Lean Operation of a Pulse Detonation Combustor by Fuel Stratification
Abstract Pressure gain combustion is a promising concept to substantially increase the thermal efficiency of gas turbines. One possible implementation are pulse detonation combustors (PDCs), as they permit stable and reliable operation. Besides, the need for part-load operation and low NOx emissions requires combustion concepts in the lean regime. The present work investigates an approach to realize lean combustion in a PDC by applying fuel stratification experimentally. The necessary increase of fuel concentration inside the pre-detonation chamber to provide reliable DDT with respect to the overall equivalence ratio is identified. Emission measurements in the exhaust allow for a quantification of the NOx emissions as a function of the injected fuel profile. A valveless PDC test rig is used, which contains a shock-focusing geometry for detonation initiation and is ignited by a spark plug close to the upstream end wall. The subsequent expansion of the burned gas and interaction of the flame front with turbulence leads to the formation of a leading shock inside the pre-detonation chamber, which is then focused inside a converging-diverging geometry. The successful initiation of a detonation wave by shock focusing is very sensitive to the pressure ratio across the leading shock, which can be influenced by initial pressure, reactant composition and flow velocity. Results reveal that fuel stratification allows for reliable detonation initiation at a global equivalence ratio of 0.65, whereas repeatable successful operation with non-stratified fuel injection is limited to a global equivalence ratio greater than 0.85.