Ignition evolution in a cluster of hydrogen lean direct injection burners

Hydrogen is a promising zero-carbon fuel for decarbonising energy production. The broad flammability range of hydrogen compared to hydrocarbons allows fuel-leaner operations, which can help mitigate thermal nitrogen oxides emissions. The initial evolution and dynamics of hydrogen flames in a lean direct injection combustor (LDIC), which consists of a cluster of nine burners, are investigated using large eddy simulation (LES) with a tabulated chemistry approach for partially premixed combustion. The comparisons between the computed and measured statistics are very good for both non-reacting and reacting flows. The evolution of the initial flame kernels are analysed in detail for three equivalence ratios and kernel locations. The results highlight the roles of local extinction, radial flame propagation, and the competition between flow and chemical timescales for a successful ignition and light-around in the multi-burner cluster configuration used in this work. The analyses of the LES data identified a simple criterion for successful ignition, which uses mixture fraction and velocity statistics from non-reacting flow. The simple criterion can guide the development of next-generation hydrogen fuelled combustors. Novelty and significance The study provides a detailed analysis of large eddy simulations of the initial flame kernel evolution in hydrogen–air flames in a lean direct injection combustor with multiple burners. The first aspect of the novelty of this work is the joint experimental and numerical investigation into the lean direct injection combustor under both non-reacting and reacting conditions. The second aspect of the novelty lies in identifying the distinct phases of the flame edge evolution, and proposing a clear and simple condition for successful ignition using the mixture fraction and velocity statistics. The identified mechanisms governing flame propagation and the proposed ignition metric are informative for the design of future hydrogen gas turbine combustors, which are expected to utilise the lean direct injection concept with multiple burners.