An autoignition study of hydrogen and natural gas mixtures under gas turbine relevant conditions in a rapid compression machine
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This study presents an experimental and modelling investigation of the ignition of hydrogen and natural gas mixtures. These mixtures were chosen due to their relevancy to the gas turbine industry. A detailed chemical kinetic mechanism for hydrogen and H2 / CO (syngas) mixtures has been updated during this study. Experimental results for ignitiondelay times and flame speeds have been compared with predictions using our newly revised chemical kinetic mechanism, and good agreement was observed. This work also used the mechanism produced during the course of this study to investigate numerically the effect of the variationin the syngas composition on some fundamental combustion properties of premixed systems at realistic engine operating conditions. Several pressures, temperatures, and equivalence ratios were investigated. Results of this study showed that the addition of hydrocarbons generally reduces the reactivity of the mixture (longer ignition delay time, slower flame speed) due to chemical kinetic effects. The amplitude of this effect is however dependent on the nature and concentration of the hydrocarbon as well as the initial condition (pressure, temperature, and equivalence ratio). Natural gas/hydrogen mixtures were also investigated as an update to a previous natural gas study. Experiments were performed at 1, 10, and 30 atm in the temperature range 850 - 1800 K, at equivalence ratios of 0.3, 0.5, and 1.0 and with dilutions ranging from 7290 %. All experiments were simulated using a detailed chemical kinetic model. Overall good agreement is observed between the simulations and the experimental results. The influence of steam dilution on the autoignition behaviour of hydrogen, carbon monoxide, syngas and natural gas mixtures under gas turbine relevant conditions was also investigated. Experiments were performed for fuel/air mixtures at equivalence ratios of 0.5, 1.0 and 2.0, in the temperature range 895 - 1140 K for the H2 and CO mixtures and 730 - 1060 K for the natural gas mixtures and at pressures of 10 and 30 bar. It was found that significant changes in the thermal properties of the mixtures affect the reactivity, whereas no chemical effect of the steam addition was observed for the majority of the mixtures investigated.