Expansion Coefficients and Propagation Speeds of Premixed n-Butane–Air Flames

The propagation speeds of premixed n-butane–air mixtures (2.0–5.7 vol%) were investigated under various initial conditions (pressures of 0.4–1.2 bar; temperatures of 289–500 K). The study consists of both, experimental measurements using two different enclosures (a sphere and a cylinder) and kinetic modeling via a dedicated computing program. The propagation speeds of premixed n-butane–air mixtures were obtained via the adiabatic model of flame propagation, which allows us to obtain these important parameters using the normal burning velocities and expansion coefficients. The expansion coefficients were calculated using thermodynamic data as the ratio of burnt to unburnt gas densities, assuming that an equilibrium was established in the flame front. The propagation speeds obtained based on the experimental burning velocities were analyzed for comparison with the computed velocities. Finally, the dependence of the propagation speed on the initial pressure and temperature was discussed.