Detonation reaction zone in nitromethane: Experimental and numerical studies

Abstract

The detonation reaction zone in nitromethane (NM) sensitised with 1% of ethylene diamine (EDA) and mixture of nitromethane and 10 % EDA is studied experimentally and by numerical modelling. The experiments involved measuring of the particle velocity history using impedance window technique instrumented with photonic Doppler velocimetry. Numerical modelling was done by EXPLO5 thermochemical code using its kinetic detonation module. The module includes slightly divergent Wood-Kirkwood detonation theory and the pressure-dependent reaction rate model, and it enables modelling of time dependent phenomena in the detonation reaction zone. Impedance window technique allows us to partially resolve the reaction zone profile. The measured particle velocity profiles of nitromethane agree with the ZND theory: A sharp spike followed by rapid drop in particle velocity over first 10 ns, and then a slower decrease toward the CJ point, which is reached after 60 ns for NM/1%EDA and 77 ns for NM/10% EDA. The reaction rate parameters are calibrated based on experimentally obtained particle velocity profiles and detonation reaction zone width. Using so obtained kinetic parameters, time distribution of parameters within detonation driving zone (including flow parameters, fraction of unreacted explosive, concentration of individual products, thermodynamic parameters of unreacted explosive and reaction products, pressure, temperature, density, etc.) is calculated starting from the von Neumann spike down to the CJ point. A sufficient agreement between experimental and calculated detonation velocities and particle velocity and pressure profiles is obtained.