Markstein numbers and unstretched laminar burning velocities of wet carbon monoxide flames

Abstract

Effects of positive flame stretch on the laminar burning velocities of wet carbon-monoxide/air flames at normal temperature and pressure were studied both experimentally and computationally. Measurements and numerical simulations considered outwardly-propagating spherical laminar premixed flames having both stable and unstable preferential-diffusion behavior. Test conditions included concentrations of hydrogen in the fuel mixture of 3-50% by volume, fuel equivalence ratios of 0.6-5.0, Karlovitz numbers of 0-0.91 and laminar burning velocities corrected to unstretched (plane) flame conditions of 130-1730 mm/s. Both measured and predicted ratios of unstretched (plane) to stretched laminar burning velocities varied linearly with Karlovitz numbers, yielding Markstein numbers in the range -6.5 to 7.6, reaching largest values near limits for the largest hydrogen concentrations in the fuel mixture. Effects of stretch on laminar burning velocities were modest at low hydrogen concentrations but approached earlier observations for hydrogen/air flames as hydrogen concentrations increased. Present and earlier stretchcorrected measurements of the laminar burning velocities and Markstein numbers for unstretched (plane) flames were generally in good agreement, aside from some exceptions at conditions where Markstein numbers were large. Predicted and measured unstretched laminar burning velocities and Markstein numbers were in fair agreement, using a chemical reaction mechanism due to Kim et al. (1994); nevertheless, additional development of the mechanism is needed to improve predictions of Markstein numbers over the test range, and unstretched laminar burning *Visiting Scholar from Helwan University, Cairo, Egypt. Graduate Student Research Assistant **Professor, Fellow AIAA. Copyright © 1996 by G.M. Faeth. Published by the American Institute of Astronautics and Aeronautics, Inc., with permission. velocities at large hydrogen concentrations and fuelequivalence ratios.