Detailed investigation of ignition by hot gas jets

Abstract

Experimental and numerical investigations of the ignition of hydrogen/air mixtures by jets of hot exhaust gases are reported. An experimental realisation of such an ignition process, where a jet of hot exhaust gas impinges through a narrow nozzle into a quiescent hydrogen/air mixture, possibly initiating ignition and combustion, is studied. High-speed laser-induced fluorescence (LIF) image sequences of the hydroxyl radical (OH) and laser Schlieren methods are used to gain information about the spatial and temporal evolution of the ignition process. Recording temporally resolved pressure traces yields information about ambient conditions for the process. Numerical experiments are performed that allow linking these observables to certain characteristic states of the gas mixture. The outcome of numerical modelling and experiments indicates the important influence of the hot jet temperature and speed of mixing between the hot and cold gases on the ignition process. The results show the quenching of the flame inside the nozzle and the subsequent ignition of the mixture by the hot exhaust jet. These detailed examinations of the ignition process improve the knowledge concerning flame transmission out of electrical equipment of the type of protection flameproof enclosure.

Generalized flame balls

“…These aspects include the problem of ignition by a hot inert gas stream, the dependence of flame speeds, positive or negative, on the flame curvature, and the stability of the stationary solutions encountered which have been called generalized flame balls. In particular, as Zeldovich flame balls are used as criteria for successful ignition in stagnant reactive gases, generalized flame balls have been shown to provide similar criteria for ignition by a hot radial stream, a step towards understanding ignition by more practical flows of hot gases such as jets [12].…”

“…at r = R. Here ψ * ≡ ψ(R − ), while h * ≡ h(R) and µ ≡ exp(h * /2) are given by (12) and (14), respectively.…”

“…One motivation for studying these solutions is that they provide a simple framework for analysing the important problem of flame initiation, intentional or accidental, by a hot gas stream; [11, p. 265] and [12]. They also provide valuable analytical information on the effect of convection, albeit for a specific radial flow, on the existence and stability of flame balls.…”

2D Mixture Fraction Studies in a Hot-Jet Ignition Configuration Using NO-LIF and Correlation Analysis

“…In our case this is found to be ±8 %; this, in turn, corresponds to to an uncertainty of ±11 % in mixture fraction scale. Previous OH-LIF and numerical investigations conducted on the same experimental configuration have shown that ignition always occured at a region close to the jet tip along the axis rather than at the sides [2]. This can attributed to the disparate mixing behaviour as can be seen in Figure 1.…”

“…The combustion cell used for the NO-PLIF measurements is a simple and well-defined optically accessible constant-volume cell [2]. It consists of two vessels with the first vessel flanged to the second chamber.…”