New laminar flame speed measurements have been taken for a wide range of synthetic gas, or syngas, mixtures. These experiments began with two baseline mixtures. The first of these baseline mixtures was a bio-syngas surrogate with a 50/50 H2/CO split, and the second baseline mixture was a coal syngas blend with a 40/60 H2/CO split. Experiments were conducted over a range of equivalence ratios from ? = 0.5 to 3 at initial conditions of 1 atm and 296 K. Upon completion of the baseline experiments, two different hydrocarbons were added to the fuel mixtures at levels ranging from 0.8 to 15% by volume, keeping the H2/CO ratio locked for the bio-syngas and coal syngas mixtures. The addition of these light hydrocarbons, namely CH4 and C2H6, had been shown in a previous numerical study to have significant impacts on the laminar flame speed, and the present experiments validated the suspected trends. For example, a 7% addition of methane to the coal-syngas blend decreased the peak flame speed by about 25% and shifted it from ? = 2.2 to a leaner value near ? = 1.5. Also, the addition of ethane at 1.7% reduced the mixture flame speed more than a similar addition of methane (1.6%). Images taken during the experiments show the addition of hydrocarbons increasing the stability of the flame. The analysis also looked at the effects of hydrocarbon addition on the Markstein lengths and Lewis numbers of the mixtures. Markstein lengths were relatively consistent throughout all mixtures investigated. The Lewis numbers were found to move closer to unity for both lean and rich mixtures as hydrocarbons were added. Compared to the experimental results the model predicts the shape of the flame speed curve and places the peak at the correct equivalence ratio. However the model predicts a slower flame speed when hydrocarbons are added.
