Flame blow-off correlation for lean direct injection hydrogen burners

Hydrogen is a promising zero-carbon fuel to achieve decarbonisation targets. Its broad flammability range compared to hydrocarbons allows fuel-leaner operations, which can help to mitigate thermal nitrogen oxides emissions. The Lean Direct Injection Combustor (LDIC) design is used to mitigate flame flashback arising under fully premixed conditions. For the LDIC used for this study, the hydrogen is injected transversely through two opposed jets into a cross-flowing air and the flame is stabilised using pilots. The global equivalence ratio of this main flame is varied by gradually changing the hydrogen mass flow rate until the lean blow-off (LBO) of the main flame occurs. The LES of these flames are conducted using flamelet based models for partially premixed combustion. The computed velocity statistics for non-reacting flow compare well with measurements. The computed flame attributes and LBO over a range of operating conditions are observed to agree well with the corresponding measurements. The physical insights obtained from the LES analyses are used to derive a correlation for the LBO, which agrees well with the measurements and LES results for two burner configurations. Novelty and significance statement This study considers flame blow-off in a lean direct injection (LDI) burner using hydrogen, which is injected transversely into an air stream. The fuel is injected upstream of the combustor entry creating a partially premixed fuel-air mixture. The novelty of this work is the joint experimental and numerical investigation of stable flames and those close to blow-off limit. The second novelty is using LES insights to derive a blow-off correlation for the LDI burner since the classical correlations do not hold well. The role of friction velocity in the blow-off phenomenon of the LDI burner is demonstrated for the first time in this study.