Measurements of hydrocarbon flame propagation in a channel

Assessing the risk of gas explosions associated with Li-ion batteries in confined geometries is challenging. When a Li-ion battery cell undergoes so-called thermal runaway, internal reactions in the cell can lead to the formation of flammable and toxic gases that expand and finally lead to rupture of the battery cell. The battery cell then acts as a source of flammable and toxic gases that fill the surrounding confinement through a turbulent dispersion process. The specific composition of the vented gas mixture is ongoing research, but flammable hydrocarbons, carbonates, and hydrogen are usually present. The subsequent explosion hazard posed by the release of these gases in confined spaces is far from understood. Given successful ignition of the gas mixture, a flame front will propagate into the reactants while producing heat and creating pressure waves. The thermal expansion causes the reactants to be pushed ahead of the flame front. The resulting flow is highly influenced by turbulence, which wrinkles the flame front and efficiently transports fresh reactants into the combustion zone and preheats them. The result is a substantially more potent combustion process, which unfortunately is extremely difficult to model. There is thus a need for more experimental data on turbulent flame propagation. In this report, the flame-propagation properties of ethane-air mixtures in a 6 m explosion channel have been studied. A section near the closed end of the channel was injected with either premixed ethane-air or pure ethane. The gas mixture was then ignited, which led to flame propagation towards the opposite and open end of the channel. The flame-front evolution was monitored using pressure sensors as well as a high-speed camera. Although the open-ended channel is not directly representative of confined spaces, the current experiments may provide valuable data in the ongoing effort to simulate flame propagation using computational fluid dynamics. If sufficient agreement between simulations and experiments in the open-ended channel can be achieved, it provides more confidence in the ability of numerical models to capture the flame-propagation properties in more complex geometries. A total of 15 individual tests were performed, and both the fuel-air equivalence ratio and the fuel-air cloud size were varied. For two of the cases, turbulence-generating obstacles were introduced to enhance the flame speed. The deflagration propagation did not lead to the formation of observable shock waves in any of the tests. Nevertheless, the combustion process continuously generates pressure waves that propagate upstream into the burnt region and downstream into the unburnt region. Reflections occur when the downstream propagating pressure waves reach the open end of the channel, thus contributing to the pressure build-up in the channel.