The maritime sector is important for the facilitation and growth of global trade. Currently, about 90% of the goods are transported by ships and as a result, the number of ships has risen, increasing the emissions related to shipping. Pollution caused by exhaust gas, especially the sulphur oxide emission, from marine diesel engines has become a global concern in recent years. Therefore, the International Maritime Organisation limited marine fuel sulphur content in both Emission Control Areas to 0.1%w/w since 2015 and globally to 0.5%w/w since January 1st , 2020. It is anticipated, that the newly implemented IMO regulations will help to mitigate negative impact of ship emissions on public health and the environment in the coastal areas. The wet scrubber system is a reliable technology for flue gas desulphurisation in marine applications and can achieve a sulphur dioxide removal efficiency of 98%. The operating costs are low, however the capital cost for installation are high and a scrubber system requires space for installation while maintaining ship’s stability. Wet scrubber systems operating in a closed loop and using caustic soda may operate without discharge to the sea and thus are allowed to operate in ports. The use of caustic soda also makes it possible to use the scrubber in areas with low seawater alkalinity. However, scrubber systems generally operate at 100%, even when the engine operates at lowload. This results in an increase of the fuel consumption and carbon dioxide emissions. Themain objectives of this research are to examine the influence of water evaporation on the sulphur dioxide removal efficiency and the (response of the scrubber) effect of dynamic loads on the scrubber efficiency. A dynamic model of a closed loop wet scrubber operating with fresh water and caustic soda also known as sodium hydroxide was created and verified. The scrubber model consists of three resistance elements, namely the venturi scrubber, the tower scrubber with a packed bed and the demister and two volume elements (lower and upper) to connect the resistance elements. The absorption of SO2 is mainly taking place in the packed bed and the two phase flow of exhaust gas and scrubbing liquid was modelled in this section. The Nerst film theory was used and extended to a two film theory in which the exhaust gas and scrubbing liquid phases come into contact through an interface and exchange both heat and mass. The gas flow in the packed bed could be modelled with a combination of resistance and volume elements as this phase is compressible. The liquid flow and liquid film thickness in the packed bed were modelled based on the conservation of mass and the liquid holdup theory developed by Billet and Schultes. A feedback control system controls the scrubbing liquid flow based on the sulphur dioxide to carbon dioxide ratio. The system includes a time constant to account for the inertia of the scrubber’s pump and pipe system. The verified model was integrated with engine data and used to run several static and dynamic simulations. The inclusion of evaporation in the packed bed leads to an increase of the scrubber efficiency in all engine loads. The extra vapour added dilutes the gas phase and reduces the mass fraction of sulphur dioxide. When evaporation is included in the analysis, the sulphur dioxide to carbon dioxide ratio leaving the scrubber is 1.88, equal to a fuel sulphur content of 0.043% on a mass base (from 3.5% in the fuel) for 100% engine load. When evaporation is not included in the analysis the previous values are 2.3 and 0.053% respectively. To increase the precision concerning the amount of water that evaporates, a higher discretisation of the packed bed is required. High engine load fluctuations and/or high input frequencies lead to overshoots and higher liquid supply, in order to keep the scrubber system efficient. In the transition from 25% MCR to 100% MCR the liquid supply exceeds the nominal value of 94 kilogram per second by by 5.3 kilogram per second (or by 5.6%). In the transition between 75%MCR to 100%MCR, for the frequency of 50 seconds the liquid supply is equal to 92.9 kilogramper second. Increasing the input frequency 5 times results in an increase of the liquid supply to 96.1 kilogram per second. The sulphur dioxide to carbon dioxide ratio leaving the scrubber was always below the ECA sulphur limit and was fluctuating around the set point, but most of the time below it. A combination of feed forward and feedback and/or a more advanced control may result in a more stable control of the scrubber, but this has to be investigated. The model functions, but more research is required for the venturi and the demister models, but also for the packed bed model. In the venturi a three phase flow is required and in the demister an analytical and dimensional analysis is required. Also, the packed bed model needs to be further developed to include the condensation effect and a more precise approach for the liquid phase. Further research can be done on the integration of the model with a diesel engine and SCR model. Also, seawater can be examined as a scrubbing liquid as this may reduce the operational costs of the scrubber. Finally, because space requirements of the scrubber are high, a structured packed bed could be an alternative to the dumped and reduce the space occupied by the wet scrubber.

Emission regulations applied to marine industry for amongst others the propulsion system of a vessel are becoming stricter due to governmental
agreements to lower the greenhouse gas emissions. Engine manufactures
are enhancing their engine designs to reduce the engine fuel consumption, which is commonly done by implementing a turbocharger to downsize the engine. One large drawback which comes with a turbocharged engine is the low torque development for the low to mid engine speed range due to limitations set to prevent unstable turbocharger phenomena. Moreover, the engine is not able to follow the power request almost instantaneously due to a time delay between the engine and turbocharger response. Formula One engineers close this gap by introducing an integrated electric machine into the turbocharger structure (hybrid electric turbocharger) to, first, take power out from the turbocharger to increase the system efficiency, and second by assisting the turbocharger to improve the engine power delivery response.

However, the understanding of the effects of a hybrid electric turbocharger on both the system efficiency as well as the engine loading capability is lacking. One turbocharger limit, the compressor surge, is not concerned in most literature what rises the need for further research up to which extent the engine can be assisted with the hybrid electric turbocharger. In this work, the effect of taking power from the turbocharger to increase the system efficiency, called turbocompounding, is investigated. Turbocharger assistance is investigated for both steady state as well as dynamic operation. The effect of assisting the turbocharger for steady state operation is investigated to increase the engine’s operating envelope. Dynamic operation comprises the investigating up to which extent the assisting mode improves the dual fuel engine’s loading capability for four types of engine loading. These types of engine loading are: one instant load step, three consecutive load steps from 0 - 100% load, a load ramp and, last, a sinusoidal engine loading.

This has been done with a simulation-based study wherein a mean value dual fuel engine model is composed based on merging two available mean value engine models, after which it is verified and validated. Thereafter power take in/out together with an air excess ratio control strategy is included by means of adding/taking torque to/from the turbocharger shaft and limiting it with eight boundary controllers to avoid impractical situations. With turbocompounding the system efficiency can be increased at the expense of a deteriorated gas exchange and increased thermal loading of the engine. The maximum quantity of recovered energy to be obtained, requires a hybrid electric turbocharger which replaces a waste gated turbocharger instead of a non-waste gated single stage turbocharger. Taking power from the turbocharger lowers the power available for the compressor which leads to reduced inlet receiver pressure and corresponding lowering of the air excess ratio and deterioration of the scavenging process.

Assisting the turbocharger for steady state operation leads to a smaller operating envelope due to the limitation of compressor surge. Combining turbocharger assistance with gas exchange bypass valves, to avoid compressor
surge, results in a rise of the low speed torque output up to an almost constant engine torque output. The system efficiency can be improved for the low speed region when the turbocharger is assisted in combination with the gas exchange valves.

The load step capability, found by limiting the minimum air excess ratio during the load step event, cannot be increased with turbocharger assistance which starts to speed up the turbocharger immediately after the load step is applied to the engine. However, the recovery time needed before a second load step can be taken, is reduced with turbocharger assistance compared to the baseline engine. When the turbocharger assistance starts to speed up the turbocharger a couple of seconds before the load is applied, the load step capability can be improved. A load ramp can be taken in a shorter period of time with turbocharger assistance enabled. For cyclic loading, the hybrid electric turbocharger operates in turbocompounding mode for the lower load frequencies, and assistance is used for the higher load frequencies. With turbocharger assistance the air excess
ratio does follow the sinusoidal engine load while the air excess ratio of the non-assisted engine always lags due to the turbocharger lag.

Further research should be done with regard to a hybrid electric turbocharger for the natural gas combustion of the dual fuel engine. Using the engine speed drop should be implemented as limitation for the loading capability determination instead of the minimum allowable air excess ratio applied in this thesis.

Environmental regulations are continuously raising the bar towards more advanced diesel engine designs ca- pable of minimizing the emissions of polluting substances. The recent IMO Tier III legislation, entered into force in 2016, is forcing the engine manufacturers to meet a NOx reduction of more than 70% from Tier II for all the ships sailing in designated NOx Emission Control Areas (NECA). Although these zones are, up to now, limited to the North American and U.S. Caribbean Sea NECAs, future regions, such as the North Sea and Baltic NECA in 2021 as well as stricter national and port regulations, are increasing the uncertainty regarding the possible compliance methods.
The Selective Catalytic Reduction (SCR) represents a flexible, proven and commercially available technology capable of reducing more than 80% of the NOx in the exhaust gas. Its adoption started in the ’70s and was aimed at the reduction of stationary source emissions. From early 2000, it has been extended to the automotive industry in order to meet the Euro and EPA legislation for heavy duty and light diesel engines. Despite the evident disadvantages of the high installation cost and the considerable space requirements, the application of the SCR is subjected to a number of operating limits such as the narrow optimal temperature window and the slip of byproducts originated from the chemical reactions. These limitations can be even more severe when the diesel engine undergoes transient and dynamic operations.
The main objective of this research is to gain insights into the behaviour of the SCR technology under steady-state and dynamic operations of the diesel engine. After an accurate literature review of the working principles, reaction kinetics and modeling approach, a first principle model of the SCR has been developed to fulfill the scope. A 1D single channel approach, discretized along the reactor length, has been adopted to sim- ulate the heat exchange and the chemical reactions occurring in the catalyst. To facilitate the integration of the designed model with an existing diesel engine model available in the Maritime and Transport Technology Department of the 3me faculty, the resistance and volume approach has been selected. After the verification of the SCR model, the integrated system "SCR+Engine" has been tested under steady-state conditions, to an- alyze the effect that the added back pressure has on the engine performance, and under dynamic conditions, to simulate "real" load case scenarios that the SCR might experience.
The designed model, although limited from the chemical reaction point of view, is able to predict NOx reduction and ammonia slip under steady-state and transient operations. It can be further used in an early design phase to investigate the feasibility of the SCR inclusion in the drive trains of ships. Future studies are recommended to optimize the model, by taking into account the sulphur influence on the reduction efficiency and the catalyst aging, and to validate it with real experiments on marine SCR systems.

Carbon dioxide emission into the earth’s atmosphere by maritime activities are a concern for the people within and outside the industry. This is because of the environmental impacts that are caused by these greenhouse gas emissions which changes the very chemistry of this planet. These impacts can be mitigated by reducing the CO2 emissions which can be achieved by several design and/or operational means. Waste heat recovery (WHR) technology is one such means that is capable of reducing emissions. This is achieved by improving the overall fuel efficiency of marine engines which reduces the fuel consumption of the vessel. This improvement is realised by harnessing the heat energy that is expelled by the engine through waste heat sources such as exhaust gas, etc.
 Organic Rankine cycle (ORC) is one of many WHR technologies that is capable of harnessing that waste heat energy from the fuel which cannot be utilised by the engine operation alone. ORC as a WHR system (WHRS) is widely implemented in land based applications due to its fluid choice flexibility, plant simplicity and net efficiency. However, it is rather new to the maritime industry because WHRS on-board ships are predominantly based on steam Rankine cycle or turbo-compounding. These systems have their own advantages but ORC-WHRS may outweigh them in certain applications on-board ships. This is especially for electrical power generation from low and medium temperature waste heat sources. However, ORC in marine application encounters challenges unlike seen in land based applications. These challenges are caused by the physical & geometrical constraints, operational profile of the vessel or uncertainties caused at sea.
 In this thesis, the implementation of ORC-WHRS to marine engines for exhaust gas is investigated and studied to understand how such an application can be beneficial. Unlike steam Rankine cycle, an ORC system has flexibility in choosing an organic fluid that is suitable based on the application. This flexibility in fluid choices are confronted by the above mentioned maritime related challenges. Hence, a screening methodology is devised in this thesis that finds a suitable fluid based on the waste heat source profile and selection parameters. These selection parameters are necessary to filter out functioning organic fluids that can be limited due to the mentioned challenges. In this thesis, the power density of the ORC plant is the selection parameter used.As mentioned earlier, the ORC-WHRS may often be subjected to off-design conditions due to the operational profile of the vessel or by uncertainties at sea. Hence, off-design performance is analysed to study the ORC system when designed at several discrete engine load points. These analysis are carried out in plant models modified from an existing steam based dynamic model and developed into a simple-ORC and a recuperative-ORC dynamic plant models. Sensitivity analysis of these models are also performed to understand uncertainties in the model output corresponding to uncertainties in model input parameter. This analysis is followed by analysis of the dynamic behaviour of the ORC plant model to varying load step functions and step duration for plants designed at discrete engine load points.
 This thesis can be extended, not only to study how ORC can be used to meet future regulations on CO2 emissions, but also on operability limitations imposed on ships. The fluid screening approach used here can also be modified based on parameters, such as toxicity, flammability, cost, specific power etc. This can present a realistic approach to an end product that can be safely and economically operated on board.