| In future aero engine turbines, the NOx emissions are to be reduced continuously. A promising concept is the premixed prevaporised lean combustion (LPP). However, inadmissable auto-ignition of the fuel sprays during premixing turns out to be a serious safety issue. In this context, the auto-ignition phenomenon of sprays was studied in the technically relevant temperature regime (800 K..1100 K) at a pressure of 0.8 MPa. The ignition process in a droplet laden continuous flow was investigated in a premixing duct by laser- and high-speed-measurement techniques. The onset of the chemical reaction was detected by planar laser induced fluorescence (LIF) of formaldehyde (CH2O), which is formed as an intermediate species during the reactions leading to auto-ignition and consumed subsequently in the hot flame. In order to study the influence of residual droplets, Mie-scattering was imaged simultaneously by a second laser (532 nm) / camera system. Additionally, high-speed sequences of the flame luminosity were taken. The chemiluminescence signal was also captured broadband and through different adequate spectral filters at the same time. With this method it was possible to discriminate between the fractions of OH* and CH* radicals as well as from radiation at longer wavelengths that was attributed to “young soot”. |
