抄録
The knowledge about fuel composition effects on the combustion behavior becomes more and more important due to strict legislative exhaust emission restrictions on the one hand and modified fuel compositions on the other hand. In diesel combustion the addition of new fuel components, such as fatty acid methyl ester and pure alkanes from the Fischer-Tropsch-synthesis, have significant effect on the thermo physical properties of the diesel fuel mixture and therefore influence the injection and the evaporation process. These processes have a strong impact on the following ignition and combustion process and therefore on the power generation, engine noise and emissions. This can be seen in gasoline and diesel injection. In the present investigation the focus was set on the ignition phase. Using a typical piezo-type diesel injector and injection pressures up to 200 MPa different diesel fuels were injected into a stationary high temperature (up to 1000 K) and high pressure (up to 10 MPa) atmosphere. By means of two different cameras the spray formation and the appearance (time and location) of premixed and diffusion controlled combustion were acquired, separately. It was found that the timing of the ignition processes (premixed and diffusion controlled combustion) was dominated by the ambient gas temperature while the location of ignition is defined by the pressure ratio between gas and fuel. The time delay between the first appearance of the lean combustion and appearance of the diffusion controlled flame was consequently also dominated by the gas temperature. At part load conditions the UV-flame appeared at 800 μs after the visible start of injection while at full load conditions the ignition delay was reduced to 250 μs. Cetane-number was not found to have big effect on ignition timing under the conditions applied. The start of combustion was found on the front or the side of the spray cone tip for all operating conditions investigated.
