A two-dimensional computational fluid dynamics (2D CFD) simulation of a low-speed two-stroke marine engine simulation was performed in order to investigate the performance of 2D meshes that allow the ...use of more complex chemical schemes and pollutant formation analysis. Various mesh density simulations were compared with a 3D mesh simulation and with the experimentally obtained cylinder pressure. A heavy fuel model and a soot model were implemented in the software. Finally, the influences of three water injection strategies were simulated and evaluated in order to investigate the capability of the model and the influence of water injection on NOx formation, soot formation, and engine performance. We conclude that the direct water injection strategy reduces NOx emissions without adversely affecting the engine performance or soot emissions. The other two strategies—Intake air humidification and direct injection of fuel–water emulsion—reduced NOx emissions but at the cost of higher soot emissions or reduced engine performance.
In the current paper, a CFD simulation study on a pent-roof, spark ignition engine was performed. The scope was to analyze the basic parameters that influence the performances of the simulation: mesh ...configuration, mesh refinement, turbulence model, and flame wrinkling model parameters. It was used as the OpenFOAM solver for spark ignition engines. The solver was modified by adding the layer addition/removal mechanism for the mesh. Further, a Zeldovich extended NOx model was implemented. Four different mesh configurations were tested with different refinement levels. A set of different turbulence models and initial parameters and different flame wrinkling model parameters were tested. It was observed how all these parameters influence the rate of heat release, cylinder pressure, temperature, the level of turbulent kinetic energy, the flame wrinkling factor, and finally the resulting concentration of nitride monoxide.
Developed power variation of turbogenerator (TG) steam turbine, which operates at the conventional LNG carrier, allows insight into the change in turbine exergy efficiency and exergy destruction ...during the increase in turbine power. Measurements of required operating parameters were performed in eight different TG steam turbine operating points during exploitation. Turbine exergy efficiency increases from turbine power of 500 kW up to 2700 kW, and maximum exergy efficiency was obtained at 70.13% of maximum turbine developed power (at 2700 kW) in each operating point. From turbine developed power of 2700 kW until the maximum power of 3850 kW, exergy efficiency decreases. Obtained change in TG turbine exergy efficiency is caused by an uneven intensity of increase in turbine developed power and steam mass flow through the turbine. TG steam turbine exergy destruction change is directly proportional to turbine load and to steam mass flow through the turbine—higher steam mass flow results in a higher turbine load which leads to the higher exergy destruction and vice versa. The higher share of turbine developed power and the lower share of turbine exergy destruction in the TG turbine exergy power inlet lead to higher turbine exergy efficiencies. At each observed operating point, turbine exergy efficiency in exploitation is lower when compared to the maximum obtained one for 8.39% to 12.03%.
This research presents isentropic and exergy analyses of marine steam turbine segments at three loads. Turbine segment is a part of any cylinder which is placed between the steam entrance to the ...cylinder and first steam extraction, between steam extractions and finally between last steam extraction and steam exit from the cylinder. Division of each cylinder to the segments allows insight into the various cylinder parts operation and an observation is the cylinder properly balanced. The analyzed marine steam turbine is composed of two cylinders – High Pressure Cylinder (HPC) and Low Pressure Cylinder (LPC), while each cylinder has two segments. The dominant part of real mechanical power produced in HPC is actually produced in the first HPC part (segment 1), while in LPC, the dominant part of real mechanical power is produced in the last LPC part (segment 4). Segments 1 and 3 have the highest improvement potential (inlet segments of both HPC and LPC) due to the highest isentropic losses and exergy destructions. HPC is much better balanced cylinder because along with isentropic, also exergy efficiencies between its segments (segment 1 and segment 2) at all loads differ lower than 7%, while the same cannot be stated for the LPC which exergy efficiencies between segments (segment 3 and segment 4) at all loads differ more than 20%. Very low isentropic and exergy efficiencies of the segment 3, at all observed loads, indicate that this turbine segment is highly problematic and at least some of the turbine stages mounted in this segment have difficulties in operation or potential malfunction. In addition, segment 3 is also the highest influenced by the ambient temperature change in comparison to other segments. The ambient temperature increase from 5 °C up to 45 °C can decrease segment exergy efficiency between 1.31% and 3.17%, if all the segments and all loads of the analyzed marine steam turbine are observed.
This paper presents a numerical investigation of heat and mass transfer inside a wet cooling tower with forced air draft, which find application in energy process industries
and oil refineries. The ...mathematical model consists of mass, momentum and energy conservation equations, water droplet trajectories and their interaction with the gas phase,
the computational domain and boundary conditions. Numerical distributions of air velocity, air temperatures, water vapor fractions and evaporation rates are shown and discussed.
The wet cooling tower achieves an efficiency of around 80%, which can be improved by optimizing the value of the water droplet size, nozzle spray angle and water-to-air flow
rate ratio. The water droplet size has a dominant effect on the cooling tower efficiency, whereas small droplets improve the efficiency up to 10%. On the other hand, the spray
angle and the water-to-air ratio lead to slight improvements, about 2-3% in the best case.
In this paper is presented an analysis of main and auxiliary steam energy flow streams from steam generators during the increase in steam system load at conventional LNG carrier. During the steam ...system load increase was presented differences in steam pressure and temperature between main and auxiliary steam flow streams. Energy power of the auxiliary flow stream is higher than energy power of the main flow stream only at the lowest steam system loads after which main flow stream takes over primacy at middle and high steam system loads. Cumulative auxiliary energy flow stream was divided on energy flow streams to each auxiliary device and energy power consumption of each auxiliary device was also investigated throughout number steam system loads. Analysis of steam production from marine steam generators presented in this paper provides insight into the operation dynamics of the entire steam propulsion system.
Fuel consumption and emissions have a very large impact on the environment, and depend on the type of car powertrain, terrain configuration, vehicle load and vehicle speed. In this paper, a ...simulation was performed using Advisor vehicle simulation software on a specific urban route. Using factory-installed sensors, engine ECU and car OBD2 connection, the current speed and fuel consumption of a car with diesel engine were measured. Using Advisor software, a simulation models of a passenger car with diesel, petrol and hybrid powertrain were made. The measured speed profile of the real car was used as input data in simulations for cars with different powertrains. The comparison of simulation and measurement results was used to validate the computer model in terms of fuel consumption. Fuel consumption, carbon dioxide emissions, unburned hydrocarbon emissions, carbon monoxide and nitrogen oxide emissions were calculated. The obtained results are expected, although the differences between individual powertrains are more pronounced than declared by the manufacturers. The highest fuel consumption and the highest emission was achieved by a car with petrol engine, and the lowest by a car with hybrid powertrain. The fact that a three-way catalytic converter installed in a car with petrol and hybrid drive becomes effective only after a few minutes of operation, when the operating temperature is reached, has a significant impact on emissions.
Fuel consumption and emissions have a very large impact on the environment, and depend on the type of car powertrain, terrain configuration, vehicle load and vehicle speed. In this paper, a ...simulation was performed using Advisor vehicle simulation software on a specific urban route. Using factory-installed sensors, engine ECU and car OBD2 connection, the current speed and fuel consumption of a car with diesel engine were measured. Using Advisor software, a simulation models of a passenger car with diesel, petrol and hybrid powertrain were made. The measured speed profile of the real car was used as input data in simulations for cars with different powertrains. The comparison of simulation and measurement results was used to validate the computer model in terms of fuel consumption. Fuel consumption, carbon dioxide emissions, unburned hydrocarbon emissions, carbon monoxide and nitrogen oxide emissions were calculated. The obtained results are expected, although the differences between individual powertrains are more pronounced than declared by the manufacturers. The highest fuel consumption and the highest emission was achieved by a car with petrol engine, and the lowest by a car with hybrid powertrain. The fact that a three-way catalytic converter installed in a car with petrol and hybrid drive becomes effective only after a few minutes of operation, when the operating temperature is reached, has a significant impact on emissions.
Wood processing is a typical example of an industry where mechanical work (machining) and heat energy (wood drying) are needed. It is therefore very suitable for the application of cogeneration which ...provides significant energy savings. Savings are greatest when biomass is used as a source of energy or, more precisely, wood chips obtained as waste from wood processing. This paper presents a comparison of the cost of woodworking plants using different energy sources. The conventional plant uses electricity from the external electricity grid and the heat generated by the combustion of fuel in the boiler. The cogeneration plant in the considered case uses the combustion of biomass for the production of electricity by a steam turbine plant and also to meet the needs for heat energy. As an energy source, wood chips that remain from the wood processing are used and can therefore be considered as free. However, such a system requires higher investment costs, but due to the rational use of its own waste for combustion, it allows a return on investment costs due to fuel savings.
Thermodynamic (energy and exergy) analysis of steam cooling process in the marine steam propulsion
plant is presented in this research. Steam cooling is performed by using Desuperheater which inject
...water in the superheated steam to obtain wet steam. Wet steam is used in auxiliary heaters for various
heating purposes inside the marine steam propulsion system. Auxiliary heaters require wet steam
due to safety reasons and for easier steam condensation after heat transfer. Analysis of steam cooling
process is performed for a variety of steam system loads. Mass flow rates of cooling water and
superheated steam in a properly balanced cooling process should have the same trends at different
system loads - deviations from this conclusion is expected only for a notable change in any fluid
temperature. Reduction in steam temperature is dependable on the superheated steam temperature (at
Desuperheater inlet) because the temperature of wet steam (at Desuperheater outlet) is intended to
be almost constant at all steam system loads. Energy losses of steam cooling process for all observed
system loads are low and in range between 10–30 kW, while exergy losses are lower in comparison
to energy losses (between 5–15 kW) for all loads except three the highest ones. At the highest system
loads exergy losses strongly increase and are higher than 20 kW (up to 40 kW). The energy efficiency
of a steam cooling process is very high (around 99% or higher), while exergy efficiency is slightly
lower than energy efficiency (around 98% or higher) for all loads except the highest ones. At the highest
steam system loads, due to a notable increase in cooling water mass flow rate and high temperature
reduction, steam cooling process exergy efficiency significantly decreases, but still remains acceptably
high (between 95% and 97%). Observation of both energy and exergy losses and efficiencies leads
to conclusion that exergy analysis consider notable increase in mass flow rate of cooling water which
thermodynamic properties (especially specific exergies) strongly differs in comparison to steam. Such
element cannot be seen in the energy analysis of the same system.
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