Formation of spiral structures in rich-hydrogen air flames at elevated pressures

Abstract

Travelling combustion fronts demonstrate the appearance of a variety of instabilities and structures and thus the revealing of the mechanisms of these phenomena is important both in theoretical and practical aspects. In this work, the mechanism of formation of spiral nonlinear wave structures in the process of propagation of a combustion wave in a rich hydrogen-air mixture at elevated pressure is studied analytically and numerically. A detailed model of the hydrogen oxidation reaction is reduced to a system of partial differential equations for the evolution of H, HO2, O2 and temperature profiles describing both low-temperature and high-temperature reactivity. It is shown to be able to successfully reproduce the characteristics of the diffusive-thermal pulsations emerging with the increase of pressure. A model for the dynamics of the low temperature flame region is separated from the reduced model by using a number of assumptions and appeared to be similar to the Sal'nikov model. It is shown that for the parameter values at which spiral waves are observed, the latter model turns to excitable regime and generates the spiral solutions. Thus it is concluded that the low temperature oxidation processes are responsible for emergence of the spiral structures at the combustion front. We think that the current work is an important step towards understanding the mechanisms of formation of spiral wave structures in expanding combustion fronts.