The interest in using alternative fuels in commercial aviation has substantially grown, as it is anticipated to be the principal means of mitigating rising fuel costs, fuel supply security, and environmental impact of aviation. Synthetic paraffinic kerosenes (SPKs), such as gas-to-liquid (GTL) derived from the Fischer- Tropsch route using natural gas, have been approved by the ASTM International committee for use as suitable blendstock with Jet A-1. The GTL fuel composition may be defined in terms of key components (normal-, iso- and cyclo-paraffins) and in terms of carbon number distributions. In order to explore effects of composition changes on targeted combustion properties, such as ignition or overall performance, surrogate blends have been produced by Shell using existing GTL and commercial solvents.

We present results from an experimental campaign conducted on the Rolls- Royce plc TRL3 sub-atmospheric altitude ignition facility in Derby, UK. The test campaign aimed to investigate the effect of GTL-like fuel composition on aviation turbine altitude ignition and combustion performance. Five different GTL-like fuels and Jet A-1 as reference fuel were tested in a representative lean-burn aviation combustor at sub-atmospheric air pressures and temperatures. The simulated altitude conditions corresponded to a flight altitude between 25,000 and 30,000 feet.

High-repetition-rate and simultaneous imaging of the chemiluminescence from the hydroxyl and from the methylidyne radicals and of the broadband flame luminosity were performed in order to temporally resolve the flame initiation phenomena. The volume-integrated chemiluminescence can be regarded as a qualitative measure of the global heat release rate in the combustor, whereas the broadband luminosity of sooty flames is dominated by the luminosity of the radiating hot soot particles and is thus representing the soot distribution. In addition, flame luminosity spectra were recorded to obtain information from the chemiluminescence spectrum of the different intermediate combustion radicals and from the broadband soot radiation.

We found that the observed ignition and combustion performance only depend weakly on the fuels investigated. However, the SPK flames showed significantly lower soot luminosities than the corresponding Jet A-1 flames for all combustor operating conditions, indicating a benefit of the SPK fuels for the environment and the combustor operability


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