The paper presents the results from a study that formed part of a bilateral project between DLR-VT and Sasol Technology Fuels Research aimed at investigating the potential influence of physical and chemical fuel properties on ignition and extinction limits within heterogeneous gas turbine combustion. The threshold of flame extinction and re-ignition behaviour of a range of alternative fuels was investigated in a representative aero-combustor sector to determine the relative influence of physical properties and chemical reaction timescales.
A matrix of eight test fuels was selected for use during the study and included conventional crude-derived Jet A-1, synthetic paraffinic kerosene, linear paraffinic solvents, aromatic solvents and pure compounds. All test fuels were characterised through full specification analyses, distillation profiles and two-dimensional gas chromatography.
The ignition and extinction behaviour of the test fuel matrix was evaluated under simulated altitude conditions at the Rolls-Royce Strategic Research Centre’s sub-atmospheric altitude ignition facility in Derby, UK. A twin sector segment of a Rich Quench Lean (RQL) combustor was employed with fuel supplied to a single burner. Combustor air inlet conditions were controlled to 41.4 kPa and 265 K. Fuel temperature was controlled to 288 K.
In addition to the standard extinction and ignition detection systems, optical diagnostics were applied during the test programme. Simultaneous high-speed imaging of the OH* chemiluminescence, and broadband flame luminosity was employed to capture the main reaction zones, the global heat release and distribution of radiative soot particles respectively.
Lean extinction points were determined using both a photodiode as well as from the OH* chemiluminescence data. The position of extinction and overall combustor ignition and extinction timescales were determined. The diagnostic methodology that was used to obtain the results reported in this paper is discussed in greater detail in a separate complementary paper.
All eight fuels, including the fully synthetic Jet A-1 fuels that formed part of the test matrix, yielded performance that was comparable to that obtained with conventional crude-derived Jet A-1.