Experimental and numerical study on ethanol and dimethyl ether lifted flames in a hot vitiated co-flow

Lifted flames of gaseous ethanol and dimethyl ether (DME) issuing into a hot co-flow are recorded with a high-speed camera. The flames of the two fuels at 433 K are studied in a co-flow temperature range from 966 K to 1149 K and at an ambient pressure of 1 atm. The experimental results show that the co-flow temperature has a substantial influence on the jet flame characteristics. It is concluded that the lift-off height is controlled by the ignition delay, whereas the fluctuation is mainly controlled by the sensitivity of the ignition delay to the co-flow temperature. A numerical study coupling the Reynolds averaged Navier-Stokes (RANS) equation with the eddy-dissipation-concept model (EDC) employing detailed reaction mechanisms is established and is consistent with the previous flame structure and lift-off height obtained by the experimental results. The radial profiles and axial distribution of important parameters reveal the acceleration of the mixing process caused by exothermic reactions and indicate the differences in the mixture fraction at the stabilization points between simple fuel (H2 and CH4) and the present fuels. The influences of the chemical reaction on the stabilization mechanism at low and high co-flow temperatures are also discussed.