Variation in Flame Temperature with Burner Stabilization in 1D Premixed Dimethyl Ether/Air Flames Measured by Spontaneous Raman Scattering

The flame temperatures in flat, laminar premixed dimethyl ether (DME)/air flames with varying degrees of burner stabilization were measured by spontaneous Raman scattering in a range of equivalence ratio (phi) from 0.6 to 2.0. Three commonly used mechanisms to describe DME oxidation were evaluated by comparing the calculated variation of flame temperature derived from one-dimensional flame calculations as a function of DME/air exit velocity with those obtained from the measurements. The results showed the necessity of incorporating radiative heat losses in the flame calculations. The three mechanisms yield similar results at phi = 0.6 and 2.0, underpredicting the temperatures more than 30 K. Differences between the measured and predicted temperatures for burner-stabilized flames are seen to indicate whether a free-flame burning velocity (S-L) is too high or too low. The results suggest a free-flame burning velocity of similar to 14 cm/s at phi = 0.6, 2 cm/s lower than the mechanisms predicted, and burning velocities closer to 49 and 40 cm/s for phi = 1.0 and 1.4, respectively. Sensitivity analysis of the DME/air flame temperature as a function of exit velocity shows that the DME decomposition reaction and H abstraction from DME become important in the rich flames at phi = 1.7 and 2.0.