Transient Performance and Emissions of a Turbocharged Diesel Engine for Marine Power Plants: Numerical Simulation and Experimental Investigation
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- Institutt for marin teknikk 
New marine power and propulsion plants have to meet increasingly stringent environmental regulations and requirements for flexible and efficient operations. Such a multi-objective task requires a systems approach in which the design of components and the operation of the system are optimized in a holistic way in order to provide the overall improvements of the system under a realistic operational profile. In this regard, mathematical modeling and numerical simulation of the power plant in conjunction with the surrounding systems and environmental loads becomes an essential tool. It is even more so with the complex operation of a hybrid power/propulsion plant with energy storage devices. In the majority of marine power/propulsion plants, turbocharged diesel engines sit as main prime movers that determine the dynamic response, fuel efficiency and emissions of the overall plant. Therefore, how the diesel engines are modeled has a significant influence on the overall performance of the total system simulator of the power/propulsion plant. A turbocharged diesel engine itself is a complex engineering system, and one should therefore model it in a good balance of accuracy and simplicity in order to use it in the power plant simulation. Furthermore, many diesel engines are designed with common components and physical laws. Therefore, reusability of a mathematical model in different contexts is important for an efficient modeling process. This thesis aims to find an effective modeling framework of a turbocharged diesel engine for simulation of marine power/propulsion plants considering these aspects. In order to achieve the goal, research works are carried out in different areas: establishment of the modeling framework for a turbocharged diesel engine, development of the marine vessel and power plant simulators to test the diesel engine models and an experimental investigation of the effects of the transient loads on diesel engines. As a modeling framework of a turbocharged diesel engine, architecture of model libraries is proposed, which has a solid hierarchical structure in terms of levels of abstraction: a technical component level, a physical concept level and a mathematical level. Following the suggested architecture enables a modeler to make a decision at each level distinctively that the decisions are more traceable than when it is done holistically. Therefore, reusability of the model is enhanced. Furthermore, a general interface structure is proposed for the thermodynamic modeling of a diesel engine process which can be used for models with different fidelity. The established framework is used to model diesel engines at different levels of fidelity, namely zero-dimensional (0D) semi-phenomenological and mean-value engine model. The former is used for simulation of marine propulsion in wave, and the latter is used for simulation of a diesel-electric power plant in a dynamic positioning vessel. Total system simulators for both cases are also developed in cooperation with other researchers in order to test the developed diesel engine model. Such a multi-disciplinary system simulator includes first-principle models of environmental loads, a vessel hull, a propeller, a shaft, a diesel engine, electrical power plant and control systems. These system simulators provide realistic loads on the diesel engine in the actual operating environments. Finally, effects of the transient loads on efficiency and NOx emissions of a turbocharged diesel engine is experimentally investigated. A sinusoidal load is one of the particular loads on marine diesel engines and is not well studied in literatures. The aims of this study are, first, to find the effect of the cyclic load compared to a constant load and, second, to validate a quasi-steady mapping method for estimation of efficiency and NOx emissions. Average specific fuel consumption and NOx concentration are measured for various load frequencies. The results suggest that the effect depends on both the mean load level and the frequency. The lower the mean load level is and the higher the frequency is, the more distinguished difference are observed. Moreover, a quasi-steady mapping method provides a relatively good estimation for efficiency in most cases. The established framework and developed simulators and mathematical models can be further used for study of the power plants in different configurations and complexity. Such a study may aim to prototype a power plant concept, to find an optimized design of the concept or to design a control system for it. The work in this thesis can also provide a structured guideline for developing a new mathematical models for diesel engines and provide the necessary a priori knowledge to build the model that are fit for the purpose.