General concept for autoignitive reaction wave covering from subsonic to supersonic regimes

TL;DR

This paper introduces a new concept of autoignitive reaction waves that can exist in both subsonic and supersonic regimes, supported by theoretical analysis and numerical simulations, revealing stable waves beyond traditional regimes.

Contribution

The study develops a general theory of autoignitive reaction waves, demonstrating their existence across a broad range of velocities and identifying a stable supersonic wave without shock structures.

Findings

Steady-state solutions exist across a broad velocity range.

A stable supersonic autoignitive wave without shock waves.

Potential for new combustor designs based on stable supersonic waves.

Abstract

We consider a one-dimensional (1D) autoignitive reaction wave in reactive flow system comprising unburned premixed gas entering from the inlet boundary and burned gas exiting from the outlet boundary. In such a 1D system at given initial temperature, it is generally accepted that steady-state solutions can only exist if the inlet velocity matches either the velocity of deflagration wave, as determined by the burning rate eigenvalue in the subsonic regime or the velocity of detonation wave as dictated by the Chapman-Jouguet (CJ) condition in the supersonic regime. In this study, we developed the general concept of "autoignitive reaction wave" and theoretically demonstrate that two distinct regimes that can maintain steady-state solutions both in subsonic and supersonic conditions. Based on this theory, we selected inlet velocities that are predicted to yield either steady-state or flashback solutions, and conducted numerical simulations. This novel approach revealed that steady-state solutions are possible not only at the velocity of the deflagration wave in the subsonic regime and the velocity of the detonation wave in the supersonic regime, but also across a broad range of inlet velocities. Furthermore, we identify a highly stable "autoignitive reaction wave" that emerges when the inlet velocity surpasses the velocity of detonation wave, devoid of the typical shock wave commonly seen in detonation waves. This "supersonic autoignitive reaction wave" lacks the instability-inducing detonation cell structure, suggesting the potential for the development of novel combustor concepts.