Detailed characterization of low temperature chemistry and the influence on turbulent burning velocities for n-heptane and iso-octane reactor-assisted turbulent premixed flames

At conditions experienced in advanced gas turbine engines, typical jet fuels can undergo low temperature ignition during the mixing of the reactants prior to their introduction into the turbulent flame. Thus, to aid in the design and the efficient usage of advanced turbine engines, it is of great importance to understand the role of low temperature chemistry on turbulent flame propagation and flame regimes. A reactor assisted turbulent slot (RATS) burner has been designed and constructed which is capable of subjecting liquid fuels to conditions susceptible to low temperature ignition prior to their introduction into a turbulent flame. The current study is an extension on previous work, which demonstrated the strong dependence of turbulent flame speeds with the extent of low temperature chemistry for n-heptane/air mixtures. Further investigation into this phenomenon has been carried out to determine the role of the observed dependence on the turbulent burning behavior with the low temperature chemistry. Fuel composition at the exit of the reactor following low temperature chemistry of n-heptane/air mixtures have been quantified using gas chromatography. Turbulent flame speeds of methane/air and iso-octane/air mixtures have been measured to provide a comparison to the previously made n-heptane/air measurements. Finally, close examination of the instantaneous flame structure for the chemically frozen and the low temperature ignited n-heptane/air, iso-octane/air, and CH4/air flames reveal differences in the degree of flame wrinkling. The culmination of these results provides a more complete understanding regarding the influence of the altering transport and kinetic properties following low temperature ignition on the turbulent flame propagation and flame regime.