LAUSR

Received: 19 August 2017 Accepted: 24 October 2018 The stabilization mechanism of non-premixed jet flames of methane diluted with helium has been investigated experimentally. Effects of fuel mole fraction, XF,O and nozzle diameter, D on the lifted flame characteristics of diluted methane jets were studied. Such methane jet flames could be lifted despite the Schmidt number was less than unity. Regimes of lifted flames were evaluated according to Richardson number and liftoff height compared with the length of developing zone. Such flames obtained using D = 9.4 mm nozzle were stabilized due to buoyancy induced convection in buoyancy dominated regime whereas for D = 0.95 mm nozzle methane jet flames could be lifted even at nozzle exit velocities much higher than stoichiometric laminar flame speed in jet momentum dominated regime. The chemiluminescence intensities of OH* radical (good indicators of heat release rate) were measured using monochromatic system for these lifted flames. It was confirmed that, in jetmomentum dominated regime an increase in radius of curvature in addition to OH* concentration stabilizes such lifted flames. Heat release rate near the triple point inferred by the OH* chemiluminescence intensity was inversely proportional to XF,O and had maximum at blowout conditions.