Accelerated ignition-shock coupling and deflagration to detonation transition by ozone kinetic enhancement of dimethyl ether mixture

Abstract

This study aims to understand the effect of kinetic enhancement by ozone addition on the Deflagration to Detonation Transition (DDT) and ignition-shock coupling in a microchannel using dimethyl ether (DME). Simultaneous high-speed chemiluminescence and shadowgraph imaging are carried out to analyze the flame front propagation, shock wave structures, autoignition, and ignition-shock coupling during the DDT process. The experimental results show that for all cases, with and without ozone kinetic enhancement, autoignition and DDT always occur in a reactivity gradient region with oblique shock cluster between the flame front and the flame acceleration-induced precursor shock. The observed DDT occurs via the Zeldovich hot spot gradient mechanism through the following stages: (1) Oblique shock cluster formation and acoustic compression between the flame front and the precursor shock, (2) autoignition initiation in the oblique shock cluster region, (3) spontaneous ignition wave propagation, and (4) ignition-shock coupling. It is found that autoignition location, oblique shock strength, induction zone length, ignition-shock coupling, and DDT onset flame velocity are very different from ozone kinetic enhancement. As the ozone addition is higher, the autoignition is advanced and the ignition location moves farther ahead of the flame front at a lower flame front propagation speed and weaker oblique shock clusters. Two different ignition-shock coupling modes are identified depending on ozone concentration. Without ozone kinetic enhancement, DDT occurs via ignition wave coupling with the precursor shock. However, ozone addition can accelerate the autoignition and initiate a direct ignition-shock coupling for DDT without interaction with the precursor shock. The present results show that kinetic enhancement in autoignition using an ignition enhancer such as ozone or plasma is critical and effective in accelerating and controlling DDT.