Book Description

Hydrogen enriched fuel generated from a variety of resources such as coal and biomass gasification provides an extra option for lean premixed combustion systems. Flashback is the main operability issue associated with this application. In the present work, boundary layer flashback in a jet flame configuration is investigated. Previous research is extended to more practical conditions where turbulent flows with alternative fuels are prevalent. The importance of burner rim conditions, recently revealed, is investigated systematically in the current work. To fulfill the research goals, a jet burner with interchangeable configuration and materials was built. An inline heater provided preheated air up to 810 K. Systematic studies addressing the quantitative influence of various parameters such as fuel compositions, inlet temperature, burner tip temperature, burner material, enclosure size, and burner diameter on flashback propensity were conducted. A comprehensive overview of the flashback limits for all conditions tested in the current study as well as those published previously is presented. The collective results indicate that the burner materials, tip temperature and flame confinement play significant roles for flashback propensity. A statistics based model demonstrated that better correlations arise when the tip temperature is introduced as an input, whereas a physical model revealed that the critical velocity gradient when flashback occurs is proportional to the laminar flame speed computed based on the tip temperature. The addition of multiple parameters further refined the prediction of the flashback propensity. The present work used a heat transfer analysis to show that the upstream flame propagation during flashback is affected by the burner material. The material with lower thermal conductivity yields larger flashback propensity but slower flame regression inside the tube. These observations can be potentially exploited to minimize the negative impacts of flashback in practical applications. A heat transfer model, developed to estimate burner tip temperature, was successful in demonstrating the potential of advanced heat transfer modeling in predicting flashback propensity of alternative fuels with a given burner configuration.