The shipping sector's rising greenhouse gas emissions are often considered “hard-to-abate”. Some ship-owners have recently adopted or started to consider the adoption of alternative fuels, but systematic studies of this are still lacking. We address this gap by studying how ship-owners differ in both actual and intended adoption of alternative fuels. We analyze data from a unique survey with 281 ship-owners in Norway, a major ship-owning country and center for maritime technology development, with descriptive statistics and analysis of variance. We find early adopters among large and established ship-owners in offshore, international cargo and domestic passenger shipping segments, which are often subjected to specific contractual demands for alternative fuel adoption. Laggards were typically small and young ship-owners operating in shipping segments where demands for alternative fuel adoption are weak. Our findings also suggest that firms' business strategy and financial and knowledge resources may have relevance for ship-owner's adoption of alternative fuels. Our study has implications for national and international policymaking, highlighting for example how contracting mechanisms can be an effective tool in incentivizing the adoption of alternative fuels.
Global marine shipping annually accounts for about one billion tonnes of CO2 equivalent greenhouse gas emissions. Nuclear power propulsion may be an option to de-carbonise some niches of the merchant ocean fleet. This paper considers the three experimental nuclear-powered merchant ships launched and operated in the world so far; the iconic Savannah (USA), Otto Hahn (West Germany) and Mutsu (Japan). They were independently developed and operated in the 1960s and 1970s for technology demonstration and learning. A fourth ship, Sevmorput (Soviet Union/Russia, 1988–to date), is a pioneer in respect of its logistics functions and propulsion system. This paper develops a theoretical framework for the sustainability assessment of nuclear propulsion in ocean merchant shipping and presents a method for exploring nuclear propulsion, relative to flag state, ports, shipping resources and ocean transport services. The experimental ships’ transport efficiency is discussed and related to contemporary oil-fired shipping of general cargo, and to recent literature presenting possible future applications of merchant nuclear propulsion in some market niches. Insights provided include: (1) the experiments demonstrate that merchant nuclear propulsion may be technically feasible; (2) port and canal access for merchant nuclear-powered ships may be difficult and restricted; (3) the up-front costs, refuelling and end-of-life decommissioning costs of nuclear-powered ships are vast and uncertain against conventionally-powered ships; (4) because nuclear fuel is comparatively low-cost, the conventional oil-fired ship cost implications of high-speed operations do not apply.
The future fuel for marine engines is not yet decided. However, it is well-known that utilizing green alternative e- fuels is a big step in the way of decarbonization. Dual-fuel (DF) engines offer great fuel flexibility with possibility of using different green gaseous e-fuels like methane and ammonia. The ignition of the lean premixed gaseous fuel in a DF engine depends on the auto-ignition of the injected pilot diesel fuel. Therefore, a proper auto- ignition of the pilot diesel is important in these engines. In the present study, large eddy simulation is carried out to study the auto-ignition process of pilot diesel in premixed methane-diesel DF combustion in a constant volume combustion chamber. The entire DF combustion processes involving methane injection, methane/air mixing, pilot diesel injection, and ignition are simulated. The numerical model is validated against experimental data. The base case has a pilot diesel injector with 8 nozzle holes. The auto-ignition process in two other cases with 4 nozzle holes are investigated and compared with the base case. Considering same amount of pilot fuel, the injection rate is assumed to be double in one the cases, while in the other case, the injection duration is doubled. The results show that the ignition process in the case with 4 nozzle holes and double injection rate is incomplete due to flame impingement on the walls. However, a reduction of the nozzle hole numbers can improve diesel pilot ignition in the case with 4 nozzle holes and double injection duration. The higher fuel mass per orifice leads to an increased fuel concentration within the diesel pilot sprays and higher combustion rate than the base case. Furthermore, more confined spray envelope in the case with double injection duration leads to an increased reactivity and more efficient auto-ignition process than the case with double injection rate.
We present the results of a numerical model which has been developed for estimating the contribution to the methane slip from different sources in a four-stroke dual-fuel marine engine running on natural gas. The model is a thermodynamic three-zone zero-dimensional full engine cycle model and considers methane slip contributions from short-circuiting, crevices and wall quenching. The model is applied to analyze the methane slip from a four-stroke dual-fuel medium speed marine engine using natural gas as primary fuel. At low loads, wall quenching is found to be the dominant contribution to the methane slip. At full load, the wall quenching contribution is comparable to the level of the short-circuiting and crevice contributions which only vary relatively little with load. At 75% load, the contribution from short-circuiting is highest. In addition, we found that in-cylinder post-oxidation of unburned fuel remaining after the main combustion is negligible.
In this reported work, multi-dimensional computational fluid dynamics studies of diesel combustion and soot formation processes in a constant volume combustion chamber and a marine diesel engine are carried out. The key interest here is firstly to validate the coupling of a newly developed skeletal n-heptane mechanism and a revised multi-step soot model using laser extinction measurements of diesel soot obtained at different ambient pressure levels in an optical accessible, constant volume chamber experiment. It is revealed that ignition delay times and liftoff lengths generated using the new skeletal model are close to those produced by the larger and more comprehensive chemical mechanisms, apart from those at the low pressure condition. The current study also demonstrates that the variation of averaged soot volume fraction with respect to the change of combustion chamber pressure captured using the revised soot model agrees reasonably well with the measurements in terms of peak values. The numerical model is subsequently applied to investigate the flame development, soot/nitrogen monoxide formation and heat transfer in a two-stroke, low-speed uniflow-scavenged marine diesel engine operating at full load condition, where optical measurements are not available. Comparisons to the experimental data show that the simulated pressure rise starts 1.0 crank angle degree in advance and the calculated peak pressure is 1.7% lower. The associated flame liftoff length is negligible, yielding higher local equivalence ratio and soot volume fraction values as compared to those under similar test condition in the constant volume chamber. With the use of the revised model, the total heat transfer to the walls calculated when soot radiative heat loss is taken into account is approximately 30% higher compared to that when only convective heat loss is considered. The averaged nitrogen monoxide concentration is 7.7% lower when both convective and soot radiative heat losses are accounted for but the net soot mass production is less sensitive to soot radiation. A sensitivity study reveals that neither increasing nor decreasing the soot absorption coefficient by 30% from the baseline setup is influential to nitrogen monoxide formation, soot mass production and heat transfer. The findings here aid to gain insights and provide a better understanding of the combustion and soot processes in large, uniflow-scavenged marine engines. The numerical model developed in this work can also be applied to explore different phenomena in this combustion system.
A numerical model (MOODY) for the study of the dynamics of cables is presented in Palm et al. (2013), which was developed for the design of mooring systems for floating wave energy converters. But how does it behave when it is employed together with the tools used to model floating bodies? To answer this question, MOODY was coupled to a linear potential theory code and to a computational fluid dynamics code (OpenFOAM), to model small scale experiments with a moored buoy in linear waves. The experiments are well reproduced in the simulations, with the exception of second order effects when linear potential theory is used and of the small overestimation of the surge drift when computational fluid dynamics is used. The results suggest that MOODY can be used to successfully model moored floating wave energy converters.
Ammonia-fueled operation of solid oxide fuel cells is a promising alternative to their hydrogen-fueled operation. However, high ammonia decomposition rates at elevated operating temperatures of the solid oxide cells lead to a significant temperature drop at the stack inlet, causing increased thermal stresses. A multi-scale model is used in this study to investigate stack performance under direct feed and external pre-cracking of ammonia. Additionally, the effects of co- and counter-flow configurations, gas inflow temperatures, current density, and air flow rate on the stack performance under direct ammonia feed are examined. The simulation results show that for gas inlet temperatures above 750 °C, the power densities with direct feed and external cracking of ammonia differ by less than 5%. Moreover, it is indicated that the thermal stresses are lowest for the co-flow case, which decrease with decreasing gas inlet temperature and current density and with increasing air flow. Finally, this study shows that under practically applicable operating conditions, the risk of mechanical failure of the cells under direct ammonia feed operation is small.
Ice-breaking cones are commonly used in the design of marine structures in cold regions. This study investigates the effects of higher-harmonic wave loads and wave runup on a 5-MW offshore wind turbine with and without ice-breaking cones under extreme wave conditions on the Liaodong Peninsula in China. Two ice-breaking cones (upward-downward and inverted types) are considered. The numerical model adopts a two-phase flow by solving unsteady Reynolds-averaged Navier-Stokes (URANS) equations using the volume of fluid (VOF) method. A phase decomposition method through a ‘Stokes-like’ formulation was adopted to obtain the parameters for each harmonics. The presence of the conical part is seen to increase the second-harmonic wave loads by up to 40%, but it has only limited influence on the fourth and fifth harmonics. The upward-downward-type ice-breaking cone increases the third harmonic, while the inverted-type ice-breaking cone decreases the third harmonic. Due to the phase difference between the first-harmonic and higher harmonics, the largest wave runup occurs at 0°, and 135° is the location with the smallest wave runup. This is because at the 135-degree location, the linear component is positive but the other nonlinear components are negative. For the 0-degree location, all harmonics are positive. By contrast, the inverted type has little effect. The high harmonic wave runup of the minimum point is backwards compared with that of the monopile, and most nonlinear wave runups are different upstream of the monopile.
A computational fluid dynamics study of the scavenging process in a large two-stroke marine engine is presented in this work. Scavenging which is one of the key processes in the two-stroke marine engines, has a direct effect on fuel economy and emissions. This process is responsible for fresh air delivery, removing the combustion products from the cylinder, cooling the combustion chamber surfaces and providing a swirling flow for better air-fuel mixing. Therefore, having a better understanding of this process and the associated flow pattern is crucial. This is not achievable solely by experimental tests for large engines during engine operation due to the difficulties of measuring the flow field inside the cylinder. In this study, the axial and tangential velocities are compared and validated with the experimental results obtained from Particle Image Velocimetry (PIV) tests [1]. The simulations are conducted using both Unsteady Reynolds Averaged Navier Stokes (URANS) and Large Eddy Simulation (LES) turbulence models. We observe in general, there is a good agreement between the numerical and experimental results. The flow inside the cylinder is studied in different locations related to the bottom of the scavenging ports during the period with open exhaust valve. Moreover, the replacement of combustion products with fresh scavenge air is analysed. The effective flow angle is calculated for the air flow through the scavenging ports. It is found that the effective flow angle is different from the geometrical angle of the ports (20°). Results illustrate better performance of LES, especially in the prediction of the tangential velocity which is crucial for the simulation of an accurate swirl and air-fuel mixing inside the marine engines. LES predicts a uniform profile for the tangential velocity at the top of cylinder which is consistent with the experimental results while URANS predicts a solid body rotation.
Numerical tests are performed to investigate wave transformations of nonlinear nonbreaking regular waves with normal incidence to the shore in decreasing and increasing water depth. The wave height transformation (shoaling) of nonlinear waves can, just as for linear waves, be described by conservation of the mechanical energy flux. The numerical tests show that the mechanical energy flux for nonlinear waves on sloping foreshores is well described by stream function wave theory for horizontal foreshore. Thus, this theory can be used to estimate the shoaled wave height. Furthermore, the amplitude and the celerity of the wave components of nonlinear waves on mildly sloping foreshores can also be predicted with the stream function wave theory. The tests also show that waves propagating to deeper water (de-shoaling) on a very gentle foreshore with a slope of cot(β) = 1200 can be described in the same way as shoaling waves. For de-shoaling on steeper foreshores, free waves are released leading to waves that are not of constant form and thus cannot be modelled by the proposed approach.