Laminar flame speed measurements of synthetic gas blends with hydrocarbon impurities

New Laminar Flame Speed measurements have been taken for a wide range of syngas mixtures containing hydrocarbon impurities. These experiments began with two baseline syngas mixtures. The first of these baseline mixtures was a bio-syngas with a 50/50 H₂/CO split, and the second baseline mixture was a coal syngas with a 40/60 H₂/CO split. Experiments were conducted over a range of equivalence ratios from Φ = 0.5 to 3 at initial conditions of 1 atm and 300 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 recent calculations by the authors 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 Φ = 2.2 to a leaner value near Φ = 1.5. Also, the addition of ethane at 1.7% reduced the mixture flame speed more than a similar addition of methane (1.6%). In general, the authors' chemical kinetic model over predicted the laminar flame speed by about 10-20% for the mixtures containing the hydrocarbons. The decrease in laminar flame speed with the addition of the hydrocarbons can be explained by the increased importance of the inhibiting reaction CH₃ + H (+M) 虠 CH₄ (+M), which also explains the enhanced effect of C₂H₆ compared to CH₄, where the former produces more CH₃ radicals, particularly at fuel rich conditions.