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45471-AC9
Study of Hydrogen/Syngas Combustion and NO Emissions at High Pressures and Temperatures
Laminar flame speeds for syngas mixtures of various compositions up to 20 atm are measured with outwardly propagating spherical flames at constant pressure using more restrictive measures for data reduction that consider deviation from the ideal flow field caused by a non-spherical confinement. In the present study, as in earlier high pressure study of flame speeds, a recently developed constant-pressure approach that utilizes a cylindrical test chamber is applied. For the first time, the effect of flow field on flame speed measurements is addressed in detail for these non-spherical constant-pressure chambers. The results from experiments and analysis indicate that deviation from the assumed flow field causes significant errors in instantaneous flame speed measurement, which are amplified in the extrapolation to zero stretch rate. A simple model is developed to study the effect of flow disturbance in cylindrical confinements. In cylindrical chambers, where the flow is typically most constrained in the plane of measurement (radial direction), failure to consider this effect results in lower values for the measured flame speed.
The effects of flow compression and flame stretch on the determination of flame speeds using spherical bombs under constant-pressure and constant-volume conditions are studied theoretically and numerically. A time-accurate and front-adaptive numerical algorithm is developed to simulate the outwardly propagating spherical flame in a closed chamber for a broad range of pressures and equivalence ratios. The results show that both flow compression and flame stretch have significant impacts on the accuracy of measured flame speeds. For the constant-pressure method, a new expression is presented to calculate a compression corrected flame speed (CCFS). Likewise, for the constant-volume method, a new expression is presented to calculate a stretch corrected flame speed (SCFS). The results demonstrate that the present CCFS and SCFS methods not only greatly improve the accuracy of the flame speed measurements but also extend the valid parameter range of experimental conditions. These findings and techniques will be implemented in future work for the determination of syngas flame speeds at elevated pressures and temperatures in a preheated spherical bomb.
An accurate spectral dependent radiation model is developed to predict flame speed and flammability of H2/CO/CO2/H2O/Air mixtures by including radiation reabsorption at high pressures. The results showed that radiation reabsorption significantly extended the flammability limits. It was also demonstrated that accurate prediction of coal syngas flammability is not possible without appropriate consideration of radiation absorption by CO2 and H2O.
