Boundary Layer Flashback of Turbulent Premixed Jet Flames at Elevated Pressures and Temperatures
Carbon emissions from the combustion of fossil fuels are a concern within the power generation sector. As a result, while natural gas is currently plentiful, strategies for using fuels derived from renewable sources (i.e., alternative fuels) must still be pursued if a reduction in carbon signature is to be achieved. Many of these potential fuels contain some level of hydrogen. The combustion of high hydrogen content fuels reduces carbon-containing pollutants. However, NOx emissions are still an inevitable result of fuel/air combustion. Hence, lean premixed combustion of hydrogen-rich fuels has been implemented along with a precise control of combustion temperatures to achieve a reduction in all pollutant species. This technology is well established for gas turbines operating on natural gas, while the combustion of alternative fuels faces additional challenges. Hydrogen-rich fuels are particularly prone to flashback.
Boundary layer flashback of a premixed jet flame has been investigated experimentally under turbulent flow conditions at elevated pressures and temperatures (i.e., 3 to 8 atm and 300 to 600 K). The data presented in this study are for hydrogen fuel at various Reynolds numbers, which are representative of gas turbine premixer conditions and are significantly higher than results currently available in the literature. Three burner heads constructed of different materials (stainless steel, copper, and zirconia ceramic) were used to evaluate the effect of tip temperature, a parameter found to be an important factor in triggering flashback. This study adds insight towards understanding of boundary layer flashback at high pressures. To confirm the accuracy and consistency of the results, similar experiments were conducted at the same operating conditions for a commercially available injector from a micro turbine combustor. In addition, this study characterizes flashback systematically by developing a comprehensive non-dimensional model which takes into account all effective parameters in boundary layer flashback propensity. The model developed using the high pressure test rig is able to predict flashback tendencies for the new data as well as the existing data in the literature, including a commercial gas turbine engine and can thus serve as a design tool for identifying when flashback is likely to occur for a given geometry and condition.