| dc.description.abstract | 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. | nb_NO |
