Flameholding Tendencies of Bluff-Body and Wall-Recess Stabilized Hydrogen and Natural Gas Flames at Elevated Temperatures and Pressures

摘要

Gas turbines are being operated at increasingly high pressure ratios and high combustor inlet temperatures in order to increase engine efficiency. Lean-premixed operation of gas turbines is common strategy used to reduce the emissions of nitrogen oxides from the engine. However, simultaneously increasing combustor inlet temperatures and pressures while premixing the fuel and air upstream of the combustion chamber to a significant risk of flashback, which occurs when the flame from the combustion chamber propagates upstream into the engines premixing zone. This can severely damage the engine. Preventing damage associated with flashback is a significant concern for lean premixed gas turbines, especially when operated on hydrogen. Hydrogen containing fuels are gaining interest because they can be generated from a variety of low cost sources (coal and biomass) and because of their potential environmental benefits. The method to prevent flashback from damaging engine hardware is twofold: combustors that are prevent flashback from occurring can be used, or upstream hardware that will not allow a flame to anchor should a flashback occur can be used, thus preventing damage. An experiment was constructed to determine the flameholding tendencies of hydrogen and natural gas at elevated temperatures and pressures, similar to those found in the premixing passageways of a gas turbine. Tests were conducted at pressures up to 9 atm, temperatures up to 750K, and free stream velocities up to 100 m/s. Flames were stabilized in the wakes of bluff body and wall features that are typical of premixer passage ways (spokes, steps, etc). Experiments were conducted with both hydrogen and natural gas in order to compare with previous work conducted with hydrocarbons. The results of these experiments were analyzed to produce correlations that predict flame extinction.