Laminar burning velocities and Markstein numbers of syngas–air mixtures

In the currently reported work, three typical mixtures of H2, CO, CH4, CO2 and N2 have been considered as representative of the producer gas coming from wood gasification. Laminar burning velocities have been determined from schlieren flame images at normal temperature and pressure, over a range of equivalence ratios within the flammability limits. The study of the effects of flame stretch rate was also performed. Combustion demonstrates a linear relationship between flame radius and time for syngas–air flames. The maximum value of syngas–air flame speeds is observed at the stoichiometric equivalence ratio, while lean or rich mixtures have lower flame speeds. The higher is the syngas heat value the higher is the laminar burning velocity of the syngas mixture. Markstein numbers show that typical syngas–air flames are generally unstable. Karlovitz numbers indicates that typical syngas–air flames are little influenced by stretch rate. Based on the experimental data, a formula for calculating the laminar burning velocities of syngas–air flames is proposed. The magnitude of laminar burning velocity for typical syngas compositions is comparable to that of a simulated mixture comprising 5% H2/95% CO and proved to be similar to methane, although somewhat slower than propane.