Effects of thermal pretreatment and equivalence ratio on DME/\({\hbox {O}}_2\)/\({\hbox {O}}_3\) detonations

Abstract

The inerting of a detonable mixture through thermal pretreatment or parasitic combustion is critical to understand for advanced detonation-based combustor design and safety. This work addresses the inerting effects of low temperature chemistry (LTC) on detonations. LTC was induced in both ozoneless DME/O\(_{\textrm{2}}\) and 1.0 mol% O\(_{{3}}\)-enhanced DME/O\(_{2}\) mixtures over a range of detonation tube temperatures (\(T_{\textrm{o}}\)) from 423 to 648 K for reactant mixture equivalence ratios (\(\phi \)) of 0.6–1.8. Upon filling the detonation tube, reactant gas temperatures increased by over 100 K in some cases but never exceeded a maximum gas temperature of 700 K, suggesting a limiting behavior such as the RO\(_{2}\) ceiling temperature. Zero-dimensional constant-volume simulations were conducted to identify chemical composition changes and heat releasing reactions with LTC pretreatment, and ZND simulations were conducted to show the evolution of thermicity with LTC pretreatment. Prolonged pretreatment at \(T_{\textrm{o}}\) greater than 573 K prior to spark ignition of detonation was observed to inert DME/O\(_{2}\) mixtures and inhibit detonation transition for all tested \(\phi \). Additionally, detonation cell sizes were measured, and increased DDT distances and detonation cellular instability at near-limit conditions due to LTC pretreatments were observed using soot foils. Numerical cell sizes were estimated using a correlation model based on center-of-exothermic-length from ZND thermicity simulations, and results showed good agreement with experimental cell sizes. Stability parameter and DDT distance analyses based on correlation models supported the observed reduction in mixture detonability and increase in DDT distances with LTC pretreatment progression.