Simulation Study of a Dual Fuel Injector
Saarinen, Ilari (2017)
Saarinen, Ilari
2017
Konetekniikka
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2017-09-26
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201709201908
https://urn.fi/URN:NBN:fi:tty-201709201908
Tiivistelmä
The need for this thesis comes from the timely objective to minimize emissions and maximize efficiency in combustion engines. The latest trend in the marine industry is to utilize dual fuel engines as the power source for vessels, allowing the engine to be run on both diesel and gas. In the gas mode, the gas is ignited by injecting a small amount of diesel, in a so-called pilot injection, into the combustion chamber. The pilot injection event, and the fuel injector creating it, is the topic of this thesis.
To be able to understand the operation of a fuel injector, mechanic, hydraulic and electromagnetic theory is presented. Next, fuel injector operation is descripted. Then, a simulation model of the fuel injector is built and verified. Sensitivity analyses are made for both the pilot injection and the full injection event, for the purpose of understanding which parameters affect the injector outputs. Finally, both the pilot injection and the full injection event are optimized in order to reach the emission and efficiency targets.
The sensitivity analysis clearly shows that the most important parameters affecting the injector performance are the inlet, outlet and filling orifices. Naturally, also the number of nozzle holes and the hole diameters play a crucial role, a smaller flow area resulting in a faster pilot injection but less injected quantity in a full injection. The pressure step and the needle spring have a lesser impact. The geometry of the needle tip is also important but hard to model accurately. In the studied injector, the control valve was so fast that it did not restrict the pilot injection speed. After optimizing the model, it was clear that the size of the outlet orifice needs to be increased, and that the sizes of the inlet and filling orifice can be kept roughly the same.
To be able to understand the operation of a fuel injector, mechanic, hydraulic and electromagnetic theory is presented. Next, fuel injector operation is descripted. Then, a simulation model of the fuel injector is built and verified. Sensitivity analyses are made for both the pilot injection and the full injection event, for the purpose of understanding which parameters affect the injector outputs. Finally, both the pilot injection and the full injection event are optimized in order to reach the emission and efficiency targets.
The sensitivity analysis clearly shows that the most important parameters affecting the injector performance are the inlet, outlet and filling orifices. Naturally, also the number of nozzle holes and the hole diameters play a crucial role, a smaller flow area resulting in a faster pilot injection but less injected quantity in a full injection. The pressure step and the needle spring have a lesser impact. The geometry of the needle tip is also important but hard to model accurately. In the studied injector, the control valve was so fast that it did not restrict the pilot injection speed. After optimizing the model, it was clear that the size of the outlet orifice needs to be increased, and that the sizes of the inlet and filling orifice can be kept roughly the same.