A new piloted premixed jet burner to study strong finite-rate chemistry effects

This paper describes the initial characterization of a piloted premixed jet burner (PPJB) designed to investigate finite-rate chemistry effects in highly turbulent lean premixed combustion. The PPJB consists of a high-velocity lean premixed central jet, piloted by a low-velocity stoichiometric premixed pilot, surrounded by a large-diameter coflow of lean premixed hydrogen–air combustion products. The configuration of a lean central jet supported by a stoichiometric pilot is similar to that of a lean premixed gas turbine combustor, but without additional complications such as swirl, recirculation, and complex boundary conditions. A significant feature of the PPJB is that under certain conditions the central jet combustion process appears to undergo an extinction–reignition process. It is considered likely that intense turbulent mixing after the nozzle drives an initial extinction process that reduces flame luminosity, with reignition occurring downstream where turbulent mixing has decreased, causing an increase in flame luminosity. Four flames are selected for further study, each with an equivalence ratio of 0.5 and with central jet velocities of 50, 100, 150, and 200 m/s. Simultaneous two-dimensional (2D) Rayleigh–OH planar laser-induced fluorescence (PLIF) imaging results are presented for the selected flames, showing that in the “extinction” region OH concentrations occur at reduced levels in isolated patchy regions, supporting the idea that extinction is predominantly occurring. Laser Doppler velocimetry (LDV) data are also reported for the flow field turbulence statistics, with the most significant result being that for the reacting cases the pilot delays the occurrence of peak turbulence intensity downstream to near the observed “extinction” region.