Implementing pressure gain combustion into a gas turbine cycle is a promising concept to significantly improve the thermal efficiency of gas turbines. Detonation based concepts, e.g. pulse detonation combustion or rotating detonation combustion, are associated with considerable losses due to entropy generation by inherent shock waves. Shockless explosion combustion (SEC) overcomes this issue by applying quasi-homogeneous auto-ignition that allows for approximate constant volume combustion accompanied by a moderate pressure increase. It is a periodic combustion process in which the fuel is injected into a constant air flow for a well-defined time span. The mixture then convects downstream until combustion is induced by auto-ignition.  However, this causes a spatial gradient in residence time of the burnable mixture. In order to compensate this distribution, a stratification of the ignition delay time is necessary which can be effectively controlled by the equivalence ratio. Thus, injecting a well defined fuel profile is crucial for achieving a quasi-homogeneous auto-ignition and is investigated here.

Since the combustion is not triggered by an external ignition source but driven by chemical kinetics only, the homogeneity of the auto-ignition is very sensitive to local hotspots that produce undesired local premature ignition. To gain profound knowledge about the influence of mixing of fuel and air flow as well as turbulence and boundary layer effects on the spatial distribution of the equivalence ratio, acetone planar laser induced fluorescence (acetone-PLIF) is applied to an atmospheric SEC test rig. The measured two-dimensional fuel concentration is compared to previously applied tunable diode laser absorption spectroscopy (TDLAS) measurements that provide time-resolved line-of-sight measurements at one distinct axial position. The results provide insight into the formation of mixture inhomogeneities by convection, diffusion and boundary layer, and how these effects can be influenced by the chosen fuel profile. This allows to identify an optimal injection trajectory as well as possible geometric improvements in order to minimize the formation of hotspots and improve the overall combustion process.


Investigation of the Fuel Distribution in a Shockless Explosion Combustor

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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