Extensive study on the detonation cell size of biogas-oxygen mixtures

Abstract

Detonation cell size is one of the most important and most widely used parameters to describe the detonation process of a given mixture. It is used in both safety analyses and the design process of experiments and engines utilizing detonative combustion. Although much research has been carried out to collect data on the detonation cell of a wide range of combustible mixtures, few studies have focused on biogas. The presented study aims to fill this gap. Several biogas compositions, initial pressures p0 and equivalence ratios Φ were tested, totaling 200 different cases. Both a decrease of initial pressure and a decrease of methane content in the biogas result in an increase in the detonation cell width. When the equivalence ratio is moved away from stoichiometric (Φ = 1) towards either lean or rich mixtures it is accompanied by an increase in detonation cell size. Additionally, ZND induction length and instability parameter χ were calculated. Induction length correlates linearly with the cell size and the χ shows that the cellular structure is expected to be very irregular. Because of that it does not suffice to report merely the average cell size. Thus, a more detailed statistical description is provided.