Development of an Ultra-Low NOx LP(P) Burner

Abstract

Within the EC framework 5 programme LOPOCOTEP Rolls-Royce Deutschland (RRD) continues to develop Lean Premix (Partially Pre-vaporized) (LP(P)) combustion systems to implement the ACARE goals to achieve further NOx reductions compared with the best combustor technology currently available. The results from the previous EC framework 4 programme LowNOx III had been used to calculate DpNOx/Foo values for an ICAO LTO cycle. The result showed that 40% from the CAEP II limit can be achieved for a medium size fan engine. Cycle and mission calculations have risen the hope that total NOx emissions can be reduced by more than 70% for a 800 NM medium range flight. The objective of the current programme is to further reduce the NOx emissions (30% CAEP II) for a more severe engine cycle and therefore a larger burner size compared to the LowNOx III programme. Flash-back and auto-ignition under all operation conditions have to be prevented. A scaling law was derived from the existing database and applied on an LP(P) module which was then tested at pressures of up to 35 bar and temperatures of up to 900 K in a single sector test rig. The applicability of the scaling laws was confirmed. Testing at take-off conditions showed single digit EINOx between 2 and 4 g/kg depending on the actual swirl-generator configuration. However, poor weak extinction was observed and gave concern regarding operability. The decision was taken to redirect the development efforts to improve operability and to increase the lean blow out (LBO) air-fuel-ratio (AFR). This led to the integration of an internal, centrally arranged pressure-swirl atomizer as pilot diffusion burner into the LP(P) burners. Due to an optimization of the aerodynamics of the LP(P) module which was performed at the same time the dimensions of the burner could be reduced while the effective area was kept constant. This burner was then initially tested at atmospheric conditions to address ignition and LBO limit. This burner showed excellent ground ignition capability at air temperatures as low as 350 K. In the best configuration one spark was sufficient. The testing of the lean extinction limit was repeatedly verified. At 350 K the LBO was always in the range between 110–130 OAFR. More detailed investigations on emissions, flash-back and auto-ignition characteristics will be performed at ONERA and Lund University.