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Flexible and multiple injections are an important strategy to fulfill today's exhaust emission regulations. To optimize injection processes with an increasing number of adjustable parameters knowledge about the basic mechanisms of spray breakup, propagation, evaporation and ignition is mandatory. In the present investigation the focus is set on spray formation and ignition. In order to simulate current diesel-engine conditions measurements were carried out in a high-temperature (1000 K) and high-pressure (10 MPa) vessel with optical accesses. A piezo servo-hydraulic injector pressurized up to 200 MPa was used to compare four single injection durations and four multi-injection patterns in the ignition phase. All measurements were performed with CEC RF-03-06, a legislative reference fuel. For the spray measurements, a program of 16 to 18 different operating points was chosen to simulate engine conditions from cold start to full load.

Differences in thermo-physical parameters of fuels have high impact on the ignition, combustion and emission. Pure rapeseed FAME and diesel fuel with a cetane number of 60 have been compared to reference fuel. In an optical accessible vessel the fuels have been injected in order to investigate the spray, the ignition and soot formation. The high cetane number fuel showed similar behavior in spray phase to the reference fuel but the FAME fuel is more present at all operating points due to low volatile fuel components. The ignition and combustion process was investigated via chemical luminescence (CL) and laser induced incandescence (LII). In engine investigations a reduced ignition delay is detected in case of high cetane-number. The more sensitive optical techniques show differences in the combustion process. The ignition behavior of the reference fuel and the increased cetane number fuel were similar until the cetane increaser of the high cetane fuel came into effect.