Turbulent jet ignition technology demonstrates great potential in achieving future emissions standards. The key prechamber structural parameters, including volume, orifice diameter, and orifice number, play critical roles in jet ignition and combustion. However, most researches considered these parameters individually, overlooking comprehensive effects on turbulent jet ignition. This study employs a constant volume combustion chamber with a prechamber system to investigate the co-effect of structure parameters (volume, orifice diameter and number) on jet ignition and combustion performance. The results show that the combustion duration increases with increasing orifice number at same orifice diameter but decreases when maintaining same total orifice crosssectional area, which is associated with the ignition behavior (jet ignition or flame ignition) in this study. Overall, both ignition delay and combustion duration are influenced by multiple prechamber structure parameters, exhibiting a linear relationship with the ratio of volume to total orifice cross-sectional area (V/A), however, there is some variation in the combustion characteristics for different prechamber structures at the same V/A. Furthermore, Damko & uml;hler number (Da) is introduced to further elucidate the relationship between structure parameters and combustion characteristics. The ignition delay shows a negative correlation with Da, however, a positive correlation is observed between combustion duration and Da. Overall, Da decreases with increasing V/A. In addition, the effect of prechamber volume on ignition delay and combustion duration remains independent of Da, however, the effect of volume is not evident on the combustion duration for larger orifice. These results highlight the importance of the co-effects of multiple structural parameters on ignition and combustion characteristics, providing guidance for structure optimization to achieve more efficient prechamber system.

Ammonia-diesel dual-fuel compression ignition engines have been recognized as a promising solution for achieving low or zero carbon emission targets in the maritime industry. However, the exhaust gas emissions of ammonia fueled engines including unburned NH3, N2O and NOx are unusually higher than traditional diesel engines, which should be controlled. Unfortunately, the formation mechanisms of these emissions in ammonia fueled engines remain unclear. This study employs the combined approach of using numerical simulations and experiments, as well as the dynamic phi-T map analysis to investigate the in-cylinder distributions and formation mechanisms of unburned NH3, N2O, and NOx with respect to mixture reactivity, equivalence ratio, ambient temperature and pressure. The result shows that the nitrogenous emissions are primarily associated with the turbulent flame propagation in the premixed mixture of 100 % ammonia energetic ratio (AER) regions. While N2O primarily forms at the NH3 flame front, and resides at the unburned NH3 boundary zones, particularly in regions like the center of combustion chamber and near the cylinder walls. Unburned NH3 is found to accumulate in areas inaccessible to the flame, such as piston ring crevices and vicinity of combustion chamber walls, while NOx emissions predominantly occur in the burned zone behind the flame front of ammonia combustion and 72.5 % of the NOx emissions comes from the fuel ammonia. The formation and consumption of NOx, N2O, and unburned NH3 emissions are determined by local variations of equivalence ratio, temperature, and AER in the cylinder. By combining the dynamic phi-T maps with CFD simulations, this study captures the emission formation processes and identifies the specific equivalence ratio-temperature generation regions of NOx, N2O, and unburned NH3.

This article provides a comprehensive synthesis of the current state of research on fault detection and diagnosis of marine diesel engines, organized along three main threads: fault taxonomy, data acquisition and generation pathways, and diagnostic approaches. Firstly, guided by the combustion functional chain and key components, a hierarchical modeling of fault modes is developed to construct a “system–component–fault” fault taxonomy. Secondly, fault-injection and parameter-equivalent simulation strategies are systematically consolidated, revealing a structural landscape in which bench-test data with controllable fault injection constitutes the primary evidence base, simulation-generated data serves as important complements, while in-service data remains underrepresented and public datasets are scarce. Subsequently, the methodological landscape of marine diesel engine diagnosis and its evolutionary trends are summarized, showing that data-driven approaches dominate, model-based and hybrid approaches provide critical support, and knowledge-based approaches play a supplementary role. Finally, future research directions for this field are discussed.

Under the 2050 net-zero emissions target, the maritime sector considers ammonia, a carbon-free fuel, to be a highly promising alternative. Scaled-model experiments following similarity theory play a crucial role in minimizing cost, energy, and time in the development of new engines. Unfortunately, although it has been conducted on different-sized diesel engines, no information is available on the accelerated development of ammonia engines. In this work, the single-valued condition and similarity law for scaled-model experiments of ammonia engines are summarized, primarily focusing on the high-pressure direct-injection mode. After confirming the accuracy of numerical simulations using experimental data from liquid ammonia sprays and ammonia engines, the potential of scaled-model experiment is studied using two ammonia engines with bore diameters of 175 mm (i.e. the large engine) and 95 mm (i.e. the small engine) under various engine speeds and 90 % ammonia energetic ratio. The results show that spray development, heat release rate, in-cylinder pressure and temperature, indicated thermal efficiency, NOx and N2O emissions are highly similar between different-sized engines, indicating the effectiveness of similarity theory in facilitating new ammonia engine development. In particular, based on the similarity law summarized in this study, the differences in peak in-cylinder pressure and temperature between the large and small engines are smaller than 2 %, while the difference in indicated thermal efficiency is smaller than 5 %. However, due to the inherent difference in surface area-to-volume ratio between the large and small engines, the small engine experiences increased heat transfer losses and reduced temperatures near the wall, leading to a higher proportion of unburned ammonia residue in the near-wall region. The above results are deemed invaluable for the intensive development of ammonia engines of different sizes.

How to reduce the exhaust NH3 and N2O emissions is very crucial for bridging the gap between the high greenhouse gas (GHG) reduction potential and the engineering application of ammonia engines with high ammonia energetic ratios (AER). In this study, experiments were conducted to explore how the diesel injection pressures and the split injections affect the characteristics of combustion, emissions, and thermal efficiency for the AER of 80 % in a LPDF (i.e., low-pressure injection ammonia-diesel dual-fuel) engine. As for the split injections, both the early first injection during the compression stroke and the postponed second injection after the top dead center (TDC) were detailed investigated. With the injection pressure of the pilot diesel increasing from 60 to 150 MPa, about 28 % reductions in the unburned NH3 and about 13 % reductions in the N2O are achieved. With the optimized split injections before the TDC, about 11 % reductions in the unburned NH3, 13 % reductions in N2O, and 1.1 % enhancements of the indicated thermal efficiency can be simultaneously achieved. For the split injections with the second injection after TDC, the exhaust temperature can be to some degree increased but result in more NH3 and N2O, alongside a decline in thermal efficiency. Numerical simulations show that the diesel spray targeting and mixture reactivity stratification can explain the mechanism behind the improved performance of the optimized split injections, suggesting the potential for further improvement by the co- optimization of diesel injection strategy and combustion chamber geometry for the LPDF operations with high AERs.

High-pressure direct-injection (HPDI) of ammonia into engine cylinder could provide superior potentials than low-pressure premixed mode in terms of unburned ammonia and nitrous oxide (N2O) emissions, but direct injection of another high reactivity fuel is usually needed to trigger the ammonia spray combustion, complicating cylinder head injector arrangement. To this end, we propose a novel concept of HPDI of ammonia into a premixed lean hydrogen mixture, in which the spark-ignited hydrogen flame enables and enhances the ammonia spray combustion via hydrogen entrainment. This study investigates the combustion and emission characteristics of the HPDI ammonia in the lean premixed hydrogen mixture using a constant volume combustion vessel by varying ambient pressure, hydrogen concentration and injection timing. For the hydrogen-air mixture with the excess air ratio (2) of 3.0 and ambient pressure of 2.5 MPa, near-complete combustion of the HPDI ammonia occurs with low N2O emissions below 10 ppm. When 2 of the hydrogen mixture is increased to 5.0, the ammonia combustion efficiency decreases to around 40 %. Decreasing the ambient pressure enhances the combustion efficiency. When the ambient pressure decreases to 1.0 MPa, the combustion efficiency could increase to 90 % with the early injection case, but with higher NOx and N2O emissions.

Conducting full-scale experimental investigations on thermal deicing in the seawater cooling system of polar ships, e.g., icebreakers, presents significant challenges in laboratory studies. Scaling methods offer a variable way to optimize the system design to prevent the ice blockages, however, research on their similarity principles remains limited. By integrating the dimensional analysis and CFD simulation results, this study proposes a similarity theory for ice melting in the sea box. First, a CFD model for the ice/seawater mixture was developed and verified against the experimental data. The verified model was then utilized to investigate the flow characteristics within the sea box and elucidate the significant feature of ice wall-climbing. Subsequently, on the basis of dimensional analysis, multiple similarity criteria with varying characteristic lengths and velocities have been estabilised. Under different ice load conditions and geometric constraints, the simulation results of scale models were compared with the prototype. Focusing on the temperature and phase fraction fields, an optimal similarity criterion has been determined. Finally, the underlying interactions of kinematics, heat transfer and phase transition were elucidated. The results indicate that the relative velocity between seawater and ice serves as the most representive characteristic velocity for heat transfer, and the temperatures of ice and hot reflux are suitable as the characteristic values for melting. These findings provide critical insights into the mechanism of thermal deicing in the sea box and offer valuable guidance for designing seawater cooling system for polar ships.

Ammonia-diesel dual-fuel engines (ADDF) offer a path to decarbonization but are hindered by low thermal efficiency and high nitro compound emissions. Synergistically optimizing the geometric compression ratio (GCR) and variable valve timing (VVT) is a potentially effective way to improve these issues. The novelty of this work lies in the synergistic parametric analysis and co-optimization of GCR and VVT for an ADDF engine, which builds upon existing single-parameter studies to fill the research gap regarding their coupled effects. Crucially, this is achieved through a novel, constraint-based coupled optimization methodology and technical pathway that respects the constraints of a real engine, an approach that has not yet been fully explored. This study employs simulation with multi-objective optimization to analyze the combined effects of GCR and VVT on an ADDF engine. The results show that the co-optimization simultaneously improves thermal efficiency and reduces emissions, proving its value for engine development. With a well-calibrated 1-D simulation ADDF model developed in GT-POWER, three considerable ways of VVT, varying valve overlap angle (Overlap), early intake valve closing (EIVC) and late intake valve closing (LIVC) are discussed. EIVC is determined to be the best among them, for it not only prevents ammonia leakage, but also improves ammonia combustion conditions, and boosts engine efficiency. The heat balance analysis indicates that the limitation of maximum cylinder pressure results in minimal changes in friction loss. Furthermore, the increase heat losses of high in-cylinder temperature caused by larger GCR can be leveraged by elevated indicated power, leading to an improvement in the total brake efficiency. The multi-objective optimization including GCR and VVT by using a genetic algorithm (GA) is then conducted to improve thermal efficiency and reduce emissions. The results show that GCR of 21.9 with a Miller degree of 60 degrees CA in EIVC strategy is optimal under 60% ammonia energetic ratio (AER). This optimal design demonstrates an 8% increase in brake torque and 6.9% in indicated thermal efficiency (ITE), while the unburned ammonia can be cut off 39%. Additionally, it achieves a 33% reduction in unburned ammonia under 40% AER, showing better adaptability to different AERs for ammonia-diesel dual-fuel engines.

This study investigates the potential of biofuels to mitigate the environmental impact of passenger vessels. Employing a life cycle assessment methodology, this research comprehensively analyzes the environmental footprint of various fuels throughout the life cycle of a passenger vessel, encompassing construction, fuel production, operation, maintenance, and decommissioning. This study demonstrates the application of life cycle impact assessment to evaluate the environmental footprint of a bio-fueled passenger vessel operating on the Baltic Sea route from Tallinn-Helsinki, Helsinki-& Aring;land, and & Aring;land-Stockholm, totaling a round-trip distance of around 700 nautical miles. Ten different fuels, including several biofuel options, were evaluated using two established impact assessment methodologies. This life cycle assessment study focused on five major environmental impact categories: eutrophication, ozone depletion, climate change, and human and eco-toxicity. A comparative analysis encompassed Heavy fuel oil, bio-hydrotreated vegetable oil, bio-dimethyl ether, marine diesel oil, biodiesel, liquefied natural gas, methanol, bio-methanol, ethanol, and bio-ethanol. Based on impact categories like Global warming potential (GWP 100) and Global temperature potential (GTP 100), the findings suggest significantly lower environmental impacts of biofuels than all other fuel options. Notably, biofuels significantly reduced environmental impact, ranging from 70 % to 90 % per tonne-kilometer across most categories. These results highlight the promise of biofuels as a sustainable alternative fuel source for the maritime transportation sector, potentially reducing their environmental footprints significantly. In summary, biofuels offer a pragmatic and timely approach to enhancing passenger vessels' sustainability and operational efficiency amidst the maritime sector's transition towards a cleaner future.

Hydrogen and ammonia are the fuels with the high potential for the future carbon-free engine systems. Considering the low chemical reactivity of ammonia, using the direct-injection hydrogen jet ignition is a promising method to realize the high-efficiency combustion of ammonia. Based on this, a systematic and comprehensive investigation of the direct-injection hydrogen jet ignition under engine-like conditions is carried out for the first time, including the jet characteristic, fuel mixing characteristic, and combustion characteristics. In particular, combined with the fuel mixing characteristic, combustion research at different ignition positions of hydrogen jet is carried out. The corresponding features are investigated in the constant volume combustion vessel with the injection pressures of 3.0 MPa, 5.0 MPa, 7.0 MPa, and 9.0 MPa and the ambient pressure of 1.0 and 2.0 MPa, using high-speed imaging technology. The fuel concentration distributions of the hydrogen jet are quantitatively investigated by the laser-induced breakdown spectroscopy technology. From the results, for the evolution of the tip penetration distance of the high-pressure hydrogen jet with the time t after injection onset, a four-stage behavior of the e-t, t, t0.5 and t0.25 dependence is proposed to explain the relationship between the tip penetration distance and t. The jet angles in the steady injection duration are between 30 and 50 degree. The equivalence ratio reduces with the distance away from the nozzle or the nozzle axis, and increases with the increased injection pressure. In the jet area of 10 mm away from the nozzle, the equivalence ratio changes from 0.2 to 4.0. The higher injection pressure could accelerate the flame development and reduce the lift-off height. The maximum burning velocities could exceed 200 m/s in the initial ignition stage as the turbulence produced by the high-pressure injection, and then quickly decrease to less than 50 m/s. The position closer to the nozzle is more conductive to the initial flame kernel. More importantly, the results reveal that a good ignition characteristic is also shown at the position far from the nozzle and slightly away from the nozzle axis, resulting from the fast-burning velocity after the initial ignition stage.

Ammonia has gained widespread attention in internal combustion engines as a promising hydrogen carrier. However, its large latent heat of evaporation leading to a severe cooling effect brings a challenge for direct utilization of its liquid injection. The present study aims to unravel the condensation features of liquid ammonia injection. First, an efficient Euler-Lagrange simulation framework coupled with a condensation model was established, and the simulation results were verified against experimental data. Then, extensive simulations of multi-hole liquid ammonia injections under various diesel engine-like conditions were conducted, and the results indicate that the proportion of condensation mass relative to its injection mass gradually increases with hole numbers. The condensation in spray transient period gathers at the nozzle exit primarily due to the large instantaneous evaporation rate. Therefore, smaller nozzles, hotter fuels, lower injection pressures and higher ambient temperatures tend to produce more condensation in the transient period. As the spray enters the quasi-steady period, the condensation region moves away from the nozzle exit and becomes widen, primarily depending on the long-term cooling effect, which is jointly affected by evaporation mass, heat transfer rate, and phase envelope. Accordingly, larger nozzles, higher injection pressures, and lower ambient temperatures can facilitate condensation. For the supercritical injection of ammonia, due to its fast phase transition, substantial condensation occurs at the nozzle exit, and its distribution is totally different from the normal evaporating spray. Finally, a characteristic isotherm, only increasing with ambient pressure, was proposed to qualitatively indicate the condensation penetration length for large-scale condensation.

Digital twin plays an important role on realizing the digitization and intelligence of the smart engine for the maritime intelligent transportation systems. However, digital twin modeling of the engine systems faces the challenges of multidisciplinary knowledge, multi-scale, real time, complex structure, etc. In this study, the hardware-in-the-loop technology is introduced into the digital twin modeling processes. A six-dimension digital twin model framework is proposed, which contains physical entity, hardware-in-the-loop, virtual equipment, application service, digital twin data, and connections. The digital twin framework is described in detail for the engine system. The application of the hardware-in-the-loop in the digital twin modeling is further expounded with the example of a single-cylinder engine test bench. The new digital twin model framework and modeling method will be benefit for the construction of digital twin for complex systems such as power plants, vehicles, ships, etc.

The pyrolysis characteristics of low-sulfur heavy oil fuel (HFO) spray under diesel engine-like conditions were investigated for the first time using both experimental and numerical methods. The high speed diffused back-imaging method was adopted to measure the macroscopic features of the low-sulfur HFO spray, and its products were sampled and analyzed by the gas chromatography with mass spectrometry. The low-sulfur HFO spray behaves as a quasi-evaporating spray under high temperature conditions, integrating the characteristics of evaporating and non-evaporating sprays. The increase of temperature shows little effect on its penetration characteristics, but a great effect on the vapor distribution. The low-sulfur HFO spray can pyrolyze at the temperature below 650 K due to the high heating-up rate and ambient pressure, and the aromatics contained in it are easy to pyrolyze, producing some oxygenate and amide components. Based on the experimental results, an integral pyrolysis model with multi-component evaporation and pyrolysis was established and implemented into the Eulerian-Lagrangian framework to simulate the low-sulfur HFO spray, and its predictions agree very well with the experimental results. The pyrolysis shows a large effect on the HFO spray evolutions. Ignoring the pyrolysis process would underestimate the droplet temperature and distribution number at the HFO spray tip and overestimate the vapor concentration of heavy-end hydrocarbons, because most of them are trapped inside the droplet enclosed by the pyrolytic residues.

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.

以液氨喷雾混合气形成和燃烧过程为对象进行数值模拟和试验验证.根据试验获得的气液相贯穿距数据对三维模型进行参数标定.结果表明:建立的喷雾模型可以在高温高压环境条件下准确预测液氨喷雾的贯穿发展过程;在喷雾混合气形成过程中液氨气化吸热导致喷雾中心区域降温效果明显,降温高达100 K;氨较高的汽化潜热使之较难蒸发,喷雾边缘处氨的质量分数多在0.1上下.利用特征时间燃烧模型对液氨喷雾燃烧过程进行初步计算,可以较好地模拟整个燃烧过程.

为揭示大型中低速柴油机气缸内喷雾发展和混合气分布特征以优化船舶推进主机动力性能与排放特性,开展了热解反应对低硫重油喷雾发展造成影响的研究.使用预混式定容燃烧弹系统对高温高压环境下低硫重油喷雾发展特性进行光学诊断测试分析,同时根据低硫重油热重分析测试结果计算出热解反应导致的质量损失率,从而发展出低硫重油热解反应模型,开展低硫重油喷雾三维计算流体动力学(3D Computational Fluid Dynamics,3D-CFD)仿真研究.结果表明:研究建立的3D-CFD仿真模型耦合低硫重油热解模型可以准确模拟低硫重油喷雾在高温高压条件下的发展特征;低硫重油喷雾在高温高压惰性环境中经历了破碎、蒸发与热解等复杂的物理化学过程,喷雾发展前期主要由易挥发的组分控制,而热解反应生成的气体与不透明物质主导喷雾后期的发展特征;低硫重油喷雾发展特性受环境密度影响大,环境密度增大时,喷雾贯穿距减小,喷雾锥角增大,环境温度对低硫重油喷雾发展特性影响较小,但影响喷雾下游不挥发成分质量,间接影响混合气形成.

In the transportation sector, ammonia used as a power source plays a significant role in the scenario of carbon neutralization. However, the engine-out emissions correlations of ammonia-diesel dual-fuel (DF) engines are still unclear, especially the nitro-compounds of great concern and GHG. In this study, the engine-out emissions are evaluated by using a four-cylinder ammonia/diesel DF engine. Various operating conditions consisting of ammonia energy ratio (AER), engine load, and speed were carried out. Unburned NH3 increases with raising ammonia content but decreases with increasing engine load and speed. The NO+NO2 tendency shows a non-linearity trend with increasing ammonia content, while a trade-off correlation is linked to N2O. The N2O emission of ammonia engine significantly weakens the beneficial effect of GHG reduction, the 30% and 50% decarbonization targets need at least 40% and 60% ammonia energy without regard to N2O effect, while at least 65% and 80% ammonia energy respectively with considering N2O. N2O presents a parabolic-like tendency with AERs. Advanced pilot-diesel injection timing helps to reduce both NH3 and N2O, but this effect becomes insignificant as the AER is less than 0.4. A combustion strategy of the rapid heat release and ammonia-governed heat release respectively are revealed.

Molecular dynamics (MD) simulation is a powerful tool to reveal the microscopic characteristics of supercritical transitions. However, the accuracy of MD depends strongly on the potential model that describes the interaction forces between atoms. In this study, four commonly used potential models for long-chain n-alkanes in MD simulations are evaluated, and a hybrid model is introduced. The vaporization and phase-transition characteristics of n-alkane blended fuels with different mole fractions are then explored under a wide variety of ambient conditions by using the hybrid model. Compared to the commonly used potentials, the hybrid model shows higher accuracy for predicting the thermodynamic and transport properties. In subcritical environments, vaporization belongs to typical two-phase evaporation with a sharp gas–liquid interface. The preferential evaporation of the light-end component is obvious, and the evaporation rate of the heavy-end component is maximized after the light-end component is consumed. Under supercritical conditions, the interface dissolves rapidly, the evaporation rates for both the light- and heavy-end components increase simultaneously, and both components coexist throughout the evaporation process. Based on the maximum potential energy and evaporation rate, a new criterion for the supercritical transition is proposed. The dimensionless transition time, which reflects the proportion of the sub/supercritical stage within the lifetime, is nearly independent of the ambient temperature and fuel composition; instead, it mainly depends on the ambient pressure. Finally, an empirical formula is obtained by curve-fitting to describe the variation in the dimensionless transition time with ambient pressure.