Autoignition in stratified mixtures for pressure gain combustion

The reliable generation of quasi-homogeneous autoignition inside a combustor fed by a continuous air flow would represent a milestone in realizing pressure gain combustion in gas turbines. In this work, the ignition distribution inside a stratified fuel–air mixture is analyzed. The ability of precise and reproducible injection of a desired fuel profile inside a convecting air flow is verified by applying tunable diode laser absorption spectroscopy in non-reacting measurements. High-speed, static pressure sensors and ionization probes allow for simultaneous detection of the flame and pressure rise at several axial positions in reactive measurements with dimethyl ether as fuel. A second, exchangeable combustion tube enables optical observation of OH* intensity in combination with pressure measurements. Experiments with three arbitrary fuel profiles show a set of ignition distributions that vary in shape, homogeneity, and the number of simultaneous autoignition events. Although the measurements show notable variation, a significant and reproducible influence of the fuel injection on the ignition distribution is observed. Results show that uniform autoignition leads to a coupling of the reaction front with the pressure rise and, therefore, induces a greater aerodynamic constraint than non-uniform ignition distributions, which are dominated by propagating deflagration fronts.