Development of a New Flame Speed Vessel to Measure the Effect of Steam Dilution on Laminar Flame Speeds of Syngas Fuel Blends at Elevated Pressures and Temperatures

Synthetic gas, syngas, is a popular alternative fuel for the gas turbine industry, but the composition of syngas can contain different types and amounts of contaminants, such as carbon dioxide, methane, moisture, and nitrogen, depending on the industrial process involved in its manufacturing. The presence of steam in syngas blends is of particular interest from a thermo-chemical perspective as there is limited information available in the literature. This study investigates the effect of moisture content (0 ? 15% by volume), temperature (323 ? 423 K), and pressure (1 ? 10 atm) on syngas mixtures by measuring the laminar flame speed in a newly developed constant-volume, heated experimental facility. This heated vessel also broadens the experimental field of study in the authors? laboratory to low vapor pressure fuels and other vaporized liquids. The new facility is capable of performing flame speed experiments at an initial pressure as high as 30 atm and an initial temperature up to 600 K. Several validation experiments were performed to demonstrate the complete functionality of the flame speed facility. Additionally, a design-of-experiments methodology was used to study the mentioned syngas conditions that are relevant to the gas turbine industry. The design-of-experiments methodology provided the capability to identify the most influential factor on the laminar flame speed of the conditions studied. The experimental flame speed data are compared to the most up-to-date C4 mechanism developed through collaboration between Texas A&M and the National University of Ireland Galway. Along with good model agreement shown with all presented data, a rigorous uncertainty analysis of the flame speed has been performed showing an extensive range of values from 4.0 cm/s to 16.7 cm/s. The amount of carbon monoxide dilution in the fuel was shown to be the most influential factor on the laminar flame speed from fuel lean to fuel rich. This is verified by comparing the laminar flame speed of the atmospheric mixtures. Also, the measured Markstein lengths of the atmospheric mixtures are compared and do not demonstrate a strong impact from any one factor but the ratio of hydrogen and carbon monoxide plays a key role. Mixtures with high levels of CO appear to stabilize the flame structure of thermal-diffusive instability. The increase of steam dilution has only a small effect on the laminar flame speed of high-CO mixtures, while more hydrogen-dominated mixtures demonstrate a much larger and negative effect of increasing water content on the laminar flame speed.