This thesis presents the numerical study of combustion under marine engine like condi- tions. The thesis is divided into two main parts. In the first part, combustion is studied in a large two-stroke marine engine with conventional diesel fuel. In the second part, two different dual-fuel combustion modes of diesel-methane i.e. non-premixed combus- tion and premixed combustion are studied. All numerical models are validated with the experimental data.
First, in a simplified geometry of the marine engine, conjugate heat transfer (CHT) calculations are applied to simultaneously solve the in-cylinder gas phase dynamics and the temperature field within the liner of the engine. The effects of different initial tem- peratures across the liner and the effects of the amount of water vapor in the air on the sulfuric acid formation and condensation in a large two-stroke marine engine are studied. An initial temperature is calculated based on heat transfer modeling and it is observed that the sulfuric acid vapor formation is more sensitive to the variation of the water vapor amount than the sulfuric acid condensation. In the next step, the effects of the turbulence modelling on the simulation of the full cycle of the engine including scavenging process, combustion, and emission formation is studied in a real geometry of a large two-stroke marine research engine. The Unsteady Reynolds Averaged Navier- Stokes (URANS) and Large Eddy Simulation (LES) turbulence models are utilized for modeling of in-cylinder turbulent flow. The accuracy of the tangential velocity and swirl flow in the top of the cylinder where the fuel is injected is crucial to predict the air-fuel mixing correctly. It is found that URANS predicts a solid body rotation for the tangential velocity in this region. However, LES predicts a tangential velocity that is uniformly distributed in the radial direction that is consistent with experimental results. Furthermore, during the scavenging process, LES is able to predict the Burgers vortex upstream of the cylinder near the scavenging ports. Also, LES predicts a higher angu- lar momentum inside the cylinder in comparison with URANS. During the combustion process, the LES model shows a moderately better performance in capturing the experi- mental pressure and heat release rate profiles than URANS. However, the predicted gas temperature at the liner wall is approximately 45 % higher for URANS than LES during the expansion stroke, which is attributed to a higher predicted turbulent viscosity in the URANS case. A higher temperature of gas beside the liner wall may decrease the sulfuric acid formation and increase the heat transfer. The higher predicted swirl by LES than that in URANS leads to an earlier and stronger interaction between the flame and the spray, decreasing the oxidation of the emissions. The second cycle LES simula- tion shows that the solutions after the scavenging process are in-sensitive to the initial conditions and the main governing parameters are boundary conditions and injection characteristics.
Next, two different dual-fuel combustion modes of non-premixed combustion and premixed combustion are studied. The non-premixed combustion is simulated and val- idated with the experimental data of a large two-stroke marine research engine under low and high engine loads. Based on the results, further methane jets penetration in the low load case leads to better air-fuel mixing and a higher combustion intensity than that in the high load. Effects of the pilot diesel fuel injection timing on combustion and emission formation and the governing mechanisms are also investigated in detail. Results indicate that the intense combustion of the accumulated methane expands the methane flame towards the piston when the pilot injection timing is retarded. The NO formation is lower in the high load case due to the lower combustion intensity. Also, retarding the pilot injection timing decreases the NO formation. Furthermore, the effect of the direction of pilot diesel injection is investigated which shows a significant effect on the methane start of combustion and intensity as well as flame propagation direction which leads to different heat transfer trends from the combustion chamber walls.
Premixed combustion is analysed in a constant volume combustion chamber (CVCC) and validated with experimental data. Results show that by simulation of methane-air mixing, the numerical model is able to capture the ignition delay time (IDT) within a maximum relative difference of 7 % to the measurements. A higher relative difference of 38% is obtained when methane gas injection is omitted and the methane-air and temperature are assumed homogeneous. Therefore, it is concluded that the simulation of methane-air mixing process is crucial in this type of combustion due to the presence of inhomogeneities in both methane fuel and temperature distribution after mixing. Creating the idealized inhomogeneities for separately investigation of methane and tem- perature inhomogeneities shows that the inhomogeneity in the temperature has a more profound influence on the IDT than the inhomogeneity in the methane distribution. Furthermore, the effects of the number of pilot fuel nozzle holes on the auto-ignition are studied. The auto-ignition process in two cases with 4 nozzle holes is investigated and compared with the base case with 8 nozzle holes. Considering the same amount of pilot fuel, the injection rate is assumed to be double in one of the cases, while in the other case, the injection duration is doubled. Results show that a reduction of the nozzle hole numbers can improve the pilot diesel ignition in the case with 4 nozzle holes and double injection duration compared to the base case with 8 nozzle holes. However, combustion in the case with 4 nozzle holes and a double injection rate is incomplete due to flame impingement on the walls.
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.
In near coast navigation, buoys and beacons convey essential information about dangers. At night-time, selected buoys send out individual blink-sequences that are marked in sea charts. International regulations require that navigation officer on watch makes visual confirmation of objects and their type in order to navigate safely. With rapid developments of highly automated vessels, this duty needs be carried out by algorithms that detect and locate objects without human intervention. At night-time, this requires algorithms that decode blink sequences and are able to classify from this information. The paper investigates this problem and suggests an algorithm that solves the problem. Convolutional Neural Networks (CNN) with Gated Recurrent Units (GRU) are developed for classification. A dedicated architecture is suggested that includes both temporal and color decoding to obtain unique precision. We demonstrate how networks are trained on synthetically generated data, and the paper shows, on real-world data, how the suggested approach yields 100.0% accurate results on 44 real-world recordings while being robust to inaccuracy in actual blink sequences. Comparison with baseline signal processing and with a recent state-of-the-art 3D CNN model shows that the new blink-sequence classifier outperforms alternative algorithms. A showcase of the results of this work is available in this video: https://youtu.be/KEi8qNnKV2w.
The number of marine scrubbers installed in industry has been on the rise over the past decade and is expected to continue in the coming years. Therefore, it is essential to ensure that the design of the scrubbers enables as an efficient operation as possible. In this study, an optimization of the exhaust cover inside an in-line scrubber was carried out. The optimization was done by combining a computational fluid dynamics model working on a simplified geometry with the method of feasible directions in order to reduce the pressure loss caused by the exhaust cover. The design is constrained in both height and width of the points making up the exhaust cover to ensure proper drainage of water and to avoid invalid designs. It was found that the optimized design reduced the pressure loss by 42% compared to the initial design. Furthermore, the scalability of the original design was investigated with the same height constraint enforced on the design variables. The result of the scalability analysis showed that the radius of the exhaust cover for the optimal designs scales linearly with the diameter of the scrubber, while the pressure loss was found to increase quadratically as the diameter of the scrubber increases.
This chapter is about emergent safety hazards in engineering systems. These
hazards are those that emerge from a system without arising from any part of the
system alone, but because of interactions between parts. We distinguish two
approaches to analysing engineering systems: one is to view them as sociotechnical, and the other is to consider them as cyber-physical systems. We
illustrate a great deal of emergent hazardous behaviours and phenomena due to
unknown accident physics, malign actions, chemistry, and biology and due to
deficiencies in managements and organisations. The method that follows the
socio-technical view consists in the representation of a system by sequential
functionally unrelated processes that can in reality influence the performance of each other via sneak paths. The method that follows the cyber-physical systems
view focuses on the analysis of control loops (feedback, feedforward, positive,
and negative) and, especially, interrelated loops. The chapter explores also the
realm of security threats due to malign actions that can trigger safety-threatening events. And finally it gives general guidance for avoiding and eliminating safety hazards when designing engineering systems.
In recent years, shipboard microgrids (MGs) have become more flexible, efficient, and reliable. The next generations of future shipboards are required to be equipped with more focuses on energy storage systems to provide all-electric shipboards. Therefore, the shipboards must be very reliable to ensure the operation of all parts of the system. A reliable shipboard MG should be pro-tected from system faults through protection selectivity to minimize the impact of faults and facili-tate detection and location of faulty zones with the highest accuracy and speed. It is necessary to have an across-the-board overview of the protection systems in DC shipboards. This paper provides a comprehensive review of the issues and challenges faced in the protection of shipboard MGs. Furthermore, given the different types of components utilized in shipboard MGs, the fault behavior analysis of these components is provided to highlight the requirements for their protection. The protection system of DC shipboards is divided into three sub-systems, namely, fault detection, lo-cation, and isolation. Therefore, a comprehensive comparison of different existing fault detection, location, and isolation schemes, from traditional to modern techniques, on shipboard MGs is presented to highlight the advantages and disadvantages of each scheme.
A conceptual design framework for collision and grounding analysis is proposed to evaluate the crashworthiness of double-hull structures. This work attempts to simplify the input parameters needed for the analysis, which can be considered as a step towards a design-oriented procedure against collision and grounding. Four typical collision and grounding scenarios are considered: (1) side structure struck by a bulbous bow, (2) side structure struck by a straight bow, (3) bottom raking, (4) bottom stranding. The analyses of these scenarios are based on statistical data of striking ship dimensions, velocities, collision angles and locations, as well as seabed shapes and sizes, grounding depth and location. The evaluation of the damage extent considers the 50- and 90-percentile values from the statistics of collision and grounding accidents. The external dynamics and internal mechanics are combined to analyse systematically the ship structural damage and energy absorption under accidental loadings.
This paper studies real-time deterministic prediction of wave-induced ship motions using the autocorrelation functions (ACFs) from short-time measurements, namely the instantaneous ACFs. The Prolate Spheroidal Wave Functions (PSWF) are introduced to correct the large lag time errors in the instantaneous sample ACF, together with a modification of the autocorrelation (AC) matrix for ensuring its positive definiteness. The validity of the PSWF-based ACFs is first examined by using the ship motion measurements from model experiment under stationary wave excitations. It is shown that the use of PSWFbased ACFs leads to better prediction accuracy than direct use of sample ACFs. The validation is then extended to ship motion prediction using in-service data from a container ship, and an improvement of the prediction accuracy by PSWF-based ACFs is again found. Finally, the effectiveness of use of the instantaneous ACFs for non-stationary wave-induced responses is highlighted by comparing with the prediction results based on the ACFs from long-time measurements.
The shipping industry is associated with approximately three quarters of all world trade. In recent years, the sustainability of shipping has become a public concern, and various emissions control regulations to reduce pollutants and greenhouse gas (GHG) emissions from ships have been proposed and implemented globally. These regulations aim to drive the shipping industry in a low-carbon and low-pollutant direction by motivating it to switch to more efficient fuel types and reduce energy consumption. At the same time, the cyclical downturn of the world economy and high bunker prices make it necessary and urgent for the shipping industry to operate in a more costeffective way while still satisfying global trade demand. As bunker fuel bunker (e.g., heavy fuel oil (HFO), liquified natural gas (LNG)) consumption is the main source of emissions and bunker fuel costs account for a large proportion of operating costs, shipping companies are making unprecedented efforts to optimize ship energy efficiency. It is widely accepted that the key to improving the energy efficiency of ships is the development of accurate models to predict ship fuel consumption rates under different scenarios. In this study, the ship fuel consumption prediction models presented in the literature (including the academic literature and technical reports, which are a typical type of “grey literature”) are reviewed and compared, and models that optimize ship operations based on fuel consumption prediction results are also presented and discussed. Current research challenges and promising research questions on ship performance monitoring and operational optimization are identified.
Traditionally, most ship hulls are optimized for ideal conditions, where the ships are sailing in calm water with full speed in full load. In the last decade, some ships have been designed for a range of draughts and speeds in calm water. However, there is still a large gap between the ideal conditions the ships are designed for and conditions (waves, wind, currents, hull roughness ets.) the ships will operate in. The target for the thesis is to develop accurate numerical models that can help ship designers narrow a part of this gap.
The main body of this thesis is three papers. The first papers compares the speed/power performance of full-scale CFD simulations, towing tank predictions, and high quality speed trial measurements from six sister vessels. Much research have been conducted comparing model- scale CFD with towing tank results. However, very few studies have compared full-scale CFD with speed trial measurements. The study includes both a ro-ro vessel and a general cargo vessel. The present study finds that including the hull and propeller roughness directly into the CFD simulations by modifying the wall-functions provides more accurate results than the traditional approach of estimating the effect of roughness using an empirical formula.
Today, most ships are designed for sailing in calm water. However, very few ships sail entirely in calm water. Before numerical simulations can be used to predict added resistance in waves and seakeeping responses, a systematic verification and validation is required to ensure the accuracy. The second paper presents such a systematic verification and validation for the KCS container ship in oblique waves. Five wave headings and six wavelengths are studied. The estimated spatial and temporal discretization errors are found by an extensive verification study to be less than 5 %. Results from the verified CFD model are compared with existing potential flow and CFD results from the literature, as well as up to three experimental data sets. The comparison shows that the present CFD results in general show significantly better agreement with the experiments than previously published CFD results.
This CFD set-up is used in the third paper to study how sailing in oblique regular waves influences the nominal wake field of the KCS ship. Five different headings are studied and the waves have a steepness of 1/60 and a wave length equal to the ship length. The present study finds that the studied incident waves make the nominal wake field highly transient. Especially the transient bilge vortex and shadow from the skeg have a significant influence on the nominal wake field. The results show that the nominal wake fraction fluctuates up to 39 % of the mean nominal wake fraction for the studied waves. The mean nominal wake fraction is higher than in calm water for all headings besides head sea waves. It is found that the stern quartering sea waves has the maximum mean nominal wake fraction, with a 16 % higher mean nominal wake fraction than in calm water. Finally the study finds that the modified advance angle on the r/R = 0.7 circle in the propeller plane varies 3.5 degrees more in stern quartering than in calm water. This increases the risk of cavitation leading to potential vibrations and loss of propulsive efficiency.
The three papers show that CFD simulations can deliver highly accuracy results, when the CFD simulations are set-up very carefully and systematic verification and validation are conducted. The results from the three papers shows that numerical simulations have a massive potential as useful tools when designing ships for the conditions, the ship will operate in.