Ignition Energy and Ignition Probability of Methane-Hydrogen-Air Mixtures

The European Commission are funding an investigation of the feasibility of using existing natural gas infrastructures to transport and distribute hydrogen, as a mixture of natural gas and hydrogen, from the point of hydrogen production to the point of use. Since hydrogen has different chemical and physical properties to that of natural gas, and these will affect the integrity and durability of the pipeline network and the ignition and combustion behaviour of released gas, it is necessary to assess the change in risk to the public that would result. The subject of this paper is an experimental study of the effect of the hydrogen content of the natural gas-hydrogen mixture on the minimum energy required for ignition, and the probability of achieving ignition given a particular level of energy discharge. It was possible to normalize the results for ignition energy such that, given information on the minimum ignition energy and the equivalence ratio at which the minimum ignition energy occurs, the lowest ignition energy for any other equivalence ratio can be predicted. The results also showed that the ignition process has a probabilistic element and that the probability of ignition is related to the equivalence ratio and the energy level of the source. It was observed that the probability of ignition increased with increasing energy of the source and that the rate of rise in probability was steepest for the equivalence ratios close to the equivalence ratio at which the minimum ignition energy occurs.