Laminar burning velocity of hydrogen and flame structure of related fuels for detailed kinetic model validation

Abstract: The laminar burning velocity and the flame structure are common targets for combustion studies aimed at detailed kinetic
model development. In the present work, fuels relevant to hydrogen combustion were considered.

The laminar burning velocity of rich and lean hydrogen flames was studied experimentally and numerically, including its
pressure dependence in rich mixtures and temperature dependence in lean mixtures. An updated version of the Konnov
detailed reaction mechanism for H2 combustion was validated, and after that it was applied to simulate the results obtained in
experiments. The laminar burning velocities of rich H2 + air mixtures were determined from spherical flame propagation data
using three models for stretch correction available in the literature. The heat flux method was employed for the first time to
measure the laminar burning velocity of lean H2 + air mixtures and its temperature dependence. A modified procedure for
processing data from unstable cellular flames was suggested, and its accuracy was evaluated. The observed difference between
the literature results obtained in stretched flames and the values measured in the present work in flat flames was discussed. The
trends in the temperature dependence of the burning velocity of lean H2 + air mixtures, indicated by the modeling but not
supported by the majority of data determined from literature values, were confirmed experimentally in the present work.

An analysis of the experimental uncertainties of the heat flux method was performed. It was shown that some of the factors
which affect the accuracy of the measurements are related to the temperature dependence of the laminar burning velocity. A
method to evaluate asymmetric heat fluxes in the plate of the heat flux burner was proposed. The work reported in the present
study resulted in the necessity to re-evaluate some of the previously published data. Based on the available information from
literature, as well as on the results obtained in the present study, recommendations were made on how to control or reduce
several experimental uncertainties associated with the heat flux method.

The structure of NH3 and CH4 flames was investigated with the aim of further kinetic model development. Intracavity laser
absorption spectroscopy was applied to record HCO concentration profiles in rich low-pressure CH4 mixtures and predictions
of two widely used kinetic models were analyzed. Minor and major species concentrations in NH3 + air flames were used to
validate four contemporary H/N/O reaction schemes and investigate the performance of the best one.