Pressure evolution during confined deflagration of n-butane/air mixtures

The peak pressures p(max) the maximum rates of pressure rise (dp/dt)(max) and the times necessary to reach the peak pressure theta(max) of n-butane-air deflagrations in two closed vessels with central ignition (a spherical vessel of 5 cm diameter and a cylindrical vessel with height h = 15 cm and diameter Phi = 10 cm) are reported, for mixtures with variable fuel content (2.3 - 5.7 vol%) and initial pressures p(0) = 0.4 - 1.2 bar, at ambient initial temperature. Adiabatic values of explosion pressures, calculated for all mixtures at p(0) = 1 bar and T-0 = 298 K, are examined against experimental values of explosion pressures observed in the two vessels. The deflagration index K-G, characteristic to deflagrations in vessels with volume V and central ignition, is calculated as K-G = (dp/dt)(max)(.3)root V and examined against composition of flammable mixtures. All characteristic parameters of them Nsed vessel combustion of n-butane-air mixtures have extreme values in the concentration range 3.8 - 4.2 vol. % (equivalence ratio 1.1 - 1.2). The obtained results are discussed in connection with mixture composition and pressure.