Laminar Flame Velocity of Components of Natural Gas

Laminar burning velocities are important parameters in many areas of combustion science such as the design of burners or engines and for the prediction of explosions. They play an essential role in the combustion in gas turbines for the optimization of the nozzles and of the combustion chamber. Adiabatic laminar flame velocities are usually investigated in three types of apparatus which are currently available for that type of measurements: constant volume bombs in which the propagation of a flame is initiated by two electrodes and followed by shadowgraphy, counterflow-flame burners with axial velocity profiles determined by Particle Imaging Velocimetry, and flat flame adiabatic burners which consist of a heated burner head mounted on a plenum chamber with the radial temperature distribution measurement made by a series of thermocouples (used in this work). This last method is based on a balance between the heat loss from the flame to the burner required for the flame stabilization and the convective heat flux from the burner surface to the flame front. It was demonstrated that this heat flux method is suitable for the determination of the adiabatic flame temperature and flame burning velocity. The main hydrocarbon in natural gas is methane, with smaller amounts of heavier compounds, mainly species from C₂ to C₄. New experimental measurements have been performed by the heat flux method using a newly built flat flame adiabatic burner at atmospheric pressure. These measurements of laminar flame speeds are presented for components of natural gas, methane, ethane, propane and n-butane, as well as for binary and tertiary mixtures of these compounds representative of different natural gases available in the world. Results for pure alkanes were compared successfully to the literature. The composition of the investigated air/hydrocarbon mixtures covers a wide range of equivalence ratios, from 0.6 to 2.1 when it is possible to sufficiently stabilize the flame. Empirical correlations have been derived in order to predict accurately the flame velocity of a natural gas containing C₁ up to C₄ alkanes as a function of its composition and the equivalence ratio.