Investigation on the laminar burning velocity and flame stability of premixed n-dodecane-air mixtures at elevated pressures and temperatures

Abstract

N-Dodecane is an important representative in several surrogates of multicomponent fuels like gasoline and jet fuels. The choice of a surrogate combination to estimate the combustion characteristics of a complex fuel depends strongly on its individual component’s combustion properties, and its physical and chemical properties. Therefore, it is essential to have a precise reaction mechanism to predict the combustion characteristics such as laminar burning velocity (LBV) and ignition delay times of individual components and the surrogate. The present work aimed to measure the unstretched LBV and burned gas Markstein length of premixed n-dodecane-air mixtures at pressure = 1–4 bar, temperature = 400–450 K, and ϕ = 0.8–1.4. The flame stability analysis of all experiments emphasized that a transition of stable to unstable flame occurred at ϕ = 1.4 due to preferential diffusion effects. The capability of existing Lewis number models to predict the transition was examined, and the BM model showed excellent agreement with all experiments. The local flame equivalence ratio estimated from the simulated reactant species profiles shot up by 15% than the global equivalence ratio for preferentially unstable mixtures. Markstein length was influenced significantly by an increase in pressure than temperature due to a substantial reduction in flame thickness. The comparison of measured unstretched LBV with available n-dodecane mechanisms indicated that JetSurF2.0, You et al., PoliMi were the best candidates. Off-stoichiometric varieties of n-dodecane-air were more responsive to pressure and temperature effects. Finally, the unstretched LBV of premixed n-dodecane-air mixtures increased/ decreased with an initial temperature/ pressure hike. Raise in initial temperature increased the flame temperature and improved the flame propagation rate. An increase in initial pressure amended the reaction rate, but decreased the flame propagation rate due to the dominance of three-body reactions and increased unburned gas density.