Ignition delay time experiments for natural gas/hydrogen blends at elevated pressures

Applications of natural gases that contain high levels of hydrogen have become a primary interest in the gas turbine market. While the ignition delay times of hydrogen and of the individual hydrocarbons in natural gases can be considered well known, there have been few previous experimental studies into the effects of different levels of hydrogen on the ignition delay times of natural gases at gas turbine conditions. To examine the effects of hydrogen content at gas turbine conditions, shocktube experiments were performed on nine mixtures of an L9 matrix. The L9 matrix was developed by varying four factors: natural gas higher-order hydrocarbon content of 0, 18.75, or 37.5%; hydrogen content of the total fuel mixture of 30, 60, or 80%; equivalence ratios of 0.3, 0.5, or 1; and pressures of 1, 10, or 30 arm. Temperatures ranged from 1092 K to 1722 K, and all mixtures were diluted in 90% Ar. Correlations for each mixture were developed from the ignition delay times and, using these correlations, a factor sensitivity analysis was performed. It was found that hydrogen played the most significant role in the ignition delay times of a mixture. Pressure was almost as important as hydrogen content, especially as temperature increased. Equivalence ratio was slightly more important than hydrocarbon content of the natural gas, but both were less important than pressure or hydrogen content. Comparison with a modern chemical kinetic model demonstrated that the model captures well the relative impacts of H₂ content, temperature, and pressure, but some improvements are still needed in terms of absolute ignition delay times.