Numerical study of inflow equivalence ratio inhomogeneity on oblique detonation formation in hydrogen–air mixtures

Abstract

In this study, numerical simulations using Euler equations with detailed chemistry are performed to investigate the effect of fuel-air composition inhomogeneity on the oblique detonation wave (ODW) initiation in hydrogen-air mixtures. This study aims for a better understanding of oblique detonation wave engine performance under practical operating conditions, among those is the inhomogeneous mixing of fuel and air giving rise to a variation of the equivalence ratio (ER) in the incoming combustible flow. This work focuses primarily on how a variable equivalence ratio in the inflow mixture affects both the formation and characteristic parameters of the oblique detonation wave. In this regard, the present simulation imposes initially a lateral linear distribution of the mixture equivalence ratio within the initiation region. The variation is either from fuel-lean or fuel-rich to the uniform stoichiometric mixture condition above the oblique shock wave. The obtained numerical results illustrate that the reaction surface is distorted in the cases of low mixture equivalence ratio. The so-called "V-shaped" flame is observed but differed from previous results that it is not coupled with any compression or shock wave. Analyzing the temperature and species density evolution also shows that the fuel-lean and fuel-rich inhomogeneity have different effects on the combustion features in the initiation region behind the oblique shock wave. Two characteristic quantities, namely the initiation length and the ODW surface position, are defined to describe quantitatively the effects of mixture equivalence ratio inhomogeneity. The results show that the initiation length is mainly determined by the mixture equivalence ratio in the initiation region. Additional computations are performed by reversing ER distribution, i.e., with the linear variation above the initiation region of uniform stoichiometric condition and results also demonstrate that the ODW position is effectively determined by the ER variation before the ODW, which has in turn only negligible effect on the initiation length.

Numerical study of wedge-induced oblique detonations in unsteady flow

“…Another setting of inflow inhomogeneity, considering the effects of non-ideal mixing, was simulated recently, illustrating several distorted reactive fronts (Iwata, Nakaya & Tsue 2016, 2017; Fang et al. 2017).…”

“…ODWs induced by a conical shock or spherical projectiles are simulated to study the initiation structures and formation mechanisms (Ju, Masuya & Sasoh 1998;Maeda, Kasahara & Matsuo 2012;Maeda et al 2013). Another setting of inflow inhomogeneity, considering the effects of non-ideal mixing, was simulated recently, illustrating several distorted reactive fronts (Iwata, Nakaya & Tsue 2016Fang et al 2017).…”

Numerical investigation of oblique detonations induced by a finite wedge in a stoichiometric hydrogen-air mixture

“…ODW structures influenced by the inflow Mach numbers and gas-dynamic parameters, such as inflow pressure and temperature, are simulated and discussed [25]. To study the ODW influenced by the fuel injection, the inflow inhomogeneity is modeled and simulated, demonstrating the distorted reaction surfaces and morphology variation of the ODW structures [26,27]. Our recent study demonstrated that there are two initiation mechanisms of ODW in the wedge-induced structures in hydrogen-air mixtures [28].…”

Numerical investigation of flow structures resulting from the interaction between an oblique detonation wave and an upper expansion corner

“…Sislian et al (2000) conducted an early study of mixing inhomogeneity in two types of ramjets and clearly observed deflagration distortion. Recent studies (Fang et al 2017;Iwata, Nakaya & Tsue 2017) have found that the inflow inhomogeneity may distort the initiation region, generating a 'V-shaped' flame and changing the surface positions. Meanwhile, abrupt variations of inflow angle have been simulated to study the effects of unsteady inflow (Liu et al 2018), revealing the hysteresis of ODW structures.…”

“…Recent studies (Fang et al. 2017; Iwata, Nakaya & Tsue 2017) have found that the inflow inhomogeneity may distort the initiation region, generating a ‘V-shaped’ flame and changing the surface positions. Meanwhile, abrupt variations of inflow angle have been simulated to study the effects of unsteady inflow (Liu et al.…”