great potential in the environmental friendliness and significant advantages in terms of low fuel oil consumption.

Although pre-chamber (PC) is regarded as a promising solution to enhance ignition in lean-burn gas engines, a lack of comprehensive understanding of PC jet penetration dynamics remains. This study proposed a zero-dimensional (0-D) model for PC jet penetration, considering the mixing of combustion products and unburned gases and floating ejection pressure. A combustion completion degree was defined employing fuel property and heat release to estimate varying jet density. Pressure differences between PC and the main chamber (MC) were referred to as the ejection pressure. Then, this model was validated against experiments from a constant volume chamber and a rapid compression and expansion machine with CH₄-H₂ blends at different equivalent ratios. Results showed that the proposed model can provide a good prediction in stationary and turbulent fields with the calibrated model coefficient. The overall jet penetration exhibits a t0.5 dependence due to its single-phase characteristic and the relative lower density compared to ambient gas in MC. The flame propagation speed and heat release in PC influence the combustion completion degree at the start of jet ejection, the mass fraction of burned gas in jet increases with the equivalent ratio. Jet penetration is primarily driven by ejection pressure, with tip dynamics barely affected by the pressure difference after the peak. Tip penetration intensity increases with increased fuel equivalent ratio and H₂ addition, owing to the faster flame propagation. These findings can offer useful suggestions for model-based design and combustion model development for gas engines.

Liquefied natural gas (LNG) is widely regarded as the midterm solution toward zero-carbon transportation at sea. However, further applications of gas engines are challenging due to their weak dynamic load performance. Therefore, the comprehension of and improvements in the dynamic performance of gas-engine-based power systems are necessary and urgent. A detailed review of research on mechanisms, modeling, and optimization is indispensable to summarize current studies and solutions. Developments in engine air-path systems and power system load control have been summarized and compared. Mechanism studies and modeling methods for engine dynamic performance were investigated and concluded considering the trade-off between precision and simulation cost. Beyond existing studies, this review provides insights into the challenges and potential pathways for future applications in decarbonization and energy diversification. For further utilization of clean fuels, like ammonia and hydrogen, the need for advanced air–fuel ratio control becomes apparent. These measures should be grounded in a deep understanding of current gas engines and the combustion characteristics of new fuels. Additionally, the inherent low inertia feature of electric power systems, and consequently the weak dynamic performance when adopting renewable energies, must be considered and studied to ensure system reliability and safety during transient conditions.

Since the implementation of the sulfur cap legislation in 2020, marine very-low-sulfur fuel oil, often known as VLSFO, has become a crucial source of fuel for the contemporary shipping industry. However, both the production and utilization processes of VLSFO are plagued by the poor miscibility of the cutter fraction and the residual fraction, which can result in the precipitation of asphaltene. In this study, biodiesel was chosen as a cutter fraction to improve the stability and compatibility of asphaltene in VLSFO because of its environmental benefit and strong solubility. The average chemical structure of asphaltene derived from the marine low-sulfur fuel oil sample was analyzed using element analysis, FTIR, ¹HNMR, and time-flight spectroscopy. The composition of biodiesel was analyzed using GC-MS. It was found that the asphaltene had a feature of a short side chain, low H/C ratio, high aromaticity, and a high proportion of heteroatoms. Both laboratory experiments and molecular dynamic simulations were applied to investigate the dispersion effect and mechanism compared with other dispersants. The dispersion effect of biodiesel was studied using measurements of the initial precipitation point (IPP), dispersion improvement rate, and morphology of asphaltene in the model oil. Experimental results revealed that biodiesel was fully compatible with heavy fuel oil and that it can postpone the IPP from 46% to 54% and increase the dispersion improvement rate to 35%. Molecular dynamics (MDs) simulation results show that biodiesel can form strong interactions with the fused aromatics structures and heteroatoms in the asphaltene; such interactions can increase the solubility of asphaltene and acts as a “connection bridge” to promote the dispersion effect of asphaltene molecules.