Temperature Measurements at the Outlet of a Lean Burn Single-Sector Combustor by Laser Optical Methods

Abstract

High overall pressure ratio (OPR) engine cycles for reduced NOx emissions will generate new aggravated requirements and boundary conditions by implementing low emission combustion technologies into advanced engine architectures. Lean burn combustion systems will have a significant impact on the temperature and velocity traverse at the combustor exit. With the transition to high-pressure engines, it is essential to fully understand and determine the high energetic interface between combustor and turbine to avoid excessive cooling. Spatially resolved temperatures were measured at different operating conditions using planar laser-induced fluorescence of OH (OH-PLIF) and filtered Rayleigh scattering (FRS), the latter being used in a combustor environment for the first time. Apart from a conventional signal detection arrangement, FRS was also applied with an endoscope for signal collection, to assess its feasibility for future application in a full annular combustor with restricted optical access. Both techniques are complementary in several respects, which justified their combined application. OH-PLIF allows instantaneous measurements and therefore enables local temperature statistics, but is limited to relatively high temperatures. On the other hand, FRS can also be applied at low temperatures, which makes it particularly attractive for measurements in cooling layers. However, FRS requires long sampling times and therefore can only provide temporal averages. When applied in combination, the accuracy of both techniques could be improved by each method helping to overcome the other's shortcomings.