Autoignition Modes in a Shockless Explosion Combustor

Pressure gain combustion as an alternative to isobaric combustion has been in the focus of research for the past decades as it potentially allows for increasing the thermal efficiency of conventional gas turbines significantly. Beside the most known concepts, such as pulse detonation and rotation detonation combustors, the shockless explosion combustor (SEC) has been proposed. In contrast to the previously mentioned detonation-based concepts the SEC process is based on a thermal explosion, hence avoiding entropy generation caused by propagating detonation waves. Conceptually, this is achieved through a homogeneous autoignition of the fuel–oxidizer mixture, which is realized by the proper stratification of the fuel concentration throughout the combustor, leading to a gradual rise in pressure. Since the process of autoignition is highly sensitive to perturbations, local deviations in the initial state of the mixture lead to a variety of autoignition modes. In this work, an SEC test rig is used to investigate the impact of different fuel injection profiles on the formation of autoignition modes. Pressure transducers are used to measure the pressure rise subsequent to the autoignition event. k-means clustering is applied to a set of pressure data to classify the measured pressure profiles. The same method was used to cluster the respective injection profiles. The results reveal that the gradient in reactivity is of major importance and can be used for increasing the pressure rise through ignition.