Detonation velocity behavior and scaling analysis for ethylene-nitrous oxide mixture

In this study, a detailed experimental investigation of the detonation propagation velocity behavior of stoichiometric ethylene-nitrous oxide in narrow channels is conducted. The experimental results in 4 mm (inner diameter) round tube indicate the detonation experiences three propagation modes with the decreasing of initial pressure (p₀), i.e., steady mode (p₀ > 40 kPa), unstable mode (40–27 kPa) and decay mode (p₀ < 27 kPa), it is confirmed that below p_c = 27 kPa the failure of detonation occurs. The maximum of the velocity deficit at the critical pressure is 35% V_CJ. However, only steady and decay detonation modes are observed in 14 mm round tube, and the critical pressure for the detonation limits is 15 kPa, at which the maximum velocity deficit is 15% V_CJ. In 36 mm round tube, there are steady and decay modes can be found, the critical pressure for detonation limits is 5.2 kPa, its corresponding maximum velocity deficit is 12% V_CJ. The results indicate that with the decreasing initial pressure and tube diameter, boundary layer displacement thickness increases and causes more losses through the flow divergence and hence the increasing of velocity deficits. A linear relationship is obtained between the normalized detonation average velocity and (p₀ · d)⁻¹ by scaling analysis. It suggests the normalized velocity and dimensionless parameter of length scale, i.e., ratio of tube diameter and ZND induction zone length (d/Δ_I) collapse to a single exponential curve.