Experiments on Stability of Syngas Combustion in a Trapped Vortex Combustor

Syngas is being studied extensively as an effective alternate fuel for various applications in recent times. Syngas combustion offers significant challenges because of varying compositions and considerably low calorific values. Trapped vortex combustor (TVC) is an established design in gas turbine engine combustors utilizing the RQL (rich-burn quickquench lean-burn) strategy for achieving stable combustion under various operating conditions and meeting stringent pollution norms at the same time. TVC design consists of a cavity in which a vortex is established where rich combustion takes place. The products then mix quickly with the main flow and then the ultra lean mixture undergoes combustion. Previous studies on methane combustion in TVC have shown that this concept helps to achieve a very wide operating range of equivalence ratios with low NOx and particulate emissions. A single cavity TVC rig is used to study the combustion and mixing phenomena. Preliminary experiments on syngas combustion in TVC have shown stable combustion even for very lean equivalence ratios (Φ~0.1). However, the dynamics in the cavity seem to differ considerably from previous methane combustion studies. The flame is characterised by equivalence ratio which might mean that mixing in the cavity is minimal. To understand the cavity mixing, acetone PLIF has been employed. These results show that the fuel jet momentum plays a very important role in determining the mixing within the cavity. Fuel mixing increases with the increase in fuel jet momentum as also with the guide vane air momentum. Flame luminosity images do not show a flame at the center of the cavity possibly indicating a lack of cavity recirculation vortex. Further comparison between methane and syngas can be carried out by employing parameters like jet momentum ratio.