Ignition and transition to detonation under chain-branching kinetics

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Hydrogen is an attractive automotive fuel because it burns without releasing CO2 or other greenhouse gases, and because it is the fuel of choice for fuel cells. Hydrogen production from hydro power or wind energy is carbon-neutral. However, because hydrogen has a markedly different behaviour when compared with hydrocarbon fuels, there are significant safety issues that need to be resolved before widespread hydrogen storage and distribution facilities are allowed in close contact with populated areas. Likewise, there are safety issues associated with hydrogen storage in vehicles in tunnels and public garages. Because hydrogen is very light and buoyant, outdoors installations can be made safe by ensuring that there is enough distance around where the public is not allowed. However, in enclosed environments, serious issues remain, mostly associated with the risk of detonation, which hydrogen is much more prone to than other fuels. Detonation is the most violent form of combustion, in which combustion rides on a shock wave which it also supports. Thus detonation waves travel at high supersonic speeds as long as they encounter combustible mixture, and they entail a pressure increase usually in the tens of atmospheres, which is quite destructive and could result in accidents more serious than for instant the recent Mont-Blanc tunnel accident. Unfortunately, major uncertainties remain on the mechanisms leading to detonation, even for hydrogen, the chemistry of which is better known than other more complex fuels, at least at relatively low pressures. In addition, there is reliable experimental evidence showing that a sudden release of high pressure hydrogen into the atmosphere may ignite spontaneously, under a mechanism that is not well understood either. The goal of the current work is to clarify the relationship between specific features of hydrogen chemistry and both appearance of a detonation and spontaneous jet ignition. To that effect, numerical simulation and mathematical analysis will be performed for a hierarchy of scenarios, starting from relatively simple ones to increasingly more complex and realistic ones.