Laminar flame characteristics and chemical kinetics of 2-methyltetrahydrofuran and the effect of blending with isooctane

Abstract

Abstracts 2-methyltetrahydrofuran (MTHF) has been considered as a potential biofuel candidate for the renewable feedstock and attractive properties. In this study, the spherically propagating flames of the MTHF/isooctane-air mixtures in different blending ratios were investigated at elevated temperatures and pressures over equivalence ratios of 0.8–1.5 in a constant volume chamber using high-speed photography technique. Laminar burning velocities were calculated through nonlinear method and correlated by mixing rules as a function of initial temperature, pressure, equivalence ratio, and blending ratio. To investigate the influence of the potential interaction between MTHF and isooctane, a detailed model was established by merging the models of the two fuels and validated against laminar burning velocity, ignition delay times and flame structure. The laminar flame velocities of MTHF were observed to increase with initial temperature while the flame velocities decrease with increase in pressure. Kinetic analysis indicates that the major consumption pathways for MTHF are through H abstraction reactions at 2 and 5 sites. The H abstraction reactions at methyl group are less competitive. Unsaturated hydrocarbons and aldehydes are produced in high concentration and are the main stable intermediates of MTHF combustion. The laminar burning velocity is sensitive to the reactions of small radicals and some intermediates such as propylene and ethylene. The laminar burning velocities of MTHF/isooctane blends increase with MTHF blending ratio. The influence of blending ratio on laminar burning velocity should attribute to the chemical factors, rather than thermal or diffusion factors. MTHF oxidation generates less proportion of propylene and higher fractions of H, OH than isooctane, reflecting positive chemical effects on laminar burning velocity as MTHF blended. According to the instability analysis, the Markstein length and critical radius shows similar flame instability among different blending ratios.