The ignition and combustion performance of different synthetic paraffinic kerosenes (SPKs) under simulated altitude relight conditions were investigated at the altitude relight test rig at the Rolls-Royce Strategic Research Centre in Derby. The conditions corresponded to a low stratospheric flight altitude between 25,000 and 30,000 feet. The combustor under test was a twin-sector representation of an advanced gas turbine combustor and fuel injector. Five different SPKs and Jet A-1 were tested at different mass flow rates of air and fuel, and at two different sub-atmospheric air pressures and temperatures. The fuel temperature was kept approximately constant. Simultaneous high-speed imaging of the OH* and CH* chemiluminescence, and of the broadband luminosity was used to visualize both the transient flame initiation phenomena and the combustion behavior of the steady burning flames. In addition, flame luminosity spectra were recorded with a spectrometer to obtain spectrally resolved information concerning the different chemiluminescence bands and the soot luminosity. These investigations were performed in conjunction with the comparative evaluation of the ignition and stability regimes of the five SPKs, which is the subject of a separate complementary paper [1]. We found that the observed flame initiation phenomena, the overall combustion behavior and the different ratios of the chemiluminescence from the OH*, CH* and C2* radicals were not strongly dependent on the fuels investigated. But, the SPK flames showed for all combustor operating conditions significantly lower soot luminosities than the corresponding Jet A-1 flames, indicating a potential benefit of the SPK fuels.

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