ISSN Online: 2688-7231
ISBN Online: 978-1-56700-524-0
Proceedings of the 26thNational and 4th International ISHMT-ASTFE Heat and Mass Transfer Conference December 17-20, 2021, IIT Madras, Chennai-600036, Tamil Nadu, India
Investigation on the effects of pressure and Hydrogen addition on laminar burning velocity and flame stability of n-Dodecane-Hydrogen-air mixtures
An experimental study on laminar burning characteristics of the spherically expanding premixed n-dodecane/H2/air flames was conducted at temperature 425K and 1 to 4 bar initial pressures. An in-house MATLAB code was used to detect the shadowgraph spherical flame edges under the constant pressure period. An inherent stretch involves the flame was removed by using a non-linear expansion extrapolation model for the multi-component mixtures. All experimental operating conditions were simulated with a 1-D freely propagating model available in CHEMKIN software using JetsurF2.0 and PoliMi1410 to compare the experimental results. The unstretched laminar burning velocity (LBV), the laminar flame thickness, the burned gas Markstein number, and the effective Lewis number were obtained over a range of equivalence ratios (0.8-1.4) and H2 fractions (0 - 40%). The influence of H2 addition on the laminar burning velocities and the flame stability was analyzed. The results show that the unstretched laminar burning velocity increases, the laminar flame thickness and Markstein lengths decrease with the increase of H2 fraction. Approximately laminar burning velocity increases three times at off stoichiometric and two times for stoichiometric mixtures when the hydrogen fraction increased from 0-40% by volume. Flame stability was studied by analyzing burned gas Markstein length. Burned gas Markstein lengths are decreasing from lean to rich mixtures for all H2 and non-H2 blended mixtures, but H2 added mixtures produce more stable flame than the pure-n-dodecane/air mixtures, and flame become stable for H2 added mixtures at equivalence ratio above 1.4. The effective Lewis number increases with the increase of H2 fractions, indicating the increase of preferential-diffusion instabilities by hydrogen addition. In addition, sensitivity analysis was conducted to identify the key reactions responsible for the enhanced reactivity associated with H2 addition. Finally, an increase of initial pressure decreases the laminar burning velocity for all mixtures observed.